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Why a Typical Home Solar Setup Does Not Work with the Grid Down (syonyk.blogspot.com)
443 points by cesarb 6 months ago | hide | past | web | favorite | 269 comments



A huge amount of the info on solar PV power on the net is absolute garbage. (I spent 5 years working on the most advanced solar performance optimization and monitoring system developed to date.) I haven't read all of this article, but so far, it looks dead on (you have no idea how rare that is!) Solar is not the panacea many people wish it was, simply due to the way God built the universe - and there's not a thing we can do about that. (And yes, the panels are now only a small part of the cost of a solar system, especially one capable of operating off-grid...)


Looks like I great article. I'll have to defer reading it. During a quick scan I saw a mention of the SMA technology that allows for dedicated outlets to be powered-up in case of grid failure.

I built a 13 kW ground-mount system feeding a pair of SMA inverters. I have tested this feature by disconnecting from the grid and enabling the outlets (one per inverter). I didn't quite get to the 2,000 W rating SMA claims but got close. Which means that with this size of an array and two inverters I get somewhere between 3kW and 4kW of power to run various devices while the sun is up.

Considering that we might have a couple of power outages a year on average (if that), I felt this was a reasonable investment. Going with batteries is just too expensive and not justifiable at all given the reliability of the grid. One way to think about this is that the grid is your battery. A stretch, I know.

Funny that there's a picture of a gasoline generator towards the end of the article. My guess is that I am likely to invest in a 5 kW to 6 kW generator before I ever add batteries to this system. Again, it's a matter of ROI. Also, I would not go with a gasoline powered generator at all. Gasoline degrades with time and could be a nightmare to maintain the system with sporadic use. I think a propane fueled generator might be a better idea. The fuel does not degrade. So long as you don't have leaks it'll be there ready to go when you need it.

I know way too many people who have been mercilessly duped by these solar companies who come in, hook them on some kind of a lease, install inadequate systems and move on to the next victim. Lack of understanding on the side of consumers has created a situation where solar is equivalent to magic and unscrupulous actors can take advantage of them. That part is sad.


> Backfeeding the power grid, according to some lineworkers I've talked to, is really not a big concern for two reasons. First, lineworkers assume lines are live until proven otherwise. And, second, no residential system is going to successfully backfeed a large dead section of grid. [...] it's really not that big a concern from a technical/safety perspective.

This is wrong and dangerous. Suddenly energising a section of grid which has been isolated from all known power sources could easily kill someone working on it. Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested. Yes, your inverter will probably overload and trip out before putting too much voltage into your local section of the grid, depending on where it's isolated. No, it's not OK to bet a random stranger's life on it.


I like to always highlight the difference between a technically correct statement and a public health and safety policy statement.

A thing may be technically correct, but for the health and safety of the public at large we need to adhere to a consistent policy with what we say in the public sphere.

Mains voltage is dangerous and kills kills kills. Never connect anything to the mains power supply unless you are licensed to do so, or employ someone who is licensed to do so. Always assume a circuit is live unless you-personally have checked and locked out the breaker with your own personal lockout device that only you have the key to.


You are supposed to have a license to plug a TV into the wall?

I'm being silly, but you are going on about how the wording of statements matters.


"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize."

https://news.ycombinator.com/newsguidelines.html


My comment is snarky, but it doesn't criticize a weaker interpretation of what they said, it points out a problem with the phrasing. The "I'm being silly" is an acknowledgement that the snark isn't really addressing the substance, the strongest plausible interpretation of "I'm being silly" is that I understood their meaning well enough.


Fair enough on the "I'm being silly"—that does take the edge out of the comment and that's good. But I'm not sure it gets rid of it.

Pointing out "problems with the phrasing" doesn't make for very substantive discussions. Also, snark is deprecated here. Please see https://news.ycombinator.com/newsguidelines.html.


I disagree with you on the phrasing aspect for this specific case. When discussing an advertising message the phrasing is extremely important.

Albeit the thread didn't invite substantive discussion on it because of the snark.


Funny enough, if you've ever done a tradeshow at a venue that has union labor, they will literally make you fill out a request and wait for a licensed union electrician to come and plug your TV (or phone charger or anything with a plug). You will then receive a bill for their time.

And if you plugged in your TV yourself, and they find out, you just unplug it immediately and wait for the licensed union electrician to come plug it in for you again.


I worked in a public university office for a while in college. Without involving the unions, we couldn't

- move furniture that didn't have wheels (so no moving of desks, side-tables, or even some of the larger waiting-room-style chairs). We were allowed to install wheels on furniture ourselves and then move it however :)

- hang pictures or anything on the wall (except when using that blue tacky stuff; you'd be surprised what you can hang with massive quantities of tacky)

- plug in a new power-strip, surge-protector, or extension-cord (we quickly learned to get the big 20-outlet strips)

- set up any kind of networking equipment, even if it was air-gapped from the university's network (we violated this all the time)

- plug in anything that drew more than a certain number of amps (an amperage level that was quite close to what many tower desktop computers were drawing at the time; we always just risked that)

Union workers were always prompt and polite when we'd ask them to do these things and they always had a "ya we know it's dumb" attitude about these requests. One time I saw the bill for the services: around $50 to plug in a surge-protector (that we provided) and $100 to nail a framed picture into the wall. The fine for not getting the union to do these jobs was something like 10x the cost of the labor iirc.


I'm curious how some unions devolve into this sort of behavior. The incentive is obvious, but I wonder if there's an organizational solution that would counter these outcomes.

On the bright side, at least you know your electricians weren't being exploited :)


> I'm curious how some unions devolve into this sort of behavior.

Well, actually there's a logical reason why only the union workers were allowed to do the mentioned things (tl;dr: company/university wants to shield themselves from liability):

- move furniture: shield the university from injury claims in case something goes wrong. For example, consider you moving a yuge chair around wearing flip-flops and you accidentally crush your toe during lifting. The university can now deny your claim as you were not supposed to have done this. In the crazy US system with its even crazier damage payouts, I wonder why this isn't commonplace.

- hang stuff on walls: the older the building, the bigger the chance that you'll hit some live wire, a water pipe or whatever is buried in the wall. Plus, again, personal injury claim risk.

- set up networking equipment: all it takes to bring the network to a grinding halt is accidentally connecting that router you planned to use for playing Counterstrike to the university network and whoops, where's that extra DHCP daemon coming from?

- amperage limit for devices: older circuit breakers tend to get a bit... trigger happy with age. Which means what will work fine now may be too much (especially surge) load in a couple of years and these issues are tricky to debug. In addition, I have seen a wild variation of power cables and extension cords when it comes to their current capacity (e.g. there exist power cords with 3x 0.75mm2 wire, these are rated for 2.5A tops aka something around 550W - but what if the component uses 800W?). Having someone trained look at all involved components before plugging them in can and will prevent fires. Not only to check if they're safe from an amperage limit, but also to check if their isolation is broken, there are scarred areas from arcing, ...


Ya it's all exactly this. The rationale for all these things seemed somewhat sane, but in practice they ended up being irrational when applied in the extreme. It's totally CYA stuff that's typical in public/government settings.

RE the wall they also said that nails and tape were also damaging to the paint (and repainting the walls was another union's thing), so the wall-hanging guy would have to log the "damage" to the wall caused by the hung item, presumably for cost/accounting purposes when it came time to repaint the wall.


> It's totally CYA stuff that's typical in public/government settings.

That CYA stuff is actually typical for any company that ever gets hit with a personal injury or other expensive lawsuit. It's pervasive in government/bigco's because they had to deal with decades of every imaginable stuff happening.

If you want to get rid of it, you gotta limit personal injury liability (which would border on being inhumane) or develop a decent social safety net with proper insurances...


> It's pervasive in government/bigco's because they had to deal with decades of every imaginable stuff happening.

This is important: big orgs—government and private—not only have more chance of having an incident (because they deal with more events because of their scale), they are often bigger litigation targets when an event occurs, because they are giant bags of money.


Those make sense... except the hanging stuff on walls is a stretch. You'd have to use a 6" nail to manage to hit a wire or pipe behind the wall. Most likely, they just don't want lots of little holes in the walls.


A person without knowledge of what is inside of a wall or why it could be a problem may indeed try to use a 6" nail to hang their picture.

There are plenty of people that don't understand(and probably don't want to understand) how things are connected. I doubt they think that the light switch magically turns on the light, or that the water magically comes from the valve attached to the wall, but the method, or desire to know the method, in which those things happen is just not in their world.


> You'd have to use a 6" nail to manage to hit a wire or pipe behind the wall

Nope. There's a type of wire called "Stegleitung", essentially a flat cable. Often enough it's simply nailed into the wall, then a thin coat of mortar is applied on the wall, and then paint.

Source: zapped myself once by hitting such a cable.

In addition, the usual injury liability is a problem.


> I'm curious how some unions devolve into this sort of behavior.

Distrust—usually well earned—of management is the main way. The incidental items that are mocked are not the issue, the issue is that without an inflexible blanket rule, management will bend any other rule to use people in nominally different job duties to replace union labor.

Also, sometimes, the rules are negotiated in part by unions other than those doing the work, to prevent their covered staff from being compelled to do other kinds of work (and selected against for inability to do so: if lifting heavy items is part of the job duties of, say, someone in a clerical union, then inability to do that well can be used as a hiring, promotional, or termination consideration for such an employee.)

Even in places (as sometimes happens) where orgabized labor and management have good day-to-day relations, there usually is a feeling—with good historical reasons behind it—that the foundation of that good relationship is a “good fences make good neighbors” style solid set of baseline rules around which, where it is important (and the little stuff that is fun to mock isn't that) negotiated exceptions can be made.


I'd wager that somewhere in their organizational past is a burned down building and an appliance connected to the mains with a wire hanger, at which point they decided that nothing is so fool-proof that a sufficient fool cannot be found.


That's not been my experience (in a previous life I did 5-6 shows a year, and was yelled at by union reps more than once for hand-carrying my own materials in). At the shows I did (which included venues like the Cobo Center, various downtown hotels, and other union-heavy shops), the union electrician would wire up an outlet for you, but you were then free to plug in what you wanted (as long as it was UL-listed).


In my country, it's required by law for every employee to have a certificate even for plugging in a toaster. The training is easy though and serves mostly to prevent injuries.


What does the training cover?

"Do not rest your tongue on the plug as you insert it into the wall."

I get that electricity is dangerous, but are there really functioning adults hired by a company that can't be trusted to plug in a simple appliance without a safety briefing first? It seems insulting to their intelligence. Or do they make everybody do this so the one or two absolute morons don't feel bad about being forced to take the "completely basic life skills" course before they're allowed to function at even a very low adult level?


What do they teach you not to do?


Question ever-expanding bureaucracy?


I hope you are not suggesting that that is in any way reasonable.


Ha! Good one ;)

Yes, it’s meant to say something like us unlicensed folk aren’t permitted to hardwire anything to the mains supply.

In Australia you’re not even supposed to replace an existing power point outlet thingo unlicensed. If course, the hardware stores sell them, and we do. But there ya go.


> In Australia you’re not even supposed to replace an existing power point outlet thingo unlicensed.

In fact you're not allowed to install any fixed wiring without an electrical license. It's ridiculous - technically you aren't even allowed to install Ethernet outlets in your own house because it counts as "fixed wiring". Other trades have just as bad a grip on legislature, you're technically not allowed to replace your own tap seals either.

> Of course, the hardware stores sell them, and we do. But there ya go.

Of course, in theory there's no difference between theory and practice... ;)


Australian protectionism re: the building industry if disgraceful.

In Victoria for example, you're not allowed to do any work on your own home if it exceeds a certain monetary value without first running through a Kafkaesque bureaucratic process to obtain a certificate.

This doesn't sound unreasonable until you realize that they don't care if you have any qualifications related to the work and don't even want to know what the work is. They simply want to confirm that you haven't done any other work (on your own property) in the last five years.

If you have, sorry, need to hire a registered builder. This prevents anyone from legally buying a home, renovating, and selling it, or even doing any significant work on your own property more than once in five years.

And if you want any other tradesperson to come to assist for anything while your doing it (installing a power point for example), then you need in person occupational health and safety training at a "registered training institute".

http://www.vba.vic.gov.au/consumers/owner-builders


That's some serious FUD you've got going on, and a total misrepresentation of what the rules actually say.

You only need to apply to be an owner-builder if you are doing your own work instead of hiring someone who is already permitted to do the work. This is no different from the US practice of having licensed contractors/electricians carrying out (or signing off on) large projects.


That's some serious FUD you've got going on, and a total misrepresentation of what the rules actually say.

You only need to apply to be an owner-builder if you are doing your own work instead of hiring someone who is already permitted to do the work.

That is precisely what we are discussing. The restrictions on doing work on your own house yourself.

And this applies to any work at at, not just work that requires licensing (plumbing, electrical etc.). Even if you're doing the overall work yourself as an owner builder, you still need to hire licensed professionals for those tasks.


Wow that is some extreme bureaucracy. So flipping houses is not a viable business in Australia, I presume.


It is, but you can't do the work yourself.


That sounds like a great way to end up buying a house with a bunch of un-licensed, un-inspected work done because the previous owner didn't want to deal with the beurocratic madhouse.


As far as I know... there's no documentation of home power systems in the US.

So the difference between "electrician installed" and "mysterious, unknown person installed" is only in the finished product.


I had house that had a high quality ceiling fan that always made noise. It was high and hard to reach but after perilous ladder work I discovered it wasn't the fan; it had been wired up wrong, the variable speed control was wired up across the two separate 120v legs supplying the home with electricity. I was surprised that the fan even worked at all that way. I don't know who wired it up originally.

I'm not an electrician so correct me if I'm wrong, but for those unfamiliar with residential wiring in US homes, ordinarily homes are supplied with two out of phase 110VAC lines. Heavy appliances like electric clothes driers and electric car charging points use the 220VAC that I available between the two "hot" lines. Everything else in the house use either one of the "hot" lines (black wires according to the national electrical code). There are actually 3 wires going to each outlet, light, etc. though the house: one black (belonging to one of the two sources of 110VAC), one white (called the neutral line, approximately 0V above ground, and one green a separate green wire that is connected to ground around the point where power enters the house.


Correct, but they're 120/240V. Or at least, should be.


It's actually 120V/~208V. If you're feeling frisky, you can confirm this by going around between random pairs of outlets in your house and comparing the right slots from two different outlets until you find a pair of them that are out of phase from each other.

Fundamentally, the power grid is based on three phase power. Typically, the average telephone pole will have four power wires on it, and one or two thick bundles of phone line or maybe cable TV, I dunno. Three of those four power lines are the three phase electricity, and the fourth is the common neutral line that is ideally near 0V, but typically fluctuates a bit.

Only three out of those four lines enter your house. One is is the neutral line, the other two are just two of the three power lines. Those two power lines are not 180 degrees out of phase, they are 120 degrees out of phase. If they were 180 degrees out of phase, the math is simple: it's obviously just 240V. Since it's 120 degrees out of phase, you end up with a sine wave that looks something like 120\(sin(x)-sin(x+pi\2/3)). (only you need to adjust it for frequency) If you're better at your trig identities than I am, you can calculate that out exactly, but for simpletons like me I just plug it into my calculator and find a local maximum of 207.846 something.

(note: In the US, we use neutral and ground to refer to the common center of the three phase power, and the wire that is buried in the ground near your house, respectively. In the UK, I think they call these two wires ground and earth, respectively. Note that the term "ground" has a very different meaning (read: one of them can kill you, the other one keeps you safe) depending on the context.)


This is not correct for the majority of US households.

Two of the phases DO NOT run to the house, a typical US household service is split-phase. The primary winding in the transformer at the pole connects between a single phase and ground, and the secondary winding is center-tapped to provide a 'neutral', with 120v on either side of the neutral. The voltages are indeed 180 degrees out of phase.

Your test would show 220-240v in the vast majority of US-based residential situations.

The 120/208 you are referring to is when all 3 phases are fed in to a WYE transformer that has 3 120v secodary windings fed from a center point, which becomes the neutral. With a WYE transformer, each phase gets 120v to ground/neutral, and the phase-to-phase voltage indeed peaks at 208v due to the 120 degree rotation between phases. This is typically only found in large residential(600+ amps), and medium to large commercial and industrial buildings with 3-phase service.

Another method would be using a 'Delta' transformer, in which one of the phase-to-phase windings are center-tapped, similar but a little different than the single-phase residential service. The two phases on either side of that center-tap will be 120v to neutral, but the 3rd phase will be 208v to netural/ground. This is usually called the 'wild' leg and is often used to power lighting loads.

Source: I've been doing this for a long time.

Also https://www.doityourself.com/forum/electrical-ac-dc/549775-l...

And https://ctlsys.com/support/electrical_service_types_and_volt...


That's interesting, and I don't doubt that you have seen a system like that, but it sounds more like what could be expected in an industrial setting with 3-phase power.

The few houses that I was involved in wiring of in the states were definitely "split phase" systems, which work like the GP describes. In those, three current-carrying wires come from the transformer - two ends and a centre tap from one winding. Those are wired in the breaker box so that the house has two circuits that are 180* off from each other, giving 110V on either circuit, or 220V between the two "hot" legs. There's a better description at https://en.wikipedia.org/wiki/Split-phase_electric_power.


Indeed. It happens all the time that a homeowner does significant wiring projects in their own home. Everything you need is available at the local hardware store or Home Depot. Some do a good job. I've also seen things like lamp cord used in fixed wiring behind walls or in attics.


I inherited some piece of furniture - I don't recall what - that my wife's ex had attached a florescent lamp to. He used a telephone cord for the 120v power connection.


People who can't explain how current, voltage, and resistance relate to each other shouldn't be allowed near wiring.


A fluorescent lamp that one would attach to furniture probably only takes 10W. That's less than 100mA at 120V; a telephone wire can handle that. Also, telephone wires once carried as much as 50VDC for ringers, so I'd expect the insulation to be adequate, if only barely. The biggest problem, I think, is that because the insulation is relatively thin, there's a greater risk of mechanical damage to it.


One slightly obscure example is someone using a European (220V) light fixture or extension cord (with plug adapters) in North America. (110V).

The current for the same wattage will be roughly double in North America. So lamps, etc. intended for use in Europe will have wiring that is undersized for the current draw if used in North America.


> I've also seen things like lamp cord used in fixed wiring behind walls or in attics.

We found exactly that, lamp cords and extension cords, when we started our remodel a month ago. The former owner did some renovation ten years ago, and was an architect so we always assumed he did a decent job. That was one of a few questionable choices he made, so we're now re-wiring the entire house.


An old house that is rewired would have a permit on file if it were done properly, and includes the name of the contractor if there is one. But there is often no proof on site.


Electrical work can be done properly without a permit having been pulled. Depends on where I suppose but even contractors often don’t get permits.


In Australia all work carried out by an electrician is required to be certified. That is to say, the electrician must, on completion of the work, hand you a certificate stating that all work is to the relevant standard. They can't reasonably withhold the certificate, and it must be provided on completion not on payment.

An organisation called TechSafe[1] is charged with carrying out random inspections.

1. https://www.techsafe.com.au/


I include pulling a permit as part of doing a job properly.


A while back there was a safety ditty from some Australian public transit organization as I recall. Things like not touching third rail and various household dangers. Perfectly sensible stuff. But there was also a line about “doing your own electrical work” which, as an American, struck me as so out of place as to be almost comical.


My brother-in-law is an electrician, and he could tell you stories for days about the horrible and unsafe practices he sees nearly every day of the week in people's homes where they've done their own work.

Everything thinks they're smart, they can do things safely, etc., while only for a much smaller subset of people is that true.


I work with industrial electrical systems so I see a lot of how things are done "the right way". The amount of horrible bullshit that I've seen in houses that's been done by licensed electricians is staggering. I'd wager for every one dodgy install done by a DIYer, there's an entire house that's been wired in the laziest spaghetti style by a 17-year-old sparky's apprentice and ticked off without even eyeballing it by the main contractor.


A fun way to trigger a dumb argument is to say something about taping (or not) wire nuts.


I mean, in the US you should be careful atleast since the US plugs expose mains voltage where your fingers might be able to reach (UK and EU plugs are much better and make it mechanically impossible to touch the exposed copper before they make contact with mains).

Generally, playing with voltages above 50V is something that should be done with care and a professional/adult present.


TR plugs are required now in the US. We replaced ours because it looks a lot better than outlet covers.


"TR" plugs are another "innovation" that someone got a patent on and then lobbied to get into the NEC. In my experience, their only functionality is to bend up the prongs on plugs when the plastic bits choose to not get out of the way.

Why should everybody have to pay a continuing overhead simply so people with small children don't have to install outlet covers?

If you're actually concerned with electrical safety, you're much better off installing solid "commercial-grade" receptacles than pretending that garbage-grade ("residential") has been rendered safe by being more difficult to use.


TR plugs don't prevent the spades from being exposed when plugging in a cord. They simply prevent a someone from inserting something into one of the slots like a bobby pin.


It's still a massive improvement.


But you can't safely guide the plug into the wall socket without looking at it. With European plugs[1], that's fine. The grounded version doesn't have that protection, but the female side has walls on the side and a protruding ground plug, so it's also safe to guide with your fingers: by the time the plug is sufficiently in to become live with power, the gap is smaller than the width of a toddler's finger.

[1] https://ae01.alicdn.com/kf/HTB1Cya9KVXXXXXoXpXXq6xXFXXXK/202...


Yes, I understand, but I'm not sure how you address that without changing literally every existing plug and outlet in the USA.


That's exactly what happened in Europe. The old ones were as dangerous as the ones currently in use in the US. They managed to make the transition in a way that was backward compatible.

Here in the US we did change our plugs, by introducing polarized plugs. We don't have to be change-averse.


Sure, and the grounding pin was also added. To get around that, every hardware and department store sells those little defeat devices (that you're supposed to ground but I'd be surprised if anyone ever did that). That's an instance where the reaction to a change leaves you less safe, not more.

https://en.wikipedia.org/wiki/Cheater_plug


You could probably require the plug leads to have rubber coating on 80% of the plug material, and recess the actual contact points slightly farther back into the receptacle, which would emulate the British plug somewhat, but good luck getting anything like that past the lobbying of groups who often cut a tiny hole in one or both blades just to save fractions of a penny per plug


Those holes mate with a spring mechanism in some outlets to keep the plug attached to the outlet more securely.


Good ones are also liquid proof.


Do you also have an RCD[1] in the mains switchboard? Each circuit breaker in my shiny new upgraded mains switchboard is also an RCD.

I still occasionally see an old switchboard with ceramic wire fuses with the fuse wire replaced with a bit of coat hanger wire, or the correct fuse wire wrapped around the terminals ten times. They often seem to be the same houses that give you a tingle if you touch any of the metal plumbing fixtures. Yikes.

1. https://en.wikipedia.org/wiki/Residual-current_device


Tamper resistant outlets are required (maybe) for new construction, but there's a lot of existing housing -- some of which has two prong, unpolorized outlets.

Hardware store still carry traditional outlets as well.


Interesting, is there some image of the TR plug, I couldn't find anything online?



Search "Tamper-resistant electrical receptacles". They don't really look all that different, there's just a mechanism in the holes that prevents some foreign objects from being inserted.


Yeah that's not really better at all. You can get the same protection with 3$ child-protection covers here.

The issue is exposed live voltage when you plug it in. Schuko and Europlugs generally don't allow this (even the flat plug is designed such that the contact aren't exposed anymore when they make contact)


I'm not a lineman but am a generally curious person, which has caused me to watch and analyze their work when I see it.

Any time I see them working directly on high-voltage lines, they connect a device that looks like jumper cables in-between the phase(s) and ground. They also put bright orange flags on this device so that it is easily visible to anyone nearby. It seems to be a great practice and seems to make things nearly fool-proof because this effectively shorts out any power that may occur on those lines.

I don't think I've ever seen a lineman work on a power line in a manner that would cause him to be electrocuted if surprise power were to occur on the line. I'd bet it's in policies and procedures somewhere, possibly even in OSHA requirements.

The requirement of not backfeeding is another layer in this multi-layer protection scheme.

If a system is successfully backfeeding the grid, something is badly wrong. If a linemen is then electrocuted by this backfeed, something is almost impossibly wrong.


It's not as foolproof as it may seem. If linemen are out working it's because something has changed the normal flow of power. If they're fixing downed power lines then all bets are off as to what the circuit diagram has effectively become. They might ground out the spur going to the break but that still leaves everything after the break ungrounded. Take for example, Joe homeowner bought a big 5kW generator and he wants to keep his fridge running. It's easy enough for someone to "install" a generator themselves without calling an electrician and just make a suicide cord to hook it up during a power outage. If the break is just upstream of the generator, or the neutral broke instead of the live line, you can have a situation where the generator is still producing a lethal voltage potential between the live line and ground yet it wouldn't be low enough resistance to short out the generator.

It's unreasonable to assume that a lineman can identify which sections of a downed line are isolated before they get to work repairing the power lines. There are circumstances where the line might even be isolated without being physically disconnected because a fuse blew downstream of where the line was grounded before the lines actually came down. Fuses will have a visual indication that they are blown but it's just a pin that sticks out the bottom and it's easy to miss when you think the only problem is a downed power line. There's an army of fools who know just enough to be dangerous and it's easy to see this on YouTube. Here's a great example of what linemen have to worry about when repairing downed lines.

https://www.youtube.com/watch?v=KiByz1E4IBU

Wouldn't you be worried working with downed lines not knowing if that guy just so happened to live across the street?


I think I would take the same advice as is given for someone handling a gun -- treat every gun as if it is loaded. Treat every wire as if it is hot. Unless you have a really good reason not to.

Not doing so is putting an awful lot of trust into a potentially large number of people that you've never even met.

Because you just don't know what some idiot has done...like the guy in the video.


I agree with your comment about back feeding and shorting lines that are supposed to be de-energized, but linemen also sometimes have to work on hot lines. They have all kinds of neat tools and techniques for doing this. Seeing a lineman with a cheater stick (fiberglass pole) or insulated gloves working on a live line is pretty neat.


During a flood I once saw a HV line that was occasionally dipping into the river. It would float down for a little bit, build up some tension, then shoot into the air creating a ~4-5 foot blue arc as the line shorted into the river before landing back in the water and producing a huge thumping sound.

That completely changed my perspective on all those quite lines dancing in the wind.


Yep, and when they work on hot lines, they treat them as such, using the protective gear you mentioned.

I cannot think of a time that I saw a lineman working on a power line that was not shorted, without protective gear.

Working on a hot wire is a whole different story because every thing around you becomes a hazard.

I do work on towers, sometimes in hot-RF environments (TV and radio antennas transmit with up to ~100,000 watts). The antennas will literally cook(like a microwave oven does) you if you get too close while they are live. For lower power situations, you can even hold your hand near the antenna -- it feels like a heat-lamp. Even at reduced levels, it can be harmful to areas of your body with poor circulation and cooling(such as your eyes), often causing damage before you're even aware of it. We wear an RF monitor when in those situations that alerts us if the RF field becomes stronger than is safe. I wonder if linemen wear a similar device that can alert them if an EM field becomes stronger than expected?


When I work on electrical wires at home, I test if they are hot after flipping what I believe is the correct fuse. If I’m right I know it won’t become hot while I work on it because I control the switches and fuses.

If I worked on wires where I was not in control of incoming power, then I can not be sure the wire isn’t hot just because I measured once. This is for example the case when working with stuff with big capacitors.

So my point is: can line workers really assume a wire isn’t hot just because they tested it? They don’t control both ends, since as you pointed out, anyone could have a) a power source or b) a faulty connection, whether it’s allowed or not. So as a line worker I’d basically just not touch anything even in supposedly dead grid sections.


I recommend shorting to ground. Even if it's your own fuse. Shorting means that if you picked the wrong fuse you notice. And when your friend comes by and flips the fuse back on you don't get a spark shower (something like this has happened to me, don't underestimate people willing to flip fuses for no reason)


A common solution for this is lockout-tagout, where you physically lock the breaker open using a lock with your name on it, and nobody can flip it until you come back and take the lock off.

Used on electrical circuits as well as dangerous machines if you need to climb inside a compactor for maintenance or something.

https://www.osha.gov/Publications/3120.html

http://www.deenergize.com/?target=Universal_Circuit_Breaker_...


That works too, though IIRC the common procedure in the industry in my country is to use a warning label/shield and hang it on the breaker box during repairs, locking the breaker box itself, then short out the circuit to ground and measure to be sure.

Locks on the breaker itself are more rare (usually for low voltage repairs where the common person might frequent the area)


When they work on train power lines, what they do is physically short them to the tracks.


You should test if they are hot before you flip the breaker, then test again after. If you only test after you are not protected against faulty test equipment or improper wiring.


Yes. This was assuming the light was shining (or equiv, that it showed 230V) before work starts of course.


I'm so paranoid I lockout-tagout my home breaker panel.


> Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested.

The lineworkers I've seen that aren't working with live wires use a special tool to ground the wires (it's a set of three clamps connected by a thick wire to a grounding rod). Once the wire's grounded, it's going to be hard to put any voltage on it.


Here's a photo just after they did that while repairing a break near my house a few months ago: https://i.imgur.com/6TckAa8.jpg

The obviously missing third top line is the one that broke. It simply snapped around the middle of the span between that pole and the pole that is outside the photo on the right. They went up in the cherry picker, cut the dangling line, and then put on those clamps.

They then covered the lower arms of the pole with orange sheets: https://i.imgur.com/zZ3DFSd.jpg

Does anyone happen to know what the orange sheets are for? They did not use them anywhere else where they grounded the wires.


I've seen lineworkers use orange covers many times, when working near live wires.

The place where they put these orange sheets in your photo looks like a disconnect switch between the wires on either side of the pole. So the wires coming from the left side of your photo are still live, and the disconnect switch itself is still live. Since they would be working near the disconnect switch (to hang the new wire), they put these insulating orange covers for extra protection.


I would also expect that a larger residential inverter could successfully backfeed the load side of a single distribution transformer (i.e. just a few houses). If the line workers are repairing a distribution transformer or its associated hardware, this could be a big deal.

I don’t know if the workers make a habit of physically disconnecting all of the houses that are connected.


I guess the point is that if your residential solar setup attempts to backfeed a dead grid, it will effectively see a short circuit which it, try as it might, will be unable to generate any voltage across, trip and your house is as dead as the rest of the grid.

For this reason, I'd be most surprised if there's a single backfeed system in existence which doesn't isolate your house from the grid once the grid goes down.

Edit: Finally got around to reading the blog post to the end and found that the author makes this exact point in the paragraph following the one quoted in the comment above.


It can also do strange things to outage reporting equipment that assumes power to be flowing a paticular way.


Great article, lots of technical details. A simple answer to the 'Why' can be found in the middle under the 'Off Grid Without Batteries' headline.

> If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,


I agree that there are a lot of good technical details. However, I wish the article had started off by saying, "It's Not Power Companies Being Evilly Evil - It's Homeowners Being Cheap" instead of waiting more than half way through it.


"there's no waveform to sync with" is technically correct and a very poor excuse

A residential no-break has no waveform to sync with as well.

Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)


It might be worth reading the rest of the article. Which points at that the big reason why you can run off grid is because solar panels without a battery store are effectively incapable of usefully powering variable loads without:

Only running at a fraction of their max available output allow enough headroom for high peak startup draw from loads, and headroom for clouds and planes passing overhead.

Frequently cutting in and out as the load regularly exceeds available supply.

Keeping the frequency sync is the easiest problem to solve, the article even covers what would happen if you tried to use a little generator to produce a sync signal.


I think that points to a bigger problem with solar and that is that it is a horribly mis-sold concept.

Most solar dealers have a one-size-fits-all product that they fit to nearly all homes without much modification. The homeowner thinks they are buying something that will save them a fortune and eliminate their need for grid power. In reality they discoverer that solar is persnickety and they will get nowhere near eliminating their grid reliance. And when you do the math you realise that it might take 10+ years to recoup the high cost of installation and by that point your batteries will need to be replaced and your solar panels will have lost some of their efficiency.

I know people who have gone fully off-grid in Ireland, but they don't just rely on solar. They supplement with wind turbines and in some case hydro power from streams.


I think you have it wrong. You make it sound like homeowners are tricked into thinking they will be grid-independent, which I don't think is a fair depiction of how the product is sold (at least in Australia, that is.) The value proposition isn't getting entirely off the grid, it's just saving a bit of cash and doing some good for the planet.

Rooftop solar is popular because the payback period is short enough for homeowners - well under 10 years here for a system that is built to last at least 20. Modules built now degrade about 0.25% per year. Solar farms built now are typically financed as 25-30 year projects.

Source: I am a data analyst at a solar engineering firm.


"Doing some good for the planet" really must take into account the toxic metals leaching from the cheap Chinese panels that took over the market in the past decade. (There are no significant US/EU PV panel mfrs left.) I've seen mid-scale arrays (30-50 KW) with 1/4 of the panels delaminating and thus leaking heavy metals (lead, cadmium, etc.) directly into the environment - or worse, into rainwater recovery systems!


I am considering solar and a big plus would be a battery as well.

Do you have any suggestions or recommendations on things to read or companies to look at? i.e. Tesla power?


And do your calculations include subsidies? In that case it's not necessarily "saving cash" but "taking a transfer payment from taxpayers."


Fossil fuels are heavily subsidized, so your point is moot.


They're not only not heavily subsidized by consumers, but one of the most taxed consumer goods you can buy (besides cigarettes).


Coal power power for example does not need to cover the deaths directly caused by it's pollution. That's a vast subsidy. Roads revive rather large subsidies from the general funds outside of gas taxes which is another large subsidy, though electric cars revive even larger subsides by not needing to pay for their use.

PS: Look at taxes for Farm use vehicles fuel to get a better picture of the actual 'subsidy' vs 'tax'. The tipping point is very much a subsidy. https://www.irs.gov/businesses/small-businesses-self-employe...


Surely the reasonable behavior would be to NOT subsidize any of these things. Your point tho is (sadly) correct.


I agree with what you wrote there, so they should justify by it not by just saying "it's a frequency issue"

As you said:

> Keeping the frequency sync is the easiest problem to solve


The grid isn't a fixed frequency. While on average the grid doesn't change phase, the reality is that the grid may be out of phase by several seconds most of the time.

When the grid comes back from a blackout, chances are that it browned out beforehand so your sync is to a low frequency and coming back it'll be high frequency because the grid wants to compensate for loads jumping back on.

Additionally the components to generate your own waveform are cheap, yes, but not that cheap, adding them to the microinverter would increase cost quite a bit.

And you'd still need a transfer switch because if you happen to be 180 degrees out of phase, which CAN HAPPEN then your panel will behave like a dead short at double grid voltage. The current flow will definitely exceed the maximum tolerances and the magic smoke goes out.

You will absolutely need a transfer switch just so you don't fry all your devices the moment the grid comes back. Even then, syncing to the grid is a rather delicate maneuver since the grid will be constantly changing phase and it'll be simpler to shut down all inverters, connect back and have it all run back up on the grid itself.


This sounds awfully complicated, near impossible. You'd need a circuit that disconnects from the grid once it detects a brown out or black out, then produces a near sine wave all by itself, then re-syncs with the grid once it comes back up and transfers back. And all that has to happen cleanly enough that even a computer connected to it doesn't glitch, truly a "delicate maneuver". No way this can be produced for less than a couple thousands of dollars!

It's called a line-interactive UPS. You can buy it for $200.


Line-interactive gets around it by simply using a inverter for both grid power and battery power, thusly being able to produce it's own sine wave inside the house. You can also use an VFI those convert grid to DC and then plug the battery in there, then convert back. Same effect.

A line interactive UPS does not sync necessarily sync you to the grid, though the electronic will usually try to keep it in sync. It's not necessary here.


You don't really need a transfer switch, just a big relay to connect the grid and your internal wiring. Disconnect as soon as the grid drops out, and sync to the grid before re-engaging. It's not a full transfer switch you require, and should be in the price range of an resettable fuse of the same amperage rating. Just add a small solenoid to trigger the spring-loaded mechanism to disengage the switch, and use a slow-ish geared DC motor to re-load the spring and re-engage the connection. It should not be hard to enable the inverter to sync that way, and these fuses aren't expensive either. And if you cut the inverter along with only some of the circuits in your house from the rest, which are still connected to the grid, you can easily ensure that no high-power devices draw power and cause the inverter to either go into overload or have insufficient input power (solar/battery) to keep the output voltage on target.


> When the grid comes back from a blackout, chances are that it browned out beforehand

Not really, but depends on the state of the infrastructure, if it was really because of a power overload, yes, but most likely "your circuit" (which could be your street or your neighborhood) got shut off, in this case there shouldn't be much difference

Yes, a phase difference of 180 can definitely happen but I guess most electronics can survive a 1/60s (I'd say even 1/10) switching time, which is probably enough to have the grid take over.

(Or of course you could have the grid and solar charging batteries then your own high power inverter for your house but that of course would mean $$$$$$)


A 1/10th switching time would be fine though if you change phase too much and suddenly some equipment might not like it.

And you'd still have to sync the inverter, having the inverter simply continue to run until it's back in sync with the grid, then just reconnect (as a previous comment wanted) is likely not an option for most consumers.

For that it would likely be cheaper to have a full DC stage as you mentioned.


It's knowledge that people in question are lacking


Most computers can't handle 100 ms power loss, unless you actively throttle power consumption as soon as you sense the loss, in order for the filter capacitors in the PSU to last that long.


Most computers are laptops today.


Or you have your inverters run a phase locked loop. When the grid is there it'll keep perfect sync, when it's not there it'll keep running. Switching back to grid power should be as easy as waiting to reconnect until your inverters are back in sync, which depending on the PLL design shouldn't take long.


Waiting to be back in sync could take forever, plus you need a Sync Check Relay. Price of those is usually "contact sales team" and they don't work reliably if you don't need more than a couple dozen kW of power. (They're intended for 1MW+ installations).

Just shut it down, flip the switch and restart. Everything else will just be prohibitively expensive because it needs to be very safe.

If you get the phase wrong then you'll either reduce the lifetime of your components or the components explode after the nearest power plant tries to pump all available power into your poor inverter.


> Waiting to be back in sync could take forever

Only if you design it to. The phase locked loop would "listen" to the mains frequency and slew to match. Slew speed is simply a design parameter you can set to any value.


A phase-locked loop would fairly quickly come back into sync with the reference frequency - that’s exactly what they’re designed to do.

I’m pretty sure companies like Victron Energy already make these kinds of systems - combination solar inverters and battery chargers that have transfer switches to be able to seamlessly switch to UPS mode when the grid drops out but can still export excess energy when it’s up.


Of course these systems are made but they're just very expensive and usually for customers of theirs that don't play around with a couple 100W panels because they want to save a buck or two in the summer.


The relay you need is a normal breaker with a solenoid to trigger the spring and a small geared DC motor to re-engage/reset the breaker.

And that's for what you need to allow your inverter to handle this automatically (you might need another voltage sensing channel to sense the grid-side of this breaker).


If this is such a hard problem, how does the $150 UPS hooked up to my home computers pull it off???


Your UPS doesn't save money by discharging its battery back to the grid when it's not in use.

Your UPS handles an order of magnitude (or more) less power than a whole-home solar installation.

None of these problems are intractable of course, but you are oversimplifying the problem a little.


I'd be willing to accept not discharging my solar system's battery to the grid when not in use, I can use it at night.

One can get a UPS affordably that will power 1500 watts of continuous power. Being able to supply just that much, or twice that much, from solar panels in a grid-down scenario would be tremendously useful, even if it's not enough power to fire up my welder.


When the grid goes back up the system would check the grid frequency and phase, and slowly match that waveform over a few minutes by making light changes.

When the two are aligned within a good-enough tolerance the system will switch back to it's regular state of mains + solar ( + batteries + wind + generator + etc / whatever).

These are all solved problems with commercial off the shelf components.


Are these commercial off the shelf components as cheap as a microinverter?


I just typed microinverter in to Google and clicked on shopping.

It looks to me like microinverters are a commercial off the shelf product?

Will a microinverter do all of the things a multi-component phase-syncing system with automatic transfer switches do? I don't see why a microinverter can't be built with these components integrated. I can't tell you if such a unit exists as I'm not well versed in the product range.

As far as a price comparison goes, I guess it only makes sense to compare a like-for-like system?


From what I know, you will need a sync check relay, ie a relay that only closes when you're synced up. Those are generally available for 1MW and upwards (one manual notes a minimum constant load on the internal grid of 500 kW or it won't work), look like about the size of half of a car battery, at a price of "contact our sales team".

Could it be made cheaper? Probably. If you get it wrong, the grid probably doesn't care but you'll briefly pump about 500W into the device that is supposed to have 500W going out of it. The reason these are big and expensive is that it requires significant safety gear so nothing explodes even in the worst case. And that safety gear is expensive. So you sell it to people who not only can afford it but also really really need it (ie, 1MW and upwards where you enter the domain of "can fry small section of grid")


Any old IGBT or even just a highly spec’d MOSFET paired with an optoisolator (a couple of dollars of parts) could do that for a small system, based on input from the inverter’s existing controller.

The specialist devices for large installations you’re talking about are only expensive because you need more expensive parts for the far larger amounts of current you’re handling (and probably because they’re made in lower volumes than commodity inverters), not because they’re doing anything particularly difficult.


I used to work with a few (16 odd) Siemens 200kVA UPS that did the syncing.

There’s no technical reason the requisite electronics can’t be built on a much smaller scale.

Home grid-tie solar inverters are clearly capable of syncing, so the electronics are already present.


grid-tie inverters are capable of syncing to a present signal, what they can't do is provide their own waveform and sync that to the grid when it comes back online.


Providing a 60Hz waveform and syncing it to the grid the easy part. You could make a standalone device that does it out of a twenty cent microcontroller.


And then you'd still have to switch over and you'd need a sync check relay for safety (if you don't and the microcontroller is off because you forgot a comma somewhere, your inverter explodes).

Additionally producing the clean sinewave that you'd need for this is not that easy, atleast not at the quality levels you want for this (if your DAC that produces the wave is off by 1% then at a 2kW load you're going to burn up 20W somewhere that doesn't like 20W being burned up)


Redundancy and fail-safes are important but can also be inexpensive. Most of the expense comes from being a niche product right now.

How is being off by 1% going to hurt anything? I'm quite sure my mains voltage is already more than 1% off.

If I get solar it had better not explode every time my air conditioner kicks on.


Your mains voltage cannot be 1% off it's own phase since it's the primary phase here and in terms of voltage a 1% difference doesn't matter.

However, if you have your own generator it matters a lot.

If your phase is off by 1 degree then that 1 degree will burn roughly .2% of the incoming power of the grid at the inverter (which is unlikely designed to handle this). If you're off by 1% you burn 20 Watts on a device not designed for it.

If your voltage is off relative to the grid by 1% then you burn the difference, at 2kW that's about 20 Watts. And that's per volt. You'd be burning somewhere around 300 W if you happen to have the grid on the higher end of the tolerance and yours on the lower.

A grid-tie inverter gets around this by simply following along the sine wave of the grid, this can be done relatively cheaply and safely with analog components so the error can be much smaller than 1% and deep into random noise territory.

If you generate your own sine wave and compare it to an existing one it's much more difficult since you have to match amplitude and phase almost perfectly.

So with grid-tie nothing will explode. With an autotransfer nothing explodes either. Wanting to seamlessly couple back in requires a lot of care and expensive components.


Oh, you're talking about when it syncs back up. I don't really see the problem.

Next to your offline-capable sine wave generator, put a copy of that cheap safe analog circuit.

Once you get almost in sync, crossfade over to the analog circuit. (If that's even necessary. It might be just fine to swap to it at a zero-crossing.)

Now you're completely in sync. Reconnect to the mains.


I'm no electronics engineer, but don't regular home UPS units already do all of this? I'm talking about the type of units sold by computer and office supply shops to provide backup power for home / SOHO IT devices.


Generally there are three types of UPS on the market.

The cheapest is VFD which is basically a battery parellel to the mains which in case of a power failure interrupts mains and inserts it's own voltage. Usually labelled as "offline" or "standby" UPS since they're not active most of the time. The output frequency and voltage is the mains output and voltage until switched over, something to keep in mind if devices are sensitive to that.

These can simply switch back to mains when it's back since they usually use a simple transfer relay.

VI (Line interactive, Delta Conversion) uses the mains frequency as orientation. They don't have a transfer and can basically just compensate whatever the mains is doing to output a 230V signal. Internally they have a inverter with AC input and AC ouput which means they measure if mains is coming back from there and adapt the signal on the internal inverter for the battery.

If mains comes back on a VI they usually change frequency very abruptly which is not ideal from some devices.

VDI is completely independent of both voltage and frequency as it first converts mains AC to internal DC, simply plugs in the battery into the DC and then converts DC to AC. They don't need to synchronize at all and are the more common for datacenters since they isolate the input fairly well from output and don't have to switch anything to go from mains to backup, DC voltage is fairly good for dealing with this. They are also most expensive.

If mains comes back on a VDI they don#t do anything of notable interest other than switching the battery charger on.


Thank you for the detailed explanation, much appreciated.


Yes. It's all pretty much the same hardware with different firmware.

Manufacturers of solar hardware love to charge you an extra $1000 for that extra firmware though...


You need more hardware when you want to sync to grid after being off grid. You need one on the inverter and a seperated output, most grid-tie inverters simply have one port for everything. If you use one port for everything you can hardly sync the house grid to the external grid since you can't both provide power and try to sync the phase.


Err, you can provide the power, you do need another voltage sensing connection to the grid though, and might want an automated breaker to not have to attend the device and re-connect inverter and grid once sync is complete. If the inverter is properly fused, you should even get away with a LED or a small display that shows you whether it's safe to reconnect or even how long until sync is complete.


As this article touches on the solar panels are the cheap part of a solar setup. If you want to run off grid the costs skyrocket.

I live in an off grid bus. My whole electrical system cost in the US$9-10000 range with only 810W of solar. The other components cost a lot more:

* ~$900 for 3x 270W Renogy solar panels

* $1500 for 3.6kWh of LiFePO4 batteries (12 100A 3.6V cells)

* $1600 for a Victron 3kW inverter / charger

* $2000 for a Honda EU3000is generator to run my AC

The rest was the Victron solar controller, color control panel (that runs Linux!), breakers, relays, transfer switch, fuses, cable, and all the other stuff you need to hook it together.

This isn't at house scale either. The cost would go up significantly to support a house scale system.


That Honda EU3000is is an 3 kW ICE-based generator, that is, it's not a part of "solar" setup proper.

OTOH not having a combustion-based backup is likely not very wise if you live off-grid. I wonder how often do you need to run it? That is, what part of your energy budget is covered by the solar energy?


What does ICE mean?

The generator is part of the whole power system. In most implementations solar is not reliable enough on its own. You need a backup. In my case that's the generator and the bus' alternator.

Right now I'm running the generator all day to power my AC. I'm not running it most nights. It could be cycled on and off but I haven't setup an auto start system for it yet.


ICE = Internal Combustion Engine


Initial cost might be high but this cost would be slowly return as you save on electricity bills. Also, all this equipment is not perishable and you can still re-sell at good price after your retirement or sell them along with house. Its no different than investing in house upgrades which adds to the house value.


Both the solar cells and the batteries have a finite lifespan, and will eventually need to be replaced.

Especially the batteries.


Inverters have to be replaced as well.


The solar controller, control panel and miscellaneous cost you $3-4k?


The controller was more than $200, the control panel is around $550.

I didn't itemize the rest because I don't have the time to list it all. The roof rack and hardware cost around $1000. There are a lot of individual items that cost around $100, (eg starter battery isolator relay, breaker panel + breakers). Heavy gauge cables are necessary and expensive. All the small things add up.


Having just done similar at a smaller scale, that's plausible. A solar charge controller for that capacity is $600-1000 on its own, and the Victron control panel mentioned is north of $500.


ICE bus ?


There are no practical electric buses. The bus itself is on the Chevy C4500 chassis with a diesel engine.


jehu garcia made an electric VW van, but i don't know much about it.

a couple also made a solar powered van, but as people say, it's probably very short on mileage (basically move a bit and rest while it charges.


ICE?


Internal combustion engine


> The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet).

It's not ideal, but this is so much better than what most installs are built with (nothing).


I thought there were shutoff devices that could detect a grid outage and instantly disconnect your home from the grid allowing your inverter to power your house until grid power is restored. I assumed something like this would be $10K but well worth it, as basically the whole point of battery-backed solar is energy independence.


From the article, the problem isn't the transfer switch but that the microinverters used on most systems don't work without the grid. If the grid goes down or is disconnected, the microinverters stop providing power.

It is possible to get inverter that will work independently, and batteries to buffer the load, but the off-grid system is a lot more expensive than normal rooftop solar system.


Look for "transfer switch".


Super useful. Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires. In the article I read, they mentioned that even home solar wouldn't work, which seemed crazy. I can now see why this is the case, and what folks should do (get a transfer switch and generator) to be able to power their home with their solar panels.


Unfortunately, adding a generator and a transfer switch will probably not enable you to get power from the solar panels. You'll also need an inverter that's designed to operate off grid; the anti-islanding feature on a normal grid tie inverter will prevent it from providing power when the grid is gone.

There are a few ways that anti-islanding systems can work, but it's reasonable to imagine that the inverter is measuring the impedance between its output and a nominal AC source: the power grid. If that impedance is too high - and it will be unless you've got a rather large generator - then the inverter will not source power.


Can you please elaborate about the transfer switch and generator - how to use them?

What about just using batteries?


Typical grid-tied solar system would still require a transfer switch, either auto or manual, they're called break-before-make transfer switches because they disconnect the mains supply before switching over to the battery + inverter system or generator. These transfer switches are mechanically interlocked so it's not possible to have both supplies connected simultaneously as this would generally be release-the-magic-smoke catastrophic.

Typical auto transfer switches are fast enough that computer equipment etc won't notice.

Edited to add: if you want truly uninterruptible power then you should do what data centres do: everything runs off the UPS all the time (well, all the computers, maybe not all the cooling system), the only thing that changes is the supply: either mains, batteries, solar, or generator. Or some combination of batteries + the other three.


There's another UPS-source option, which is also my favorite, flywheel!

Back in the 00s I visited a DC that two very large flywheel UPS that were being trialed to replace the battery room.


Flywheels are alive and well in the DC industry. They are used for those crucial seconds while the generator starts up. And as a backup for the UPS-es. (After all, those batteries might not be in top shape all the time.)

Though I imagine eventually battery tech will take over.


If the flywheel can be integrated in to the generator design then generator startup can be almost instantaneous. Synchronisation would still take a few moments.

I don’t know if anyone is building systems like that though?


Yes, they are. Hitek builds those. The 2007 outage of 365 Main in SF, which took down many major web sites, was due to control problems with a set of ten of them.[1] Each unit had a motor/generator, a flywheel, and a Diesel engine on the same shaft. There's a free-wheeling clutch between the Diesel generator and the rest of the system, so the Diesel does not rotate when idle. The Diesel is started by its own starter motor, and when its RPM reaches that of the generator, the clutch engages and it starts powering the generator.

PG&E had a transformer fire which caused large voltage swings. The flywheels kept the generators turning, and the ten Diesel engines started OK. Then outside power came back up, and after a time delay, the Diesels shut down. Then outside power failed again, and because of a timing incompatibility between the power control and engine control, some of the engines would not restart that soon. There was a minimum "off" time on the engine; it had to stop before it could be restarted.

The engines that did start were not enough to handle the load; they overloaded and their controllers shut them down, shutting down the whole data center.

[1] https://www.datacenterknowledge.com/archives/2007/07/24/gene...


Thanks for the info. I used to work in a data centre in Adelaide doing physical infrastructure and security, so this is right up my alley.


> release-the-magic-smoke catastrophic

What's your source for the first part of this phrase?



Also fun is looking at all the components that have released their magic.

Dave Jones has a good video on it (well series to a degree): https://www.youtube.com/watch?v=SoeVNaz7KGc


The Jargon File.

Magic smoke is injected into electronic components at the factory, in order to make them work. If you let the smoke escape the package, your part has failed permanently. But as long as the smoke remains inside, there is still a chance you can repair any failure by cooling the part off for a while.


> Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires

Huh, where can I read about this?


I read about it in The Almanac [1]. Also, note that the map that shows higher and lower risk zones doesn't actually indicate what locations may be affected by outages. They only show where the affected lines are, but those apparently feed homes/buildings that appear to be in the clear.

1: https://www.almanacnews.com/news/2018/07/25/pge-may-cut-powe...


TLDR: Power lines are a cause of wildfires, and PG&E may shut down power on some transmission lines in times of extreme fire danger.

https://www.sfchronicle.com/business/article/For-PG-E-cuttin...

https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power...


Interesting fact: years ago it was designed to build electric infrastructure above the ground because air friction addsup about 20% of electricty, free. It wouldnt be possible underground. But then, you know, whole State of amedium size country like California, would have no power interruptions in heat spikes.


Even just going to pge.com i get an interstitial about it, but no detail.

A couple links:

https://yubanet.com/regional/pge-shutting-off-power-during-h...

https://www.mercurynews.com/2018/06/12/pge-could-shut-off-po...


My dad has a 7kw system with the SMA inverter with emergency power outlet for 1.5kw. Works ok, as said the main issue without batteries to buffer is stability.

I have a Magnum 3000w Hybrid inverter in my RV with 320w of solar with a MPPT solar controller. The solar controller feeds the batteries and the inverter draws from batteries or charges them with UPS grade change over. Magnum hybrids can do interesting things like if the sun is out and I am running the air conditioner off generator or shore power it will pull batteries down to float voltage and invert excess power to lower draw, I usually get about 1 amp reduction with 320w of panels. You can also dial in your shore amps and if a load needs more the inverter will step in and provide the overage from the batteries. Nice if you driveway surfing and only have a 15 amp outlet but want to run the microwave or whatever. The RV is basically a giant UPS with generator.


Having just finished a 450W solar system on our RV, along with new big-ass 200ah battery, I was shocked to find out that house systems have no battery backing. Because I have had to explain to everyone that asks “can it run...?” that you can run anything you want if the battery can handle it, the solar is just a battery charger and doesn’t directly run anything.

But as one who is considering residential solar, I guess there’s more research to do as home solar apparently doesn’t work that way at all (though it probably will when I do it).

Side note: thanks for the inverter mention. That’s next on the list, and the Magnum sounds to be worth a look.


I went the Victron route on my setup, primarily because they make whole systems that can talk with each other. I had originally been looking at the Magnum, though.


I guess in all of my searching when buying, I never discovered that Victron makes inverters, despite having one of their charge controllers (seems like Xantrex gets all the mentions for high-end inverters). I'll check them out, thanks.


I almost went Victron, they have a nice selection of equipment with some nice features. I was however put off with their documentation, very lacking, was not 100% sure what I needed to put the system together, they have like 3 different kinds of communications buses.

Magnum on the other hand has excellent documentation and a somewhat simpler product line that integrates well together, remote, inverter, battery monitor. Their comm bus is just RS-485 and documentation can be found, I wrote a node server to display info in realtime along with my Morningstar Tristar solar controller which uses modes over TCP.

My understanding is Victrons load support feature does not go down as far as Magnum, 10 amps vs 5 if thats important .They have a very good reputation as does Magnum, different league than cheap inverters.

Here is a video I did of the Magnums search watt function as some wanted to see, also shows how it deals with large loads and the web interface I wrote for it: https://www.youtube.com/watch?v=l_jqzY1wNDU


> To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while

It doesn't seem like a battery or capacitor to handle blips like an airplane flying overhead would need to be very large?


No, but using a small battery means using a battery that get heavily charged/discharged by such events, and therefore has a short lifespan (less than a year, probably, if you used the kind of battery that's in a UPS.) The reason the battery banks for solar are so large isn't just to capture the entire daytime output for night-time use, but also so that they can have a lifespan closer to that of the solar array itself.


> heavily charged/discharged by such events, and therefore has a short lifespan (less than a year, probably, if you used the kind of battery that's in a UPS.)

But surely such events (i.e. grid power outages) are pretty rare. In Australia it's rare for the power to be out more than once a year.


That's interesting! Is it like an SSD where you plan for a certain amount of cells to fail or does it reduce load on the cells so they last long individually?


The latter.

Whenever your battery gets super discharged, picture this happening inside it: https://www.youtube.com/watch?v=r-YbQN_twpw

Notice how running the current the other way will break up the formed crystals, but it won't actually re-dissolve them. That's what it means for a battery to wear out. (Battery electrolytes are chosen specifically to be resistant to this, so the effect is mainly visible as a thin "rust" of deposited crystals on the battery's anode, rather than the full-scale crystals seen here.)

A similar but distinct process occurs when overcharging a battery, where, instead of splitting the electrolyte molecules apart, you're reacting and bonding them together to form new molecules or molecular complexes, with the reaction usually being one-way rather than an equilibrium reaction. (For lithium batteries this process is exothermic and catalyzed by the presence of the product—thus lithium battery explosions.)

It's much better for the life of the battery if it basically just hovers around 40-60% charge for its whole useful life, since then you're just generating tiny seed crystals (on discharge) and then re-dissolving them (on charge), where those crystals are small enough that they can be fully re-absorbed.

And this is true even in battery-cell technologies that require a "deep charge cycle" to erase their "battery memory." Battery memory is basically the electrolyte causing enough crystalline rust specifically on the anode to increase its resistance. A deep discharge can capture and erase this rust—but it still shortens the battery's lifespan, because you're still producing non-reabsorbable large crystals within the electrolyte.


Thank a lot for sharing! That was interesting. So the desire to hover around 50% requires 2X larger batteries as would otherwise be necessary?


Yup. Though I've heard (as it concerns deep-cycle batteries) not to let them drop below 50% charge rather than keep them in a certain range. So, for example, when I purchased a new house battery for our RV, I got a 200ah battery knowing I can only make use of 100ah before recharging. Or put another way, figure out how much you'll use between charges (or in the case of solar, how much to tide you over until the sun comes up), and double it.


Not quite. Planning for battery failures is hard because they have different failure modes. For example, the battery could fail to dead short, which is the functional equivalent of an cell in the SSD dying and then setting the SSD on fire. Or the cell might just actually catch fire during normal operation if you overload it.

To my knowledge, the best and safest battery system is to have each battery individually monitored by a charge controller with the capability to fully disconnect the battery at will.

The downside is that this will be expensive so people usually settle for just eating the rare chance of a dead short battery.

Additionally, batteries that you just leave around doing nothing will probably die at some point too. You don't want it sitting around you want to use it for efficiency or else you swap your battery and find out it was dead too.

To reduce burst loads on batteries you could use supercaps if you find ones that can handle the voltage and current (that will be very expensive).


> Additionally, batteries that you just leave around doing nothing will probably die at some point too.

This wouldn't happen if batteries were designed to act like nuclear reactors, where the "fuel" (the fuel rods; the electrolyte) can be completely removed from the substrate that makes it react (the neutron medium; the anode+cathode.)

But a battery that can withdraw its anode+cathode from the solution would be damned expensive. It'd make more sense as an architecture if you had just a few, super-large battery cells, e.g. giant vats of lead-acid.

It might be possible to design regular battery cells such that they wouldn't start degrading until they were first exposed to a voltage load, though. (I think the "50 year" Duracell NiCd batteries have this property—they probably have an antifuse oxide layer between the anode/cathode and the electrolyte, that gets broken down when you put load on the circuit.)


That reminds me of a recent NASA project where they kinda built small nuclear fission batteries with less than a couple tons of weight (IIRC down to 100kg)

These would be kinda neat as off-grid generators and you can take the nuclear element out (and it would last longer but still be radioactive).


Actually they do have those: https://en.wikipedia.org/wiki/Flow_battery


Generally speaking, lead acid batteries, and lithium batteries, last longer if they are never (rarely?) deeply discharged.

If you need 100Ah from your batteries you’re better off provisioning as many times more up to some cost-benefit analysis.


Both, really. Having more ceels gives you reserves obviously, but since the per cell load is reduced, each cell degrades slower.


That you could do with a super capacitor, but not with a battery.

I know of some railway train setup, which is deployed in Saudi Arabia by Siemens, that uses a combination of battery and super caps to power the train. While the train starts it takes the sparking current from the super caps. While riding it will take the energy slowly from the batteries. While deceleration it will recuperate and will charge up the super caps, because they can be charged easily with a high current. So the super caps are used as a high available energy buffer with very fast charge and discharge capabilities. While the battery is only used during the times of less energy consumption. Also at the stations the super caps are super charged very quickly. With that concept, they can run the train the whole day with only 40% discharge of the battery. The battery is actually way smaller then in a Tesla.

This concept can be applied also locally. The problem: these super capacitors are way expansive so you need to design them to your specific requirements.


Slightly beside the point you are making - would there be a problem if the train makes an unscheduled stop between stations for any reason?


I must correct myself. It is in Qatar.

AFAIK, that should be possible.

Here is a presentation about the topic. The interesting information is in last pages. https://www.siemens.com/press/pool/de/events/2015/mobility/2...


You can do it with a battery. An 18650 that can supply a hundred watts is $5 or less. Even limited to half its discharge depth for longevity, it can take you through "blips" two minutes long.

I wouldn't want to ride a battery pack like that all day and every day, but it should be fine for emergencies.


Also, while not necessary trivial, it is not hard to throttle consumption of devices, and if it's with two circuits, one for devices that care about voltage, and one for devices that actually brown out. The latter is easy to scale by just reducing the voltage far enough that it doesn't sink too much power, and devices like e.g. desktop or server computers are theoretically easy to rapidly throttle, e.g. by reducing cpu clock to a few hundred megahertz, halting HDD operations or even cutting their power (most are made to handle hot-swap well). A large, modern CPU with 140 W TDP can cut usage within 10 ms to 10W, but dram can't scale that way due to how it works, or rather, this scaling is not supported in mainstream hardware.

If you use a small supercapacitor, which commonly has a minimum discharge time of about 2~20 seconds (similar to Lithium-ion pouch cells "LiPo", which are available with different "C" ratings, and negatively correlated gravimetric/volumetric energy density and maximum average discharge power (i.e., optimizing discharge current vs time to maximize the ratio of total power extracted divided by time until empty). You need more metal in the electrodes and the plate/foil that aggregates the current of the individual electrodes, leaving less space/weight for the parts that actually store energy.), you can use much more advanced power reduction techniques for electronic devices, as you have time for something approaching a proper shutdown. Compare e.g. the time your Laptop takes until it is off from the moment you close the lid.

Oh, and yes, these capacitors are cheap. One about 1kg / 1 liter size for about 100$ can provide 20kW average power, for 2 seconds. The main difference is that they don't care (much) if you cycle them at 100% depth of charge, apart from internal losses heating it up and thereby causing damage.


Maybe this applies in normal markets, but in Puerto Rico the grid is both shit-tier reliability and horribly expensive. Rooftop solar and lithium batteries in an off-grid format are both far more reliable and far cheaper than the grid, assuming a 5% cost of capital. I might throw in some LP or diesel generation capacity too, but solar plus battery is an easy choice.


Of course. Islands are one of the only places where solar truly makes economic sense - having to ship your fuel in changes the economics equation a LOT...


That’s a good point. If a grid is unreliable then an off-grid solar investment would have to factor in the opportunity cost of things like spoiled food, productivity (can’t work remote with no power), amenity offerings (restaurant with A/C versus not) and so on.


Are lithium batteries the best choice here? They have superior energy density, but IIRC there are choices that are heavier but cheaper (per kWh installed), like ready-made car acid-lead batteries, or industrial Ni-Cd batteries.

What do people actually use?


Tesla PowerWall is only an Apple-level premium (and not a Vertu-level premium) for what it is. I would probably just go with 1-4 of those for residential unless getting something more capable. I don’t own a house yet, though.

My ideal situation would be a microgrid with 10-20 homes (in a compound/neighborhood or condo building) and some commercial/office, which pushes all the electronics costs down to something more reasonable.


Not sure for Solar, but most HAMs using field radio setups still use deep cycle marine batteries as they withstand abuse and are much cheaper.


The big benefit lead acid batteries have is that it's easy to find surplus SLA batteries from businesses, and even new cells aren't that expensive.

That said, I've started seeing lithium batteries slowly catch on in amateur radio as the price on the LiFePo4 cells go down. Especially for portable setups.


What would you say grid uptime (%-wise) is there for you right now?


Depends on where. There are a couple of remote areas with no power still, but generally in San Juan and the areas where most people live it has been good in q2, with a couple of multi-hour outages. Still, at $0.35/KWh in a high sun place solar is obvious.


I've read the detailed reports for outages in the West and the North-East, and they touch on alot of the same concepts that were in this (awesome) article.

Does anyone know, what's a good resource for learning more about power generation, grid regulation, etc.? The relationship between frequency/voltage and available vs. demanded current, frequency sync, grid maintenance, etc.…


If you have a reasonable electrical background I would suggest this textbook:

Electrical Machines, Drives and Power Systems by Theordore Wildi


This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. It used minimal components (& simple ones), no batteries, nothing fancy but was enough energy to supply a community of several single family homes in a completely off grid system.


> This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid.

So, your example of energy options other than solar is solar with hydro storage? Or did you mean “other than photovoltaic” when you said “othet than solar”.


Yeah, meant to say conventional PV solar.


Fascinating. By chance, would you have a link or article for further reading?


During 2017, I saw a lot of news articles talking about how the Evil Power Companies were being Meanie McMean by not letting people with solar panels use them when the grid was down. The implication (in many news articles) was that these powerless people with solar panels could use them to power their home while the grid was down, if only the evil power company didn't require that solar not work if the grid was down.

I don't remember seeing any articles that blame the power company for home solar not working off-grid... I do remember seeing articles saying that most home solar installations won't work if the power grid is down, but nothing that implied that the power companies were behind it.


In Florida it was popular around hurricane season after we lost power.

I'm glad I finally understand why because all that I'd seen reported was the solar systems installed must be turned off. I'd always assumed all these systems (many of which are meant to be used in a storm + lower electricity costs) had a transfer switch.



So much complexity to deal with synchronizing AC frequency. I wonder if DC wouldn't be a better choice for a modern power grid?


High-voltage DC [1] is being used to transport power over longer distances because it can be cheaper and there's less power loss.

Like a sibling commented here, the costs would be enormous to convert an AC grid into a DC grid. AFAIK are there two reasons that the grid is AC: generators produce AC, and AC is so easy to transform up and down. That transforming is essential since you want to transport energy at high voltages [2] but you don't want 380kV in someone's house.

[1]: https://en.wikipedia.org/wiki/High-voltage_direct_current [2]: https://en.wikipedia.org/wiki/Electric_power_transmission#Ad...


Your right that AC is super easy to transform. But it’s quite easy to build generators that produce DC.

They’re frequently called dynamos and you find them on old bikes to power the lights.

With modern electronics doing DC-DC transforming is pretty easy (because modern electronics is basically magic). And the reason why high voltage DC transmission is a thing, is because you can get way more power down the same wire with DC compared to AC.

Many high voltage DC lines used to be high voltage AC that was converted to increase the transmission capacity without building more cables.


AC also allows for smaller switches and relays, as you are guaranteed to hit 0 V within a phase, so you can disconnect loads without giant sparks/arcs.


Within half a phase. And not to nitpick, but the important part isn't that it's 0V, it's that it's 0A which isn't the same point when dealing with inductive loads.


But, apart form installation costs, a low voltage DC power network inside homes might make sense (e.g. 12V or 24V). There's a lot of modern electronics that doesn't depend on the regular powerline voltage anymore. Unifying their power supplies into a central unit should have some benefits.


> a low voltage DC power network inside homes might make sense (e.g. 12V or 24V).

It wouldn't work. The needed wires would be like garden hoses.


Yup, there's a reason even POE is 48 volt in a lot of applications


I recall seeing somebody that did exactly that, largely because it was way more efficient for solar setups. It is a bit ridiculous to take DC power from solar panels, convert to AC power, then plug a standard home electronic power supply into it which... converts it back to DC.

Might not work for everything (eg, refrigerator? Microwave?) but it could be worthwhile to run a secondary DC network.


It will certainly not work for devices with high power requirements. So ovens, washing machines, etc. are out. But computers, TVs, routers, phone chargers and all the other small stuff might profit.


The costs to refit would be enormous.

I think there are some issues on longer lines with things like inductance, cable size requirements, etc as well.


My cheap and simple 15-minute UPS device has waveform generation (?) and a battery. Surely with solar you often have to have huge batteries?

In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.


> In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.

Not a subject matter expert by any means but depending on how much sun you get, there are probably better options than solar for you (solar might not be the right choice for you).


Solar is increasingly popular around here though (latitudes 60-65) which I only assumed also meant that storage was also handled with batteries. Seasonal storage is probably not, but at least generation during the day and use during the night must be.

I learned from the article that lower temps helps efficiency, so perhaps our climate with short days and subzero temps for 5-7 months is still viable because of higher efficiency?


Keep in mind that thermal storage is cheap compared to electrical, just not efficiently reversible. E.g. you heat up a block of paraffin in a tub of water and it takes a lot of energy without large temperature changes due to the phase change. The output temperature would require rather large radiators or floor/wall heating.

At this temperature you could even dump waste heat of a computer (well, CPU and GPU, maybe DRAM, not the rest) into this thermal storage.


I'm curious why a large capacitor or inductor cannot be used to provide momentary power for things like electric motor starts, and to smooth out events like a plane briefly occluding the sun.

I built an audio amplifier in college that had a couple of huge capacitors on the power supply (about the size of a can of soda). It would keep the amp running a few seconds after I shut off the power.


Fundamentally, the size involved. Your amplifier's capacitors were extremely large for the power the amplifier was using, as their purpose was to reduce the ripple voltage from the power supply.

One of those "1 Farad" car stereo caps (not the classiest example) can store 72 joules (watt-seconds). So to handle a 1kW excursion for 5 seconds, would take over 70 of them. Possible, yes. But probably not worthwhile.

The frustrating thing about this article is that it keeps conflating fundamental physical problems (like needing to store energy to deal with peaks), with the limitations of currently-productized circuit topologies. It's not hard to imagine an inverter that would do something similar to MPPT without needing to pull/dump the maximum power possible, would manage a small bit of local storage (a combination of caps and abused batteries), and could intelligently load shed (with "kind" brownouts) on multiple outlets.

It's also not hard to imagine an inverter (brushless motor) air conditioner that would be a lot kinder of a load, and could even operate at variable power.

But of course with the current state of homebuilding, these are bespoke ideas better filed as "off the grid". Which is the entire larger point - an "off the grid" system fundamentally costs more in materials and also presently application engineering time, than the on-grid systems being sold to homeowners.

(Although I do have to wonder about adding a piece to the current puzzle that would generate/manage a local grid frequency, and shed excess power using off-the-shelf electric heaters.)


> over 70

This doesn't sound that bad to me. Size isn't much of an issue, houses have room for them. Prices for them seem all over the place:

https://www.alibaba.com/showroom/1-farad-capacitor.html https://www.amazon.com/dp/B00381UKD0/ref=psdc_2230642011_t2_...

The idea with a capacitor is they shouldn't degrade like batteries do.

The same with an inductor, which is just a coil of wire.


$30 x 35, assuming a 50% discount for wholesale [0], is still $500. This may be worthwhile, but it's certainly not negligible.

Electrolytics do wear out. Lifetime hours versus temperature/ripple current is a key design parameter.

[0] And assuming stuff designed for the car stereo market actually meets its advertised specs. I just went to Youtube to verify that said devices weren't just a can with other components inside of them. A video with a freehanded jigsaw set to hip hop confirmed.


Just to be clear, the caps were bought from the Caltech EE supply desk. They weren't for car stereos. It was before car stereos became a thing.


I was just using car stereo caps as an easy-to-reference bound. (I'm not in tune with current cost of bulk energy storage caps)

As I was saying before, the main difference from your amplifier was the amount of power involved. In general, audio amplifiers have large capacitors on the power rails to smooth out the ripple voltage, and will coast for quite some time as they don't actually need that much power for typical music and volumes.

Here's a similar example - high current USB charging bricks, with a power indicator LED. If you have no devices connected and unplug it from the wall, the LED will stay on for quite some time. The LED just doesn't draw that much current (say 10mA) compared to the capacitance, which has been designed for smoothing the full charging current of 10A. Also the LED will happily ride the voltage down from 5V to its junction voltage of 2.5V or whatever, using even less current. And due to the logarithmic nature of your eyes (ears), you don't fully perceive that dimming.


The caps were way, way excessive for the application, I was just having fun putting them in. And they didn't just smooth out the power, they were capable of running the amplifier for a few seconds. (It was a 125 watt Universal Tiger amp.)

I do know that caps decay over time, but have no idea how that compares with batteries. I expect, though, that long life caps could be built.

I also wonder about using inductors instead. They are, after all, just a coil of wire.


I feel like you're asking the equivalent of why we use DRAM instead of SRAM, or spinning rust instead of flash. And I don't want to shout that down because, as in the latter, constraints do change. But the current state of things is fundamentally based on a cost tradeoff.

https://electronics.stackexchange.com/questions/42084/can-yo...

https://electronics.stackexchange.com/questions/326177/energ...

Perhaps in the future we'll have supercooled inductors providing power storage, and not requiring periodic changing the way say batteries do. Alas, it's just not right now.

As an aside, it's amazing how little power it actually takes to produce worthwhile sound out of modern speakers. I once wanted to test some tower speakers without a proper receiver around, so I wired up a breadboard with some stupid opamps around poorly-heatsunk transistors, powered by a lab supply. The speakers turned out to be disappointing, but not because of the amplifier!


Thanks, that does answer the question.


Inverter drive home AC systems that are reasonably priced do exist, you can get a mini split for under $1000 now with variable drive compressor and fans. I was shocked last time i looked that up actually, as i had similar thoughts a few years ago for this application and barely anything was on the market.

There's also inverter drive microwaves, and fridges even. My friend's new condo has an inverter drive fridge


Capacitors are for DC. You but them in your amplifier after the supply, when you have DC.

Electric motors, especially the simple ones found in compressors for cooling, are running from AC. You can't put a capacitor into the AC path. You can only convert it to DC, charge the capacitor and then convert it back to AC. Where we are back to the original problem.


> Capacitors are for DC.

The output of solar panels is DC, too. The capacitors would be placed in the DC side.


The real problem is having insufficient power to provide AC, not the need to use slightly better logic in the inverters.


Of course, if you want to run off the grid, the first thing is to minimize your electrical appliance. Get a laptop, the laptop will serve as your TV, computer, radio, etc.

No TV, no Washer/Dryer (you will hand wash), No regular fridge, get a small 12v fridge. No microwave, use stove to heat up food. No A/C, design the space to not get hot, high windows, under the shade, facing away from the sun. Maybe a small fan. The biggest optimization begins with your appliances.

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