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Show HN: $200 Solar Self-Sufficiency  Without Your Landlord Noticing (medium.com/nikodunk)
491 points by nikodunk on July 21, 2017 | hide | past | favorite | 182 comments

I built a very similar system into my Jeep-house.

I have two 100W panels on the pop-top roof, a charge controller and a dedicated solar battery (isolated from the engine-starting battery) that runs my fridge, water pump, UV treatment lamp, interior lights, air compressor and charges all my electronics (laptop, kindle, cameras, etc.) directly from 12V DC.

I can leave the Jeep parked without running the engine for days and easily have enough energy to meet my needs.

The system has been amazing, and it's fantastic to be electricity self-sufficient in remote West Africa, where grid power is often non-existent

More details and photos here: http://theroadchoseme.com/jeep-build-complete

I can't remember how I did it specifically, but I believe there's a way to wire up a second battery to your alternator where it only charges it, and your vehicle will never draw from it. Could be a way to keep it topped off while cruising around.

It's called a battery isolator, and it's basically a monster diode from the alternator to the battery. Very common setup for RV's, etc.

I had one set up in my Jeep so that it would charge the deep cycle marine battery for my fishing pontoon's electric motor... way, way faster than anything you plug into the wall.

I think you might mean solenoid?? It's controlled by the ignition. When the key is on / car running both batteries are in parallel. When the ignition is cut, the solenoid isolates a few circuits that are wired on the backup battery side of the solenoid.

This is what I have in my vanagon. I run the radio, fridge, interior lights and some 12v / USB outlets.


Both no doubt exist. A diode would let the secondary battery charge, but never let the engine draw on it; a solenoid-driven contactor would let the engine both charge and draw on the secondary battery, but only when the engine is running.

Combining both might not be the world's worst idea, depending on the design purpose. The diode alone would allow the secondary system to draw from the primary battery, potentially drawing it down far enough that it couldn't turn over the engine. The contactor would prevent that by completely isolating the two circuits while the engine is off; the diode would prevent the secondary battery being drawn down while the engine is on. If you need to draw from the secondary to turn the engine over or draw from the primary into your hotel load, you can short across the diode-contactor pair with one side of a set of jumper cables.

The devices used in better RVs are a solenoid which combines the batteries but only when the vehicle battery is above a certain voltage, typically set for a mostly full battery with surplus alternator energy available.

This avoids the voltage drop of the diode which confuses the charging situation for the house battery. It is also save the 2-5% power loss and heat dissipation on a diode.

As a bonus, you get a switch to manually engage the solenoid for engine starting when the vehicular battery is weak.

I've always known it as a battery isolator, and have purchased/installed 3 of them, and that's what I bought them as.



AKA a variable split relay, VSR. Use one in our campervan, still haven't made the upgrade to solar for longer stays where you don't want the engine on, but it's good to keep the leisure battery topped up.

I doubt it's a solenoid. Solenoid can be used for galvanic separation in AC circuits not DC. Maybe you mean relay?

It is a Solenoid, it's exactly what I have: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

I have exactly that! Here's my setup in more detail: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

Just wanted to say, I've enjoyed following your journey on Instagram! Stay safe out there.

A question: How much did the solar aspects of your rig cost?

And a comment: You might want the ability to tap your solar battery to start the Jeep, if you're going to leave it parked that long.

I have a setup on my van and it was about 700$:

100w panel: 100$ Mppt Charge controller: 100$ 100ah batteries x2: 400$ dc breakers, fuses, wires: ~100$

My setup is enough to run a fan 24/7, multiple led light, charge phone & computers (~2x a day). Takes about two days of rainy weather before the system capacity drops below 50% DOC (which is where you should disconnect loads).

Wouldn't tapping the other battery be a simple matter of a pair of jumper cables?

I mean, I guess it'd be nice to have wired in, but I can't imagine the time-savings would ever catch up to the initial amount of work.

On TJ and older Wrangler the tray on the opposite side battery tray is empty. People will run dual battery setups that way. There are even options for all Wrangler models to put dual batteries in the stock location. $100 to $200 on a TJ Wrangler.

The cost and amount of work to do it is minimal.

Depends on how close the two batteries are to each other.

I mean, I guess you could physically remove the solar battery, and hand-carry it to the ground just in front of the engine compartment, but now the hassle factor is getting rather high...

The setup did not cost much. A couple of hundred for the panels, a hundred or so for the charge controller and a couple of hundred each for the two batteries.

I have an isolator so I can jump the Jeep from the solar and visa versa. Wiring details here: http://theroadchoseme.com/diy-jeep-wrangler-jk-isolated-dual...

Most modern motor-homes I've seen/used have a solar panel for trickle charging the leisure battery.

Some other good examples of retrofits here: http://www.goalzero.com/solarlife/stories/en-route/

Cool! The one thing I notice the author gets wrong is (out of modesty perhaps) claiming the system isn't very financially successful. But it actually is!

> 200W system payback period: $300 / $48 = 6.5 years until payback

> Either way you cut it, this is not a money saving machine. Energy prices are just too low.

That represents like a 16% rate of return with little risk, which any investor would take in a second.

However, the $66 battery expires after about 8 years, you're saving more like $40, not $48, to amortize the cost of replacing the battery every 8 years. So the actual rate of return is more like 13%, which is still very attractive. You'll never find any investment/savings product that returns half that well at such a low risk and is so accessible to anyone with $300.

We've hit the point where solar is very economical! It's exciting!

You can also get cheaper batteries and larger panels off Craigslist for much less. You can easily find much larger panels for around $100.00 - same kind you see on roofs. Batteries are more difficult to find cheap, but 6 volt golf cart batteries are readily available and low cost. Sometimes you can also find the 12V 35 AH wheelchair batteries (same as what the author used) cheaply too.

Point being, if you look around, solar electric generation at a small scale can be done even cheaper than purchasing off Amazon for some of the components (inverters and charge controllers are mostly exempt - unless you go to a hamfest).

Very good point! Hadn't thought of second-hand components. That'd help with the environmental footprint, too!

Unfortunately it isn't a 16% return because he can't sell that system for what he paid. If you buy a stock at $300 and sell it for $348, that's a 16% return. But for him, he probably would have trouble selling all of that for $100 (the battery will be worthless in about 2 years given how far it is being discharged and very few people buy these things on craigslist for anywhere near what they cost). If he can sell it in 6.5 for $100 he has now made $400 in 6.5 years, a 4.5% annual return.

Being able to sell the system is irrelevant as long as the system will last indefinitely (or say, 30 years, which approximates the same value anyway). Everything but the battery is solid state and should last indefinitely -- or certainly more than 8 years. I already excluded the battery as a consumable to calculate the 13% rate of return. But one thing you are right about is the other parts will fail eventually, dragging the return down as well.

Solid state parts can last decades though. The best way to calculate the rate of return would be to actually get accurate numbers for lifespans for all the parts and amortize them. It's probably greater than 4.5% and lower than 13%. Regardless, at near zero risk, even 5% is a great return these days, so it's totally worth doing.

Since you like the stock analogy -- a share bought at $100, that earns $10 a year, and that for whatever reason we confidently expect to keep earning $10 every year for decades, returns a 10% rate of return. The fact that the stock now sells for $50 makes no difference, as long as we believe we are right and the market is wrong about the likely future earnings.

Honestly I think even my number is a little optimistic because I doubt his battery lasts 2 years. Most lead acid batteries are only good for 100-200 100% cycles. I also doubt that the PWM controller or the inverter last 30 years. I've seen failure rates as high as 50% for cheap PWM controllers like that after 10 years. The inverter is likely similar. Sure you can buy stuff that will last 30 years but that will be much more expensive. 8 years seems like an appropriate amortization schedule which puts my $100 at 6.5 years as a little generous.

> as long as we believe we are right and the market is wrong about the likely future earnings

In a liquid market like the stock market, the odds of this being true is small. Recognizing a 10% return against a stock that's crashed 50% borders on, depending on if you're investing your money or others', delusion and fraud, respectively. There is no liquid secondary market for home-solar components, however, so approximating cash flows and amortization schedules works.

(If you've heard the terms "mark to market" and "mark to model", this is what they're talking about.)

Yup, it's very hard to make a good return in the competitive stock market, but easy to make a good return in the market you have exclusive monopoly access to: making investments that cut your own personal costs of living

> Solid state parts can last decades though.

But every year we seem to get better silicon. Better CPUs, GPUS, SSDs, etc. Same holds for photovoltaics.

To run with the investing analogy, it's like claiming you bought a bond with a 5 percent return, when six months later interest rates shift in the bond market. Now the rest of society is getting 7 percent returns, and you have to sell your to sell your bond at a discount to compensate. Sure you can hold the bond to maturity, but you're still missing out on that 2 percent return in the greater market.

To run further with that same analogy, what if you expected bond rates to keep increasing for 50 years? It would not seem wise to keep your savings in a checkings account for these same 50 years, to then get the highest rate.

Yet that's what most of us keep doing with solar, missing out on a good deal because it gets better every year.

Exactly! Thank you!

Assuming these are real, not nominal rates, who cares? I'd rather maybe miss out on the extra 2% than definitely miss out on the original 5%. Why be jealous?

You can also hedge your bets by gradually increasing your investment (maybe even "dollar cost averaging" or some other strategy)

For solar, that could mean getting a small system like the OP describes, trying it for a year or two, then expanding it a little more every year or two with the latest cheapest most effecient panels. This should work even better than dollar cost averaging does for securities, since you know it's unlikely the cost of panels will go up.

Those calculations also assume he'll use all of the energy it produces, every day, with no loss; it's a back-of-envelope best-case calculation, at best.

If we're getting into the nitty-gritty, then let's also include energy cost inflation into the equation. These numbers are for PG&E which is roughly equivalent for SF:

    2001: 0.10c kw/h
    2017: 0.28c kw/h (as per my recent bill)
That's an average of 10% increase in energy cost per year!


Isn't 2001 during the Enron fucking with the West Coast for profit years? A quick review of wikipedia suggests that in 2001 prices may have been held artificially low. A quote by Gray Davis seem instructive:

> "Believe me, if I wanted to raise rates I could have solved this problem in 20 minutes."

2.8x increase over 16 years is a CAGR of 6.6%, not 10%.

(1.066 ^ 16 = 2.8)

Correction acknowledges!

Hahahaha that's an awesome point and not something I'd thought of.

But it seems that on your recent bill they're including the service fee in that – I'm only paying 14 I believe? Also, wasn't energy super expensive in 2001 due to deregulation? (I'd need to research this, not sure).

Given his current setup, you have a good point.

However, with a setup that includes say, his refrigerator, there'll be more than enough load to ensure no collected energy is ever "wasted"

Indeed, this is why the number of solar farms being planned is sky rocketing at the moment across many countries.

Another way to maximise output of your panel is to make sure it's in the best location, taking into account seasonal change of the sun depending on your location, avoid shading etc. The azimuth (direction) and tilt of the panel is make a big difference to your output.

Shameless plug, you can forecast your output using the (currently free beta) Solcast API.


US forecasts update every ~30 minutes.

I played around with a solar savings calculator a while back out of curiosity, there is an excel spreadsheet on an Australian website I believe that's pretty thorough, but it's not the only one.

In short, I don't think it pays to sell electricity back to any utility (they pay back 1/2 of what they charge you) and a battery system probably won't be worth it unless you truly want to stay off the grid. Get a system that's enough for your maximum daytime usage, that's the fastest way to break even, and spend the least amount of money. For such a system, given my local electricity rates, the break even point was ~15 yrs. a decade ago, and it's 7-8 years now. If you can find cheaper panels/inverter the break even can be ~6 years, after which you'll only be left with a much smaller electricity bill. It even makes sense to add panels later if your usage increases.

The way the break even time has been shortening is very exciting, more people will be able to afford it; and if you can, it's a no-brainer to do it sooner rather than wait.

Thanks to put that in number. I was unsatisfied with the "not good enough" conclusion after reading it, but couldn't exactly say why.

CO2 footprint probably also is better than mentioned. Certainly, it would take 4+ year to pay back for it, but what would have been the footprint for those 4+ years using coal based electricity? It's not only "how does the system perform", it's also "how does it compare".

Well but 6.5 years sound s like a lot of the parts are getting replaced 1.x times which increases costs again.

Wow that's a really good point.

I work in solar, and your panel really, really, REALLY needs to be secured from wind. Luckily, they make ballast mounts that don't require screwing into the roof[1][2].

[1]: http://www.orionsolarracking.com/commercial-roof-mount/balla... [2]: https://www.civicsolar.com/products/racking-mounting/applica...

Funny that we live in a world where one renewable energy source is powerful enough to (literally) blow away another.

Right which is why I believe that after the coming consumer solar revolution there will be something similar with wind energy. Especially with newer VAWT designs and areas that have a lot of wind.

They compliment each other so wind can continue producing at night.

For anyone curious, a VAWT is a Vertical-axis wind turbine (https://en.wikipedia.org/wiki/Vertical_axis_wind_turbine). I always thought these were less efficient than the conventional designs but they're clearly simpler.

Conventional designs struggle with low winds, gusty winds and winds coming from wrong direction. VAWT designs generally fare better with such non-ideal conditions, which are going to be common in residential sites.

Got it! Thanks for the input. Damn that drives up cost, though. I'll work on securing it with weights and post an update.

If that thing catch up wind and fall you'll surely have to pay a lot more. It's surprisingly quick how wind can shift large surface like this.

Fun stuff. I've built several systems just like this one for camping, they let you keep things like iPads or laptops charged and they aren't noisy like running a generator.

Something that my wife discovered was that an igloo "lunchmate" cooler was perfect to hold the battery and charge controller. Makes it easy to carry. I recommend using Anderson Powerpole connectors (https://powerwerx.com/anderson-power-powerpole-sb-connectors) to make it easy to set up and tear down. I typically use one pair of colors for the connections to the battery, and another pair of colors for the panel to charge controller.

During Iraq/Afg conflict, US army started investing in solar systems because they realized every fuel (alot used for generators) convoy that doesn't have to make runs to outposts means less exposure to attacks by enemy. Solar systems can help lower fuel consumption for generators.

I heard fairly high percentage of US veterans back at home are more interested in solar systems because they saw the high cost of moving fuel around.

Ironic. We supposedly went there to secure our energy source and we learned solar system is a viable solution...

I think an argument could be made that, going there to secure our energy sources forced us to LEARN how to make a better, viable option.

Damn, that's some inside advice. Let me try it out and I'll post a follow-up! Thanks so much!!

+1 on the Powerpole connectors, I used them on a small solar system very similar to what's described in the article and they work great.

> Unless you live on an RV or a boat it doesn’t make financial sense yet

If you're curious about what a system for an RV does look like, I work remotely full time in an RV and built my own system: https://therecklesschoice.com/2016/04/29/diy-rv-solar/

6.5 times the solar, 15 times the storage, 20 times the inverter (but mine is overkill for us honestly).

And cost?

> We installed a fairly large (for an RV) completely custom solar power system all by ourselves for right around $3000.

Sorry, saw that. 15x the cost.

Are you stationary or do you move around? Four batteries + solar panels can get somewhat heavy and eat into your total capacity, so I'm curious if it's an issue.

We are very mobile, usually stay in one place for a week at a time and then move a couple hours away. You're right about weight though, we are right at our GVWR (11,000 pounds) when fully loaded. The batteries weigh 100 pounds each and the panels are another 15 pounds or so each. That said though, we get terrible gas mileage already so the extra 500 pounds for everything doesn't change it much.

A couple nice things about SF on this topic:

1. Davis Stirling (Housing related laws) mandates that building associations cannot prohibit owners from installing solar panels. Basically, they have to work with you to find a way and can't just say no.

2. As of this year, SF is the first city to require that all new buildings (10 stories or less) have solar installed.

Another excuse to raise rent...

It's been clearly shown that they don't need excuses to raise rent.

Solar on an apartment building wouldn't impact the cost too much. The real issue is whether construction/zoning is allergic to density.

How many buildings are being built in SF that are 10 stories or less ?

A darned lot of them. SF is very much a low-rise city, vast swaths of the city are no more than 2-3 stories. Part of why there is such a housing crunch...

Please bolt the panel down, if wind picks it up and blows it off the roof it could easily kill someone.

Okay I'm gonna have to look up a mate who works in statics – not sure what to believe from the discussion below (good sources on both sides) :). My gut says it wouldn't move either, but I'm not about to gamble with others' lives. In the meantime, I'll weigh down the four corners with massive cinder blocks (so as not to block sunlight).


I really doubt the wind is going to pick up a 2'x4' ~20lb panel like that when it's flat on a roof. Now if he had lifted an edge to try and get a better angle with the sun that would IMO be a much larger issue.

>I really doubt the wind is going to pick up a 2'x4' ~20lb panel like that when it's flat on a roof.

thus the difference between the air speeds over the panel and under the panel in this case equals to the wind speed. To compare - Cessna wing loading is 15lb per square foot and it is generated at the minimum no-stall speed required by the FAA for general aviation of something around 70 miles/hour, and in that situation the speed difference between over the wing and under the wing is obviously significantly less than the 70 miles/per hour that wing moves through the air with. Thus it is pretty possible (to be sure one can just plug the numbers into any aerodynamics calculator on the web) that this panel at 8 square feet would generate multiple tens or even like 100lb+ lifting force at storm/hurricane winds of like 70 miles/hour and may pretty easy lift itself at the 30-40 miles per hour wind (which do happen on occasion in SF/BayArea). This is basically the same basic aerodynamics (Bernoulli speed difference) that tears buildings' roofs off in hurricanes.

That's not how wings work. https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

Most obvious problem aircraft can fly upside down.

you're trying to argue with the Bernoulli law. I wouldn't recommend it :) Even your link clearly states:

"{The upper flow is faster and from Bernoulli's equation the pressure is lower. The difference in pressure across the airfoil produces the lift.} As we have seen in Experiment #1, this part of the theory is correct."

Re-read my original comment - it is pretty much stating the same as the cited text above.

The link you posted refutes the "Equal Transit" Theory which is deriving the speed difference from the wing asymmetrical shape using very simple approach. Which has nothing to do with my original comment as i was applying the [correct according to Bernoulli law and your link] theory of pressure difference generated by airflow speed difference to airfoils without regard to whether they assymetrical (Cessna wing) or symmetrical (solar panel).

Read the full page.

"The symmetric airfoil in our experiment generates plenty of lift and its upper surface is the same length as the lower surface. Think of a paper airplane. Its airfoil is a flat plate --> top and bottom exactly the same length and shape and yet they fly just fine."

Wings are angled into the wind. The curved shape primarily minimizes drag rather than generating lift.

As to hurricanes most roofs are sloped. Yes, faster moving air has lower pressure, but if you run the equation it's a fairly weak effect. So, it has little to do with stall speed.

No, that could easily happen. The parent was right, that panel should be secured in some way. Wind gusts can do some crazy things.

First, there are no hurricanes or tornadoes in that area.

So, you can work out max wind via historical data, but 85MPH is not going to be enough to move it over that lip. The skin effect around a building drastically reduces the forces involved.

You aren't accounting for a million other things that can happen.

I have no problem saying bolting something to the roof is a good idea, I just don't think the wind in that area is going to lift that specific object. Move sure, lift no.

So, saying any if the actual significant reasons to bolt it does haze zero influence on my objection.

Mother Nature is stronger than you think: http://i.imgur.com/3fqbBgY.gifv

Cars are much easer to move than a heavy panel flat to the ground.

And I am being serious here, if you notice to car rotated and got slightly lifted but not flipped into the air or moved very far. But most importantly, the wind is much stronger a few feet in the air vs 1 inch from the ground.

Coastal city, flat panel on a roof.

That's a when not if scenario waiting to happen.

"Really doubt" is probably a poor level of confidence with regards to a decision that may or may not kill someone.

Tell that to the average car driver.

But sure, bolt it down. Minimal effort vs minimal risk is something people do all the time. My point is the actual risk is very close to zero.

20lbs is nothing for a strong gust of wind on a roof.

Flat roof, low profile, is very different from even an 1/8th inch gap on a slanted roof.

You really need to stop replying to every reasonable comment pointing out a very real risk with all this ignorant nonsense. You know not a thing about air flow on that roof (or anyone else's), and you seem to be utterly clueless as to how powerful even mild gusts of wind can be. Trying to convince people they DONT need to take reasonable safety steps, even when presented with knowledgeable arguments that are clearly better informed than yours, is incredibly irresponsible. Please reconsider.

Run some actual math > fear.

Yes, in a slightly different situation this would be an issue. But, wind is not magic fairy dust that can lift arbitrary loads.

Look, there is a reason why people secure stuff on rooftops. What are you arguing here: That it's okay to leave shit around because the chances are low that it will kill somebody?

Just stop with the flawed logic.

No, I have no problem saying securing stuff is generally a good idea. If nothing else it makes it harder for someone to steal it.

My point is the specific bad thing described is unlikely to happen. And sure I got a lot of knee jerk reactions but nobody actually did any kind of meaningful calculation demonstrating an issue.

It's not a knee jerk reaction. You have limited view of the problem. I've lived next to a three building being constructed as a kid. The amount of stuff flying is unreal. You aren't accounting for cats, earthquakes, determined birds, malicious intent, gravel under the panel+wind, strong rain that may move the board and angle it.

Your sole argument is, historical wind speeds won't lift it. That is not realistic, naive and outright dangerous thing for which people actually get badly hurt or die.

But, I don't see you slowing down in this thread, so I doubt safety concerns will reach you.

>It's not a knee jerk reaction.

Followed by a knee jerk reaction without any facts backing it up...

> That is not realistic, naive and outright dangerous thing for which people actually get badly hurt or die.

PS: Potted plants are often placed on the top of flat roofs with a lip and don't get tossed off it by the wind. The reason has to do with how the wind is deflected over the building and the obstructions around it. Often pushing them in opposite directions from the wind because of a giant counter rotating vortex of air. But, be happy with your inaccurate and over simplified model of how the world works.

Thank you for trying to reach this person. I think they perceive the safety recommendation as a direct attack on logic and mathematics.

Ehh, I just said I had no problem tying something down. Especially in earthquake country. Just that wind was unlikely to lift a panel, but rather than admit they where wrong everyone keeps doubling down as if wind where the only issue.

You've never seen a panel dismount itself through wind force only.

The last place I worked we did this (though with some permission). One of the guys made friends with some people at a thin film solar plant down the street. He got a bundle of manufacturing rejects (300w panels that only made 280) for free. We strung them up on the roof and were raking in the kWh. Enough to charge 3 electric vehicles without paying the power company.

This makes me wonder why the panel manufacturer doesn't bin panels like they do with CPUs? Surely they could sell them for less than the 300W panels, but more than zero?

Most do. The panels you see on rooftops are all generally exactly the same size but could generate anywhere from 315w/panel to 250w/panel depending on binning. No idea why that company didn't.

When I was shopping Itek panels, I got a prices for 270W, 280W, 290W, and 300W. I suspect most companies do binning.

Will the landlord notice? Maybe not. Will the wife notice all the wires all over the place? You bet!

Because men love electronics projects and women love keeping a tidy house and ruining their dreams, am I right?

> Because men love electronics projects and women love keeping a tidy house and ruining their dreams, am I right?

I don't think this is accurate. Personally, I've had a lot of trouble finding people of either gender who are interested in electronics.

I might be overstepping here, but it sounds like maybe you should talk to you wife and see what can be done to minimize the negative externalities caused by your hobby? It's hard to imagine she would actually want to ruin your dreams. I don't have a wife, but I know my girlfriend became a lot more supportive once I started keeping half-finished projects in the spare bedroom, and started putting in an effort to clean up my projects a bit more before letting them out. Just my $0.02 obviously.

I'm a female electronics hobbyist. Definitely sarcasm. :)

I believe bonniemuffin was being sarcastic.

Hahaha both of those comments were some of the most entertaining on here!

I have a similar setup at my apartment in India. It is functional since more than two years now. Its total 140Watt panels, popping out of my bedroom window [Photo: https://photos.app.goo.gl/S4WR5gbrGu0z8IQB2]. It has a 12V battery and 10A solar charge controller. It produces good enough energy to power my room. I hate inverters, all my lights/fans in room are based on DC 12V. I use car chargers to charge mobile phones and to run a LED wall clock.

> Renters don’t need permission from their landlords to place things on their windowsill and rooftops if it’s not altering the building

This has never been the case in any apartment community I've lived in, ever. Every time I've looked into anything like this, the lease says I have to follow community rules, and those rules include stuff like pool hours and parking but also say I can't put foil in my windows, have a window AC unit, etc.

I'm sure there are some landlords who won't notice or won't care if you do this, but it's just not true in general that renters only need permission for things that alter the building.

Good point. I'll clean up the language there. I've never lived in a non-ac unit and non-satellite dish place, but I probably have friends who do. How to work around that then? You could only use an ESCO (energy service company) on the east coast or cleanpowerSF for those scenarios.

> I'll clean up the language there. I've never lived in a non-ac unit and non-satellite dish place

Well, satellite dishes are legally protected by an FCC order, but that doesn't apply to other things.

The fact is, making any sort of broad statement about what you can or can't do, landlord be damned, is a tough thing. You get into a morass of local and state laws that may very well vary from jurisdiction to jurisdiction. This is assuming, of course, it's not just easier to extend the courtesy of talking to the landlord in advance.

That's the downside to living in complexes!

Quite a side note: If you're renting in SF, your landlord needs to provide you with heating (http://sfrb.org/topic-no-257-minimum-heat-requirements)

Thanks for pointing this out! I think our main problem was with the non-insulation of the property. Though I haven't been here for a winter yet. There's also the landlord leverage problem though with cheap apartment gems in expensive places (like SF), as I'm sure you know: "Oh you want more insulation? Sure, I'll fix your insulation/heating. Woops! The rent just went up?"

Obvious Problems:

1: You're not using a pure sine wave inverter so right off the back you are losing significant efficiency (Most the things you're charging use DC power anyways so it would be better to just get a nice DC charger).

2: If you are discharging your battery past 50%, you're going to significant reduce it's life span.

Ditto re: battery capacity. Using all 35 Amp-Hours repeatedly will destroy the battery. Anode terminals dissolve during discharging. They are electrolytically plated (thickened) during charging. So repeated full-discharging can reduce their solid volume to such an extent that they cannot be fully restored during charging.

In general, "deep-cycle" lead-acid batteries shouldn't be discharged to less than 50% of their rated capacity to ensure a healthy, long life in an off-grid solar setup like this one.

So more like 17 yrs to repayment - as long as he hasn't already bricked his battery.

I asked this myself too.

Aren't most electric devices used today DC?

Everything that runs off a battery is DC.

However, for the past 4 months, I've been charging all my devices off solar/battery (working-travel vacation in a van). I have run into some issues with certain devices not accepting charge. I think it has more to do with the device charges themselves than the power source.

For example, my girlfriends Motorola Droid Turbo won't charge at all anymore off the 2.1 amp usb chargers. My S7 has no problems. Her cheap windows laptop will also sometimes refuse charge temporarily. Battery voltage is reliably between 12.3-13.0, which makes me think it's an issue with the chargers themselves.

For heating, you could bring in a small refrigerator rather than a resistive load. Get something besides heat for your power.

But then you would need to run the refrigerator even when it's hot...

An ETH mining 1070... :)

hahaha, now THAT'S a hack!!

He mentions fridge/freezer - I'll just draw attention to this project[0] where the smart guy uses a chest freezer as a fridge with an external thermostat. It has better insulation and design (cool air stays in when open), so ends up much more efficient and can be run on minimal power. Just 90 seconds of run time per hour.

There are other ways to do this in mobile setups, or with inverters in any setup, using mini-freezers, simple electronics to turn the inverter on/off and a small panel. See /r/vandwellers[1].

[0] - https://www.treehugger.com/kitchen-design/man-retrofits-free...

[1] - https://www.reddit.com/r/vandwellers/search?q=freezer&restri...

Nice hack. Can it power a fan for a night? That might save you some money in cooling, which would help with payback.

I won't be using it for my apartment but it has great potential for an off the grid light power use workshop. Good job, thanks for showing.

Just a note, the biggest expense these days in solar power installations, home, is the manpower and incidentals needed to install it. Reduce that and solar power replacement begins to look good. As we saw here, where there were no installation costs.

Hey! It can power a fan overnight no problem. A large box fan uses around 45W, so this could run it for 10hours on a day's charge. Good point!

To your point of expense – the installation cost is what bummed me out, too. That's exactly why the hack is so effective if someone in your family can self-install it! I agree. Similar to an AC unit or a satellite dish that most people just install themselves...

we have a table fan specially made for solar is 11.5W, costs about $14.7

It better be attached well. If there's a windy day, and that thing flies off and kills someone, you will not only be liable, you will have to live for the rest of your life with it.

Very true. I've tested this thoroughly and it won't. Obviously there's always a residual risk, which I've mitigated by moving the panel to a window further back on the roof. Then I'm going to see if the panel's moved after a year. Another solution would be outdoor glue, but that messes with the ephemeral nature of the project. Thanks for the input!!

What's that puppy's wind loading in an 80mph gust?

It absolutely needs to bolted down.

JFYI, the back of the envelope calculation is about energy "created", this assumes that you actually consume it, i.e. that on average you would use that energy (while it is within the battery capacity range), if you leave for - say - 1 month, it is 1/12 less.

Good point! I think the next step in this project would be to hook it to some device with high constant consumption, like the fridge, to make sure the energy gets used up every day. Currently I find it difficult to use everything it's making, as you say. It's like having more tomatoes in your garden than you can eat -> sell the tomatoes.

I've been using rooftop solar for many years; I live in an RV (for a total of about 7 years, spread across two different RVs, both with solar on the roof). I currently have a 400W system. It makes extremely good economic sense in my case, because it enables me to live comfortably off-grid for weeks or months at a time; which can save hundreds of dollars a month in RV park fees, when I'm traveling.

But, the talk of powering water heater, heating, AC, etc. from a little DIY solar system is extremely optimistic. I've done the math, and I couldn't run my AC from the number of solar panels that I could fit on my roof. I can fit 900 watts worth, an additional couple hundred watts on the truck, if I really wanted to get extreme and was willing to connect/disconnect them every time I drove the truck away from the RV. That's just not enough. It could power a small window unit as long as the sun is up, but overnights would kill a small battery bank dead (like dead dead, not just discharged, as repeatedly discharging below about 50% reduces the life of lead acid batteries by a huge amount) in short order.

With a big enough inverter and a bigger battery bank, you can run microwave or toaster oven for short periods of time (I do). But any big amperage device that runs for extended periods of time (like heating, AC, and water heater) is not in the cards for small solar systems.

Battery replacement also needs to be taken into account. In my experience, you get about 3 good years, and another year of limping along, from this kind of workload on this kind of battery. He's being more kind to his batteries than I am to my batteries (I usually end up running down to about 60% each day when off grid), so he might get another good year. But they probably won't even be limping along after five years.

But, the good news is that solar panels are extremely durable. They're often warrantied for 25+ years! And, the expected output after that length of time is still pretty good. So, if batteries get better, our systems today will get better just by replacing one component, because everything else is gonna keep working forever (well, cheap charge controllers die sometimes, but the panels are practically forever parts).

For water heating, you could skip the electricity step. I suppose that would gain you a factor two or three at least in the available wattage.

Yep, solar water heating is a time-tested way to get energy from the sun and put it to use. A lot of the earliest solar power deployments (like Carter's White House) were solar water heaters.

There are even a few cheap off-the-shelf solar water heaters on Amazon these days (when I first researched the problem a few years ago, it was strictly a DIY project if you wanted panels small enough for an RV). Getting water to the roof is usually a difficult problem in an RV (requires breaching the roof without introducing leaks, and finding a path through the walls from the existing water heater to get there), but my current RV has an easier path than my previous one, so I might give it a go next time I've got a free weekend.

Can't imagine why OP has an inverter in the stack when everything connected to it is DC.

Because it's easier and I don't want to fry my $1500 laptop with some hair-brained project's DC-power spike. But I admit that's not really well thought through and an earlier version of this project was DC only. Also, the main inspiration for this project was DC only, as I mentioned in the article (but reposted here: https://arstechnica.com/gadgets/2015/08/op-ed-how-i-gave-up-...)

After Hurricane Ike (and 8 days without power) I built almost this exact setup to power my CPAP machine in case of another long-term power outage.

I've been chatting a bit about thermal building design. This article reminds me that for most entertainment or work, we don't need much energy.

Cost comes from AC, heater, fridges. Other household appliances too but these are transient.

But with carefully dimensionned walls, you can slow the heat spread enough to avoid AC most of the time.

Surely we could keep our energy needs low if we wanted to.

Have you talked to your landlord about adding solar panels to the roof? He/she could install them and connect them to your apartment's service, which means you would get the power and the savings -- though you might reasonably expect some of the savings to go towards higher rents in the future. With the tax advantages, it's almost a no-brainer.

It's even possible to apportion power between multiple units with PG&E in California. They even allow "neighborhood solar", where you can benefit from a larger system installed elsewhere, like over a parking lot.

I would also +1 the other comments about thinking really hard about whether your system is safe in the event of high winds. Solar panels are basically large sails, you'd be surprised what a 50 or 60 mph wind gust (likely to happen once or twice a year) can do. If you plan on doing this, check your lease - many landlords forbid putting things on the roof or hanging outside windows, or running wires on the exterior of the building.

Doesn't PG&E charge customers who have residential solar installs a higher rate, because they have residential solar installs?

In a word, no. They do now tack on a monthly minimum fee that only applies if, over the course of a year, you use less than the sum of the monthly minimums. So, if you install a project so large that it zeros out your bill, you'll end up paying $100 or so per year to be tied to the grid. Otherwise, the rates are the same as you would pay without solar.

I'm hoping to build a similar system in the next year or two. Biggest difference is I plan on building battery banks out of lithium-based 18650 cells. You can salvage them from old laptop batteries, even dead ones (one bad cell can bring the whole battery down, even if the other cells are fine). 18650s are also used in Tesla's car batteries [0] and Powerwall. They literally just cram thousands of them in there. There are some youtubers who have done tons of stuff with them [1][2].

[0] https://youtu.be/NpSrHZnCi-A

[1] https://www.youtube.com/user/jehugarcia

[2] https://www.youtube.com/user/nocrf50here

I wonder if you can mount this over a roof rack for a plug-in hybrid car like he Chevy Volt/Bolt. It'd be an amazing way to charge your car.

Although, 200 W might be a bit too low for the Chevy Volt. It draws circa 100 W when charged via the slow charger that you plug in to an outlet.

> It draws circa 100 W when charged via the slow charger that you plug in to an outlet.

1kW - 2kW, surely? 100W would take days to charge.

These already exist as self-contained kits: https://www.amazon.com/dp/B00GV3XRDW/ref=asc_df_B00D5RVMAM50...

What I think would be interesting is to use a relay to fall back to grid power once the battery dies.

Nice! 600 bucks though?! I guess I'd have to sell this package for 600 for any kind of profit margin... Reading the reviews on Amazon of the Yeti system though, I'm not sure they've solved all the issues for 3x the price.

How safe is it to keep that battery indoors? Don't batteries need some ventilation?

It's a sealed lead acid(SLA) battery which is different from a wet/flooded battery, which do require periodic topping off with water and ventilation.

For a project like this, SLA is the way to go.


As canoebuilder said. I initially thought the same thing :). Believe me I googled the shit out of this so as not to drown the house in hydrogen.

This is awesome. The one question on my mind is: is there really no barrier to doing this, like regulation of some kind? I would imagine there's an added fire risk with that kind of battery at home?

> I wish I could run a water heater, heating or fridge off this system to use the excess 270Wh of the daily energy production.

Or better yet, be able to sell the excess power. In the future power grid this will be possible.

It's possible today, almost everywhere in the USA. In fact, the power company will usually buy it from you at the same rate that they are charging. My house is turning the meter backwards as we speak.

To do this, you need extra components to protect your house, the power grid, and the electricians who work on it.

If we are talking about being green, what is the carbon footprint of manufacturing all those things vs the equivilent carbon to geberate thr electricity the solar panels provide?

That's at the bottom of the article:

Production footprint PV multicristalline: 4200kWhee/kW [1] * 0.1kW = 420kWh embodied energy

Production footprint lead-acid battery: 321kWhee/kWh [1] * 0.5kWh = 161kWh embodied energy

Total Footprint: 581kWh

Annual energy production system: 155kWh/y

Payback period: 581kWh / 155kWh/y = 4+ year footprint payback

Cool. One caveat in SF (and elsewhere, I'm sure): since I work from home my electricity usage is way higher than the PG&E norm (which itself seems aspirationally low). Of course, PG&E uses this to charge me huge "overage" charges so using a solar panel to offset some of those charges might actually make this economically viable.

One of the biggest cost/safety/longevity factors here is the usage of a storage battery. This is necessary because OP presumably uses most power at night, and is unable to use the grid as virtual storage due to all the complexity that brings.

If one's usage was mostly in the day or even constant, they could forgo the storage batteries and setup a system to supply specific loads, making up any shortfall from the grid. This would take a different type of "inverter" to avoid becoming grid-tied. I'm imagining a production circuit being based around a 170VDC bus (power factor? who cares!), but that's probably currently rare/custom/expensive. You could DIY the same type of thing with a nominal 12V bus (or 48V, depending on your loads) and DC distribution, from off the shelf components.

I find the title kind of click baity, "$200 solar self sufficiency for my bedroom" would be more accurate

Hey. You're completely right :) My original title was was "Solar Self-Sufficiency for Renters", but my mates in marketing told me to clickbait it the f up. Would you have clicked on the former, though?

Personally, I would. What you wrote is very interesting, and interesting content can stand for itself. No need to clickbait things up.

Your friend gave you good advice.

Your "mates" can f right off. It debases an otherwise very interesting article. If you're interested, here is another similar setup that went entirely DC http://www.lowtechmagazine.com/2016/05/how-to-go-off-grid-in...

it adds to the misinformation regarding solar energy and going off-grid

You could save some energy by driving Led lights directly from the 12V battery. Not through an inverter.

Doeasn't matter in this case though since one of the things he's running is electric heater. When you are usin lights you are just getting bit more heating comming from inverter.

Does the panel produce the same amount of energy every season? I know that in most of Europe the production during summer months is way higher than during winter and that needs to be taken into account

San Fransisco is at about the same latitude as Gibraltar, so while he will see seasonal fluctuations unless he changes its angle of incidence (but hes laying it flat, so...) However, he will not see as big a difference as, say, somebody in Germany.

Very cool project and great writeup! It seems like every week I learn about a new Google microservice (Google Sunroof here).

The author's calculations for the capacity of the battery are very wrong and the battery will not last many years the way he's using it.

Deep cycle lead-acid batteries should not be discharged below 50% (known as Depth of Discharge, or DoD) unless you really want to kill them quickly. The author's calculations assume he can drain the battery 100% (35Ah), which while technically correct, will kill his battery very quickly.

Unfortunately the manufacturer doesn't provide any data on the capacity over discharge cycles at different DoD's [0], but I can guarantee the author will significantly shorten the battery's lifespan by discharging it so deeply.

If you want some idea of the effect of DoD on battery health, Hoppecke have a very good chart in their datasheet on page 43. [1] At 50% DoD, the battery will last for approximately 3000 cycles, or 8 years. At 90% DoD, the battery will only last for 1500 cycles or 4 years.

If you want to go for 100% DoD in solar, you're looking at Redox flow or Lithium battery technologies, both of which are more expensive than Lead-Acid.

There are other problems with this setup as well. At $17, the charge controller is very unlikely to support an equalization charge mode, which is required to periodically balance the cells within the battery to ensure a long lifespan. The author would be better off skipping AC entirely and charging their MacBook/iPad from a car charger which operates on 12V. DC lights can also be purchased quite inexpensively. The AC inverter is likely putting out something closer to a square wave than a sine wave, and the low voltage cut-off is far too low to avoid damaging the battery.

This is really a case of "you get what you pay for" and for such cheap components, the system will not perform well or last for very long.

If this sounds really negative, I'm sorry. I want more people to become energy independent, but if you follow the author's example, you're going to have a very bad time. If you are seriously interested in going off grid, you should invest in quality components like Victron, Outback, Studer, Hoppecke, etc. Something like the Victron EcoMulti would be a good choice for someone who wants an easy to use system that's been designed for longevity. [2]

[0] http://www.expertpower.us/exp12350

[1] https://www.hoppecke.com/fileadmin/Redakteur/Hoppecke-Main/P...

[2] https://www.victronenergy.com/solar-pv-inverters/ecomulti

To be fair, the DoD vs cycle numbers aren't as dire as they first look. Even an ideal deep-discharge battery would have a 1/x curve, as the real metric is total energy stored, which is proportional to DoD*ncycles vs DoD.

For instance, for the two datapoints you gave. At 50% DoD, the battery will have stored 1500 times its capacity over its life. At 90% DoD, the battery will have stored 1350 times its capacity over its life. This is only a 10% degradation.

How hard would it be to add regenerative braking to that ? if not already installed.

Why not build a small super-capacitor or lithium ion bank that you'd charge at work?

Also, unless you have perfect weather (I.e. the Bay Area) and require no energy for HVAC this system is almost useless.

Far more cost-effective would have been to skip the battery and just put a cheap chinese pure-sine-wave grid-tie inverter to bridge between the wall outlet and the panel.

It's simple- it has a 110V line cord and plugs into the outlet, sending current the opposite way of normal. Do a search on your favorite e-commerce site for "grid tie inverter" and you'll see what I mean.

These cheap inverters have most of the same safeties as the UL 1703 certified variety, and as long as you don't exceed current ratings (not likely with a little 200W panel) you're able to apply the power to your electric bill, without futzing with a lead-acid battery.

Please do not do this. For one, it's illegal. All grid-tied solar systems require either a transfer switch or to automatically disconnect when the grid loses power. This is so that you don't electrocute an electrician working on lines he or she thinks are dead. Second, most non-"net" meters don't read negative currents. So if you are generating more than you're using, they'll keep spinning forward and you'll get charged for more than you actually used. Third, the fines if you're caught are pretty high because of the safety issues.

So many here say "it's illegal" without pointing to a single law. There is no such law to point to.

No municipality anywhere outlaws plugging in CE-approved appliances into your home's outlets. Even if half of them did, this would still be worthy of bringing up for the other half.

Even if it was illegal, wouldn't make such laws just or logical. Florida, after all, made off-grid living illegal. http://www.collective-evolution.com/2014/03/09/florida-makes...

Now what this approach _is_ is probably against the policies of your local electric utility, but they're incentivized to disallow anything that goes against their business interests, and can argue might somehow not be safe. Take for example HECO, Hawaii's electric utility, economically devastated by grid-tied PV. http://khon2.com/2014/03/19/state-investigates-illegal-photo...

The way a grid-tie inverter works is like trying to jump on a merry go round that's already moving. In the happy path, the inverter keeps the PV power detached until it's ready to find its moment and sync it up to the grid. As soon as that grid signal goes away, the inverter is no longer capable of finding the signal to continue injecting current. The PV panel doesn't cause an explosion if it suddenly goes from 0% output to 100% output to 0%, so it's not exactly a big deal for a grid-tie inverter to perform this matching- it's in fact central to its functionality.

Whether the grid goes down, your breaker trips, or you unplug the 110v line cord yourself, these things all function the same- safe for anybody foolish or unfortunate enough to directly contact the inverter's output lines with their bare hands. These things don't hurt electricians, whether they have 5 safety interlocks (fundamental to any grid-tie design) or 2-3 additional ones sometimes proscribed by certain electrical codes.

"non-'net' meters" are getting to be few and far between, and utilities don't like older models because they require manual meter readers to go door-to-door. Naturally, you should be aware of what your specific electric situation is before getting into by trying one of these things out, but this is a weak argument against DIY grid-tie (much better arguments against exist).

An amazing number of people don't understand how electric meters work. If your grid-connected panel puts out 200W (call it 2 amps) and your apartment is pulling 3 amps total, the electric meter will spin at a rate proportional to 1 amp. It doesn't require any intelligence or fancy technology. If your apartment is pulling 1 amp net, the electric meter will not spin any faster than 1 amp, no matter how old it is. The only difference between new and old meters is whether a surplus of 1 amp is read as -1 amp or 0 amps.

On the off chance you're dumb enough to hook more unregistered PV capacity onto your property than your monthly use merits, utilities may assess fines or lockouts, but none will charge you for the excess generated as if it was consumed. Most are required by law to pay you for it (though an insultingly low rate).

Am also a bit alarmed by how many downvotes I got for the words "cheap chinese", as if that was a red flag for safety. Inverters of every kind, from respected brands in respectable configurations, have gotten _really_ cheap (the same model I installed 10 years ago now costs 1/10 what it cost 10 years ago). They're also almost invariably now made in China.

The fact is, even if your inverter is an incendiary device waiting to happen, you have a large number of built-in safety devices: a circuit breaker and hopefully enough common sense to keep the inverter away from flammable objects, and not to bury the inverter in a ratpile of shredded newspaper and gunpowder. I'd consider the cheap inverters far more likely to simply konk out far before their time than cause any kind of safety hazard. Circuit breakers save lives.

As a worthy counterexample, a faulty inverter (though probably a faulty inverter installation, considering the fire spread) caused this house fire: http://www.telegraph.co.uk/news/earth/energy/solarpower/1209...

Couldn't you risk shocking some poor electrician that thought the power was turned off? Maybe the inverter has some sort of safety system that I don't know about; I'm no expert on this.

The two big reasons not to do this are his own words: "cheap" and "chinese."

Wow that's really great input. I'm going to check this out and write a follow-up! This would allow me to credit the power directly to my fridge bill, as opposed to just using it for lighting and devices!

Do not do this. You could kill a utility worker, and it's against the law for safety reasons.

Edit: Net metering/grid tie guidelines require inverters that will shutdown upon loss of utility power. Also, a disconnect switch must be on the exterior of the building/facility, clearly identified, and on record with the utility.

Bonus points if you Google "lock out tag out".

So does this mean that you can offset your electricity cost because your solar panel just sends the electricity it generated back into the grid (and credits you for it)? How could I verify that it's working?

It looks like you might also have to sign some sort of a contract with PG&E. Is this true? https://www.pge.com/includes/docs/pdfs/b2b/wholesaleelectric....

Does that work with a regular meter? My internet sluething says some people have been charged for the electricity the produce because they don't have a "compatible" meter.

If you hook up a ton of these and actually generate _more_ than you consume at any time, you will actually _pay_ the power company for the power you push back into the grid. You have to get a special meter that can measure the direction of the flow. I have bought two residential roof-mounted solar systems and this is what they told me. If you never generate more than you use, maybe you're ok.

If you have a traditional electromechanical meter, that should normally be able to run backwards, with electronic meters, it depends.

If you're going to break the law, isn't it easier to just tamper with the electric meter or run an extension cord to your next door neighbor's outlet?

Not if you want to avoid stealing.

Using means not permitted by the law and your contract with the service provider to (attempt to, at any rate) reduce your utility bill would seem to be stealing.

No, it would be breaking an agreement or somesuch. If you're generating your own power you're not taking anything from anyone else, so it's not stealing.

"These cheap inverters have most of the same safeties as the UL 1703 certified variety"

I've seen inside enough cheap chinese power equipment to know that is most likely not true.

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