Hacker Newsnew | comments | show | ask | jobs | submit | danielweber's comments login

30% capacity loss is generally considered EOL for battery packs. (And that typically happens at 1000 complete charge-discharge cycles.) The Volt should have gone 1000 * 380 miles = 380K miles before hitting that.

On paper, I wanted a Leaf over a Volt, but the real world difference shows that differing battery technology still matters a lot. I dunno how Nissan built such a bad pack but there you go.

reply


> The Volt should have gone 1000 * 380 miles = 380K miles before hitting that.

And might have if not subjected to worst-case conditions which EV drivers do not subject their cars to. What are the real-world results in terms of battery capacity declining? They don't seem to be anywhere near that.

So again, as I already said in my first comment, I'm not seeing how this is really relevant - much less some sort of fatal proof.

reply


stupid edit: The second sentence of the first graf should say:

"""The Leaf should have gone 84 x 1000 = 84K miles before hitting that."""

40K miles to 22% loss is about 50% faster than it should die.

reply


Yes. It's foolish to compare the cost of consumable gas vs consumable electricity.

Much better is consumable gasoline versus battery depreciation. Electricity costs nearly disappear.

This was an old adage among the homebrew EV crowd: buying a battery pack is pre-paying for your fuel for the next N years.

The Powerwall[1] is about 35 cents per KWh, assuming it can handle 1000 full cycles. ($3500 for 10KWh capacity.) A decent EV can get 5 miles out of that, so the battery depreciation is 7 cents a mile. That's a multiple of the electricity cost, which is about 2 cents a mile if you don't try for any time-of-day billing.

[1] This is just my best comparison of the actual cost of a Tesla battery.

reply


30mpg at $2.25/gal is 7.5c per mile. Versus 9c for an EV (7c battery, 2c elec), this is a $1500 over 100k miles. If we consider the other maintenance costs, I think they are nearly equivalent.

reply


This thread is rapidly entering territory where only a comprehensive comparison of TCO will suffice (not that those won't be biased either way), but the price of the battery is only one part of the price of the car. 70k$ amortized over 300k miles is still 23ยข/mile.

I understand Tesla's luxury-first strategy and hope the future part will pan out, but at the present time it is very weird to be making a cost based argument.

reply


If you can amortize the battery cost over the miles driven, electric cars ought to be cheaper than gas cars. Less maintenance (no spark plugs or oil changes), less consumables, and the purchase price is about the same (see my first phrase).

If Better Place had worked out, it would have let people shift the battery ownership elsewhere. But it didn't.

reply


Yes. When comparing electric cars to gasoline cars, just assume the electricity is free.

The real money for the electric car is the depreciation of the battery pack. A penny or two per mile is a rounding error compared to that.

reply


I pay $0.21/kWh for electricity (electricity generation and distribution charges combined) and usually get between 3.0 and 3.6 miles/kWh (lower in winter; hope to be somewhat higher in summer).

So, electricity is costing me 6-7 cents per mile before considering the inefficiencies of the charger, so likely 7-9 cents/mile at the meter.

For a typical 12K miles/year driver, those costs are order of magnitude the same as the battery pack depletion (for my LEAF anyway).

reply


If this were proven true, there would be a completely manic gold-rush of capital into the area. Flying cars that operate at less than 1/10th the energy of cars on the road now?

This would very quickly move from "let's wait for NASA to do more tests" to "let's beat NASA to the test."

That's all assuming it's real, of course. I'd bet against it.

reply


Where are you getting that 1/10th number from?

The most thrust anyone was getting was 750mN at 2.5KW. At that efficiency you need to have something that produces >32.7W/g just to hold itself up. That's rocket engine territory: http://en.wikipedia.org/wiki/Power-to-weight_ratio

We barely have supercapacitors that'll deliver that sort of power output. For a few seconds, maybe. Not accounting for the mass of the device itself.

Hopefully if this ever turns out to be something the efficiency will improve. But I'm not holding my breath.

(Number taken from here: https://news.ycombinator.com/item?id=9474610 )

reply


Who says this will use less energy? The remarkable property of it is the (seeming) violation of conservation of momentum, not its efficiency.

reply


I thought his name was Copernicus.

reply


Copernicus came up with the theory. Galileo became a heretic for how he popularized it.

reply


You are planning to charge the thing overnight and use it exclusively during the day, nearly exhausting it each time?

The battery is going to wear out well before 10 years. If you oversize your battery so you are only pulling out half the charge in the battery[1], you can probably get 1500 cycles out of it[2]. That's still less than 5 years.

(This is a common pattern if you are trying to price-compare an electric car to a gas car. For the electric car, the electricity cost is a rounding error compared to the capital cost of the battery, so you can just about assume electricity is free, and worry instead about how long the battery will last.)

You will get a much bigger bang-for-the-buck by demand-shifting: if the biggest load is cooling your building in the heat of the day, run the A/C overnight to superchill a heat sink that can be accessed during the day. No battery installation needed.

[1] Toyota did this with the Prius. They purposefully did not use the full range of the battery because they wanted the battery to last 7+ years.

[2] http://batteryuniversity.com/learn/article/how_to_prolong_li...

reply


It comes standard with a 10 year warranty, with an optional 10 year extension. If they don't have different numbers than you, I don't see why they would even attempt that.

reply


Warrantied to what, though. That you can still get 20% capacity levels in year 10, or that it will still turn on? This might be considered "normal wear and tear."

3000 deep cycles is really pushing what the industry knows to be state of the art.

Maybe they are just taking the economic chance that most people won't be deeply cycling these batteries, and planning to do replacements for those who actually put it through its paces.

reply


> Warrantied to what, though.

That's a good question, and it makes a big difference.

> That you can still get 20% capacity levels in year 10, or that it will still turn on? This might be considered "normal wear and tear."

Given that you can optionally warranty it for an additional 10 years, I doubt it's nearly that bad. If people are confused as to how they how they hope achieve 10 years reliability, and they are willing to warranty 20 years, they must have something up their sleeves.

> 3000 deep cycles is really pushing what the industry knows to be state of the art

I suspect that the powerwall's true capacity is higher than it's rating, and it uses that reserve so it's not doing deep cycles, similar to another commenter's assertion to how the Prius gets it's 7+ year rating,

> Maybe they are just taking the economic chance that most people won't be deeply cycling these batteries, and planning to do replacements for those who actually put it through its paces.

I think a combination of most users not fully cycling every day, extra reserve capacity to keep it from deep cycling, and some subset of people not using failing warranty conditions may all contribute.

reply


For each person that load-shifts, it slightly reduces the payoff for the next person to load-shift.

In the UK, the peak demand is already in the evening[1], because solar has eaten the cheap lunch during the day (which it was supposed to do, but it means that each additional solar panel is going to have a harder job paying for itself). And the demand difference between low and high is about 30GW to 40GW.

[1] http://www.gridwatch.templar.co.uk/

reply


Great point about marginal benefits of load shifting. I do think we're so far from that reduction being significant at this point that it's worth attempting.

I believe peak demand in most non-industrial areas is already evening, because residential areas tend to have less efficient energy use than commercial spaces due to density, and everyone is home at the same time, often doing energy intensive tasks such as cooking, using the A/C, opening the fridge. I heard from someone at a power company that advertisements during the Super Bowl are a major issue, because everyone opens their fridge and flushes the toilet at the same time, and power supply has to spike for 3 minutes and then return to normal.

reply


There's about $10,000 worth of work in a battery. It's not just a hunk of metal, it goes through a very complicated and energy intensive creation process.

The cost of the raw lithium is about 1% of the cost of the battery. It's engineering it in a very precise way that's expensive.

reply


The battery costs $3000 - that is likely a cap on the cost of the work involved in producing it.

reply


You'd think, but that depends on how many times you can sell the same battery. As others have said, it's plausible that this is a way for Tesla to make use of used car batteries.

reply


I really doubt that's true, just because it's too early for it. There are approximately zero used Tesla batteries available right now. The fleet is just too new. Maybe in another ten years.

reply


When the used batteries start piling up, it's best for tesla if this system is already in place. Entirely possible that this will be new and subsidized batteries initially. They will need to find a use for the old car batteries.

reply


Could be, but they're jumping the gun a lot if that's the main idea. Tesla sales didn't really ramp up until 2014, and the batteries will probably last at least 10 years in the cars themselves.

In any case, they wouldn't need to subsidize these batteries. $350/kWh is a pretty decent price, and consistent with estimates of what they cost in Tesla's cars.

reply


Is the precision itself so energy-intensive, though?

reply


What if it's in the garage and someone hits it with the car and pierces the cells?

I didn't see "insurance" anywhere on that Tesla page. Ideally my insurance company won't pitch a fit about about me installing this in my house, but will Tesla guarantee that?

reply


Does your insurance company allow you to keep one liter of gasoline in your garage? It has the same energy content as the Powerwall, is insanely flammable, is frequently implicated is home fires, and regularly causes human deaths.

(Ok, a burning lithium battery will release more energy than its storage capacity, but I'm not finding a nice reference, Tesla knows all about containing cells to prevent chain reactions, and one liter of gasoline is still enough to burn down your whole house.)

reply


Gas fumes are very flammable, but the gasoline itself will flow down and out of my garage, and the fire would be very easy to contain with a simple garden hose.

A gas can also will not light on fire just because it gets hit with a car. It would take malicious use of a gas can -- splashing it on a wall and then lighting it on fire -- to match the default configuration of a Powerwall.

reply


I don't think you use the same gasoline as the rest of the planet if that's your experience.

reply


You ever try to put out a gasoline fire with a garden hose?

reply


While you are correct, you can at least snuff out a gasoline fire.

Lithium fires do not require oxygen, so your typical Class ABC fire extinguishers won't actually work on it. You need a class D (dry powder) extinguisher, which is very rare and expensive.

reply


While true for lithium fires, a venting lithium-ion battery is not a typical lithium fire.

According to the MSDS for lithium ion batteries, fires involving them can be extinguished with a typical ABC fire extinguisher.

Lithium batteries (not the rechargeable kind) are the ones that need a class D extinguisher.

Edit:

> CO extinguishers, halon or copious quantities of water or water-based foam can be used to cool down burning Li- ion cells and batteries. Do not use for this purpose sand, dry powder or soda ash, graphite powder or fire blankets.

> Extinguishing media Use water or CO2 on burning Li-ion cells or batteries

http://www.uscg.mil/hq/cg4/cg432/docs/msds/MSDS_LiIon.pdf

reply


Using water on an electric fire sounds like a dumb idea to me. But yeah, the MSDS does seem to say that...

reply


A venting lithium ion battery isn't usually an electrical fire.

reply


And what of all the molten wires that _were_ charging said battery?

reply


Overcharging a battery isn't the only way to cause it to vent :)

Obviously there should be a physically separate circuit for cutting off power in the event of catastrophe. That's pretty much rule-of-thumb for large li-ion battery banks.

reply


> Lithium fires do not require oxygen

I thought fire is by definition a combustion reaction, meaning some kind of material reacting with oxygen. What's fire, then? (I feel like a little kid, having to ask that...)

reply


Generally, a fast exothermic reaction. Oxygen may be the most popular oxidant, but not the only one. Lots of stuff burns in pure chlorine gas, for instance.

reply


Some substances bundle together their oxygen source (think of rocket fuel, or napalm), so they don't need to consume it from air.

reply


It's possible for something to burn hot enough to split water molecules apart. I don't know if lithium metal qualifies, but that could be what the MSDS is referring to.

reply


It's common advice not to leave rags that have gasoline on them sitting in your garage because in enough heat the fumes from the evaporating gasoline will combust. Gasoline is very volatile, we've just gotten fairly good at managing it.

reply


Or a vapor reaching an open flame. Common source of human immolation.

reply


edit: my karma https://news.ycombinator.com/reply?id=9471929&goto=threads%3...

reply


edit: my karma http://i.imgur.com/rjNrXTc.gifv

reply


Moderation is pretty weird in this thread. I got voted down for pointing out that the US power grid is likely to experience problems when entire residential neighborhoods full of Tesla owners try to charge their Model S at once.

I don't think many people around here understand (a) just how efficient gasoline really is at storing energy, and (b) just how much energy is used by a typical passenger car.

reply


Talk to your insurance people. Usually when you have expensive items, you can get a specific rider for it.

For example, a friend had a rack with about $80k of servers in his basement a few years ago. I believe he paid an additional $400 for coverage.

reply

More

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | DMCA | Apply to YC | Contact

Search: