Dot Physics

Battery to power a house for a week

I saw this post about Panasonic’s home battery. The claim is that this will lead a battery that can power a house for a week. I wonder if I can estimate how big this battery would be.

First – to estimate the energy a house consumes. My first approximation is that you could probably run a house off of a 5000 Watt generator, but this probably isn’t the average power use for a house. It is probably lower. I am going to go with an estimate of 2000 Watts as the average power over 1 day. How much energy would this be for 1 week?

i-1af26a264d089361acab68801f5d0ded-2009-12-30_la_te_xi_t_1_9.jpg

The article above claims that it is a lithium ion battery. According to Wikipedia, the energy density of a lithium-ion battery is on 0.46-0.72 MJ/kg. For the purposes of this calculation, I am going to go with an energy density of 0.8 MJ/kg. I can calculate the mass of this house battery as:

i-b6ca0bc0c8f9d7f41e40c04876c783f1-2009-12-29_la_te_xi_t_1_4.jpg

This is around 3000 lbs. Of course, this calculation assumes a 100% efficient battery – or maybe that is already taken into account into the wikipedia energy density. Anyway, even at 3000 lbs, this is possible for a house, right? How big would it be? The wikipedia page lists the volume energy density as 0.9 MJ/L, so this would make the volume:

i-fcbe42ffbc9b04a4022467eaa8b78853-2009-12-29_la_te_xi_t_1_5.jpg

This isn’t too bad – like the volume of a small refrigerator.

I, for one, welcome such a battery. Even without solar panels or something, this would be awesome for the cases where we lose power in the house.

Update

I made some changes thanks to commenter Emory K (Emory K gets 10 bonus points). I don’t know what I was thinking, but I said there were 24 hours in a week. Hint – that is wrong. I guess I shouldn’t blog on vacation or I am bound to make mistakes.

Comments

  1. #1 Emory K.
    December 29, 2009

    (24hr / 1 week) ?

  2. #2 Rhett Allain
    December 29, 2009

    @Emory K

    You are TOTALLY correct. I have updated the post to correct the error. Thanks!

  3. #3 Phillip IV
    December 29, 2009

    In 2001, the average American home consumed 737 MJ of electricity per week, while the average Japanese home consumed 341 MJ/week. Since Panasonic’s batteries are aimed (for now) mostly at the Japanese market, they’ll probably aim for something in the neighbourhood of 400 or 500 MJ. Assuming 0.9 MJ/L, that’d work out to 0,45 cubic metres – still quite a bit of space, but manageable.

  4. #4 george.w
    December 29, 2009

    Having endured 3 days in winter a few years ago, I agree this would be very cool. But this is a battery that would flatten your house if it ran away with itself. Would love to have them on the market for a little while before I install one.

    Maybe they’ll become a standard home appliance. A week’s buffering ability would certainly make solar and mini-wind more practical though. If nothing else, it would let you buy electricity during low-demand hours when it’s cheaper.

  5. #5 george.w
    December 29, 2009

    Having endured 3 days in winter a few years ago, I agree this would be very cool. But this is a battery that would flatten your house if it ran away with itself. Would love to have them on the market for a little while before I install one.

    Maybe they’ll become a standard home appliance. A week’s buffering ability would certainly make solar and mini-wind more practical though. If nothing else, it would let you buy electricity during low-demand hours when it’s cheaper.

  6. #6 Nomen Nescio
    December 30, 2009

    that is going to be one expensive battery. i would hope more that Panasonic’s achieved a breakthrough in Li-Ion battery lifetime than for them to have improved the energy density.

    and yes, as george mentioned, if that thing shorted out the best you could hope for would be a devastating house fire. the worst-case scenario would more resemble a gas explosion.

  7. #7 James
    December 30, 2009

    Humm… From my last power bill, 370 KWh/month (pretty consistent over the last couple of years) = 1332 MJ. 32 day billing period, so that’s 287 MJ per week. Still a nice fire if it goes bad.

    So how about the same calculations for a high-speed flywheel? (Or a bank of small ones.) No exotic chemistry to catch fire (deal with possible failures by putting the unit in a pit), no significant conversion losses, trivially easy to measure the amount of stored energy to prevent over-charging…

  8. #8 hans wurst
    December 30, 2009

    should still be hr/day …

  9. #9 Rhett Allain
    December 30, 2009

    @hans,

    AHHHHHH. Ok, how about now? (fixed it).

  10. #10 MadScientist
    December 30, 2009

    Now multiply that number by the number of households in, say, the USA (~100M) and you get some idea of the amount of lithium needed. Not so bad I guess since it’s one of the most common elements – refining it is an issue though. Think of the floor loading and the fire and explosive hazard too. Given the violence of poorly crafted Li-Polymer batteries in laptops over the past 8 years, I wouldn’t want a giant sized sucker near me.

    Small-scale power sources all have their uses (from batteries + solar panels through RTGs – including the RTG that LANL is developing for domestic use), but for cities you just can’t beat off-site generation. Even if wind and solar thermal power become big things, I suspect some material will have to be cycled to store and release energy – perhaps a nitrogen/hydrogen system or an oxygen/hydrogen system.

  11. #11 Richard Eis
    December 31, 2009

    Stackable sets of batteries would seem the way to go. With material between them to prevent a massive fire hazard.
    You might be able to get away with a smaller battery if you are constantly recharging it from a renewable source.

    You could also have some of your appliances with their own solar panels to offset consumption further.

  12. #12 Shawn Smith
    December 31, 2009

    @MadScientist:

    … suspect some material will have to be cycled to store and release energy – perhaps a nitrogen/hydrogen system or an oxygen/hydrogen system.

    Assuming you can get a reasonable hydrogen storage system working. And where is all that hydrogen going to come from? Getting it from hydrocarbons (least expensive) creates lots of CO2. Getting it from water requires a bunch of energy, which has to come from somewhere. Unless the stored hydrogen is in some kind of non volatile (and somewhat heavy) molecule, I don’t want large amounts of it stored too close to my house.

    I ask these questions because of this article by Robert Zubrin, which I haven’t independently verified. Is he full of crap, or are you talking about something completely different?

  13. #13 Larry
    January 1, 2010

    I’d want my battery outside, or in a fire proof box vented outside in case it explodes. Neat idea, you could even make money with your battery by shifting power from low load to high load times on the grid. Feed roof solar power into it as well.

  14. #14 Nomen Nescio
    January 1, 2010

    hydrogen, however stored, is an energy storage and transport system, not an energy source. it’s another kind of battery technology, whether you burn it (to fuel a heat engine of some sort) or feed it to a fuel cell for electricity. yes, you have to spend energy to get hydrogen, just as you must spend energy to recharge a Li-Ion cell. the only question is which one’ll work better for the particular battery application you have in mind.

    i don’t know what the current market prices of H2 are, but i’d be very wary of any assumptions that they would have to remain static in the face of vastly increased demand. Zubrin may have a point about it currently being too expensive to run cars on, but that tells us little about its cost in a world where cars do in fact routinely run on it. sure, his back-of-the-envelope estimates show that we can’t power any great number of cars on hydrogen produced by the method he picks, but he never demonstrates that that method is the only one we could reasonably pick for such an application. it may be the most commonly used one today, but we don’t need (or want) to run any fleets of vehicles on hydrogen today.

    (and estimating the heat loads on a hypothetical hydrogen tank hypothetically launched from Jupiter as it hypothetically reenters Earth’s atmosphere…? the man cannot be writing at all seriously. i don’t even know why he threw that line in there, given that the number he mentioned can only have come straight out of his nether regions. he’s grinding an axe, and i’d like to know why.)

  15. #15 Fran Barlow
    January 1, 2010

    The other problem with H2 is embrittlement of metals. They are devilishly slippery to hang onto.

    The other question here is that if it were economic to put such a battery in a house, it would be even more economic to put a really large version into a housing development since the pooled resource is going to be used more efficiently than one subject to the kinds of volatility of an individual user. You could also isolate the battery-bank more easily and cost-effectively. But then, why not do it at the level of whole towns and cities?

    Load curves there are even more predictable. Of course, at that scale vanadium flows might be best.

    I’ve also heard that Phosphor-ion batteries are being developed with rapidly improved charge/discharge cycling times and reliability.

    As others have pointed out, fly-wheels are a possibility, and one might add, in places where hydro is a factor, retro-fitting pumped storage may be more cost effective and cast a smaller footprint.

  16. #16 Fran Barlow
    January 1, 2010

    “they” above refers top H2 molecules of course

    Hence:

    those H2 molecules are devilishly slippery to hang onto

  17. #17 MagicMavis
    January 2, 2010

    @James

    “No exotic chemistry to catch fire (deal with possible failures by putting the unit in a pit),”

    Dig the same pit. Experience same problems of keeping the pit separate from whatever the weather throws at your region. Add batteries to said pit. Enjoy?

  18. #18 MadScientist
    January 3, 2010

    @Shawn #12:

    The generation I’m thinking of will be outside of cities – perhaps a solar thermal plant to convert ammonia to 3H2 + N2 or some such; it has to be some chemical that can be cycled, not react just once like hydrocarbon + water = CO2 + H2. Alternatively of course you can electrolyze water but that’s quite a job and I can’t imagine how it would be practical on a large scale. It will be interesting to see what solutions people come up with. The gas cycling is for energy storage and must rely on surplus energy. I can’t imagine how the needed volumes of gases could be stored either; you could pump them into sandstone deep in the ground but the energy losses along the way are getting pretty big (conversion of the gas, pumping for storage, pumping back out).

    In rural areas large(ish) batteries + solar panels or wind generators + LED lighting can certainly provide all the light that people would need. In cities you have issues of shading and roof area vs. living areas so solar panels are of virtually no use in cities.

    We’ll be burning fossil fuels as the primary source of energy for decades yet, so I imagine some power plants in the next 10 years may convert hydrocarbon to H2 and pump the CO2 into the ground or else simply burn coal and chemically capture some fraction of the CO2 to pump into the ground.

  19. #19 MadScientist
    January 3, 2010

    @Shawn: Ooops … I missed a comment on Zubrin’s article. I haven’t checked his numbers for the energies of reactions, but he is absolutely right about consuming far more energy producing hydrogen than you could possibly get out of burning the hydrogen. I should probably print his article and go through his calculations – I’d like to see if his estimate of a 650L hydrogen fuel tank is correct (but I do agree with him that hydrogen is not a sensible fuel for vehicles). The only sense in producing hydrogen is to do it with surplus energy and to burn it later to provide energy when you want it. Many hydroelectric plants do things which sound equally silly and waste a lot of energy – buying surplus power from the (mostly coal-fired) grid to pump water up into the reservoir so that the water turbines can be run a little longer when the gates are opened.

  20. #20 issy53
    January 4, 2010

    At the power level of a city use a Lofstrom loop.

  21. #21 rant
    January 4, 2010

    We already have a super energy source (Sun) & super flywheel (Moon).

    Most ‘modern’ ‘essential’ gadgets could easily be vastly more efficient if the engineers quit designing 20th century products in 18th century horse & buggy paradigms and marketed with 21st century brain-numbing advertising. What’s the difference between texting while in a car today and telegraphing from a railroad car in the 1900s? Do you want to be so reliant on electricity that you basically live inside a battery? AM crystal radios worked without electricity, can internet? Has anyone even bothered to try? The heavy reliance on the electrical plug-in is making people somewhat less creative, batteries may be a step up, but its good to think of the human body as more than just freight to be carriaged around in petro/electro wheelchairs and coddled by electro-chemical stimulants. Why the heck can’t cell phones operate from fat storage cells? I know some large folks that talk all day, they could burn off a lot of mass with all that chatting! /rant

  22. #22 Nomen Nescio
    January 4, 2010

    AM crystal radios worked without electricity

    i quite assure you, they did not. the receivers might have seemed to, but only because the transmitters were using that much more electricity on their behalf.

  23. #23 jimos
    January 12, 2010

    This Lithium/Ion battery is just plain crap.
    I live on a boat, and the only batteries which are used as long life stationary batteries are lead batteries.

    I have lead batteries of approximately 1100Ah in 24V. Ah is the only unit you can rely on. This type of batteries can never be discharged less than 33%, so only 750Ah can be used. You also need a 24V/220V converter : XANTREX TRACE are best (220V because I live in France, there are 110V version).
    1100Ah lead batteries weight 1000kg.

    The devices using most power are :
    - central heater (for heating and especially water circulation during winter) : 60Ah per day
    - refrigerator : 15 to 30Ah per day
    - ‘sleeping’ devices that people don’t want to switch of (TV, DVD…). Personaly, I plugged them on a switch-plug to switch them of all in a row.

    That means I can live approximately one week without recharging it.
    Recharge is about 10% constant load with the TRACE, so 70Ah, and takes more than 10 HOURS…

    Most important : 1100Ah batteries price : 2500$. Life expectancy : 15 years.

    What are the numbers for Lithium/Ion ?

The site is currently under maintenance and will be back shortly. New comments have been disabled during this time, please check back soon.