[IgorPartola]

Energy density is a big one. To store 5 kW * 24 hours (barely enough to power my house's essentials), I would need 286 of these (http://www.amazon.com/VMAX857-Battery-Performance-minnkota-t...). They are not small. Also, that would cost me nearly $32,000 in just batteries.

My ideal setup for this would be something like 20 kW * 7 days. That would fill my basement pretty easily.

[jacquesm]

That's a very expensive battery for the given capacity. If you want to be efficient check out the gel batteries used to power golf carts and forklifts. You'll need 24 2V cells if you want to do this efficiently both from a cost perspective as well as to reduce line losses between batteries and inverters. (24 and 12V are really not adequate for larger power installations).

[IgorPartola]

Such as these? http://www.batterystuff.com/batteries/golf-cart-products/

I don't really see orders of magnitude jumps in power/$. Or am I looking for the wrong thing?

[jacquesm]

No, more like these:

http://pics.camarades.com/v/jacques/renewables/batteries/IM0...

Sold in bulk. That's a 48KWh bank and it cost about $US 5K

[IgorPartola]

This is roughly 2.5 times cheaper than the marine battery I found first, definitely not orders of magnitude.

This is $5k for 2 kW * 24 hours. So 3 of these at $15k total would roughly replace my $700 generator + $10 worth of gasoline for emergency situations.

To truly run my house where it would be adequate at 20 kW or 24 hours or so, I'd need 10 of these at $50k. To run my house of for a week (where I live, the last major power outage lasted three weeks), I'd need $350k. For that amount of money, I can just buy a very nice house in Florida and go down there when the power goes out.

Now, if I go top of the line, I can get a 22kW generator (http://www.homedepot.com/p/Generac-22-000-Watt-Air-Cooled-Au...) for $4,700 + gasoline at $2.30/gallon where I live. This will not even require me to go out and start the thing as it kicks on automatically, much like a battery backup does.

Battery powered houses just don't make sense cost-wise, and at this price disparity it's not a question of spending a little more: $350,000 vs $4,700. That's two orders of magnitude. It's not the clean option, but given that it's standby power, I'd rather see us invest in more efficient power plants (nuclear and wind) than home batteries.

[jacquesm]

I think you're more than a bit power hungry. My house consumed < 5 KWh max per day, so even running to 50% discharge that bank would power the house for up to 5 days.

It's much easier to save on consumption than to create capacity, especially stored capacity. You don't really realize just how much energy goes into AC, heating, washing and so on until you've lived off the grid for a bit. And then you'll quickly learn how to conserve energy. I'm currently living in an on-grid house, the old habits die hard, my computers are probably the biggest consumers here.

Anyway, if 22KW is your power budget then don't bother going off-grid without a generator.

Battery powered houses make perfect sense if you're able to conserve power, if you can't then of course it does not make sense.

[IgorPartola]

That I suppose is the line for me. I am unwilling to go to a point where I cannot use my washer/dryer, dishwasher, AC, etc. I believe the majority of the developed world is with me on this, though of course there is a minority that have other priorities.

[sah88]

~30kwh is the national average for daily use. 120 is crazy high unless your blasting an AC or heat all day. At 12 cents a kilowatt hour that's a $438 monthly bill.

Even 30 is pretty damn high. For someone living off grid with a purpose built/renovated structure ~5kwh a day gives you quite a lot to work with.

[IgorPartola]

True, but you want to be able to handle peak usage too. When 2 kW well pump kicks in, I don't want the lights to dim. AC is 3-5 kW and more to start, and so on.

Yeah, if your goal is to live off the grid to save the planet, that's a different story. Then the only question is how much will your Lithium based battery (mining, manufacturing, transport, recycling) affect the planet vs buying wind power from your local utility. If you want to do a little good and save a little money, putting batteries in your house is not the right thing to do. If you want to be independent of the grid in case of emergencies get a wood stove and a gas (or better diesel) generator. All around, I don't see where whole house battery backup fits into any scenario. I see data centers using these batteries, not residences.

[jacquesm]

I did the shorting current calculation on that battery in the pic elsewhere in this thread. The fuse was there for decorative purposes only, at those currents everything is a fuse, the one Ththing you really have to hope for is that it will douse fast enough and that there will be no air/fuel or H2/O2 mixture nearby. That's the main reason I built this pack into a little building (underground bunker really) of its own near the house but not so near that it would be a problem if it would break down.

The inverters were housed in the second half of that bunker so as far as the house was concerned nothing changed.

The whole system was capable of producing 11KW, two tandem 5.5KW inverters ganged to produce 240 V for well pumps and other large consumers (welder, plasmacutter).

It worked super good but you really had to keep an eye on the charge level when running big tools, the plasmacutter would drain the battery in about an hour.

But running the plasmacutter was the exception, not the rule so most of the time it was just powering a very low level of loads compared to most houses.

I really miss the system, and the farm it sat on.

[sliverstorm]

That's the beauty of lead-acid- it has one of the best (if not THE best) surge currents.

For example, the ~70Ah battery in my truck has a cold cranking amps rating of 700A, or 8.4kW out of just one battery.

[schiffern]

>To store 5 kW * 24 hours (barely enough to power my house's essentials)

So based on 5 kW average, your electric bill is… 3650 kWh/mo? That's about 4x the U.S. national average for a household (903 kWh/mo).

Is this correct, or is 5 kW an overestimation?

[Gravityloss]

5 kW constant? Do you have the sauna on all the time?