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Say I want to provide power to my house off the grid (i.e. without relying on utility companies). Say I have a method of generating power elsewhere (e.g. wind power).

Is it possible to "farm" the power, save it in a large enough "battery" (I'm imagining something the size of a barrel here) and have it power a conventional house for, say, a week?

I would very much like to learn about the feasibility of this proposition.

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closed as too broad by Anindo Ghosh, JYelton, Joe Hass, Matt Young, tcrosley May 12 '14 at 12:23

There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.If this question can be reworded to fit the rules in the help center, please edit the question.

It's certainly possible, but the batteries are likely to be much larger than a barrel. – DoxyLover May 12 '14 at 3:32
Ah, so the energy density is the limiting factor of this plan? – JDS May 12 '14 at 3:35
Speaking very roughly, the "average" house needs about a kilowatt of power (not including electric heat). A week contains 168 hours, so you're talking about 168 kWh of electric energy storage, or 14000 Ah worth of 12V batteries, or about 600 MJ. The best battery technologies give you about 2 MJ/liter, so your intuition is right: you'd need about 300 liters worth of batteries, which is a rather large barrel. – Dave Tweed May 12 '14 at 3:38
Specific answer: Yes. Voting to close as too broad. – Anindo Ghosh May 12 '14 at 3:52
On the other hand, if you're going to use lead-acid batteries as being cheap and reliable, the energy density is about 0.34 MJ/L, so you'd need 1800 liters. Plus, if you want to avoid deep discharge you'll need a 100% margin on capacity, so the end requirement is 3600 liters. And that's a lot of cognac. – WhatRoughBeast May 12 '14 at 4:03

It is probably the cost, rather than the size, of the battery which will limit how large a battery you'd be likely to install in practice. This site claims the "true cost" of a battery only a third the capacity of what Dave Tweed calculates would cost around $58k for Li-ion or $105k for lead-acid (converted from Euros to dollars). They claim lead-acid would actually be more expensive due to having higher transportation cost, shallower usable depth-of-discharge (DOD), and much shorter cycle life which would lead to multiple replacements over the same time period.


In practice you might not install enough energy storage to run for "a week" unless you had good reason to believe your offline generator e.g. "windmill" might produce little to no energy over that long a time period. The cost could be substantially reduced by only storing 1-2 days worth, or even less depending on reliability of the source of generation.

For example, with a solar setup, the house might be powered "directly" (not counting inverters etc) from the solar panels during the day, with enough extra solar capacity to also charge the battery during the day; the house would only run from battery at night. Thus the battery capacity required would be enough to get through 1-2 nights and maybe a few especially cloudy days. As energy usage tends to go way down while people are sleeping, capacity required to run from battery at night would be much less than day. Paying particular care to reduce usage, e.g. efficient appliances, LED lighting and so on would further reduce cost.

The assumption here is that generation is cheaper than storage, notably for solar, which has gotten much cheaper the last few years. If you needed more energy to run from during the day, you'd install more solar panels rather than more batteries. The batteries are just for when the solar panels aren't getting enough sun to power the house.

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The one week period is appropriate for wind power. This happens once in ~10 years IIRC. Furthermore, this is typically a week in winter when solar doesn't produce much energy either. This is a major reason why these sources can't become major sources. Low wind conditions can extend for tens of thousands of square kilometers, so you do need a similar storage at grid level (~50K$/household, plus industry demand - you'd be looking at trillions not billions) – MSalters May 12 '14 at 10:49

If you can stretch the meaning of battery a bit there are some neat mechanical based solutions, such as this one (No advertising intended).

The idea is using a huge fly-wheel connected to a brushless motor: when you have energy to spare you speed it up, when you need energy you get it from the motor that can work as a generator too. Mechanical solutions have their problems such as friction, vibrations, dimensions, costs and such, but these guys' prototype adresses them in a smart way. Their fly-wheel is enclosed in an air thigh conainer from where most of the air is pumped out in order to reduce air friction, moreover they use some magnetic bearings and the whole rotating mass is not a solid block but a sort of metal net that auto adjusts its shape reducing vibrations (negative reaction everywhere!) and dramatically cutting costs since a big metal wheel that goes that fast would need to be manufactured with very strict tolerances. About dimensions... I did not do the math but I think that such a thing may have a higher energy density than most modern batteries.

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If OP can get the electricity to the flywheel somehow, this seems like a very good solution indeed. – arne May 12 '14 at 7:26
Well I think you can even move the flywheel... I just skipped the "for a week" part. The best option for such a situation is a portable generator. – Vladimir Cravero May 12 '14 at 7:28
That crowdfunding project is plain stupid. It will never happen. – Joe Blow May 12 '14 at 10:49
That may be... The idea is nice anyway – Vladimir Cravero May 12 '14 at 10:53
Here's a company that builds such flywheels commercially. Don't know if they are "successful" but at least it demonstrates the idea is feasible. power-thru.com – Matt B. May 12 '14 at 20:10

Size of house, how much electricity do you use a day, time of year (heating/cooling). A small cottage or two bedroom apartment, with 12v or lower lighting and devices, would do much better than a large 4 bedroom house, with 120V electric stove/fridge/Inefficient TV running at all times. I mean, I'm good with a laptop, ipod radio, and a lamp for most of the day, plus two mini fridges. Easily done with Solar + Battery in some states.

Highest power draws are (Electric or HVAC) Heating or Cooling and Fridge/Freezer. Electric Stoves and Television or Hi-Fi Stereo are the other typical high draw usage. If you manage those, then the rest is very feasible under off the grid power.

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Fridges and Stoves can be easily powered with (bottled) gas, so there's two major draws less. – arne May 12 '14 at 7:24
Heating in many climates is a much bigger energy user than fridges and stoves (can be 100x in northern Europe), but that too can be done with bottled gas. – MSalters May 12 '14 at 10:52

Since this question is broad and ridiculous, here's a broad answer

It could be the OP is not aware IT DEPENDS HOW LONG YOU WANT TO RUN IT FOR.

It's commonplace that if you're living in, say, the Caribbean, you might have battery back up. Imagine a big box the size of a suitcase.

They simply use "car batteries" - maybe a few of them, maybe a dozen of them. And some electronics to make it work.

It will run the whole house fine, but only for a short time -- maybe a few hours.


If you wanted to run a house "for days" it would need an incredibly large amount of battery power - picture "rooms full" of batteries. In the real world it would be impossible and you couldn't do it. But for a few hours - sure, no problem.

So again, what you describe is completely commonplace, you can see it anywhere in, for example, the Caribbean, but it only runs for a few hours at best.

Hope it helps, OP

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