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My utility company charges me more for electricity in the summer. Is there any way I could "save up" non-summer electricity (eg, a giant battery?) and then use it during the summer, saving myself money?

Other power companies charge more for electricity during "peak hours" daily, so even saving electricity for 16 hours or so could be useful.

I realize that it's probably not possible to build such a device/system in practice right now, but is this at least theoretically possible?

How much more would peak/summer electricity have to cost to make this useful?

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No. Because if it ever made economic sense to do this, the power company will be doing it themselves instead of selling at a discount. – user2963 Sep 26 '12 at 22:27
@zephyr: Not necessarily true; there are many reasons why a company may not go into a certain line of business. As the Wikipedia link shows some companies do do that, it not only shows theoretical possibility but actual viability. – Gnubie Sep 29 '12 at 22:11
up vote 4 down vote accepted

It is definitely possible in theory. There are several methods used by power companies on an industrial scale:

For example, in Wales, UK, the Electric Mountain pumps water from a lower lake to a higher one at night and lets it down during the day:

From your question, it seems you wish to do this at a domestic level. If your power demands are not too great, it could be as simple as buying many Uninterruptible Power Supply devices.

Note that any form of mass energy storage carries a lethal risk should the energy be accidentally (or malevolently) and uncontrollably released, for example, due to containment failure. Hence, it is not something to be undertaken without professional advice.

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A small addition: a UPS will work but their efficiency is often not great. It works from a physics perspective but is hardly economical. – Alexander Sep 26 '12 at 19:33
My biggest expense in the summer is my AC (uses twice as much power as everything else combined). It burns 3500 watts and is on maybe 6 hours a day during the 91-day summer. I'm guessing a UPS large enough to hold the electricity to power this during the summer would be unfeasible? – barrycarter Sep 30 '12 at 1:41
Likely. Perhaps you could look into other ways of cooling your home instead, such as setting up sun shades or atomising water in front of a fan: – Gnubie Oct 1 '12 at 9:21

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