October 16th, 2019


Is it worth using a battery to take advantage of cheap overnight electricity?

I was chatting about gas boilers being phased out (kinda, maybe), and wondering about the costs involved in switching away from burning fossil fuels to heat my house to using electricity instead.

Electrical radiators are 100% efficient (you literally turn all of the electricity into heat). So you don't have to worry about central heating systems - you can just put a heater wherever you want one.

The problem is that gas is under 3p/kWh and electricity is 13p/kWh.

Storage heaters are one way around this cost - they work by heating ceramic bricks (or similar) at night (when electricity is cheaper) and releasing the heat when you need it. An alternative would be a battery to transfer the electricity itself from nighttime to daytime. You'd need a *really* big one for heating though.

Checking here there's a graph halfway down how much energy homes in different countries use each year for heating. Britain comes out at just over 12,000 kWh. (Which is about £360 with gas, or £1,440 with electricity.) Assuming you use central heating for half the year, that's about 67kWh/day. Probably in some kind of normal curve, but let's ignore that for the moment.

There's an electrical tariff in the UK called "Economy 7" which gives you cheaper electricity overnight. Just under 9p/kWh. If you had that, then you could charge a battery up overnight, and heat the house up during the day. Again, for simplicity's sake, let's assume you sleep under a huge pile of blankets, and only need the heating on in the morning and evenings.

So you want to shift 66kWh each day. You can get a battery pack installed for a bit over £500/kWh. So you're going to need to spend £33k up front to get a few installed.

And you then save 4p/kWh. Or £480/year. So your payback time is...about 66 years. Which would be an even bigger problem when you take into account that most batteries are only warrantied for 6,000 cycles. Or under 20 years if we cycle once a day.

I'd say that really, really wasn't worth it. And we'd need battery costs to come down by a a factor of ten to make it worthwhile.

(Have I made a mistake in my maths? Or missed a point somewhere? If so, leave a comment!)

Original post on Dreamwidth - there are comment count unavailable comments there.

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