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Comment by mandelken | Hacker News Reader

Using electricity to heat water is a waste of a high quality (i.e. low entropy) energy source. Carefully tuning when to use electrical water heaters and calling this energy storage is not quite right.

There are much better ways to heat water for domestic use, depending on the climate and context, such as solar panels, heat pumps with ground drilling, industrial heat waste, etc. These are standard technologies being used in large parts of the world.

For more info I recommend the excellent book Sustainable Energy Without the Hot Air by MacKay (pdf freely available at withouthotair.com).

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The intention is to use primarily waste energy from times when production exceeds demand. The side effect is that you have a set of consumers that can take or shed load quickly and on demand, having a stabilizing effect on the grid. Grid stabilization is an important problem when using energy sources with less predictable power output such as wind and solar.

Residential heating with electricity is obviously wasteful, at least in temperate and cold climates when they are regularly used.

But for he tap on your kitchen sink, it can in many cases be the most efficient solution. That’s because an electric heater is a far smaller investment than running a gas pipe installing a furnace. Or, with a central furnace, to run th gap until warm water gets to the tap, then letting warm water in the long pipes go to waste when you turn it off.

As a rule of thumb, when using fossil fuels to make electricity, grid electricity is 1/3 efficient, and cost three times as much as having an appliance that uses the fossil fuel directly.

Of course there's plenty of details that make that statement an over simplification! The point is that you can recuperate your investment in a fossil fuels based heater extremely quickly.

Another problem with using electric water heaters is that they pull a high amount of amperage. Assuming you're going tankless, a water heater necessary for the temperatures in the northeast states could easily use over 100 amps. If you fill the bathtub, turn on the oven, and charge the car at the same time, you could trip your main breaker.

Electricity transmission can be expensive, both in terms of initial and recurring costs (which include safety provisions, wire maintenance, surge handling, regulation compliance, etc.). If you have a solar 10m away generating unnecessary power, heating water might be an OK option.

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