Comment by epistasis
18 hours ago
> An efficient steam turbine is largely inaccessible to hobbiests and I am scared of steam/pressure.
Thermal electricity generation really benefits from scale and extremes. The Carnot efficiency is proportional to the temperature differential between hot and cold. Even so-called "low quality" heat from a standard nuclear rector design is far hotter than anybody should deal with at home and it only gets ~1/3 efficiency. And dealing with small turbines is really inefficient too.
This is where batteries and solar really shine. They scale so well, and are extremely economical and electrically efficient.
Heat storage works well when you get beyond the scale of individual homes, but it's hard to make it work. I'd love to see something related to heat pumps in the future for homes, but district heating, such as could be accomplished by converting natural gas systems to heat delivery, are probably required for it to make sense.
Yeah, sadly, it seems almost impossible to get anything higher than 30% efficiency (theoretically with a Stirling engine, if you can find one, haha) out of a thermal battery without extreme pressures and temperatures.
Back-of-the-napkin math felt promising. A 1kg block of sand heated to 500 degrees Celsius should contain about 100Wh of electricity. Scaling that capacity up is easy, as it's just about adding sand or temperature (+ an effective method of transporting heat across the sand - maybe sand + used motor oil?).
Assuming 80% efficiency, tariff arbitrage (buy electricity during off-peak hours and use it during high-price hours) would pay off very quickly. In my area (Australia) it would be a matter of months - but the low real-world efficiency and lack of parts make it impossible.
It could work for heating during winter, though perhaps an AC/heatpump with the condenser a couple metres underground would be better value for money.
Heat storage can work for individual homes on the shorter scale. If you heat your home with in-floor heating (lower temperature requirements) you can have ~1-2m3 buffer tank that you heat up during the night and then use the stored heat during the day to heat your home. Works very well.