Caleb James DeLisle on Nostr: Hydrogen is a really nice thing to do with excess electricity. Electrolyzers are ...

Hydrogen is a really nice thing to do with excess electricity. Electrolyzers are fairly easy to build and will take all the power you can throw at them. DIY electrolyzes are about 50-60% efficient, but they make something that's very high value. Hydrogen can be burned, used in an engine, or made back into electricity in a fuel cell. Fuel cells are expensive but it's 50% efficient conversion of H2 to power, gasoline engines are 30% at best.

At first glance, the hydrogen cycle seems extremely lossy, but all of the loss exits as heat. If you have a fuel cell in of your house and you run it in winter months when solar is not plentiful, the loss is all heat which you need in the winter anyway. On the generation side, the loss is also heat - and interestingly, you can make hydrogen at any temperature you want. If you're insane, you can run an electrolyzer at 1000C/1832F and the reaction will actually require 50% less electricity because the heat is contributing to the reaction. Just to give you a picture of what we're talking about, 1000C is about the melting point of copper, well past that of aluminum. Metal glows red. It's a real engineering nightmare.

Generally speaking, the value of heat rises as the temperature rises. Heat at 20C/68F can warm your house in the winter, but it's otherwise kind of useless. Heat at 100C/212F makes great domestic hot water, heat at 200C is into the zone where it can be used to boil water and run a steam turbine. So the higher the temperature, the more useful the waste heat.

Another fun thing about hydrogen electrolysis is that you can do it at any pressure you want. You do use a little bit more energy because it's producing gas bubbles with additional energy stored as pressure, but it allows you to generate hydrogen directly into a pressure tank if you want to.

Hydrogen storage is a more difficult problem. A 50% efficient electrolysis cell makes 15g of H2 per kWh. If you're storing H2 in bags, you have 89 grams per cubic meter so about 6 kwh per cubic meter. Over 3000 cubic meters of H2 from 20MWh.

Compressed H2 at 200 bar (3000 PSI, SCUBA pressure) is 15g / liter, conveniently the same number as 1 cubic meter in a balloon. So 200 liter "big tank" corresponds to 1.2 MWh.