You use a certain amount of energy computing blocks. How do you get back or redirect that energy? Isn't it mostly lost as heat?

If your datacenter produces currency, that currency belongs to the datacenter owners and operators, not the electric grid operators. You could spend currency importing additional fuel but that was true regardless of what task the datacenter was doing to produce currency. You could be renting out cloud storage or crunching numbers for LLM chatbots.

Is Bitcoin mining the most efficient way to turn electricity back into some form of currency? I doubt it. One compelling alternative is turning air and water into ammonia, which can be used to fertilize crops or burned as a fuel for mechanical or electrical output. Or you could perform those other datacenter tasks.

Moreover, Bitcoin is convertible into electricity at variable rates, not a fixed rate. I can't buy Bitcoin now and have any confidence about how much or how little electricity it will buy in 5 years. Supposedly this is the great weakness of fiat - that my fiat dollars will buy an unknown amount of real goods.

I suspect this unknown is the chief appeal of Bitcoin. Bitcoiners seem to hope that Bitcoin will increase in trade value vs real goods, while they (and I) believe fiat will tend to decrease in trade value vs real goods.

If you think Bitcoin will continue to increase in trade value vs real goods forever, why? Whatever wonderful mathematical properties it has can be duplicated in other cryptocurrency. Do you think all cryptos matching or exceeding the current properties of Bitcoin will go up in value forever?