Proof of stake (PoS) is certainly the future for consensus. Ethereum has a built-in proof-of-work difficulty ramp up already started (a time bomb) and has had plans to move to PoS since the beginning.

I'm guessing there's wasted electricity that solar panels generate at inconvenient times? If the power is "free" (not being used for anything else) at least they can mine Bitcoins.

Bitcoin miners fall behind the curve fast enough that if you aren't running them full time with cheap electricity you are losing money.

the plan for ethereum is to switch to proof-of-stake, but that has definitely not been figured out yet. I could also see a more private blockchain supporting stuff like this. Maybe it's not open to anonymous participants, but is still more distributed than a single company.

I find movement to PoS perhaps the most important milestone toward large scale adoption of Ethereum or any cryptocurrency-related technology. PoW just isn't feasible for large scale deployment: way too much energy is wasted for consensus.

Ethereum burns ~1 million dollars of electricity per day. But they seem to be on the way to moving to POS.