I think we are already starting to see people use alternative forms of energy. I think the overuse of energy is a big misconception to be honest. The way the mining process is designed forces people to seek the cheapest forms of energy. Which inevitably forces people to look for countries with an excess. If anything the whole process is energy efficient. On top of that you are turning bad money into sound money so even if it was was an inefficient process the outcome will be a much more stable decentralised currency which is a good use of resources in my opinion