Any crypto system that has an energy problem also has an economic problem. When a transaction requires the same amount of electricity as an average household uses in a month, then each transaction will cost someone a full months electric bill. That will either have to be paid with extremely high transaction fees or "absorbed" by the value of the currency in ways that make it unsuitable as an actual currency.

This is true regardless of the environmental impacts of the specific energy source, and while solar and wind are decreasing in price, it is unlikely costs will drop so much to make this issue negligible.