I do agree with you there, but that will not be their only revenue stream - they will also be looking at giving electricity to houses too, which is a huge market if you can undercut competitors and eliminate middle men through the blockchain.
Also, if you read in to how much energy is actually left surplus by certain renewable energy factories it is enormous. Although I am still unsure if Envion will succeed, I think that they will do well, depending on what they mine and how difficult it becomes.
Yup I agree let's see time will tell.