Gratuitous use of electricity is anti-economical regardless of the source.
This makes investments in renewable energy infrastructure more profitable and paid off sooner. A solar farm has more demand and higher margin for its products.
On the other hand, it means cheap coal energy is also financially productive.
What is anti-economical is the unfair price competition due to externalities not captured by coal energy's pricing.
Why not focus on the source of the electricity rather than what the electricity is used for?
> proof-of-waste
It's Proof of Work. Productive work has value and in this case, it's widely distributed censorship-resistant validation of transactions.