The miner and the power plant operator are often the same entity. They turn the mining equipment on when they want to dump energy, and off when they have more productive places to sell it. Seetee is a good example.
If you own the mining hardware, why would you do that? You are better off running that hardware 100% of the time (using batteries or similar when necessary). Mining hardware is expensive.
Only when you are actually better off. isn’t there a crossover point between the outside market needing/paying for electricity and mining? Or is mining the most effective return in all cases?