> Hardware for mining cryptocurrency is self-financing in a relatively short period of time when the electricity is "free"
No it isn't. I know because I looked into it.
Assuming the price of bitcoin doesn't rise or fall, a cutting edge bit of dedicated bitcoin mining hardware will pay for itself in 3 years if operated continuously on free electricity, and will be effectively obsolete in 5 years, as difficulty increases and rewards drop.
So if you only operate the hardware 50% of the time it'll be obsolete before it's paid for itself.