I know it's a joke, but the if you buy equipment to mine bitcoins, you don't let it sit idle waiting for those few times a year that electricity prices are low.
You computer will be obsolete before you've made a return on investment.
The same problem applies to H2, etc, if the process is rarely used and the setup to do the process is expensive, then it's cheaper not to.
A plant that can produce H2 from electricity might be more expensive than the value of the power discarded.
