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The down-side of hydrogen power is that Hydrogen is created from hydrocarbons -- fossil fuels. I understand splitting water into hydrogen and oxygen is far more expensive.
This is often true, but not necessarily so. There are power sources that produce 24/7, in spite of the fact that power is needed much more during daylight hours.
Nuclear is a good example. What do you do with the power in the middle of the night? We don't have a battery system to store it, although the system in the state water project that pumps water uphill from one dam to the higher, to be used at a later time, functions sort of like a battery. But you could also use that unused, cheap, excess energy to crack water into hydrogen.
Most power systems have a power curve that is optimized for maximum efficiency at peak output. So it is cheaper and more efficient to run the system full-bore, than it is at half capacity. But you have to find uses for that power, perhaps hydrolysis is one.
