Hydrogen and oxygen can be generated at the same time at the point of power generation. Our power plants are sized for peak demand, but have few ways to store excess capacity. Running coal plants is very polluting. Running nuclear plants is a deferred radiation pollution/storage issue; howver, current plants could have the off-peak capacity used to generate H2 and O2. Additionally, off shore tide action, wave action, current, hydroelectric dams, wind energy, ocean thermal differential (indirect solar), and direct solar power can all be used with hydrogen and oxygen generation during any off-peak (e.g. - middle of sleeping hours, during off-peak fluctuation during the day, etc)) or high-generation time (e.g. - wind is blowing, sun is shining, current is flowing, heavy rain waters are being released, etc.).
I view this as more efficient than the electric cars all plugged into the grid. Transmission losses are staggering, the infrastructure would also need to be upgraded, and there is no way to "store-up" energy on the grid when cars are not plugged-in charging.)
This CAN be a regenerative type of energy. Coal is not, but hydroelectric, currents, wind, solar, methane from sewage, or even wood burning are. The coal and wood are also not as green, even with super scrubbing stacks. Oil will not be here forever. We are consuming it far faster than it could ever be made; unless, we start extracting it from peanuts or other plants (indirect solar). Besides, plastics are also valuable and require our precious oil as well.
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