Who said that batteries are the only way of energy storage. Hydrogen is discussed because of that. And yes, energy production also need to switch to reach CO2 emission goals.
It's more efficient to charge a battery and drive with an electric motor than use electricity to create hydrogen and use that to drive a car.
Hydrogen might become useful for things like planes, where electric isn't good enough yet.
If you span some ten-thousand solar panels in e.g. Northern Africa your problem is not the loss of energy because you have far too much green energy. Same is true for nearly all summer months when it comes to photovoltaic on the roofs of houses. There is too much of it.
in theory it extract O2 from the air and produces H2O (otherwise known as water). But the devil is in the details. Also, green energy is mostly photovoltaic/wind ... so panel/wing environment costs and transport costs factor in.
