You place a bunch of solar panels in a sunny place that also has water.
Then you directly power the grid when it is sunny and all power is needed.
When not needed, you power the catalyst, storing the hydrogen.
When it is dark, you use the hydrogen to create power and (maybe) heat.
Realistically you'd have to store almost all of your electricity -- compare solar output, a very short midday peak, with electricity demand, which in many places is nearly constant over time. Almost of all of it would go through the 50%+ storage losses, which means the solar part (PV + inverter + etc.) of your costs are more than doubled, amortized per kWh. So economically, practically anything is better than local hydrogen storage. (Under the premise that solar PV is not effectively free, which is an understatement to put it mildly).
[1] http://en.wikipedia.org/wiki/Electrolysis#Electrolysis_of_wa...
[2] http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/f...