[ephbit]

Let's say you want to use the system for heating with a heat pump.

Your energy consumption for heating might be ~ 3000 kWh/month during the winter months (Nov-Mar) for a moderately insulated house.

Assuming your PV produces only 10 % of the demand during these 5 months (so you have to rely on stored energy for the remaining 90 %) and your heat pump delivers a Coefficient of Performance of 3.5 then you'd need to store ~ 3900 kWh.

As to my back of envelope calculation, one standard 50 l bottle of hydrogen contains ~ 30 kWh worth of energy when filled at 200 bar.

So you'd need ~ 130 such standard bottles to store enough hydrogen.

That's quite a lot. But of course with a well insulated home, you'd maybe only need a third, so that'd be 3-4 bundles (with 12 bottles each).