You need to be patient using these slow ways of charging.
But as you said:
If there is no electricity at all you need patience anyway.
Same is with our thermal solar systems (hot water) on the roof:
In summer we have too much hot water, in winter when you would really need it to support the heating system, there is NO !
(At the moment a pile of snow at the collectors)
Solution would be to bury a huge, well isolated tank deep in the earth and to store the hot water in summer for wintertime.
But its quite a good feeling.
I had really remorse in summer when the old
system started to boil water wasting fuel oil.
Now we use a gas heating & solar system (less pollution, no more bad smell in the basement)
New built houses are equipped with heating pumps and floor heating system and are isolated perfectly.
But our old house is a good, solid house.