best use of off–grid electricity surplus?
Off grid you would really need to consider some EESU storage which is still hard to get, or a limited amount of battery storage.
You need battery storage so that you can start a motor when your supply is putting out enough only to run the motor. You can live without lighting, but you will not. Solar power is consistently absent at night.
Providing some power for nearby neighbours who are on grid might be the best solution, cutting their grid usage. In exchange they might supply you with some grid power.
You would of course pump extra water while you have power, refrigerate some water to allow you to have refrigeration when power is short.
Likewise heat up water so you can take a bath at your convenience, or heat your home with that heat.
If you have a lake above a falls, and use the fall to generate hydro power, use excess power to pump water back up over the hill to the lake.
Charging up the battery of the e-bike or Volt, rather than using the grid for those purposes may not be important if one is off grid. you probably do not have enough range to use a volt or e-bike.