In storage use an interval timer. The thing is if you want to power grow lights or controller for a still it might be profitable. Calculate your potential kWh gain, times whatever best suits your purpose then decide whether or not the new control system is worth it. Some horsee applications ain't worth it, they eat more hay than the worth of their plow power. If you decide on heating water with a hundred watts or so, you'll need to store it in a vacuum flask or at night the BTU loss will have you spinning your wheels. How about a photoelectric 10 watt LED nightlight with appropriate battery? Or burglar alarm with 200 db piezoelectric screamer?
