Are there any non-battery means of storing excess energy produced by solar electric panels? My utility pays back less than 20% for solar supply of what they charge for use, and batteries are very expensive -- takes many years to pay back the return on investment for batteries. I am looking for a way to offset energy use throughout the dark hours. Maybe feed a heat pump that heats hot water that could then be stored for use by my heating/domestic hot water systems throughout the evening hours to reduce fuel oil use? Seems like there must be something cheaper than batteries that isn't going to wear out... even a tower with a motor and pulley and weight to power a generator on the way down or something. In the warmer months I can heat the pool and using the air conditioners during the day will mostly use up the solar capacity-- maybe the simplest thing is to put in some electric heat pumps to put the excess heat into the house during the day in the cooling months?