Question regarding solar hot water heating
new guy here. I've got a solar water panel 4x10 and a solar 80 gallon tank. Live in Hawaii in sunny Kihei Maui. Still, we need more than just solar heating of water. About five years ago I bought a Craigslist propane water heater and plumbed it downstream of the solar tank and left the electric element off in the solar tank. It worked good. My wife was happy to have full time hot water. But I bought a lot of propane. Anyway the propane tank has rusted out finally. I often felt that propane heaters with their annular doughnut shape, aren't the best storage tanks of hot water, cooling it at night. I wonder what to do. So far, I've suggested to my wife to turn on the element at the breaker just when needed. But, that's unreliable. Likely the element will get left on all day. I've also thought of buying a propane tankless heater to top up the water from the solar tank. Does that work well for anyone? Can propane instant heaters handle warm or hot water input? I also think about getting a second panel. Maybe also a larger solar tank. But I want a practical solution. Any thoughts about the best type of water heater after solar preheating?