We live near San Jose CA. The air is warm Apr to Oct, but our water gets cool mid-Sep to mid-May. We’re upgrading the never-replastered 40-year-old pool with an auto safety cover, variable speed pump, etc. It’s 20k gal 12’x36’, and I’d like it to be 80°F Apr-Oct. A gas heater costs ~$1500, and Rheem estimates gas would cost $400/yr. A heat pump costs ~$3000, and Rheem estimates 1500 kWh (Hayward 2000 kWh), though 150 kWh (300 kWh) is Jun-Aug when the solar cover alone has sufficed, so perhaps that’s pessimistic. CA power is tiered, so my first kWh costs $0.13 and my last costs $0.34. Installed solar thermal ranges from $5k-$8k.
Gas seems cheapest, but costs will only rise, it seems wasteful, and I fear we won’t use it. Solar thermal is expensive upfront, requires perhaps 1 kW more pump power, and runs water over my roof. We could offset a heat pump’s electric usage with solar photovoltaic panels (PV): at 1.75 kWh per year for each watt at my location, and $4/W installed ($2/W materials), running a heat pump off grid-tied PV panels is about the same cost as solar thermal. Versus gas, it’s like a 20-year bond that yields 5.5%, which is a decent return. Unlike solar thermal, when the heat pump is not used the PV generates useful power, and the heat pump can generate heat even if it’s cloudy. PV also generates perhaps 6x more useful BTUs/sqft, which gives us room to offset more of that expensive $0.34/kWh electricity. The bad: a heat pump is loud, upfront costs are high, and electric use will be high in Apr/Oct.
I know this has been a controversial topic in the past, but PV is cheaper now, I only need heat a few months of the year, and I live in a sunny climate. So, what do you think?