keydiver wrote:I think part of the confusion is that I was comparing it to a standard electric hot water heater, a little off topic,sorry. A typical electric hot water heater uses $500+ per year in electricity, so the payback for solar hot water is very short.
Is it really, though? Even at $500/year and if it costs $5k to install you're looking at 10 year break-even which is similar to PV these days.
But for my house, we only use about 6 therms / mo for non-heating months (only gas use is for water heater and HVAC) which is like $7-8/mo or ~$100/year. This is with a standard water heater. I'd have a very hard time justifying a 50-year payoff when the system will probably need to be replaced at least once in that time. Never mind that I'll still have a gas bill unless solar hot water systems are good enough to store enough hot water for showers in the morning. (Would have to find room for a tank - I guess with the tankless heater I'd have room)
Or I could spend $5k on 1.5 kW of PV (after rebates) that will generate about 2000 kWh/year. With 1 therm of gas having about 30 kWh of heating, that's 66 therms equivalent - enough to power a resistance electric water heater of similar efficiency to the current heater - or with a hybrid water heater that would leave me with well over 1000 excess kWh/year to drive the LEAF. Or do the tankless high efficiency hot water heater and don't worry about the minimal amount of gas the house uses - one of the tankless units would probably cut my gas usage by 30-50% compared to my current heater.
Electricity at a retail price of $0.14/kWh the same $5000 investment has the potential to save a lot more money - 2000 kWh is about $280 worth compared to under $100 for 60-70 therms of natural gas.
Obviously the amount of hot water one uses plays a big role here - conservation is probably the biggest winner here - install those low-flow shower heads!