I bought a house in Hawaii in 2014 which had 2 4'x8' solar thermal panels, a 120 gallon solar tank with 1 upper grid tied 4500W element. The previous owners had had multiple problems: leaks, replaced one panel, etc. all of which was disclosed. While it worked, it worked very well providing way more hot water than my wife and I need. But by now, both panels have failed completely.
With Hawaii's electric effective rate of about 30 cents/kWh I installed a 6.6kWh photovoltaic (PV) system soon after buying this house. I've closed the rooftop thermal panel water feed and am now using the single 4500W grid tied element for hot water. This does provide plenty of hot water for showering at about 110 degrees F (43 °C) but we would like hotter water for dish washing.
Given that the existing solar type water tank is 15+ years old I know I'll be replacing it one way or another soon. Although solar thermal panels are very good at heating water I'm just not going to spend another $1000.00 x2, plus labor, plus likely another large solar specific tank just to have the same problems in another 5 to 10 years. (The water is very hard here!)
My alternatives as far as I can tell are as follows:
- Replace the existing solar tank with a conventional water heater and observe the effect on my electric bill, maybe add to my PV system later as necessary
- Replace the existing solar tank with a hybrid heat pump tanked water heater. These are expensive and new technology without a good track record.
- Maybe some type of dedicated DC output solar PV system to power a resistive element with grid back up.
Any advice or recommendations?
A couple more notes: First, I have a grandfathered net metering PV system agreement with the local privately owned Hawaii electric company but they have now changed the agreement for new PV customers. They are now backpedaling on net metering as hard as they can!
Second, I'm retired and don't have the tax liability I once had, so the solar tax credits mean much less to me. It will take me years to use up the credits from my current PV installation.