That whole setup cost $13,000. It provided 100% of our hot water needs from March to September and offset the need for natural gas from September to March. It all went to hell when the very hard water destroyed the storage tank. The system had a 20 year warranty. The manufacturer was out of business 7 years after installation. The system was removed at the 8 year point when I re-roofed the house. A local solar installer was happy to take the panels off my hands. Nobody really wanted them and they were useless absent the storage tank. The "payback" was supposed to be derived from avoiding what was projected to be very high natural gas prices. That never materialized. Another huge green fail.
For the first couple of years, my system was a home made 4X8' collector, just circulating water from and to the hot water heater tank with a pump and a differential controller.
I drained it down each winter as it gets to 30 below zero here.
Then heated the water from a heat exchanger on our System 2000 oil fired boiler.
Then I got 2 4X8 Grumman flat plate collectors and the pump for $150.
The "professional" installer had never been able to get it to work.
In 2 days, I had it working with a new differential controller.
I made an open vented system through a heat exchanger near the hot water tank.
I use the same low toxicity propylene glycol mix as I use in my vehicles.