A couple of oddities you might note. First off, the plumbing required for the water heater tank is a little... convoluted.
The cylinder you see on top of the tank is a heat exchanger. Our system is an active, closed loop system, which means that the solar panel has loops of tubing filled with distilled water, and the distilled water circulates through tubing into the exchanger, where it heats water in the exchanger that is then circulated into the holding tank. Kind of a nifty system, if you ask me. Ours is guaranteed for 30 years.
The exchanger is kind of loud when it's circulating. It doesn't bother me, but you can definitely hear that the exchanger is working. If you're the type of person who wants things ultra-quiet and your water heater is in your house, you probably shouldn't get a solar heater.
Because the temperature of the water in the tank varies, you can't always set the dial on your shower in the same place and get the same temp. If it's been sunny, the water will be hotter, so you'll need to run more cold. If it's been cloudy, it will be cooler, so you'll have to move the dial warmer. Not difficult, but different if you're used to water that's always 105 degrees.
It can be entertaining to see how hot the water in your tank actually gets just from the sun. We have a little electronic doodad that shows the temperature both on the roof in the solar panel and in the bottom of the tank. I took these pictures over the weekend, when the high was 95 degrees.
See the little dot at the top of the graphic? That tells you the temperature on the roof, in the solar panel. In this case the temperature was 143 degrees.
The temperature at the bottom of the tank (denoted by the dot in the water tank) was 136 degrees, but since hot water rises, the temp at the top of the tank was likely higher. Any time there's more than a 10 degree difference between the temperature on the roof and the temperature at the bottom of the tank, the water will circulate, exchanging hotter water for cooler water.
So far we have not noticed a change in our electric bill, but we have been running the A/C more in the last month since August/September is usually the hottest month. If we continue to have sunny days, we will likely be able to leave the breaker for the water heater off completely until October! I am certainly hoping that is the case - it's very neat to have your water heated by the sun!