Solar thermal is as simple as "the wheel". Invented tens of thousands of years ago, "the wheel" is to this day the best way to move things around on dry land! Do we not buy tires because we think they might invent a better wheel next year? Do we think there will be a breakthrough? Until we learn to levitate, the wheel will remain the best way to move things around on dry land. The same principle is true for solar thermal – heating water with the sun.
Solar thermal is a simple, mature technology, which has had very little change in the last 40 years. Solar thermal hot water systems are used all over the world in huge numbers, because it is the most cost effective way to heat water. It also can have a bigger effect to reduce global warming, than virtually any other type of product or system. The U.S. Government is again recognizing these realities and making residential solar hot water affordable to most families by providing a 30% Federal Tax Credit.
Solar thermal is as simple as running water through a black material (usually copper). The black material absorbs the sun’s energy and conducts heat to the water inside. The flowing water comes back warmer. If your desired water temperature is close to daytime air temperature (like an 85 degree pool on an 80 degree day), the panels are usually "unglazed". If the desired water temperature is 130 degrees for domestic hot water (DHW), the panels should always be "glazed" with a clear material over the absorber to trap the heat. This insulates it from heat losses to the relatively cool ambient air.