When most people think about solar, they think about photovoltaic panels that generate electricity, but they don’t often think about solar thermal. When considering heating water, solar thermal is incredibly efficient by comparison.
For example, some of the highest performing photovoltaic panels achieve an efficiency of 20% compared to nearly 75% from the highest performing solar thermal panels. This enormous difference in efficiency is simple. The sun lets out thermal energy and when used directly, as in the case of solar thermal, there are not many losses. There are more losses, as is the case with photovoltaics, freeing up electrons in the process of converting solar radiation into electricity and back to thermal. Since around 75% of the sun’s energy that falls on a solar thermal panel is made useful, it ends up saving space.