What is the best solar thermal system?
“Best” is a relative term. We’ll answer your question in terms of most practical, most reliable or most energy efficient, but these all depend on where you live. For any climate where it freezes, the use of a closed loop glycol-based solar thermal system might be the only practical choice. A solar thermal drain-back system is also used under these conditions, but these are not as popular because they are not quite as reliable. For warmer climates, the most energy-efficient system is a system called thermosiphon. It requires no electric pumps to operate (in technical terms, this makes it a passive solar thermal system). The sun heats the fluid until it rises to the top of the panels, where it flows into a tank or heat exchanger. From the heat exchanger, only the hottest water is skimmed off from the top of the tank as you draw down the hot water.
