Your family uses hot water every day. Solar energy gathered during the day can be stored in an insulated tank to provide hot water long after the sun has gone down. It is cost effective. A batch uses line pressure to send water to and from a solar-heated tank located in an insulated box outside the house. A thermosiphon system calls upon water heated in the collector to rise by convection into a tank that must be placed at least 18 inches above the collector.
Passive systems have no automatic freeze protection.
They must be drained manually or left idle in freezing weather. The three active water heating systems are draindown, drainback, and closed-loop antifreeze. A draindown system pumps drinking water under line pressure through the solar collectors. A drainback system pumps water from a small tank through the collectors and a heat exchanger. A closed loop antifreeze system pumps a non-freezing fluid through the collectors to a heat exchanger in a sealed system.