A typical system will reduce the need for conventional water heating by about two-thirds, minimizing the cost of electricity or fossil fuel and the environmental impacts associated with their use. Systems Active systems use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. Direct systems use pumps to circulate water through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. Indirect systems pump heat-transfer fluids such as a mixture of glycol and water antifreeze through collectors.
Heat exchangers transfer the heat from the fluid to the water stored in the tanks.
Because the water in the collector loop drains into a reservoir tank when the pumps stop, this is still a good system for colder climates. Passive Systems Systems that move water or heat-transfer fluid through the system without pumps are called passive systems. Because they contain no electric components, passive systems are generally more reliable, easier to maintain, and possibly longer lasting than active systems. Batch heaters or integral collector storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun. During the winter, they must be protected from freezing or drained.