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All solar water heaters utilize collectors to capture solar energy as heat.Solar water heaters are either active or passive. Active systems use electric pumps, valves, and controllers to move fluid through the system. Active solar water heater systems have the potential to be more efficient, but they tend to cost more, need more maintenance, and require electricity. When retrofitting a home, active design is usually selected because it offers greater flexibility regarding the location of the solar collectors and storage tank. Passive systems have no pump or electrical requirements. They are not as efficient, but they cost less, require less maintenance, and are more reliable.