Solar water heaters do three basic operations before the hot water comes out of your faucet:
1. Energy Collection: Sunlight, short wave energy, is collected and converted to heat which is long wave energy. The solar collector is mounted on or near your home facing south. As the sunlight passes through the collector’s plastic or glass “glazing,” it strikes a metal or rubber absorbing material. This material converts the sunlight into long wave heat, and the glazing prevents the heat from escaping much like a greenhouse. It is like leaving a car parked in the sun with its windows rolled up. The temperature inside a glazed solar collector on your roof can easily reach 300°F when there is no heat transfer fluid flowing through it.
(The most common types of solar collectors used in solar water heaters are glazed flat plate collectors. A glazed flat plate collector consists of a shallow rectangular box with a transparent plastic or glass “window” covering a flat black plate or selective “Chrome” coating. The black plate is attached to a series of parallel tubes or one serpentine tube through which water, or other heat transfer fluids pass.)
2. Energy Transfer: Circulating fluids like water in an “Open Loop” or Propylene Glycol in a “Closed Loop” transfer the collected energy in the form of heat to a storage tank. Heat energy is transferred from the collector to the water storage tank. In some water heaters, hot fluid is pumped from the collector to the storage tank. The pump is powered by electricity that either comes from an electrical wall outlet or a small photovoltaic module located near the collector.
3. Energy Storage: Solar-heated water is stored in an insulated tank until you need it. Hot water is drawn off the tank when tap water is used, and cold make-up water enters at the bottom of the tank. If additional heat is needed, it is provided by electricity or fossil fuel energy by the conventional “backup” water-heating system.
Solar water heaters tend to have larger hot water storage capacity than conventional water heaters. This is because solar heat is available only during the day and sufficient hot water must be collected to meet evening and morning requirements.
How well an active solar energy system performs depends on effective siting, system design, location, and installation. Solar thermal water heating systems, which use the sun’s energy rather than electricity or gas to heat water, can efficiently provide 50 to 90% of your hot water needs—without fuel cost or pollution and with minimal operation and maintenance expense.
Real homeowner Video on a installed Ruud Solar water heater.
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