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Benefits of Solar Water Heaters
by staff writer

Increasing interest in solar water heating systems is being driven by rising energy prices. The initial costs are higher than traditional gas or electric water heaters, but solar water heaters can operate more efficiently and can save money in the long run. In many cases, a traditional water heater is still installed as a backup. This setup still delivers savings since water entering the traditional water heater is preheated. The amount of hot water a solar water heater produces depends on the type of system, collector area, and potential solar energy. Choosing the right system is critical to achieve peak energy efficiency.

roof mounted solar water heaterAll solar water heaters utilize collectors to capture solar energy as heat. Flat plate collectors are well-insulated boxes containing a black adsorber plate shielded by several layers of glass or other transparent material. Light travels through the glass and strikes the adsorber plate, turning the light's energy into heat. Fluid is circulated through tubing attached to the back plate to collect and transfer the heat to where it is needed. Evacuated tube collectors have two lines running through the inner tube, which is the adsorber. A vacuum between the inner tube and the outer tube minimizes heat loss. Evacuated tube collectors have the ability to effectively collect heat in cooler climates and during cloudy days. Unsurprisingly, evacuated tube collectors are more expensive than flat plate collectors.

active closed-loop solar water heating systemAfter fluid has been heated in the collector, it flows to an insulated storage tank -- where it is ready for use -- or to a heat exchanger. Some solar water heaters have a storage tank attached to the collector, but most often they are independent units. A storage tank may not be required for some applications, like heating a swimming pool, but it is a very common component in most installations.

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.

Systems are also classified as direct (open loop) or indirect (closed loop). Direct systems use solar energy to directly heat the water you will drink, shower with, etc. Indirect systems separate the fluid that circulates through the solar collectors from the water that you will consume. The primary difference in equipment is whether a heat exchanger is used to warm the potable water. Indirect systems are almost always active due to the increased circulation requirements. Climate and the potential for freezing temperatures are major considerations when choosing between direct and indirect systems.

Indirect solar water heaters may use water in the solar collector loop, but it is also possible to use a combination of water and glycol. The combination of water and glycol is a very typical antifreeze mix which has a lower freezing point than water (as low as -60°F). Glycol is toxic, so heat exchangers are typically double-walled for safety. Indirect systems are more expensive and require more maintenance, but they offer the benefit of operating in areas that experience freezing temperatures.

Many people don't realize that solar water heaters can function in almost any climate. Their effectiveness depends on available solar energy, but also on the temperature of the water source. If a solar water heater can increase the temperature of incoming water from 60°F to 90°F, this can provide a
substantial energy saving when used in conjunction with a traditional water heater. That’s 30°F that you don't have to heat with gas or electricity!

Careful research is required to size your solar water heating system appropriately. Consider your family's average water usage, local climate and the potential for freezing weather, and the efficiency of the system
you are interested in. It is also advisable to make sure there are no restrictions in the local building codes or neighborhood covenants before installing a solar water heater.

With proper planning, installing a solar water heater can protect you from rising energy costs, reduce your carbon footprint, and make your homestead a little more self-sufficient.