System Maintenance for a Solar Water Heater

Maintaining Solar Exposure

• A solar water-heating collector is a glass-topped, insulated rectangular metal box containing copper tubing that circulates liquid. In direct systems, the tubing contains water heated by the collector and conveyed directly into the house or a storage tank. In indirect systems the tubing contains heat-absorbing fluid that circulates through a heat exchanger installed in a tank, heating the water in the tank. Anything that diminishes the solar exposure of the collector is an issue on the maintenance list. Eliminate encroaching shade. Trim back tree limbs that have grown out and cast shade on the collectors. Keep in mind that the sun’s track over an average day changes shade patterns: a collector fully exposed at 10 a.m. may be shaded at 2 p.m. Check the collectors at different times to verify maximum solar exposure.

Collector Cleaning

• Not only large objects create shade; a mere coating of dust on the glazing of the collector also diminishes the solar energy reaching the tubes. Other debris that may accumulate on the glass surface, including bird droppings and leaves, affects system performance, as well. Hose down the glass regularly and, when required, clean by hand with a sponge or squeegee and mild detergent. Inspect the glass for cracks and deteriorated seals annually.

Plumbing, Pumps and Valves

• Significant leaks in the system are usually evident. Visually examine pipe insulation and fittings for corrosion or subtle leakage regularly. In active systems, thermostat-activated electric pumps convey heated water to the storage tank. Pumps should be cycling on and off by 10 a.m. on days with adequate sunlight. If you can’t hear the pump operating, suspect a malfunction in the thermostat or a bad pump. Also listen for improper pump operation at night, a sure sign of a defective thermostat. A solar collector incorporates a temperature pressure-relief valve at the plumbing outlet as a safety feature. If the valve is dripping, manually operate its spring-loaded lever to verify proper opening and closing of the valve. If dripping continues after manual operation, replace the valve.

Heat-Transfer Fluid

• In an indirect system, the fluid that conveys heat to the exchanger in the storage tank requires periodic flushing. While this procedure is best performed by a professional, the do-it-yourselfer can at least examine the fluid for signs of contamination or age. If the color of the fluid has shifted to dark brown, flushing and refilling is required. Where the local water contains dissolved minerals, a professional flushing procedure may include use of acidic descaling solutions to dissolve deposits. In climates where temperatures drop below freezing, the heat-transfer fluid contains non-toxic anti-freeze, which must be replaced during the flushing and refilling process.