Modern, high-quality solar hot water (SHW) systems are reliable and long-lasting if designed and installed properly. Many systems installed more than 30 years ago are still going strong. However, most systems this old and older have needed repairs and component replacement from normal wear and tear. In some cases, repairs or alterations are needed because of design and/or installation flaws.
SHW systems are fairly simple appliances—not as straightforward as a tank-style water heater but nowhere near the complexity of a car. Seeing, hearing, smelling, and touching components (carefully) can assist in diagnosing problems before any troubleshooting equipment and tools are used. Experienced technicians use their senses to determine the status of a solar water heater. Unusual, high-pitched noises and burning odors are associated with bearing wear from the pumps. Burning smells can also indicate electrical problems, such as burned motor windings, loose connections, or damage from excessive voltage or current. Visual inspection can reveal controller malfunction, leaks, and fluid levels.
If all appears normal after a quick inspection and the sun is out with the pump(s) energized, measuring the temperatures of the collector loop supply and return can provide valuable information. If pipe temperatures allow it, feel the two pipes, with one hand on each pipe. If pipes are too hot to touch (above about 120°F), measure their temperature with an infrared thermometer. A noticeable difference in temperature between the two pipes indicates that the collectors are adding heat—the system is working.
Cold supply and return pipes are a symptom of no flow—check the pump(s) or controller first. Both pipes being hot and at the same temperature is likely only to occur in a system with an external heat exchanger. This indicates that the collector loop pump is operating and the controllers have turned it on but that the heat is not being exchanged to the home’s potable water. A malfunction in the domestic hot water (DHW) pump or an obstruction on the DHW side of the heat exchanger is indicated. More detailed symptoms are component-specific.
What goes wrong and why depends on the SHW system, the climate, and the water conditions. Dave Menicucci, an ex-Sandia National Laboratories engineer, compiled the surveyed results of hundreds of systems that had experienced failures and needed service calls in the past three decades (see “Assembly and Comparison of Available Solar Hot Water System Reliability Databases,” bit.ly/SHWreliability). The survey indicated that most problems resulted from component failures. Failures due to installation and maintenance were in the minority.
The fact that valves accounted for the highest percentage of reported problems can perhaps be attributed to hard water and open-loop thermosyphon and direct forced-circulation (DFC) systems. The relatively high problem rates of valves also include a significant number of freeze-protection valves, which are used only in very mild climates, in lieu of true freeze protection, which is accomplished by drainback and antifreeze-based systems.
My company’s experience was that controllers and sensors were the major component problem, and pumps were second. Valves were not as much of an issue, but that’s likely due to freeze-protection valves being eliminated in most local installations after the late 1980s. The rest of the component problems listed, which fall in the 6% to 16% range, jibe with our field experience.
Modern flat-plate collectors are fairly simple appliances, and durable especially if they are certified by the Solar Rating & Certification Corporation. They experience lifetimes exceeding three decades and can probably last 60 years or more if not abused. That said, these are some problems that can be encountered with collectors.