Solar energy systems require periodic inspections and routine maintenance to keep them operating efficiently. Also, from time to time, components may need repair or replacement. You should also take steps to prevent scaling, corrosion, and freezing.
You might be able to handle some of the inspections and maintenance tasks on your own, but others may require a qualified technician. Work that requires going up ladders, walking on roofs, soldering or hot work, or cutting back tree limbs should be performed by a professional service for safety reasons. Ask for a cost estimate in writing before having any work done. For systems with extensive damage, it may be more cost effective to replace, shut off, or remove the solar system than to have it repaired.
Periodic Inspection List
Here are some suggested inspections of solar system components. Also read your owner's manual for a suggested maintenance schedule and keep track of previous maintenance activities in order to manage preventative maintenance intervals and better track elusive problems
- Collector shading
Visually check for shading of the collectors during the day (mid-morning, noon, and mid-afternoon) on an annual basis. Shading can greatly affect the performance of solar collectors. Vegetation growth over time or new nearby construction may produce shading that wasn't there when the collectors were installed.
- Collector soiling
Dusty or soiled collectors will perform poorly. Periodic cleaning may be necessary in areas with specific sources of soiling such as birds or dust from plowing and if rain is not sufficient to rinse them off.
- Collector glazing and seals
Look for cracks in the collector glazing, and check to see if seals are in good condition. Plastic glazing, if excessively yellowed, may need to be replaced.
- Plumbing, ductwork, and wiring connections
Look for fluid leaks at pipe connections. Check duct connections and seals. Ducts should be sealed with a mastic compound. All wiring connections should be tight.
- Piping, duct, and wiring insulation
Check that all valves are in the proper operating position. Look for damage or degradation of insulation covering pipes, ducts, and wiring. Cover the pipe insulation with protective plastic or aluminum wrapping and replace if necessary. Protect wiring in conduits
- Roof penetrations
Maintain flashing and sealant around roof penetrations as needed. Watch for any signs of water leakage on the underside of the roof (if visible).
- Support structures
Check all nuts and bolts attaching the collectors to any support structures for tightness. Watch for corrosion on steel parts- and clean and paint if necessary.
- Pressure relief valve (on liquid solar heating collectors)
Actuate the lever to make sure the valve is not stuck open or closed.
- Dampers (in solar air heating systems)
If possible, make sure the dampers open and close properly and are in the proper position.
- Pumps or blowers
Verify that pumps or blowers (fans) are operating. Listen to see if they come on when the sun is shining on the collectors after mid-morning. If you can't hear a pump or blower operating, then either the controller has malfunctioned or the pump or blower has. The problem is often the starting capacitor, which can be replaced without replacing the pump or motor.
Solar water heating controls consist of a temperature sensor on the solar collector outlet, another at the bottom of the solar storage tank, and a circuit (delta-T controller) to start the pump when the collector is hotter than the tank and stop the pump if its not. If the pump is running at night it could be that the collector sensor is short circuited or the tank sensor open circuited. If the pump is not running during the day the reverse could be the case and the resistance of these sensors should be compared to reference value to determine which one has failed. A common problem is temperature sensors simply falling off the surface they are intended to measure- ensure that they are fastened with a lug or stainless steel clamp.
- Heat transfer fluids
The propylene glycol antifreeze solutions in liquid (hydronic) solar heating collectors need to be replaced periodically. The pH (acidity) and freeze point of the fluid can be measured with hand-held instruments and replaced if out of specification. It's a task best left to a qualified technician. If water with a high mineral content (i.e., hard water) is circulated directly in the collectors, mineral buildup in the piping may need to be removed by adding a de-scaling or mild acidic solution to the water every few years.
- Storage systems
Check storage tanks, etc., for cracks, leaks, rust, or other signs of corrosion. Steel storage tanks have a “sacrificial anode” which corrodes before the tank does and should be replaced at an interval recommended by the supplier. It is a good idea to flush storage tanks periodically to remove sediment.
Preventing Scaling and Corrosion
Two major factors affecting the performance of properly sited and installed solar water heating systems include scaling (in liquid or hydronic-based systems) and corrosion (in hydronic and air systems).
Domestic water that is high in mineral content (or "hard water") may cause the buildup or scaling of mineral (calcium) deposits on heat transfer surfaces. Scale buildup reduces system performance in a number of ways. If your system uses water as the heat-transfer fluid, scaling can occur in the collector, distribution piping, and heat exchanger. In systems that use other types of heat-transfer fluids (such as propylene glycol, scaling can occur on the surface of the heat exchanger in contact with potable water that transfers heat from the solar collector to the domestic water. Scaling may also cause valve and pump failures on the potable water loop.
You can avoid scaling by using water softeners or by circulating a mild acidic solution (such as vinegar) through the collector or domestic hot water loop every 3–5 years, or as necessary depending on water conditions. You may need to carefully clean heat exchanger surfaces. A "wrap-around" external heat exchanger is an alternative to a heat exchanger located inside a storage tank.
Most well-designed solar systems experience minimal corrosion. When they do, it is usually galvanic corrosion, an electrolytic process caused by two dissimilar metals coming into contact with each other. One metal has a stronger positive electrical charge and pulls electrons from the other, causing one of the metals to corrode. The piping connection from the copper pipe to the steel tank should thus be a “bi-metallic” type of connector that uses a plastic sleeve to separate the dis-similar metals. The heat-transfer fluid in some solar energy systems can also provide a bridge over which this exchange of electrons occurs.
Oxygen entering into an open loop hydronic solar system will cause rust in any iron or steel component. Such systems should have copper, bronze, brass, stainless steel, plastic, rubber components in the plumbing loop, and plastic or glass lined storage tanks.
Solar water heating systems, which use liquids as heat-transfer fluids, need protection from freezing in climates where temperatures fall below 42ºF (6ºC).
Don't rely on a collector's and the piping's (collector loop's) insulation to keep them from freezing. The main purpose of the insulation is to reduce heat loss and increase performance. For protecting the collector and piping from damage due to freezing temperatures, you basically have two options:
- Use an antifreeze solution as the heat-transfer fluid.
- Drain the collector(s) and piping (collector loop), either manually or automatically, when there's a chance the temperature might drop below the liquid's freezing point.
Using an Antifreeze Solution
Solar water heating systems that use an antifreeze solution (always propylene glycol, never or ethylene glycol because of toxicity) as a heat-transfer fluid have effective freeze protection as long as the proper antifreeze concentration is maintained. Antifreeze fluids degrade over time and normally should be changed every 3–5 years. Since these systems are pressurized, it is not practical for the average homeowner to check the condition of the antifreeze solution. If you own this type of system, have a solar heating professional check it periodically.
Overheating occurs when there is little hot water use in the home but the sun continues to heat the water. The controller will turn the pump off when the solar storage tank hits an upper limit (default 180F but often set lower to prevent scalding). The collector will continue to heat up, which most systems can tolerate, but can lead to discharge of fluid out a pressure relief valve and premature degradation of the heat transfer fluid. Draining the fluid back into a drainback tank can avoid this damage to the fluid caused by overheating. Some systems include a solenoid valve that will open to drain some water from the tank if overheated.
Draining the Collector and Piping
Solar water heating systems that use only water as a heat-transfer fluid are the most vulnerable to freeze damage. "Draindown" or "drainback" systems typically use a controller to drain the collector loop automatically. Sensors on the collector and storage tank tell the controller when to shut off the circulation pump, to drain the collector loop, and when to start the pump again.
Improper placement or the use of low-quality sensors can lead to their failure to detect freezing conditions. The controller may not drain the system, and expensive freeze damage may occur. Make sure that the freeze sensor(s) have been installed according to the manufacturer's recommendations, and check the controller at least once a year to be sure that it is operating correctly.
To ensure that the collector loop drains completely, there should also be a means to prevent a vacuum from forming inside the collector loop as the liquid drains out. Usually an air vent is installed at the highest point in the collector loop. It is a good practice to insulate air vents so that they do not freeze. Also make sure that nothing blocks the airflow into the system when the drain cycle is active.
Collectors and piping must slope properly to allow the water to drain completely. All collectors and piping should have a minimum slope of 0.25 inches per foot (2.1 centimeters per meter).
In integral collector storage or "batch" systems, the collector is also the storage tank. Placing large amounts of insulation around the unglazed parts of the collector and covering the glazing at night or on cloudy days will help to protect the collector from cold temperatures. However, water in the collector can freeze over extended periods of very cold weather. The collector supply and return pipes are also susceptible to freezing, especially if they run through an unheated space or outside. This can happen even when the pipes are well insulated. It is best to drain the entire system before freezing temperatures occur to avoid any possible freeze damage.
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