Category: Active Solar Heating

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 might be able to handle some of the inspections and maintenance tasks on your own, but others may require a qualified technician.

For help finding a qualified technician, see the Learn More resources listed on the right side of this page (or below if you’ve printed out this page). Ask for a cost estimate in writing before having any work done. For some systems, 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.

• 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 construction on your house or your neighbor’s property 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 dry, dusty climates.

• 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

  Look for damage or degradation of insulation covering pipes, ducts, and wiring.

• Roof penetrations

  Flashing and sealant around roof penetrations should be in good condition.

• Support structures

  Check all nuts and bolts attaching the collectors to any support structures for tightness.

• Pressure relief valve (on liquid solar heating collectors)

  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.

• Pumps or blowers

  Verify that distribution 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.

• Heat transfer fluids

  Antifreeze solutions in liquid (hydronic) solar heating collectors need to be replaced periodically. It’s a task best left to a qualified technician. If water with a high mineral content (i.e., hard water) is circulated 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.

Source: EERE, U.S. Department of Energy

When screening potential contractors for installation and/or maintenance, ask the following questions:

* Does your company have experience installing and maintaining solar water heating systems?
Choose a company that has experience installing the type of system you want and servicing the applications you select.

* How many years of experience does your company have with solar heating installation and maintenance?
The more experience the better. Request a list of past customers who can provide references.

* Is your company licensed or certified?
Having a valid plumber’s and/or solar contractor’s license is required in some states. Contact your city and county for more information. Confirm licensing with your state’s contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.

Source: EERE, U.S. Department of Energy

The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it’s best to have a qualified, solar thermal systems contractor install your system.

After installation, properly maintaining your system will keep it running smoothly. Passive systems don’t require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system’s owner’s manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn’t provide a natural rinse.

Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part after or two after 10 years.

Source: EERE, U.S. Department of Energy

Before you purchase and install a solar water heating system, you want to do the following:

* Consider the economics of a solar water heating system
* Evaluate your site’s solar resource
* Determine the correct system size
* Determine the system’s energy efficiency
* Estimate and compare system costs
* Investigate local codes, covenants, and regulations.

Source: EERE, U.S. Department of Energy

* Direct circulation systems

Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.

* Indirect circulation systems

Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

Illustration of an active, closed loop solar water heater. A large, flat panel called a flat plate collector is connected to a tank called a solar storage/backup water heater by two pipes. One of these pipes is runs through a cylindrical pump into the bottom of the tank, where it becomes a coil called a double-wall heat exchanger. This coil runs up through the tank and out again to the flat plate collector. Antifreeze fluid runs only through this collector loop. Two pipes run out the top of the water heater tank; one is a cold water supply into the tank, and the other sends hot water to the house.

Passive solar water heating systems are typically less expensive than active systems, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

* Integral collector-storage passive systems

These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

* Thermosyphon systems

Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.

Illustration of a passive, batch solar water heater. Cold water enters a pipe and can either enter a solar storage/backup water heater tank or the batch collector, depending on which bypass valve is opened. If the valve to the batch collector is open, a vertical pipe (which also has a spigot drain valve for cold climates) carries the water up into the batch collector. The batch collector is a large box holding a tank and covered with a glaze that faces the sun. Water is heated in this tank, and another pipe takes the heated water from the batch collector into the solar storage/backup water heater, where it is then carried to the house.

Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a demand (tankless or instantaneous) water heater for backup.

Source: EERE, U.S. Department of Energy

Solar water heaters – also called solar domestic hot water systems – can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use – sunshine – is free.

How They Work

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.

Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

Three types of solar collectors are used for residential applications:

* Flat-plate collector

Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

* Integral collector-storage systems

Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.

* Evacuated-tube solar collectors

They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.

Source: EERE, U.S. Department of Energy

Before you buy and install a solar water heating system, you need to first consider your site’s solar resource. The efficiency and design of a solar water heating system depends on how much of the sun’s energy reaches your building site.

Solar water heating systems use both direct and diffuse solar radiation. Even if you don’t live in a climate that’s warm and sunny most of the time—like the southwestern United States—your site still might have an adequate solar resource. If your building site has unshaded areas and generally faces south, it’s a good candidate for a solar water heating system.

Your local solar system supplier or installer can perform a solar site analysis.

Source: EERE, U.S. Department of Energy