How to select potential contractors for installation and/or maintenance of solar water heater

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

Installing and Maintaining a Solar Water Heating System

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

How to Select a Solar Water Heater

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

Two types of active solar water heating systems

* 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

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

Sizing a Solar Water Heating System

Sizing your solar water heating system basically involves determining the total collector area and the storage volume you’ll need to meet 90%–100% of your household’s hot water needs during the summer. Solar system contractors use worksheets and computer programs to help determine system requirements and collector sizing.
Collector Area

Contractors usually follow a guideline of around 20 square feet (2 square meters) of collector area for each of the first two family members. For every additional person, add 8 square feet (0.7 square meters) if you live in the U.S. Sun Belt area or 12–14 square feet if you live in the northern United States.
Storage Volume

A small (50- to 60-gallon) storage tank is usually sufficient for one to two three people. A medium (80-gallon) storage tank works well for three to four people. A large tank is appropriate for four to six people.

For active systems, the size of the solar storage tank increases with the size of the collector—typically 1.5 gallons per square foot of collector. This helps prevent the system from overheating when the demand for hot water is low. In very warm, sunny climates, some experts suggest that the ratio should be increased to as much as 2 gallons of storage to 1 square foot of collector area.

Source: EERE, U.S. Department of Energy

How Small Solar Electric Systems Work

Solar electric systems, also known as photovoltaic (PV) systems, convert sunlight into electricity.

Solar cells—the basic building blocks of a PV system—consist of semiconductor materials. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms. This phenomenon is called the “photoelectric effect.” These free electrons then travel into a circuit built into the solar cell to form electrical current. To see a simulation of the photoelectric effect, please view our animation. Only sunlight of certain wavelengths will work efficiently to create electricity. PV systems can still produce electricity on cloudy days, but not as much as on a sunny day.

The basic PV or solar cell typically produces only a small amount of power. To produce more power, solar cells (about 40) can be interconnected to form panels or modules. PV modules range in output from 10 to 300 watts. If more power is needed, several modules can be installed on a building or at ground-level in a rack to form a PV array.

PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day.

Because of their modularity, PV systems can be designed to meet any electrical requirement, no matter how large or how small. You also can connect them to an electric distribution system (grid-connected), or they can stand alone (off-grid).

Source: U.S. Department of Energy – Energy Efficiency and Renewable Energy

Small Solar Electric Systems

A small solar electric or photovoltaic (PV) system can be a reliable and pollution-free producer of electricity for your home or office. And they’re becoming more affordable all the time. Small PV systems also provide a cost-effective power supply in locations where it is expensive or impossible to send electricity through conventional power lines.

Because PV technologies use both direct and scattered sunlight to create electricity, the solar resource across the United States is ample for small solar electric systems. However, the amount of power generated by a solar system at a particular site depends on how much of the sun’s energy reaches it. Thus, PV systems, like all solar technologies, function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

Source: EERE, U.S. Department of Energy

What is Passive Solar Home Design?

Your home’s windows, walls, and floors can be designed to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design. Unlike active solar heating systems, passive solar design doesn’t involve the use of mechanical and electrical devices, such as pumps, fans, or electrical controls to move the solar heat.

Passive solar homes range from those heated almost entirely by the sun to those with south-facing windows that provide some fraction of the heating load. The difference between a passive solar home and a conventional home is design. The key is designing a passive solar home to best take advantage of your local climate. For more information, see how a passive solar home design works.

You can apply passive solar design techniques most easily when designing a new home. However, existing buildings can be adapted or “retrofitted” to passively collect and store solar heat.

To design a completely passive solar home, you need to incorporate what are considered the five elements of passive solar design. Other design elements include:

* Window location and glazing type
* Insulation and air sealing
* Auxiliary heating and cooling systems, if needed.

These design elements can be applied using one or more of the following passive solar design techniques:

* Direct gain
* Indirect gain (Trombe wall)
* Isolated gain (Sunspace).

When incorporating these design elements and techniques, you want to design for summer comfort, not just for winter heating.

Your home’s landscaping can also be incorporated into your passive solar design.

Source: EERE, U.S. Department of Energy