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Solar Water Heaters

Solar water heaters=E2=80=94also called solar domestic hot = water systems=E2=80=94can be=20 a cost-effective=20 way to generate hot water for your home. They can be used in = any=20 climate, and the fuel they use=E2=80=94sunshine=E2=80=94is = free.

How They Work

Solar water heating systems include storage tanks and solar = collectors.=20 There are two types of solar water heating systems: active, which = have=20 circulating pumps and controls, and passive, which don't.

Most solar water heaters require a well-insulated storage tank. = Solar=20 storage tanks have an additional outlet and inlet connected to and = from=20 the collector. In two-tank systems, the solar water heater = preheats water=20 before it enters the conventional water heater. In one-tank = systems, the=20 back-up heater is combined with the solar storage in one tank. =

Three types of solar collectors are used for residential=20 applications:

Flat-plate collector

Glazed flat-plate collectors are insulated, weatherproofed = boxes that=20 contain a dark absorber plate under one or more glass or plastic = (polymer) covers. Unglazed flat-plate = collectors=E2=80=94typically used for solar=20 pool heating=E2=80=94have a dark absorber plate, made of = metal or polymer,=20 without a cover or enclosure.
Integral collector-storage systems

Also known as ICS or batch systems, they feature one = or more=20 black tanks or tubes in an insulated, glazed box. Cold water = first=20 passes through the solar collector, which preheats the water. = The water=20 then continues on to the conventional backup water heater, = providing a=20 reliable source of hot water. They should be installed only in=20 mild-freeze climates because the outdoor pipes could freeze in = severe,=20 cold weather.
Evacuated-tube solar collectors

They feature parallel rows of transparent glass tubes. Each = tube=20 contains a glass outer tube and metal absorber tube attached to = a fin.=20 The fin's coating absorbs solar energy but inhibits radiative = heat loss.=20 These collectors are used more frequently for U.S. commercial=20 applications.

There are two types of active solar water heating systems:

Direct circulation systems

Pumps circulate household water through the collectors and = into the=20 home. They work well in climates where it rarely freezes.
Indirect circulation systems

Pumps circulate a non-freezing, heat-transfer=20 fluid through the collectors and a heat=20 exchanger. This heats the water that then flows into the = home. They=20 are popular in climates prone to freezing temperatures. =

Passive solar water heating systems are typically less = expensive than=20 active systems, but they're usually not as efficient. However, = passive=20 systems can be more reliable and may last longer. There are two = basic=20 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=20 evening hot-water needs.
Thermosyphon systems

Water flows through the system when warm water rises as = cooler water=20 sinks. The collector must be installed below the storage tank so = that=20 warm water will rise into the tank. These systems are reliable, = but=20 contractors must pay careful attention to the roof design = because of the=20 heavy storage tank. They are usually more expensive than = integral=20 collector-storage passive systems.

Solar water heating systems almost always require a backup = system for=20 cloudy days and times of increased demand. Conventional=20 storage water heaters usually provide backup and may already = be part=20 of the solar system package. A backup system may also be part = of the=20 solar collector, such as rooftop tanks with thermosyphon systems. = Since an=20 integral-collector storage system already stores hot water in = addition to=20 collecting solar heat, it may be packaged with a demand=20 (tankless or instantaneous) water heater for backup.

For more information about solar water heating system = components, see=20 the following information:

Heat=20 Exchangers for Solar Water Heating Systems=20
Heat-Transfer=20 Fluids for Solar Water Heating Systems

Selecting a Solar Water Heater

Before you purchase and install a solar water heating system, = you want=20 to do the following:

Consider=20 the economics of a solar water heating system=20
Evaluate=20 your site's solar resource=20
Determine=20 the correct system size=20
Determine=20 the system's energy efficiency=20
Estimate=20 and compare system costs=20
Investigate=20 local codes, covenants, and regulations.

For information about specific solar water heater models and = systems,=20 see the Product Information resources listed on the right side of = this=20 page (or below if you've printed the page).

Installing and Maintaining the System

The proper installation of solar water heaters depends on many = factors.=20 These factors include solar resource, climate, local building code = requirements, and safety issues; therefore, it's best to have a = qualified,=20 solar thermal systems contractor install your system.

After installation, properly maintaining your system will keep = it=20 running smoothly. Passive systems don't require much maintenance. = For=20 active systems, discuss the maintenance requirements with your = system=20 provider, and consult the system's owner's manual. Plumbing and = other=20 conventional water heating components require the same maintenance = as=20 conventional systems. Glazing may need to be cleaned in dry = climates where=20 rainwater doesn't provide a natural rinse.

Regular maintenance on simple systems can be as infrequent as = every 3=E2=80=935=20 years, preferably by a solar contractor. Systems with electrical=20 components usually require a replacement part after or two after = 10 years.=20 For more information about system maintenance, see the = following:

Solar=20 Water Heating System Maintenance and Repair=20
Solar=20 Water Heating System Freeze Protection=20
Scaling=20 and Corrosion in Solar Water Heating Systems

When screening potential contractors for installation and/or=20 maintenance, ask the following questions:

Does your company have experience installing and = maintaining=20 solar water heating systems?
Choose a company that has=20 experience installing the type of system you want and servicing = the=20 applications you select.
How many years of experience does your company have with = solar=20 heating installation and maintenance?
The more = experience the=20 better. Request a list of past customers who can provide = references.
Is your company licensed or certified?
Having a = valid=20 plumber's and/or solar contractor's license is required in some = states.=20 Contact your city and county for more information. Confirm = licensing=20 with your state's contractor licensing board. The licensing = board can=20 also tell you about any complaints against state-licensed = contractors.=20

For contractor information, see the Professional Services = resources=20 listed on the right side of this page (or below if you've printed = it=20 out).

Improving Energy Efficiency

After your water heater is properly installed and maintained, = try some=20 additional energy-saving=20 strategies to help lower your water heating bills, especially = if you=20 require a back-up system. Some energy-saving devices and systems = are more=20 cost-effective to install with the water heater.

Other Water Heater Options

Conventional=20 storage water heaters=20
Demand=20 water heaters=20
Heat=20 pump water heaters=20
Tankless=20 coil and indirect water heaters

Printable=20 Version

Skip=20 footer navigation to end of page.=20

Content Last Updated: September 14, 2005

Evaluation Tools

Financing & Incentives

Product Information

Professional Services

State & Local Resources

Related Links

Reading List

Solar Water Heaters

How They Work

Flat-plate collector

Integral collector-storage systems

Evacuated-tube solar collectors

Direct circulation systems

Indirect circulation systems

Integral collector-storage passive systems

Thermosyphon systems

Selecting a Solar Water Heater

Installing and Maintaining the System

Improving Energy Efficiency

Other Water Heater Options