| 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. |
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| 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. |
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| 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.
There are 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.
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| 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.
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| 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. |
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| For more information about solar water heating system components, see the following information: |
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Selecting a Solar Water Heater |
| Before you purchase and install a solar water heating system, you want to do the following: |
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| For information about specific solar water heater models and
systems, see the Product Information resources listed on the right side
of this page (or below if you've printed the page). |
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Installing and Maintaining the 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. |
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| 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. |
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| 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. For more information about system maintenance, see the following: |
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| When screening potential contractors for installation and/or maintenance, ask the following questions: |
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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.
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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.
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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.
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| For contractor information, see the Professional Services resources
listed on the right side of this page (or below if you've printed it
out). |
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Improving Energy Efficiency |
| After your water heater is properly installed and maintained, try some additional energy-saving strategies to help lower your water heating bills, especially if you require a
back-up system. Some energy-saving devices and systems are more
cost-effective to install with the water heater. |
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Other Water Heater Options |
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| Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems.[39] The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.[40] |
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| Solar water heaters facing the Sun to maximize gain |
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| As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW.[41] China is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020.[42] Israel and Cypress are the per capita leaders in the use of solar hot water systems with over 90% of homes using them.[43] In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005.[18] |
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