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Solar water heaters

Solar water heaters -- sometimes 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.

Active Solar Water Heating Systems

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

flat panel

solar collector
s and a heat exchanger. This heats the water that then flows into

the home. They are popular in climates prone to freezing temperatures.

Passive Solar Water Heating Systems

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 consist of a storage tank covered with a transparent material to allow the sun

to heat the water.  Water from the tank then flows into the plumbing system. 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 is heated in a collector on the roof and then flows through the plumbing

system when a hot water faucet is opened. The majority of these systems have a 40 gallon


Storage Tanks and Solar Collectors

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 collector 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


pressure solar 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.

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 tankless or demand-type water heater for backup.

Selecting a Solar Water Heater

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


Estimate the cost and energy efficiency of a solar water heating system

Evaluate your site's solar resource

Determine the correct system size

Investigate local codes, covenants, and regulations.

Also understand the various components needed for solar water heating systems as

solar air project, including the


Heat exchangers for solar water heating systems

Heat-transfer fluids for solar water heating systems

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.

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 pre heat solar water heater contractor. Systems with electrical components

usually require a replacement part or two after 10 years. Learn more about solar water

heating system maintenance and repair.

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 with solar accessory?

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


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.

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.

solar water heater, device that uses solar heat energy to produce hot water. A

typical solar water heater consists of a solar collector mounted on the roof of a

building and connected to a water-storage tank. Depending on the system, unheated water

either can be circulated from the tank through the collector to be heated directly or

can be heated by a high-capacity heat-exchange fluid that was warmed in the collector

and transfers its heat through tubes in the water in the tank. While heat transfer from

the solar collector to the unheated water can be facilitated passively without

mechanical means, “active” solar hot water systems use electricity to circulate the

heat-exchange fluid and to operate mechanical pumps and controllers.

Although the practice of using the sun for heating water for domestic use can be

traced back to several ancient cultures, it was not until 1891 that the first patented

high pressure solar water heater

system was sold commercially. Invented by Clarence Kemp in Baltimore, Maryland, the

system was called the “Climax” and was popular in California and other warm American

states. Given the comparatively high cost and inconvenience of using conventional fuels

to heat water, many households were eager to invest in these solar hot water heaters.

However, the Climax system was limited in that the heating element doubled as the

storage tank, thus restricting the amount of hot water available. In 1909 William J.

Bailey patented a system that separated the water-storage tank from the solar heating

element, forming the basis of the design of solar hot water heaters used today.