SOLAR WATER HEATER
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 collectors 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.
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 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.
