What is Solar Water Heating? 
Also called solar domestic hot water systems—is a cost-effective way to generate hot water. They can be used in any climate, and the fuel they use—sunshine—is free.
How They Work
Solar water heating systems include a
storage tank and solar collectors. There are
two types of solar water heating systems:
active, which have circulating pumps and
controls, and passive, which do not.
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.
Types of Solar Collectors:
1. Flat-Plate Collector
Glazed flat-plate collectors are insulated, weather proofed 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 for this type of collector.2. 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. These systems should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
3. 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 which, inhibits little heat loss. These have been approved as the best collectors used for U.S. solar systems.
There are Two Types of Active Solar Water Heating Systems:
1. Direct Circulation Systems
Pumps circulate water through the collectors and into your building. They work well in climates where it rarely freezes.
2. 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
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:
1. Integral Collector-Storage
Passive Systems
This system works best in areas where
temperatures rarely fall below freezing.
They also work well in buildings
with significant daytime and evening hot-water needs.
2. Thermosphere System
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 our installers will pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than an Integral Collector-Storage System.
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 Thermosphere Systems. Since an Integral-Collector Storage System already stores hot water in addition to collecting solar heat, it may be packaged with a demand (thank-less or instantaneous) water heater for backup.