Solar Water Heaters

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

In the simplest terms, we use a collector to harness solar thermal energy in order to heat water. One or more collector units use evacuated tube technology to heat water that is circulated through a heat exchanger manifold at the collector and sent to a hot water storage tank. In cold weather climates where freezing is a concern a heat exchanger and antifreeze is used to transfer thermal energy to a storage tank filled with potable water.

A 110-volt pump circulates the water-glycol through standard copper tubing just like those found under your kitchen sink. An electronic controller-unit regulates the flow of solar heated water to the storage tank. The storage tank is used as an auxiliary tank that stores the preheated water that is feed to your existing electric or gas heated water heater tank. The gas or electric hot water heater acts as a backup to provide hot water when your solar system cannot.

 

 

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.

 

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.

 

Courtesy of: Energy Savers