Solar Water Heaters

Improve Enrgy Efficiency with Solar Water Heating   
 Water heating can constitute 15% to 25%, or more, of the energy use of a home. The approximate annual cost to operate water heaters ranges from $200 for a minimum efficiency gas-fired unit to as much as $500 for a minimum efficiency electric unit. Solar water heaters are available that can reduce annual operating costs by 50% to 80% or more using “free energy” from the sun. These systems typically are cost-competitive with electric water heaters and also can be cost-competitive with natural gas-fired water heaters. Solar water heaters come in two distinct designs: active and passive systems.
In an “active” system, when sunlight heats one or more solar collectors sufficient for water heating, sensors and a controller activate a pump to circulate a fluid: either potable water from the storage tank or a food-grade antifreeze solution in climates exposed to freezing conditions. As shown in Figure 1, the fluid is drawn from the colder bottom portion of the storage tank up to the collector for solar heating, and then circulated back to the top of the storage tank. Where antifreeze solutions are used, the solar heat is transferred to water in the storage tank through a heat exchanger. When the water in the storage tank is warmer than the collector, the controller and sensor
 FIGURE 1 : ACTIVE WATER HEATER

  

 

 

 

 


A “passive” system combines the solar collector and storage in one complete unit separate from the conventional gas or electric water heater storage tank. The storage can be directly coupled with the collector (an integral collector/storage system, as shown in Figure 2) or located above the collector using the natural flow of heated water upwards to drive fluid circulation (thermosiphon system). Passive system design requires no pumps or controls for operation as sunlight heats water all day. When hot water is used in the home, water from the passive solar storage tank is drawn into the conventional gas or electric water heater storage tank, thereby avoiding the need for electric or gas-fired heat to turn on. Providing energy-efficient houses with solar water heating systems provides peace-of-mind that home owners are contributing to environmental stewardship while helping their bottom-line expenses.
 FIGURE 2 : PASSIVE  WATER HEATER