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What is Solar Hot Water?
Some Facts
Solar hot water
systems are usually designed to provide 90% of the building’s hot water needs
during peak production. Although there
is still the need for a backup source, solar energy can reduce a home’s fuel
consumption by 80% or more.
In fact, for
systems being operated on a continuous basis, if financed at market rates, the
system earns money from day one—that is, the cost savings per month exceeds the
monthly loan payment. Depending on the
size of the system, it will pay for itself entirely in just a few years
Solar hot water is
among the most cost-effective means of supplying energy to a home. It is less
expensive than grid-based sources of electricity including coal, nuclear, and natural
gas. Solar hot water use has doubled in
the United States
over the last ten years, and it could provide 5% of commercial energy demand and
15% of residential demand by 2015.
The main components of our closed-loop solar hot water systems are:
(1) Solar collector panel. Usually mounted on your roof, the collector captures the heat from the sun and transfers it to the liquid circulating through the panel.
(2) Solar storage tank. The solar storage tank is where the heat energy captured by the collector panel is stored for later use.
(3) Heat exchanger. The heat exchanger transfers the heat energy captured by the collector panel is transferred to the potable water that is stored in the solar storage tank. In our pressurized system, the heat exchanger is integral to the solar storage tank. In our drainback system, the heat exchanger is in the drainback tank.
(4) Control system. The control system consists of the differential controller and the circulating pump(s). The differential controller compares the temperature difference between the solar storage tank and the collector panel. When the collector panel temperature is 20 degrees higher than the storage tank temperature, the controller turns on the pump(s) and circulates the water through the system until the temperature difference is only a few degrees, then turns the pump off.
How Does It Work?
Solar collector panels containing a heat transfer fluid (a mixture of water and food-grade glycol) are installed on the roof at a favorable angle to the sun.
Temperature sensors are installed on the collector panel and on the storage tank. When the temperature in the collector panel is 20 degrees higher than the temperature in the storage tank, the differential controller turns on the system pump(s) and circulates the water from the collector panel through a heat exchanger where the heat is transferred to the storage tank.
Water continues to circulate until the temperature of the water in the storage tank is within a few degrees of the collector temperature. Then the differential controller turns off the pump(s). As hot water from the storage tank is used, this cycle is repeated.
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