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What is Passive Solar Water Heating?

B. Turner
B. Turner

Passive solar water heating is the process of using solar energy from the sun to heat water for homes and buildings. This hot water enters the home through water supply pipes, and is used at showers, sinks, and other plumbing fixtures. Unlike active solar technologies, passive solar water heating does not rely on any pumps or mechanical equipment to heat or supply water. Instead, these systems rely on principles of thermodynamics and gravity to take advantage of natural heat energy. Like all solar systems, solar water heating can cut energy costs while preserving limited resources like oil or coal.

Buyers can choose from two basic types of passive solar water heating systems. The most economical, and simpler of the two is an integral collection and storage unit. This system consists of an insulated water storage tank that is often painted a dark color to attract and absorb solar energy. Water supply pipes enter the box, and the water inside is naturally heated by the sun. This water then passes into the home for use at plumbing fixtures, and more fresh water enters the tank for heating.

Woman with hand on her hip
Woman with hand on her hip

While these integral units are generally low maintenance and provide free hot water, they are typically only effective in warm climate zones. Those in other types of climate zones may benefit from a thermosyphon system, which include a solar collector panel and separate storage tank. The tank must be mounted on the roof, while the collector panel can be mounted on the ground or a storage rack. As the water in the system is heated, warm water travels up to the tank due to principles of thermodynamics. This water is available for use in the home, while fresh water supplies pass through the collector to repeat the cycle.

Thermosyphon systems tend to be the more expensive of these two systems, and are also the most complex to install and maintain. The roof-mounted storage tank often requires more structural support than what is offered by the average roof. This may require reinforcing the roof to properly support this tank.

Passive solar water heating systems require less upfront investment than an active solar water heating system. These systems also involve fewer operating components, and are less likely to break down. This means that they require less maintenance and last longer on average than active solar systems. Buyers should be aware, however, that passive solar water heating systems are not completely reliable. These systems can't supply hot water during cloudy periods or storms, and often require a backup system in the form of a standard hot water heater.

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