All About Solar Water Heating Systems

Solar water heaters are the most inexpensive and cost-effective way to go solar. These solar thermal systems may be used in any climate to great effect. While initially more expensive than conventional water heaters, solar hot water systems take advantage of free solar energy to save money over time. Federal, state and local incentives and rebates also cut down on those initial costs by at least 30 percent.

Types of solar water heaters

There are two general types of domestic solar hot water systems. Active systems have electronic controls and circulating pumps to move water throughout the system. Passive systems do not have any mechanical components and use convection, gravity or other natural forces to draw hot water through the system.

There are two types of active systems as well: indirect and direct flow systems. Direct systems circulate water through the collectors (described below) and into the home in a continuous cycle. Indirect systems utilize a medium, or heat transfer fluid, which runs through the collectors, absorbs solar heat, and then passes through a heat exchanger (typically within close proximity to the storage tank to prevent heat loss as the heated water travels), where that heat is transferred to the water supply.

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Water heater components

A solar water heater consists of two main components: the collector and the storage tank (add pumps and controls for active systems). There are three types of solar thermal collectors in residential use. The most popular of these is the flat plate collector, which are large, flat and contain a metal absorber plate that collects and transfers solar heat to water flowing through tubes attached to the absorber.

Evacuated tube collectors are more sophisticated, expensive and more efficient than flat plate collectors. They are therefore better suited for mild climates, such as those found in the northern half of the United States. Evacuated tubes consist of metal absorbers encased in parallel glass tubes. A header pipe runs across the upper side of the tubes. A transfer fluid (typically an anti-freeze solution) runs through the tubes, collects the absorbed solar heat, and carries back to a heat exchanger where that heat is transferred to the water supply. There are several different designs for evacuated tube solar water heaters, which you may explore .

Integral-collector storage (ICS) systems are used for passive water heating applications. In this instance, the storage tank itself is the collector. These systems consist of a tank, painted black, encased within a glass or plastic glazing. Solar radiation is collected through the glazing and absorbed by the tank. Convection, the tendency of warmer fluids to rise, works within the tank, pushing the warmer water to the top, where it is drawn for use within the home.

Thermosyphon systems are similar to integral collector storage systems. They are also called batch solar water heaters because they have a batch collector on the roof, which holds water within a tank that is itself within a box with glazing on one side. The water is sent, using only the pressure of the home water supply, into the collector where it’s heated. Convection causes the warm water to rise. It’s drawn from the batch collector and flows down into a storage tank within the house to be used for hot water. Such systems can work in colder climates but must have a drain valve so that the water can be drained from the collector in anticipation of a freeze.

Storage tanks for solar water heaters are usually heavily insulated to prevent heat loss as the water waits to be used in the home. Most of the time, they’re placed within the home, often right next to the pre-existing conventional water heater, which is used as a back-up on cloudy days. Storage tanks should be sized to properly fit your family’s daily water usage. This helps to prevent too much standing water inside the tank.

The problem with freezing

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Direct systems, which circulate water directly through the collectors, are best suited for warm climates where there is little chance of freezing temperatures. Frozen water within the solar collectors will severely damage the system, often irreparably. For that reason, indirect systems are popular in northern climes, where anti-freeze solutions (propylene or ethylene glycol) are used and the water supply does not leave the storage tank.

Cost of a solar water heater

Solar water heaters cost a lot up-front compared to conventional electric or gas systems. Prices range from $6,000 to $9,000 installed. Although in warmer climates, where less parts and freeze-prevention are required, initial costs can fall dramatically. Passive, ICS systems are the cheapest and often built by the homeowners themselves.

There are two main factors that make solar water heaters economically feasible. One is government incentives (sometimes local utility incentives as well). The federal government will pay for 30 percent of the system. Many states also have their own tax incentives for solar water heaters, usually comparable to the federal program. Many states exempt parts and materials from sales and use taxes, as well as property taxes on any increase in home value as a result of the installed solar system.

The second factor lies within the solar water heater itself. As expensive as it may be up front to install, from then on you are drawing on free solar energy to heat your water. Water heating is second only to space heating and cooling in the amount of money spent each year by the average American family. Which means that savings on utility bills will pay for the system over time. Payback periods for solar water heaters are often less than 10 years, while the system will last much much longer than that. Talk to a solar installer here to find out more specific information for your situation.

System maintenance

Solar water heaters require very little maintenance. Active systems of course may be prone to electrical failures from the pump or controls. Passive systems, with their lack of moving parts, are virtually maintenance free. In systems using a transfer fluid, that fluid will need to be changed every five years or so.

For more specific information and to find out which solar water heater is best suited to your home and climate, talk to a professional solar water heater installer today.

Posted on August 18 in Solar Thermal by .

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