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Solar Hot Water Heaters

Solar hot water systems allow you to use the sun's heat to provide your home with hot water - for drinking, for your pool, and even for heating your home. Although the initial cost of purchasing a solar hot water heater is higher than conventional hot water heaters, the cost to produce hot water is cheaper. Unlike the conventional heaters, the fuel is free.

The primary consideration in deciding to use a solar hot water heater is how much solar energy is available. Choose an unshaded, south facing location to place the solar collector. A common location for the collectors is on the roof. You can determine how much solar energy will be available to you by your location through the National Renewable Energy Laboratory's (NREL) solar maps.

A solar water heater will work in almost any location, but climate affects which type of system should be used. For example, solar hot water systems in the north require glycol to prevent freezing. Additional information on how to choose which type of system will be most suitable for your location is provided by the Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE). The Partnership for Advancing Technology in Housing (PATH) has a fact sheet on solar hot water that gives costs and benefits, and links to field results.

The Spirit of Today House in Sarasota Florida has a solar water heater that provides 50% of the household's hot water needs. (photo courtesy of NREL)

How Does it Work?

Solar hot water heaters take advantage of the sun's energy to heat water, or in colder climates, the heat transfer fluid such as water-glycol mixture. A tank, similar to the tank of a conventional water heater, stores the heated water. Active systems use a pump to circulate the hot water.

The components that make up solar water heaters include the collector, a storage tank and an electric pump (in active systems). The two types of water heaters are passive and active. Active systems require a pump to circulate the water while passive systems do not. The amount of hot water a solar water heater produces depends on the type and size of the system, the amount of sun available at the site, proper installation, and the tilt angle and orientation of the collectors. You may need a conventional backup system to supplement the solar water heater for times when your solar water heater is unable to keep up with the demand. Check your local building codes as they might require a conventional water heater as backup.

The job of the collector is to absorb the sun's energy to produce heat. The heat then warms water or another fluid used in the system to produce hot water for domestic use, indoor space heating or to heat swimming pool water. The three types of collectors are flat-plate, evacuated-tube, and concentrating. The most common is the flat-plate collector. This type of collector consists of an insulated, weather-proofed box containing a dark absorber plate under covered by transparent or translucent covers.

Types of Systems

Depending on the quality of your water, you will choose from either a closed loop (indirect) or open loop (direct) system. An indirect system may be used where hard water may cause scale buildup in the system. This system uses a heat transfer fluid to collect heat and transfer the heat to the household water. An open loop system simply circulates potable water through the system, without the need of second fluid to provide heat transfer.

Open loop active systems use pumps to circulate household water through the collectors. This is the more efficient system and has lower operating costs. However, if you are in a location with hard or acidic water, scale and corrosion are likely to damage the system, and this type of system is usually not recommended. Open loop active systems are more appropriate for milder climates. Areas that are subject to freezing temperatures require some type of freeze protection.

Closed loop active systems heat the household water indirectly with a heat transfer fluid, typically a mixture of glycol (for freeze protection) and water. These types of systems are typical of cold climates subject to freezing temperatures. They are generally more expensive to buy and install and require the glycol to be checked every year and changed every three to ten years.

Active systems require the use of pumps to circulate the water. In order to maximize solar energy usage, small solar electric panels are available to power the pump. Although passive systems are generally more reliable, easier to maintain, and less expensive, they are less efficient.

Equipment Certification

Similar to major appliances, solar water heaters are labeled by to address performance and maintenance factors. The Solar Rating & Certification Corporation (SRCC), a nonprofit, independent third-party organization formed by the state energy officials, and consumer advocates, certify and rate solar water heaters. The national standard OG-300 addresses safety, health, durability, reliability, installation, performance, operation and maintenance procedures and concerns. Systems that meet the standard contain the SRCC OG-300 label.


It is best to have a professional perform the installation of a solar hot water. When the system is installed, be sure you understand the components and are familiar with it.

You may also learn about the installation process through the Solar Rating and Certification Corporation

 Solar Water Heater Maintenance
 Single Family Water Heaters
 Multifamily Water Heaters
 Database of State Incentives for Renewable Energy
 DOE's National Renewable Energy Laboratory - Solar Hot Water
 DOE - Residential Solar Heating Retrofits

Content updated October 6, 2004

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