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Solar water heaters -- sometimes called solar domestic hot water systems -- can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use -- sunshine -- is free. How They Work Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't. Active Solar Water Heating Systems There are two types of active solar water heating systems: · Direct circulation systems Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes. · Indirect circulation systems Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.   Passive Solar Water Heating Systems Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems: · Integral collector-storage passive systems These consist of a storage tank covered with a transparent material to allow the sun to heat the water. Water from the tank then flows into the plumbing system. These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs. · Thermosyphon systems Water is heated in a collector on the roof and then flows through the plumbing system when a hot water faucet is opened. The majority of these systems have a 40 gallon capacity.   Storage Tanks and Solar Collectors Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank. Three types of solar collectors are used for residential applications: · Flat-plate collector Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors -- typically used for solar pool heating -- have a dark absorber plate, made of metal or polymer, without a cover or enclosure. · Integral collector-storage systems Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather. · Evacuated-tube solar collectors They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications. Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a tankless or demand-type water heater for backup. Selecting a Solar Water Heater Before you purchase and install a solar water heating system, you want to do the following: · Estimate the cost and energy efficiency of a solar water heating system · Evaluate your site's solar resource · Determine the correct system size · Investigate local codes, covenants, and regulations. Also understand the various components needed for solar water heating systems, including the following: · Heat exchangers for solar water heating systems · Heat-transfer fluids for solar water heating systems Installing and Maintaining the System The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it's best to have a qualified solar thermal systems contractor install your system. After installation, properly maintaining your system will keep it running smoothly. Passive systems don't require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system's owner's manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse. Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part or two after 10 years. Learn more about solar water heating system maintenance and repair. When screening potential contractors for installation and/or maintenance, ask the following questions: · Does your company have experience installing and maintaining solar water heating systems? Choose a company that has experience installing the type of system you want and servicing the applications you select. · How many years of experience does your company have with solar heating installation and maintenance? The more experience the better. Request a list of past customers who can provide references. · Is your company licensed or certified? Having a valid plumber's and/or solar contractor's license is required in some states. Contact your city and county for more information. Confirm licensing with your state's contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors. Improving Energy Efficiency After your water heater is properly installed and maintained, try some additional energy-saving strategies to help lower your water heating bills, especially if you require a back-up system. Some energy-saving devices and systems are more cost-effective to install with the water heater.  

Conventional storage water heaters remain the most popular type of water heating system for the home. Here you'll find basic information about how storage water heaters work; what criteria to use when selecting the right model; and some installation, maintenance, and safety tips. How They Work A single-family storage water heater offers a ready reservoir -- from 20 to 80 gallons -- of hot water. It operates by releasing hot water from the top of the tank when you turn on the hot water tap. To replace that hot water, cold water enters the bottom of the tank through the dip tube where it is heated, ensuring that the tank is always full. Conventional storage water heater fuel sources include natural gas, propane, fuel oil, and electricity. Learn more about fuel types available when selecting a new water heater. Since water is heated in the tank until the thermostat setpoint temperature is reached, energy can be wasted even when a hot water tap isn't running due to standby heat losses, which result from the tank losing heat to the surrounding environment. Only tankless water heaters -- such as demand-type water heaters and tankless coil water heaters -- avoid standby heat losses. Some storage water heater models have heavily insulated tank, which significantly reduce standby heat losses and lower annual operating costs. Look for models with tanks that have a thermal resistance (R-Value) of R-24 and above to avoid adding an insulation blanket (electric water heaters only). Gas and oil water heaters also have venting-related energy losses. Two types of water heaters -- a fan-assisted gas water heater and an atmospheric sealed-combustion water heater -- reduce these losses. Visit the Energy Basics site to learn more about how conventional storage water heaters work. For low energy bills the best choice to consider are heat pump water heaters and solar water heaters. These water heaters are usually more expensive but they have significantly lower annual operating costs that result in short payback periods. Selecting a Storage Water Heater The lowest-priced storage water heater may be the most expensive to operate and maintain over its lifetime. While an oversized unit may be alluring, it carries a higher purchase price and increased energy costs due to higher standby energy losses. Before buying a new storage water heater, consider the following: · Size and first hour rating · Fuel type and availability · Energy efficiency and costs. Installation and Maintenance Proper installation and maintenance of your water heater can optimize its energy efficiency. Proper installation depends on many factors. These factors include fuel type, climate, local building code requirements, and safety issues, especially concerning the combustion of gas- and oil-fired water heaters. Therefore, it's best to have a qualified plumbing and heating contractor install your storage water heater. Be sure to do the following when selecting a contractor: · Request cost estimates in writing · Ask for references · Check the company with your local Better Business Bureau · See if the company will obtain a local permit if necessary and understands local building codes, etc. If you're determined to install it yourself, first consult the water heater's manufacturer. Manufacturers usually have the necessary installation and instruction manuals. Also, contact your city or town for information about obtaining a permit, if necessary, and about local water heater building codes. Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency. Read your owner's manual for specific maintenance recommendations. Routine maintenance for storage water heaters, depending on what type/model you have, may include: · Flushing a quart of water from the storage tank every three months · Checking the temperature and pressure valve every six months · Inspecting the anode rod every three to four years. Improving Energy Efficiency After your water heater is properly installed and maintained, try some additional energy-saving steps to help lower your water heating bills. Some energy-saving devices and systems are more cost-effective to install with the water heater.