Water Heaters

Solar Water Heaters

Becoming more popular

Free fuel and clean operation are just two reasons people add solar water heaters to their homes. A homeowner switching to solar from an electric water heater could save up to $500 in the first year of operation, with savings increasing as electricity rates rise. Solar heaters cost a lot more but can usually be paid off in three to seven years. A passive system can set you back $1,000 to $3,000, and an active system costs between $2,000 and $4,000.

Most solar systems don't work entirely on their own; they are either integrated into storage water heaters or have one as a backup.

Active solar water heating

Active solar water heating can take place in two ways:

  • Direct circulation (open loop) - Pumps are used to circulate household water through the solar collectors and back into the home. Good for warm climates.
  • Indirect circulation (closed loop) - A heat transfer fluid (non-freezing) circulates through the solar collectors before traveling to a heat exchanger. Heat is transferred to the home's water. Good for cold climates.

In either method, a solar collector is mounted on the home, facing south. Sunlight is absorbed and converted to heat, which is prevented from escape thanks to glazing. Two popular types of solar collectors are:

  • Glazed flat-plate - A thin, rectangular box consists of a transparent glass or plastic cover over a dark absorber plate. Tubes attach to the plate and carry air, water, or a heat transfer fluid.
  • Evacuated tube - Several rows of glass tubes contain black metal pipes full of heat transfer fluid.

Heat transfer fluid flows through the collector and transfers heat to water in a storage tank. A pump powering fluid movement is controlled by electricity, either in the form of an electrical wall socket or via a small photovoltaic module beside the solar collector.

Passive solar water heating

Less expensive but not as efficient as active systems, passive systems have the potential to last longer and can be somewhat more reliable. There are two main passive solar water heating systems:

  • Integral collector storage (ICS) passive systems - Also known as batch systems, these consist of an insulated glazed box, home to one or more black tanks or tubes. Cold water travels through to be heated, then on to a conventional water heater. They are basically preheaters, and outdoor pipes mean a danger of freezing in cold climates.
  • Thermosyphon systems - A solar collector and storage tank are installed on the roof. When water is heated, it rises to the top of the tank, while cold water sits at the bottom to be warmed. These are the most expensive of the passive systems, and planning must be thorough because a heavy tank will have to be situated on the home's roof.

What to look for

Talk to an experienced solar-water-heater installer to find out whether your home provides the right conditions to make it worthwhile. Find out if others in your area have solar systems and ask how they have found the experience.

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