Did you know that heating water is your third largest energy expense, accounting for about 14% of your utility bill? Wondering about how solar water heaters work?

Here's a quick primer on solar water heaters, with some information from the Department of Energy.

We know: All About Solar Water Heaters

What’s a solar water heater?

Solar water heaters use the sun to heat either water or a heat-transfer fluid (something like antifreeze) in collectors generally mounted on a roof. Heated water is then stored in a conventional-style water tank.

How much can I save with a solar water heater?

One analysis by the Florida Solar Energy Center (FSEC) found that solar-water heater owners saved as much as 50-85% annually on household utility bills over the cost of electric water heating. However, solar water heaters are more expensive to buy and install than conventional water heaters: solar water heater ($1,500 to $3,000) gas water heater ($350 to $450) electric water heater ($150 to $350).

Here’s an average example:

If you purchase a solar water heater for $2,000 that provides an average of 60% of your hot water each year, that system will save you $24 per month or $288 per year. This system has a simple payback of less than 7 years. For the remainder of the life of the solar water heater, 60% of your hot water will be free, saving you $288 each year.

What kinds of solar water heaters are there?

There are basically two kinds:

Passive solar water heaters have no moving or mechanical parts
Active solar water heaters use a circulation pump and some type of temperature control

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.

What’s a solar collector?

A solar collector is the system used to gather and retrain the sun’s radiant heat. Most home solar water heaters use a flat-plate solar collector. It consists of an insulated, weather-proofed box containing a dark absorber plate under one or more transparent or translucent covers.

How do I shop smart for a solar water heater?

Look for a solar water heating system that is certified by the Solar Rating & Certification Corporation (SRCC), a nonprofit, consumer organization.

A certified solar water heater carries the SRCC OG-300 label, and the system performance is listed in a published directory.

Find out if the manufacturer offers a warranty, and, if so, what the warranty covers and for how long. If the dealer you are buying the equipment from goes out of business, can you get support and parts from the manufacturer, or from a local plumbing contractor?