In this article:

Benefits of Solar Water Heaters
Solar Water Heater Considerations
Solar Water Heater Collectors

If you’re in the market for a new solar water heater, you will need to do some research and shopping to find the right product for your needs. Of course, your choices are many. When evaluating your options, it is important to have a clear idea of what kind of system you are looking for. Before selecting a solar water heater, you’ll need consider your lifestyle, climate zone, budget, and environmental impact goals.

Here are four important questions to answer before shopping:

1) How much how water do you want to generate? Lifestyle has a major impact on how effective your domestic solar water heater will be. If you have a large family and a great demand for hot water, especially during the day, an active system with a larger collector will probably fit your family’s needs.

On the other hand if your household is only one or two people and activities like laundry are infrequent, a smaller “batch” or passive system might be better. A quick way to determine your expected household hot water use is to simply multiply occupants by 18 gallons. A family of four uses about 72 gallons of hot water a day for laundry, bathing, cleaning, and cooking. This number will help you gauge not only the collector you need, but also the reserve tank necessary for keeping your family in hot water.

2) Where do you live? Most systems are configured based upon expected output of hot water for a specific climate. In sunny, warmer areas like Florida, Arizona, and Southern California, you can generate a tremendous amount of hot water using a relatively small system. In colder regions a larger collector will be required, and an active system may be needed to satisfy the home’s hot water needs.

It is also important to understand if there is a potential freezing risk for your system. In colder areas you may have to select a “drainback” tank model, or a system that will automatically monitor the temperature to reduce the risk of a pipe bursting in your collector.

3) What is your budget? Solar heated domestic water does not have to be expensive. When compared to photovoltaic arrays, solar water heaters have a much faster return on investment and are much more affordable. For only a few hundred dollars you can build your own batch-style system--and even commercially manufactured systems for warmer climates can be very affordable.

Before shopping, be sure to get exact estimates from your plumbing contractor and check with local housing code officials to make sure you won’t have any hidden costs once installation begins.

4) How green do you want to go? If you are going to purchase a solar hot water heater, the benefits will be many, but a common goal is to reduce the overall need for carbon-based fuels like coal or natural gas. While the “greenest” and most economical option would be to simply alter your lifestyle so that you don’t use as much hot water (like taking “navy” showers, washing your cloths on cold water only and turning down the temperature on your current hot water heater) installing a solar water heater can make a significant positive impact on the environment.

To really go green, try to find systems that don’t require any additional energy to function. This can include choosing a simple batch heating system or passive system that uses thermodynamics to power the circulation process. Another way to avoid having to plug-in your system is to purchase a solar powered circulation pump. Once your new system is installed, altering your lifestyle to take advantage of the solar powered hot water is an excellent way to optimize your environmental impact. By using a majority of your hot water in the mid- to late afternoon you can help ensure that you will be getting the most from your new system.

Once you have determined your hot water needs, system style, size, and budget, you are ready to go shopping. Below are links to reviews of a few popular solar domestic water heaters on the market today.

Benefits of Solar Water Heaters

Of the reasons to install a solar hot water heater, the primary one is saving money on your monthly energy bills. According to the U.S. Department of Energy, hot water heaters account for 10 to 15 percent of a single-family home's monthly energy bill.

By using the sun to augment the delivery of heat to your water, you can significantly reduce the amount of gas or electricity used to heat water.

By some estimates, homeowners can save over $500 in their first year of operation and, with the more aggressively priced commercial systems, should see a complete return on investment in as few as five years. This is especially true in homes that use electric hot water heaters, which tend to be less efficient than gas systems.

With power prices expected to rise significantly over the next decade, adding a solar solution to your home could save you thousands of dollars over the lifetime of the system.

Solar Water Heater Considerations

When building or buying a solar hot water system, keep these things in mind:

1. Be sure to include a freeze valve on your system. A freeze valve will keep your system from freezing solid and cracking. These valves often sense when the water temperature is about to dip below freezing and bleed enough water out of the system to circulate relatively warm fresh water. These are a must-have for passive systems.

2. Install a shut-off, bypass, and drain spigot on your system. These valves allow you to detach the solar hot water collector without completely disconnecting the water to your existing hot water tank. They can come in very handy, especially if your system does not have a freeze-prevention valve.

3. Install scald guards on your system if you live in a sunny climate. Solar water heaters work at times work so well they can present a scalding danger to the home's occupants.

4. Rebates abound! And many states now offer additional rebates. In some cases, these can almost completely offset the purchase price of the system, which allows for an even faster return on investment. Find out if rebates are available in your state.

Solar Water Heater Collectors

The collector is the part of a solar water heater system that collects the warmth from the sun and transfers it to the water. An example of the simplest collector is the old fashioned 'hot box,' which is a recycled hot water tank that has been stripped of its shell, painted black, and placed in a well-insulated box with a glass lid. Though incredibly basic, this is actually an effective system that is easy to build and install for very little investment.

The next step up is a hot box collector that uses a black absorber plate to collect the solar radiation. These collectors usually have a dark absorber plate placed under one or more glass or clear plastic covers. The plate transfers the sun's heat to copper tubing (painted black as well, usually with an electrostatic paint). This is superior to the hot box in delivering larger volumes of heated water. Absorber plate collectors have a much lower profile and weigh less than a rudimentary hot box, making them an attractive low-cost solution for existing homes (and especially economical for heating swimming pools).

The top-of-the-line technology for solar hot water heating is an evacuated-tube collector. This type of system features rows of transparent glass tubes that run parallel to one another. Some styles employ glass tubes within tubes or have a metal absorber tube attached to a fin. With the latter type, the fin's coating absorbs solar energy but inhibits heat loss. A vacuum is created inside the tubes, which eliminates conductive and convective heat loss, which seriously diminishes the efficiency of the more basic collector systems. Evacuated-tube or vacuum-style collectors can achieve surprisingly high water temperature, sometimes in excess of 300 degrees F.