Going Green, Saving Green
By Bob Calandra
Pool and spa owners who want to go green — and save it — need only look to the sun.
Over the past 30 years, solar technology has evolved into an environmentally friendly alternative to gas or oil for heating pools that also makes financial sense. In fact, solar pool heating is the most cost-effective use of solar energy in many climates, according to the U.S. Department of Energy.
Although the initial upfront cost is between $2,000 and $12,000 — depending on the size of your pool or spa, the number of collectors needed, and your geographic location — solar heating systems typically pay for themselves in two to seven years, according to the U.S. Department of Energy (DOE). After that, the energy needed for comfortable swimming or soaking is gratis.
"Pools are an easy mark for solar," says Dave Menicucci, of the DOE's Sandia National Laboratory in Albuquerque, New Mexico. "The technology is very straightforward and the installation is very straightforward."
Pools and Solar
Most solar pool heating systems contain the following:
• Solar collectors, typically panels fixed near the pool — often on a roof — through which pool water is circulated to be heated by the sun
• A filter to remove debris before water is pumped through the collectors
• A pump to circulate water through the filter and collectors and back to the pool
• A flow control valve, an automatic or manual device that diverts pool water through the solar collectors
• Sensors, often mounted next to collector panels and in the pool, to monitor water and collector temperatures — and determine whether water should be directed or bypassed through the heating system
• A vacuum breaker and freeze prevention valve are used in some northern climates. The vacuum breaker allows the collector loop to drain properly. The freeze valve protects the system in case water is left in the piping.
Water is pumped through the filter and then the solar collectors, where it is heated before returned to the pool. In hot climates, collectors can also cool the pool during peak summer months by circulating the water at night.
Solar-heating your pool or spa can be done nearly anywhere in the U.S., but sizing a system depends on many factors — pool size, length of the pool use season, average regional temperatures, desired pool temperature, the collectors' directional orientation and tilt, and if you use a pool cover. (If you do, you can decrease the required collector area.) Solar system contractors use computer programs to determine specific system requirements and collector number and sizing.
Collector Confidential
The heart of the system is the solar collectors, typically flat panels that come in a variety of sizes and can be mixed and matched. As a general rule, their total surface should equal 50 to 100 percent of the surface area of your pool. If you live in Florida and enjoy year-round pool use, for example, the collectors should equal 100 percent of the pool's square footage — roughly 450 feet of collectors for a 15-by-30-foot pool, according to the DOE. In northern California, where most people use pools six to eight months a year, the typical system size is 60 to 70 percent of the pool surface area.
Glazed collectors have copper tubes, a black metal absorber plate, and are stored in a glass-covered insulated case. Because they produce higher temperatures, they are most commonly used for heating spas, hot tubs and indoor pools (as well as in-home hot water), and can cost $60 or more a square foot.
Unglazed collectors are typically used to heat outdoor pools. The panels are usually made from durable polypropylene plastics with an ultraviolet light inhibitor to extend panel life and cost around $20 to $25 a square foot; sometimes, unglazed copper or copper-aluminum is used.
Positioning solar collectors is like real estate. It's all about location, location, location. You want them in an unshaded area, as close to a southern exposure as possible. But collectors don't necessarily have to be situated on the roof. They can be elevated on a rack or ground-mounted near an existing slope.
"Some people make them a shade structure," Menicucci says. "When you are sitting under it, it's cool because you are removing the heat as well as keeping the sun off of you. It's waterproof, so you could even have a barbecue under there." Some municipalities prohibit solar collectors that are visible from the street. Menicucci recommends working the panels into an architectural feature, and there are systems that specifically camouflage or hide the collectors to make them more aesthetically pleasing.
Once installed, a solar heating system should last about 20 years if properly maintained. If the pool's chemical balance and filtering system are checked regularly, there's little maintenance required, but glazed collectors may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse.
The bottom line: Look above for one answer to go green and enjoy your daily dip, knowing that you're helping both the environment and your bank account. After all, you've got it made out of the shade.