One of the most logical uses of solar energy is to heat a home swimming pool, since sunshine and swimming weather are so closely linked. The simplest and least expensive way to warm an unheated pool with sunrays, or to ease the load on a gas or electric pool heater, is to cover the water with a transparent plastic blanket, commonly made of heavy, double-thickness polyethylene.
By preventing evaporation (which can account for up to 55 percent of a pool’s heat loss) while still permitting sunlight to warm the water, a plastic cover can raise the temperature of a pool by as much as 10° F. on a sunny day. Used in conjunction with a conventional heater, a pool blanket can pay for itself over a single season in reduced energy bills.
But full-fledged solar systems, available from solar equipment-dealers and from some pool-supply stores, are even more effective. Most pools are heated to around 80° F; in warm weather, a solar system can do the job unaided by a standard gas or electric heater. In cooler weather it can save considerable energy by preheating the water before it passes into the conventional heater.
Because the basic plumbing necessary to circulate the water through the solar collector panels is already included in the pool’s filter system, a solar heating loop need only tap into the existing pipes- usually at a point just beyond the filter but before the conventional heater, if any.
A one-way check valve prevents water from draining back into the filter from the elevated collectors, and a manual or thermostatically-controlled gate valve allows pool water to bypass the solar heater on cloudy days, or whenever the pool has heated up sufficiently. The existing swimming-pool pump will often be powerful enough to circulate water through the panels, but the panel manufacturer or dealer may recommend that you retrofit a larger pump.
Solar collector panels for pool heating are simpler and lighter than the ones that are designed for hot-water systems, requiring no insulation or glazing. Many are copper; others are merely 3-by-8-foot sheets of molded plastic, honeycombed with channels through which the water circulates.
The panels must be mounted on a roof and oriented toward the sun in the same manner as other solar collectors. If nearby south-facing roof surfaces do not provide the proper angle, you can secure the panels to an inclined roof rack, but covered with %-inch plywood (the lightweight pool panels will sag in the middle if they are not supported). In many cases, however, the simplest way to mount the collectors is to build a nearby cabana-style shelter with its roof oriented due south and pitched at an angle equaling your latitude.
To heat the water adequately, you will need collector panels with a total surface area equal to half the area of your pool. To ease installation, use schedule-40 PVC pipe and, whenever possible, PVC valves and fittings to make the plumbing connections. Buy the type of pipe that is specifically labeled for outdoor use; the plastic is formulated with a stabilizer that enables it to withstand prolonged exposure to sunlight. The PVC pipe ordinarily used for indoor plumbing degrades rapidly in the sun and must be painted if it is used outside the house. You can buy pipe, fittings, and any other hardware not included with the panels, at plumbing and home-improvement stores.