Taking advantage of the sun's energy to heat a swimming pool makes great economic sense. Since a pool already has a pump for the filter system, no additional motors are needed to build a solar pool heater. The pump already circulates water from the pool through the filter and returns it to the pool. It's a simple matter of tieing into the pool's return line to divert it through a solar collector and then back to the pool. Some basic plumbing experience is helpful.
Connecting To The Existing System
After the water flows through the pool's filter, make a break in the return line. Insert a "T" joint in the line. Then install valves on both "T" outputs. On the "straight through" output, install another "T" joint, and connect the straight through output of that joint to the pool return line. The valve inserted between the two "Ts" is used to control how much water will be diverted to the solar collector. During the evening when there is no sun, you do not want to send any water through the solar collector, nor do you want to circulate water through the collector when the pool reaches the temperature you want it. The two valves give you control on how much, if any, water is sent to the solar collector. The solar collector input is connected to the valve coming from the first "T", and the collector's output is connected to the second "T". All of this piping should be done with the same diameter pipe used by your pool's filter system, to make connections easier.
The Solar Collector
In its simplest form, the solar collector can be a large box painted black, in which black PVC pipe is "snaked" back and forth for maximum exposure to the sun. A glass cover keeps heated air inside the box. You can build your own solar collector box using black PVC pipe with the same diameter to match existing pump lines. Connecting collars and couplings can be secured with either glue (allow 24 hours of drying time) or with stainless steel clamps. You may choose to purchase a commercial collector and install it yourself. Commercial units are designed to be very efficient and will hold up to the rigours of weather.
Mounting The Collector
Solar pool collectors can be mounted on the roof of a house, on the roof of a tool shed or building that houses the pool pump, or even flat on the ground. Ground installations that are close to the pool require the least amount of piping. Do not install collectors on roofs unless you are capable of working on roofs and take all safety precautions. Roof collectors must be securely attached to withstand strong winds. The larger you build the collector, the more heat it will produce, but you must have the available roof or ground space. Collectors should be installed facing south with no shadows from trees or other structures to block sunlight. East and west orientations are usually acceptable, but north-facing panels are too inefficient to use.
Automating Temperature Controls
Rather than using manual valves which you will have to open and close to regulate pool temperature, a combination of motorised valves and water temperature sensors can be installed. Companies such as Solar Direct (www.solardirect.com) sell pool heater controls, sensors and motorised valves that the do-it-yourselfer can install. Some basic electrical knowledge is helpful for installation of sensors and motorised valves, but such a system automates the flow water to the solar collector. If the temperature in the pool is cool, the system can automatically divert the flow of water to the solar collector by opening the valve to it and closing the "straight through" valve. When the temperature in the solar collector is cool, as it would be at night, the system can automatically bypass the collectors.