Solar pool heating is real deal for Mainers

Posted May 21, 2010, at 8:17 p.m.

The other day I got a phone call from a large solar collector manufacturer who wanted to purchase one of our solar tanks. I asked what the project was and was told it was a 115 collector solar heating system for a swimming pool in Massachusetts.

That has to be one big pool.

This is the time of year that pool owners are opening their pools and waiting for them to heat up from the sun or they are using a fair bit of fuel to heat up the pool.

Solar pool heating is a real deal for pool owners in Maine. Solar pool collectors are relatively inexpensive. They usually are made of thin plastic tubes that the pool water circulates through, picking up solar heat in the process.

The tubes, which are black, are on a south-facing roof or other surface that catches a fair bit of sun during the day. Whenever the collector is about 10 degrees warmer than the pool, a diverter valve diverts the flow from the pool to the collectors, warming the water. The flow diverts away from the collectors when the collectors cool down.

The beauty of such a system is that it costs about the same as a fossil fuel system.

Once it is installed, you do not need fuel. A solar pool system gets a pool usable before Memorial Day for those of us who are not polar bears and keeps the pool at comfortable temperatures for the entire pool season until Labor Day.

Installing a solar pool system can be a do-it-yourself project that would take less than a weekend.

The rule of thumb for solar pool system sizing is that the amount of collector surface should be half of the pool surface.

Most of the heat loss from a swimming pool is by evaporation of water off the pool surface, so the collector size is directly proportional to the pool size.

Using an insulating pool cover will help a lot during the early part of the season to supplement the solar heating system. And in some areas, a pool cover can be a simple passive alternative to a complete system. A pool will not heat as well just using a cover but it is better than nothing. A cover also helps to reduce chemical use when the pool is not in use.

Many folks have built their own solar collectors with some success. Some systems are as simple as a very crude placement of black coiled well tubing on the roof. A more effective system is a simple grid that is made from well tubing or PVC pipe that is glued together. Any pipe that is placed on a roof should be painted black. It also needs to have the ability to move with the natural expansion and contraction that results from heating and cooling.

This time of year, while pools are still rather cool, a system can operate well into the night when the air temperature is warmer than the pool. In this case, the solar system is affording the owner a real performance bump.

There are other economical ways to heat outdoor pools, such as heat pumps and gas and oil systems, but when one considers the initial costs and operating costs, a little warm-up time from the sun early in the season is well worth not having to purchase fuel.
