Solar panels are great! Especially with propane and electric going through the roof. I have a new pool and installed solar straight off. During October of last year in New York, we saw a net rise of 1 degree per day running at only 6 hours per day with about 55% coverage (solar panels to pool size).

However, there is no "air purge" problem. Any (correctly installed) roof system will be designed to "drain back" into the pool when not running. There MUST BE a vacuum breaker installed close to the high point of the panels in order for this to happen. This means that the system is full of air everytime it turns on and will blow air into the pool for the first 30 seconds or so of operation. This is true of roof top systems, it is not true of smaller systems that are at or below pool level. Drain back puts much less stress on the solar system (no pressure build up due to expanding water as it heats, no water weight on the roof and piping when not running, and, the biggest issue - no reverse pressue trying to collapse those expensive panels as the water tries to drain back into the pool but can't). All of the major manufacturers install as drain back.

The biggest issue with solar is that it is harder to run an efficient pump, as the THD is normally higher than the low speed of a 2 speed pump can handle. My builder pretty much refused to put in anything but a 2HP pump, so I am looking at alternatives myself.

We installed 8 4x14' panels for an 800 sq/ft pool. I have just opened for my 2nd season, but am expecting to be swimming in 80degree water within a week or two!