A good solar company can do marvels by analyzing your current setup and tuning things. Unfortunately, from what I can tell, it appears that they are rather rare. We ended up in a dispute with the first company that did work and had a second company come in to fix what they did...and it was a learning experience all around.
General comments:
- The main idea with the panels is to get the minimal flow rate that both a) clears out all air from every panel in the series within a reasonable amount of time and b) keeps the difference between heated water returning to the pool and existing pool water within an acceptable threshold so that you are not losing too much efficiency due to airflow/wind/cooling before the water gets back and yet not having the pump run any faster than it needs to.
- The piping between panels and series of panels is critical, and depending on where panels are located you might want some to get a greater or lesser flow rate than the others (e.g. a north facing roof here in san diego is very inefficient so I send less water to those panels than to the south ones).
- Placement of panels and the roof temperature sensor are critical to having a good system
- Odds are that your pump will need to run at least 2100rpm, and perhaps up 2700 if you have a very tall house and bad pipes/panels. I run my variable speed at 2300. 2400rpm may heat more but it is noisier than I'm willing to tolerate and the pump uses markedly more power with each ~100pt increase in rpm (almost an exponential curve with ~2000rpm being where it really takes off).
- An automation system is almost necessary to ensure the system only turns on when needed and during the most optimal hours (nothing is worse than finding out that pool has been cooling because the water lost more heat going up to the roof and back than it gained from the panels, just a timer wont work as clouds passing over the house can bring temps down fast). The automation system should also prevent the system from continually cycling between solar and other forms of heating(you set a minimum threshold to activate, and a lower threshold to keep running). I have my system only allow solar to run from 9:15am-4:15pm daily. Before and after the pump still runs for filtration and chem mgmt reasons but at a much lower speed.