I am making the plunge into solar heating for the PE2. Next weekend I am going to install the system, and if our estimate that the heater is 75% or more of the electrical usage, my kWh usage should drop dramatically. The system is going to pull water from the outlet intended to drain the spa, it will be pumped by a 5 gpm RV pump, the water will then get heated by 2 20 foot solar panels and get put back int the tub through the waterfall. If it works as it is supposed to, the solar panels will heat the water as high as 125 degrees in one day (although I will probably set the solar thermostat at 110 so that after the sun is down and the tub cools it should drop to the perfect temp). I am going to turn the spa heater down to 80 so that it never turns on. Assuming this drops my electric bill, I will leave the breaker on and let the circulation pump continue to go. If the bill is too high, I will install an in-line UV filter in the solar infrastructure and turn off the breaker completely. One way or another, this tub will no longer cost me $150/month.
(btw, the cost of the system was $950)