There has been some amazing developments in the area of geothermal heating and cooling recently. Costs are only 10% to 20% higher than a standard central air system and the energy use is reduced by up to 80%. I don't know about your area but here in Dallas the A/C is the biggest expense of the year. Geothermal heating/cooling units remove the heat from the water in winter and use it to heat your home, hot water heater, and some people have it for in-floor heating as well (Mmmm, cozy). Then in the summer, you flip a switch and the unit runs in reverse, removing heat from your home and putting it into your pool.
I remember a few years back we took a trip to Phoenix and took an after-dark dip in the pool. It turns out that the pool was officially closed at dusk and someone had simply forgotten to lock it up! We got a stern talkin' to. But that was sublime having the warm pool all to ourselves for about 20 minutes...
Just something to think about. You might be able to get back into that pool!
http://www.geothermalheatpumpforum.org/geothermal-heat-pump-discussions/706-using-swimming-pool-as-heat-sink.htmlThen again, some people are using a geothermal heat pump to heat only their pool. And others are using a solar pool heater with a UV system to kill off the algae, etc. Runs completely off the solar and continuously pumps the water through the UV tube. Greatly reduces chemical use, too. Depends on your budget. I've seen some home-grown solar pool heaters that you could put together over a weekend (you'll have to get used to the pipes going in and out of the pool probably... unless you can tap into the pool cleaner pipes. Too many variables. Does your pool have a waterfall or an attached hot tub? If so, you should be able to tap into those pipes.
Hope that helps.