If you ask around for the cheapest way to heat your pool in Texas, you'll probably get a unanimous answer – a solar pool heater.
"By the end of 2010, the United States had 15.3 billion kilowatts of installed solar heating capacity—and roughly 85% of this capacity was used to heat swimming pools. In fact, there are more solar pool heating (SPH) systems installed in the United States than any other type of solar energy system. The widespread adoption of SPH can be attributed to the popularity of residential swimming pools in Florida, California, Arizona, and Texas. In these climates, outdoor pools can be used almost year-round, and SPH provides the most economical solution for actively heating these pools during stretches of cool weather. The initial costs of a SPH system are comparable with heat pump and liquid fuel pool heaters, while the operating costs are far less. The lower cost of SPH systems is due to their simplicity and efficiency."[1]
There are several types of pool heaters available in the market that prevents you from the brunt of fluctuating electricity rates in Texas. Here are some options for you:[2]
[1] http://www.homepower.com/articles/solar-water-heating/domestic-hot-water/saving-solar-pool-heating
[2] http://aquacal.com/blog/post/122-What-is-the-Best-Type-of-Heater-for-a-Swimming-Pool