An estimated 33,000 solar pool heating systems were installed in 2001 according to the Solar Energy Industries Association (SEIA).WASHINGTON, D.C. 2002-03-20 [SolarAccess.com] A new record of 10,144,918 square feet of unglazed solar collectors were produced by the four leading manufactures of unglazed solar thermal collectors. Those companies are Aquatherm, FAFCO, Inc., Heliocol USA, Inc. and Harder Industries. The 33,000 systems estimate is based on an average solar system size of 300 sq. ft. per pool. Unglazed solar collectors provide low-temperature water heating (75 to 95 degree F). These collectors are inexpensive, unobtrusive when integrated into building design and simple to install. According to the Florida Solar Energy Center, energy performance certifications of unglazed solar pool heating panels indicate production of an average of 1,000 BTUs per square foot, per day, and assuming solar system operation of an average of 5 hours per day for 5 months per year (a very conservative average for the parts of the country that utilize solar swimming pool heating systems,) the energy output of this quantity of solar systems translates into an electrical generating facility of approximately 594 MW. With the average cost of a 300 square foot solar pool heating system about $3,500 (around $12 per square foot,) the installed price per MW equivalent energy production is about $274,000 (about half the cost of a modern, combined cycle gas turbine generating facility). Solar pool heating systems routinely pay for their installed cost in avoided energy purchases in two to three years, while avoiding significant quantities of air emissions. There are 180,000 pool heating systems sold annually, including solar, natural gas, propane, fuel oil and electric heat pumps. This translates into 1 in 5 pool heating systems were solar energy systems. The application of solar thermal technology for pools and spas has been showing steady growth over the years, including the 13 percent growth in 2001 over 2000.