While Balboa Park has many green spaces, the buildings at the park are turning greener and saving energy and money.In 2008, the buildings at the park saved $400,000 per year in energy costs. In the last two years, they have saved $750,000.Park officials said the energy-saving measures were originally started to simply save money."That led to us recognizing that there were opportunities in natural resources, so there was a way to do both," said Rory Ruppert, the Director of Environmental Sustainability for the Balboa Park Cultural Partnership.At the Reuben Fleet Science Center, 10,000 square feet of solar panels were added on the roof in 2007. Inside, the center is illuminated by energy-efficient light bulbs, such as LEDs, which use 95 percent less energy and last longer than traditional bulbs.Inside the IMAX Theater, sensors automatically adjust the air conditioning based on attendance inside the theater."It knows there are people in there and it then adjusts the temperature as people come into the theater, so you're not running the heating and air conditioning if theres no one in there," said Paul Siborosky, the center's exhibits director.The Fleet Science Center has also been awarded Silver LEED certification. The center's neighbor across the park, the Natural History Museum, is believed to be the oldest museum in the country to be awarded LEED certification.Inside the Natural History Museum, energy-efficient lighting is also used as well as a sophisticated heating and air conditioning system that saves energy by giving different areas of the museum different temperatures."They get exactly what they need. No more, no less," said assistant building engineer Shawn Whisman.In the future, Balboa Park is looking to save even more money and more energy."By 2015, our objective is to save a million and a half annually," said Ruppert.Ruppert said cooperation between the museums in the park and the city of San Diego has been a key to success.The city is giving Balboa Park $2 million in federal stimulus money for more sustainability projects.