As Kristi Sandoval, a senior at Texas State University, pumps her legs on an elliptical machine in the schools' gym, a tiny cord transmits the energy she creates to a metal box on the wall. From there, the pulse enters the campus power grid, where it might go to fuel the lights above Sandoval's head or a professor's coffee pot across campus.

For Sandoval, just the thought of it makes her run a little faster. "On these elliptical I do more than I've done before on any other treadmill or exercise bike," she said. "I think it's wonderful that they thought of doing something like this, because a lot of people enjoy using these machines and now we're helping save the environment a little bit."

Texas State, in San Marcos, is one of two state universities developing the biggest "human power" plants among just a handful on campuses across the nation — converting the sweat energy of exercising students into electricity to fuel their campuses. A new, larger plant is being developed by the University of North Texas. After six months of capturing student workout power at Texas State, it remains unclear if the school's investment is paying off in power cost savings. But some school officials say that's not really the point. More important, they say, is teaching students about their effect on the environment and their ability to take action to preserve it.

Details of how exactly to use the power generated by UNT students won't be determined until the equipment is installed in August, said Laurie Klein, UNT's assistant director of recreational sports. At Texas State, electricity produced by exercising students is fed back into the campus electrical grid, said Glen Hanley, director of campus recreation. The concept of using exercise equipment to generate power is fairly new; ReRev, a Florida-based company that partnered with Texas State and North Texas, has been in business for less than two years. Texas State was the seventh university in the nation to buy into the concept, and the first in Texas, Hanley said.

ReRev provides technology to retrofit workout equipment to convert kinetic energy into electrical power. What normally would be lost as heat energy is captured to power lightbulbs, air conditioning and televisions. “Students have grown up with green and renewable energy," said ReRev spokeswoman Beth Bennion. "They think it's neat, cool and progressive."

UNT, pending approval by university administrators, will have 36 machines. Texas State has 30 that were installed in December. It costs each university approximately $20,000 to install the human power converters. But the amount of electricity generated is relatively unknown to both the universities and to ReRev. Hanley said ReRev estimates Texas State will break even on the investment in seven to eight years, but said university facility administrators have said it may take as long as 15 years.

The amount of energy the machines produce greatly varies and depends on the exerciser's weight, age and gender, which determine how intense the workout is. Those factors, combined with a lack of field test data — because of the concept's newness — means students are not just hamsters generating the power, but guinea pigs testing the system.

According to the company's website, a 30-minute workout produces 50 watt hours of electricity, though Bennion said that estimate was "very rough." That amount of energy could power a fluorescent light bulb for about three hours or a laptop for about one hour, according to the U.S. Department of Energy. A student would have to exercise for about an hour and a half to keep a flat screen TV on for an hour. And it would take an endurance athlete to power a hair dryer for an hour. That would take more than 18 hours of exercise.

But Hanley said mass-producing energy is not the goal. “We're hoping [students] will kind of get the concept to be more environmentally aware. We're hoping they will turn off their TV when they're done with it, or they'll turn off their light in their residence hall room," he said. "We knew we were not going to produce enough electricity for the whole building, but we wanted the students to be aware of what we’re doing and to do something right for the environment."