Furman University, Associated Press
In this Nov. 17, 2011 photo provided by Furman University, Haley Gray works out inside Furman University’s fitness center. Furman students are converting muscle power into electricity. Students who exercise in the school's health center are actually helping power the campus, since the 15 or so elliptical machines are hooked up to the power grid. One 30-minute workout roughly produces enough electricity to power a light bulb for several hours or a desktop computer for a half-hour.

GREENVILLE, S.C. — Students at two South Carolina colleges can reduce their campus' carbon footprints as they sweat off those extra holiday calories.

Elliptical machines in fitness centers at Furman and the University of South Carolina are connected to the power grid through a system that converts human energy into carbon-free electricity. Granted, the wattage is low. But self-powered gyms weren't the point.

The system is an ideal education tool at a school that requires all students to pass a "mind and body" health course, said Furman fitness director Scott Murr.

"You're doing something for you and the planet," he said when a reporter visited earlier this month. "It may even help you get a higher quality workout." Nodding toward the closest occupied machine, he added, "The harder she works out, the more power she's putting back into the building. It means we buy less dirty power from Duke Power."

A typical 30-minute workout can power a laptop for an hour, but a sweat-dripping "athletic" workout can power four, according to Florida-based ReRev, which installed the retrofitted machines at both colleges.

A flat-screen TV near the entrance of Furman's gym broadcasts how much power the machines are creating at that moment and, in graph form, throughout the day. Classes and popular workout times generate spikes. Separate screens show weekly wattage and total output since the system was installed in June 2010.

Murr called Furman's system on 15 machines the state's first human power plant.

The University of South Carolina installed one later in the summer with 10 ellipticals in USC's fitness center in downtown Columbia. However, that system lacks an external display of watts like the one at Furman.

Charles Anderson, fitness director at USC's Strom Thurmond fitness center, said he planned to look into adding one, noting the technology continues to change. Currently, a poster near the 3-foot-by-1-foot conversion box explains the system, but a visual would help students grasp the concept, he said.

"Hopefully, this is something that will spur more research, get people thinking about other things they can do to produce extra energy," Anderson said. "In a building our size, we're not ever going to have a huge offset. It's a step, an educational step to get people talking."

Murr and Anderson say low-impact ellipticals are typically a gym's most popular equipment.

Furman students in a "mind and body" class confirmed they'd choose the ellipticals even if they weren't hooked to the power grid, but they praised the system as an easy way to help the environment.

Meg Austin, 19, of Chattanooga, Tenn., said the graphics are a good motivator, and she liked the idea that she could be powering the TV in front of her.

"It gives me added incentive," agreed a slightly breathless Melanie Shumate, 21, of Dallas. "It's a great thing. It's a way all students can give back."

Faris Armaly of Greenville said he liked that his workout energy isn't wasted. Pointing to his machine's screen, the 19-year-old neuroscience major said, "I can see how many calories I'm burning here, and that turns into real energy. It's like an added bonus."

At Furman, students led the effort.

Each year, Furman seniors give their soon-to-be alma mater a gift. By vote, the Class of 2010 chose the renewable energy ellipticals over two other possibilities, including another green energy idea of public bicycles for on-campus use. The class ended up raising far more than the $17,000 required, Murr said.

Recouping the cost through energy savings would take 12 to 15 years, based on what Furman pays per kilowatt hour. A year's worth of workouts would power a dorm suite for a month, he said.

Furman and USC are among roughly 30 colleges to install the ReRev system since Hudson Harr, 25, invented it in 2008 shortly after graduating from the University of Florida, which initially told him no. After a pilot program on 15 machines at the Gainesville Health and Fitness Center proved successful, his alma mater became the second install, Hudson said.

"I was always fascinated by renewable energy — new things we could harness. I started to get into kinetics, which exists all around us that we're not taking advantage of," Harr said. "Then I walked into a gym for a daily workout and realized, 'This is so consistent.'"

Now, hundreds of machines are in college gyms nationwide, with the largest installation at the University of North Texas, with 36. Harr hopes the systems inspire similar-minded college students to come up with their own ideas for renewable energy.