It's one mean, green machine and it's saving Wesleyan up to $5,000 a day in energy costs. Wesleyan's new Cogeneration system - or CoGen, - uses natural gas to simultaneously generate electricity, heat and steam for university use. It began operation in February after an 18-month installation process. "Buying electricity from the grid is expensive and non-efficient,” says Peter Staye, associate director of utilities management. “With CoGen, we are generating 81 percent of our own power. It should pay for itself in five years." CoGen operates similar to a vehicle with an extreme super-duty engine. The natural-gas fired, turbo-charged, four-stroke…