Remember Beacon Power, that startup using 2,800-pound flywheels to cut noxious emissions? Well, three years later, the company is wrapping up construction of its first plant, a 20-megawatt operation that just happens to be the world's largest. The Stephentown, NY facility is home to 200 of these flywheels, which store and output energy as needed, essentially matching the power supply with the demands of the grid. The result, the company promises, is reduced energy waste and stable electrical frequencies hovering around 60Hz. And while the plant's already up and running at 18 megawatts, it won't be until later this month that Beacon finishes building it out so that it reaches its full capacity. Full PR and champagne-popping celebration plans after the break.