Each retrofitted machine has a controller box that feeds into the central ReCardio processor and finally into an inverter that taps directly into the building's electrical system. Any elliptical machine could create up to 300 watt-hours of energy after a retrofitting that costs approximately $300 per machine (the cost would decrease with big orders, and additionally would be offset by big tax credits). At one dollar per watt-hour, that makes the system significantly cheaper than solar power, which can cost $10/watt-hour. For a given machine, about 100 watts are generated for an average hour of usage (depending on the specific machine and intensity). Ten hours of usage creates enough power to charge your cell phone 397 times, or the equivalent of the battery of a 2004 Prius. Based on usage in the current installations, Harr says that a $5,000 ReCardio installation would pay itself off in half the time of an equivalently priced solar installation.