Images: A visit to 'negawatt' central

Demand response companies act as middlemen between utilities looking for ways to lower power grid demand and customers who get paid to participate in energy efficiency programs. EnerNoc says it has 1,500 megawatts under management, about the same capacity as 15 peaking power plants.

EnerNoc is now looking to get into energy management, where it will track customers' energy usage and try to make it more efficient. For example, by viewing usage data, it could spot times during the week when a university could change its lighting and heating schedules to save energy.