Energy efficiency has been called the low-hanging fruit for reducing carbon emissions, because it actually pays for itself. But it can be difficult to get people to take simple steps to save energy, and it's hard to maintain those savings over time. For example, people offset the savings from a new efficient refrigerator by changing their habits or buying a plasma TV.

A company called OPOWER has what appears to be a successful strategy for dealing with this human element of energy efficiency. It has increased participation in energy efficiency programs from about 5 percent to 80 percent for the utilities that have used it so far, and the savings appear to be sustained.

So far, since its founding in 2007 the company claims its program has saved over 90 million kilowatt hours of electricity. The company has even attracted the interest of the White House--last week President Obama dropped by, highlighting the company as a source of the green jobs he hopes to help create.

The company's approach is based on the idea that people want to fit in. OPOWER first lets people know how their energy use compares to that of their neighbors. Then for each billing period the company gives them a single tip that they can act on, also connected to what they're neighbors are doing, such as "Most people in your area keep their AC at 78 degrees." They also tell people how much energy they will save.

It's obvious how this could work with people who are using more electricity than average. But for those using less than average, the company also compares them to their "efficient" neighbors to motivate change.

The company makes use of public information (such as from the tax assesor's office and weather data) as well as third-party demographics to tailor results. If a person is renting, OPOWER doesn't recommend insulating the house, for example. It also has software that looks at energy use patterns to identify likely sources of energy waste. Power spikes during hot days greater than that shown in neighboring houses could suggest someone has an inefficient air conditioner.

It seems like a promising approach. But it's not going to solve the world's energy problems on its own. On average the program has cut energy consumption by a modest amount--about 2.5%.