Minneapolis ? Daylight-saving time ends tonight. Do you know where your savings are?

Two years into yet another experiment with our clocks, the original reason for it – saving energy – hasn’t been borne out. In fact, some economists assert that people may be using more energy as a result.

“One thing I’m certainly skeptical about is the beneficial effect the policy is supposed to have,” said Matthew Kotchen, a professor of economics at the University of California at Santa Barbara.

Kotchen found that the darker fall mornings at the end of the daylight saving season led to a 2 percent to 4 percent increase in residential electricity consumption in the southern Indiana region he and his partner studied. That cost individual households $3.29 per year while increasing greenhouse gas pollution from generating the electricity.

Energy savings have been at the center of daylight-saving proposals for more than 200 years, since Ben Franklin argued that it would conserve vast amounts of candle tallow. The U.S. first adopted daylight saving time briefly during World War I, and Congress has been fooling with it ever since, often sparking objections from farmers, airlines and parents of young school children, who might have to wait for buses in morning darkness. Since last year, the season has been four weeks longer than it was from 1966 through 1986.

Kotchen’s study, published in October by the National Bureau of Economic Research, focused on 25 Indiana counties where three different time schemes were resolved into one in 2006. He determined that savings in electricity for lighting during daylight saving months were more than offset by increases in demand for heating and cooling during the hours residents were usually at home.

Those effects might be more dramatic in the South, where air-conditioning demands are strong even in early spring and late fall, Kotchen noted. In the North, the extension of daylight saving time has meant darker mornings spring and fall, and a likely increase in lighting by early risers, who might also be trying to reheat a house after a long night of cooling.

Kotchen’s study did not examine effects on natural gas heating, common in many parts of the country.

Sheldon Strom, executive director of the Center for Energy and Environment in Minneapolis, said he wasn’t surprised by Kotchen’s findings. But daylight saving still doesn’t have any effect on home refrigerators and other devices, particularly computers, that are often drawing power day and night, Strom added. Nor does it affect most business use, which is double that of households.