With winter coming, Texas electricity provider TXU has started a new program designed to warn homeowners about the potential dangers of variable electricity rate plans.

Variable rate plans are designed to offer lower electricity prices than fixed-rate plans can generally offer, and ostensibly to take advantage of drops in the cost of fuel as well.

However, TXU warns that some variable electricity rates will rise dramatically in the autumn. With usage low, consumers' electricity bills will not change substantially, potentially even falling overall, but when energy usage jumps again in the winter those bills can rise sharply.

TXU notes that some electricity companies will raise prices by as much as 200 percent above the introductory rate over the course of the first few months. The company found one plan that reached as high as 23 cents per kilowatt-hour in a state that averaged 12.3 cents per kilowatt-hour in 2009, according to the U.S. Energy Information Administration.

In response, the electricity supplier has created its No Vari-a-BULL Sweepstakes, offering low, fixed-rate electricity prices along with the chance to win a Chevrolet Volt electric vehicle.