Natural gas pipelines and power utilities across the United States struggled for several weeks to keep lights on and homes warm through the coldest winter in decades, but it may take many months for the cost and the fallout of the so-called "polar vortex" to work through the energy chain. As sub-freezing temperatures spread in January and February, spot natural gas prices spiked at many gas delivery points in the Midwest, Northeast and New York, pushing wholesale power prices above $100 per megawatt-hour for days at a time. Customers will soon receive gas and electric bills, reflecting the higher cost of gas in January. In unregulated power markets, January bills will present a "double whammy," said Nick Akins, chief executive of American Electric Power Co, one of the largest U.S.