Pipes for TransCanada's planned Keystone XL pipeline are stored in Gascoyne, N.D. The U.S. House has voted to approve the proposed project, which would allow crude oil to flow from Canada to the Gulf of Mexico. The Senate plans to vote Tuesday on legislation that would greenlight the project. Andrew Cullen/Reuters/Landov hide caption

itoggle caption Andrew Cullen/Reuters/Landov

Beacon Power President and CEO Barry Brits, at the company's plant in Hazle Township, Pa. He says a loan from the Department of Energy made it possible for his company to develop its flywheel energy storage technology. Jeff Brady/NPR hide caption

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Pumpjacks at the Inglewood oil fields in California in March. Some of the most controversial methods of oil extraction, like fracking, oil sands production and Arctic drilling, are also expensive. That's made them less profitable as the price of oil continues to fall. Richard Vogel/AP hide caption

itoggle caption Richard Vogel/AP

Vera Cole is president of the Mid-Atlantic Renewable Energy Association, a group arguing against proposed rules in Pennsylvania that would put stricter limits on how much grid-connected solar power homeowners can produce on their property. Jeff Brady /NPR hide caption

itoggle caption Jeff Brady /NPR

Pump jacks are seen in an oil field over the Monterey Shale formation near Lost Hills, Calif. Much of the U.S. oil industry wants to lift an export ban that followed the 1970s energy crisis. David McNew/Getty Images hide caption

itoggle caption David McNew/Getty Images