Hydropower is currently the largest source of renewable energy in the country, and the US Department of Energy is working to make it more efficient and environmentally friendly.
Four areas represent the future of hydro energy: tidal power, marine current power, wave power and osmotic power. In a candid note on its research page, the Department of Energy admits, "Every tidal and marine current project faces a cost efficiency issue and the cemetery of inventions is full of projects technically viable but economically bound to death."
But that doesn't mean they're not trying. More than two thirds of the research budget of its Water Power Program is dedicated to developing new technologies; it lists more than 300 projects in various stages that are working to turn the energy of moving water into electricity to power our homes, devices, and cars.