Waste heat recovery is a key concept in Europe, sadly lost here in the U.S.

In Copenhagen they've integrated their energy generation, waste management, and the heat supply for all of the city's buildings.

It's hard to imagine any city in the U.S. embracing the idea of waste-incineration plant smokestacks in their neighborhoods. But that's what they've done all over Denmark, in the interest of capturing waste heat, reducing CO2, eliminating fossil fuels -- and reaching nearly total energy efficiency.

Novel ideas, too new and risky for American cities? Hardly. Copenhagen has been doing this since 1903.