DC -- as in direct current? You bet. Today we use AC (alternating current) power developed by Nikola Tesla, but back in the late 1880s, Thomas Edison's DC was king. The problem was that it couldn't travel very far without a loss of power, and AC, with its higher voltage, could.
So why are green builders looking at DC today? Using AC always results in a loss of energy, both because of the inversion needed for the various voltages of electronics and appliances in our homes and because most of those electronics use DC. Computers are a prime example. If you feel that big "brick" on your power cord after using your computer for a long time, it's hot. That heat is energy, lost during the inversion of AC to DC.
Until we started looking at alternate sources of energy, there wasn't much to do about the energy loss -- AC was still more efficient overall and that's how our power grid was designed. However, the use of solar panels has changed things. They generate DC, which is usually fed back into the power grid ... which uses AC. You see where this is going. If you have a way to use DC power directly in your building, however, you could take the energy you're generating via solar panels (or wind turbines, or whatever you want) and use that to power electronics that already use DC without the energy loss. Currently, there are "microgrids" available that work with existing AC systems and supply energy to power things like compact fluorescent lighting panels, but many green construction experts are predicting a return to DC in the future.