Imagine a building so energy efficient that it can generate what power it needs with the solar modules on its own roof -- a net zero energy building. It's not a pipe dream. We've been building them in the United States for a decade. The U.S. Department of Energy wants the "ZEB" to be the standard for new buildings. Why is it important to match renewable energy output with the demand for power on a building-by-building basis? And after ten years of zero-energy design, why do we only have eight buildings to show for it? In this month's briefing Denis Du Bois talks with David Orr, who designed and built the largest zero-energy building in the U.S. If you think that's cool, wait until you hear what Orr is doing for an encore.