Now is the time to plan for the integration of significant quantities of distributed renewable energy into the electricity grid. Concerns about climate change, the adoption of state-level renewable portfolio standards and incentives, and accelerated cost reductions are driving steep growth in U.S. renewable energy technologies. The number of distributed solar photovoltaic (PV) installations, in particular, is growing rapidly. As distributed PV and other renewable energy technologies mature, they can provide a significant share of our nation's electricity demand. However, as their market share grows, concerns about potential impacts on the stability and operation of the electricity grid may create barriers to their future expansion. This book describes the Renewable Systems Interconnection (RSI) that the U.S. Department of Energy launched in 2007 to facilitate more extensive adoption of renewable distributed electric generation. The technical and analytical challenges that must be addressed to enable high penetration levels of distributed renewable energy technologies are also addressed in this book. Because integration-related issues at the distribution system are likely to emerge first for PV technology, the RSI study focuses on this area. This is an edited, excerpted and augmented edition of various government publications.