In many ways, solar energy is already a practical alternative to fossil fuels and nuclear power. Its renewable nature, the opportunities it provides for decentralized delivery, and its unmatched environmental benefits have made it a desirable option in the transition to new energy sources. Solar systems have proven to be technically feasible and many are already economically competitive with conventional systems in several energy markets. Applications of solar energy for residential hot water and space heating, industrial cogeneration and process heat, and electric generation are in the marketplace meeting the demands of residential consumers, commerce, and industry. As the Harvard Business School Energy Project has concluded, no technological breakthrough is required for solar to make significant contributions to our energy needs; active and passive solar heating for a variety of uses is "a here-and-now alternative to imported oil."1 While the most extensive uses of solar technology are currently limited to residential water and space heating, recent advances in photovoltaic cells, biomass, and solar-wind suggest that this limit is temporary and that commercial prospects will continue to grow. Indeed, since the 1973-74 oil embargo the economics of solar energy have undergone sustained improvement while the economics of conventional energy sources have either stagnated or steadily declined.