Solar energy technologies carry along important advantages for electric utility and other users. First, the solar resource has no "fuel" cost and is abundantly available. In many parts of the world, the sun shines intensely on a daily basis, providing a nearly unlimited power resource for devices that convert the sun's insolation(1) into useful energy. Second, solar daily output often matches air conditioning loads, and thus provides high value. Third, most solar equipment is modular, meaning that capacity can be increased or decreased incrementally depending on demand. Solar power plants can, therefore, be readily matched to changes in load growth, decreasing the risk and cost associated with capacity additions. Fourth, most photovoltaic technologies can easily be operated in remote off-grid areas. There is no need for connection to transmission and distribution lines and minimal need for maintenance and monitoring. Finally, solar technologies are environmentally cleaner than conventional energy technologies. Solar thermal and photovoltaic devices produce no operating wastes, no air pollution, and little or no noise.
Even with these advantageous characteristics, solar energy technologies currently face some limitations for widespread use. While the cost for solar thermal and photovoltaic devices has declined substantially over the past few decades, many applications still are not fully cost-competitive with conventional technologies. Also, like wind power, solar energy relies on a fuel source (sunlight) that reaches the Earth's surface intermittently, resulting in storage and load-matching problems. Nevertheless, solar energy currently plays an important role in some energy sectors (for example, off-grid electricity applications) and is expected to have a broader role as the development and commercialization of solar technologies continue.