The U.S. Department of Energy has been monitoring the development and use of clean energy technologies for the past several decades and evaluating their potential for reducing harmful carbon emissions. Within that timeframe the main technologies that have emerged are solar power, wind power, light-emitting diodes (LEDs) and electric vehicles. High costs have hampered the widespread adoption of these technologies, but the recent expansion of large, existing organizations into the clean energy market is helping to dramatically reduce the costs. Experts note that reduced costs are helping to increase the implementation of clean energy technologies for consumer use.