Throughout history, these sources have been successfully harnessed and used to provide energy. Almost 2,500 years ago, the Greeks designed their homes to use winter sunlight for heating. Large, south-facing windows were used to collect solar heat, which was stored in massive walls and floors for gradual release throughout the night. The wind has also been used as an energy source for centuries. Some of its early uses include propelling ships and pumping water.
Today's technological advancements have developed more efficient means of harnessing and using renewable energy sources, and these sources are gaining increasing popularity. They offer us alternatives to nonrenewable energy sources such as oil, coal and natural gas which, when burned can cause acid rain and contribute to the overall warming of the Earth known as the "Greenhouse Effect." Existing renewable energy installations are making significant contributions to the US energy supply, and research activities are demonstrating the far-reaching impact that a greater reliance on renewable energy sources could have on our country's energy security. In addition, on-going and planned research offers still more possibilities.