Another way that builders can reduce environmental impact is to reduce the energy requirements of a building. This can be done in several ways. One is to provide an alternative, nonpolluting source of energy. The first alternative energy source to be developed was solar power. With solar panels-wide, flat sheets of special material -it is possible to produce electricity from the rays of the sun. Builders can install solar panels on the roofs of buildings and connect them to cooling or lighting systems. Once the panels are installed, they provide energy at no cost and with on pollution.