Contrary to popular belief, the world of the future will be as dependent on photovoltaic energy as we can imagine today. There are three reasons for this. First of all, photovoltaic systems have advantages over other technologies in the choice of installation points. They can be mounted on roofs or even become part of buildings, such as skylights. Second, even ground-mounted photovoltaic collectors can make efficient use of open space. Flat panel photovoltaic technology is the most economical way to produce renewable energy. Third, abundant sunlight is common and usually abundant, and the amount is predictable everywhere. In the United States, for example, cities and settlements cover about 140 million acres of land. Only 7 percent of this area -- rooftops, parking lots, walls along highways, building surfaces and other dual-use ways -- could meet the country's energy needs. Using photovoltaic as a basic form of energy, there is no need to deliberately open up new land.