Solar power involves using solar cells to convert sunlight into electricity, using sunlight hitting solar thermal panels to convert sunlight to heat water or air, using sunlight hitting a parabolic mirror to heat water (producing steam), or using sunlight entering windows for passive solar heating of a building. It would be advantageous to place solar panels in the regions of highest solar radiation. In the Phoenix, Arizona area, for example, the average annual solar radiation is 5.7 kWh/(mday), or 2.1 MWh/(myr). Electricity demand in the continental U.S. is 3.71012 kWh per year. Thus, at 20% efficiency, an area of approximately 3500 square miles (3% of Arizona's land area) would need to be covered with solar panels to replace all current electricity production in the US with solar power. The average solar radiation in the United States is 4.8 kWh/(mday), but reaches 89 kWh/m/day in parts of the Southwest.
China is increasing worldwide silicon wafer capacity for photov