The total solar insolation on the continental United States is estimated to be 1:87 10 15 W. A typical solar cell has a conversion eciency of 10 percent. Using the 1990 consumption rate of electricity per year, determine how long it would be before the entire surface of the continental United States were covered with solar cells if all of the electricity were produced this way. Assume a constant electrical energy consumption growth rate of 3 percent per year.