The yearly average solar flux incident on a horizontal surface in the United States is about 180 W/m2. The average total energy demand in the United States is approximately 100 quads (100 × 1018 J) per year. Assuming an average efficiency of PV cells of 14% and a biomass conversion efficiency around 1%, estimate the percentage of land required to provide the energy of the country by these two renewable technologies. (The total land area of the United States is about 9.2 × 106 km2.)