A solar-power-tower plant is considered for Alabama, Birmingham. Heliostats with a total area of 400,000 ft2 are to be used to reflect solar radiation into a receiver. When the solar irradiation is 250 Btu/h.ft2, steam is produced at 160 psia and 600 oF at a rate of 15 lb m/s. This steam is expanded in a turbine to 2 psia pressure. The isentropic efficiency of the turbine is 88 percent a I The estimated cost of this plant is $17,000/kW, and the plant is expected to operate 4500 ha year at the power output determined in part (a). If electricity generated is to be sold at a price of $0.11/kWh, how long will it take for this plant to pay for itself