A homeowner decides to install photovoltaic cell system on the roof of his house to meet the electricity needs of the house. The capacity of the solar system is 6 kW and the cost of solar cells is $1.3/W. If the house-owner currently pays an average of $125 for the electricity per month, determine how long it will take for the photovoltaic system to pay for itself. Assume the homeowner can meet approximately 80 percent of the electricity needs of the house by the solar system.