English: The United States uses about 4 trillion kWh/year of electricity, at rates from $0.01/kWh to $1.00/kWh, with an average of about 11.2¢/kWh. The chart shows how many gigawatts of solar power can be installed economically, i.e. cheaper than grid rate vs. the installation cost, both with the 30% federal tax credit (ITC), and without. For example, with the ITC, at $5/watt 5,000 megawatts can be economically installed, close to the total that has been installed as of early 2012, at a time that U.S. residential installations were averaging about $5.20/watt. At $4/watt this increases to 33,000 megawatts, at $3/watt to 308,000 megawatts, and at $2/watt to 816,000 megawatts. Without the ITC, no photovoltaics can be economically installed if the cost is above $5/watt, and at $1/watt, almost the entire country can economically install photovoltaics, both with and without the ITC. Data is from https://ases.conference-services.net/resources/252/2859/pdf/SOLAR2012_0630_full%20paper.pdf A graph showing the method used is at http://www.keiser-analytics.com/graph.html