Swanson's law Swanson's law Swanson's law is the observation that the price of solar photovoltaic modules tends to drop 20 percent for every doubling of cumulative shipped volume. At present rates, costs halve about every 10 years. It is named after Richard Swanson, the founder of SunPower Corporation, a solar panel manufacturer. Swanson's law has been compared to Moore's law, which predicts the growing computing power of processors. Crystalline silicon photovoltaic cell prices have fallen from $76.67 per watt in 1977 to $0.36 per watt in 2014. Plotting the module price (in $/Wp) versus time shows a dropping by 10% per year.
Doubling time or approximated by dividing 70 by the percentage growth rate (more roughly but roundly, dividing 72; see the rule of 72 for details and a derivation of this formula). The doubling time is a characteristic unit (a natural unit of scale) for the exponential growth equation, and its converse for exponential decay is the half-life. For example, given Canada's net population growth of 0.9% in the year 2006, dividing 70 by 0.9 gives an approximate doubling time of 78 years. Thus if the growth rate remains constant, Canada's population would double from its 2006 figure of 33 million to 66