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 in five years, and an Egyptian proverb of the time was "If wealth is placed where it bears interest, it comes back to you redoubled." Examining the doubling time can give a more intuitive sense of the long-term impact of growth than simply viewing the percentage growth rate For a constant growth rate of "r%", the formula for the doubling time "T" is given by Some doubling times calculated with this formula are shown in this table. Simple doubling time formula: For example, with an annual growth rate of 4.8% the doubling time is 14.78 years, and a doubling time