In the ongoing effort to deploy more sustainable energy technologies, there is no more gratifying sight than the now-familiar plot of PV module price declines that have occurred as the cumulative manufactured volume has grown, as illustrated in Figure 1. Plotted on a log-log scale, the values chosen for the average sales price tend to fall along a (somewhat) straight line. This downward trend is sometimes referred to as “Swanson’s law,” after Richard Swanson of SunPower, who noted the linearity in 2006.
The price decline evokes comparison to Moore’s law, which suggests that the behavior might be expected to continue into the future. Moore’s law famously, over the course of four decades, predicted the doubling of the number of transistors on an integrated circuit every one to two years. Though there is healthy debate regarding the extent to which the PV module price trend can continue, there is nevertheless a natural tendency to extend the line into the future as a way to predict future PV module prices.
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