The most popular cell types are silicon cells and thin film, multi-junction cells (due to cost) and dye synthesised solar cells (for reasons of efficiency, however, they represent a marginal part of sales). Among those commonly available, monocrystalline panels are the most expensive, but due to their being the highest efficiency they are the preferred choice. Cheaper cells are polycrystalline cells, while the cheapest option is amorphous silicon cells (table on Fig. 1 – based on [1]).

As technology advances, manufacturing techniques improve, and the price of the panels themselves falls. Richard Swanson - founder of SunPower Corporation, a solar panel manufacturer - has proposed the equivalent of Moore's Law for solar panels. Swanson's law [2] postulates that the price of solar photovoltaic panels tends to fall by \( 20\% \) for each doubling of the cumulative quantity shipped. This is an empirical law. Prices for crystalline solar cells fell from $76.67/W in 1977 to a projected $0.74/W in 2013, were $0.63/W in 2017 to reach a price of $0.21/W in 2020 [3] ( Fig. 2 – based on [4]).