Figure 91 is a graph showing the improvements in efficiency of 4 categories of solar cell technology from 1975 to the present day. The graph is far too complex to describe in detail as there are about 187 labelled nodes distributed along 18 traces and the 4 categories have been further subdivided into a total of 26 technologies. The origin of the graph is at the bottom left hand corner. The horizontal axis has 9 tick marks. Starting just right of the origin, these tick marks are labelled 1975, 1980, 1985, 1990, 1995, 2000, 2005, 2010 and 2015. Between each of these tick marks there are 4 unlabelled tick marks for the intervening years. The vertical axis, labelled 'Efficiency (%)' has 14 tick marks. Starting at the origin, these tick marks are labelled 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48 and 50. I shall summarise the traces for the four main technology categories. Multifunction Cells and Single Junction GaAs: Start at an efficiency of 16% in 1983 rising to 44% in 2013. Crystalline Si Cells: Start at an efficiency of 15% in 1977 rising to 24% in 2013. Thin-Film Technologies: Start at an efficiency of less than 1% in 1976 rising to 18% in 2013. Emerging PV: Start at an efficiency of 7% in 1991 rising to 12% in 2011.

 5.5 Electricity from sunlight