Figure 97 consists of three maps labelled 'a', 'b' and 'c'. Map 'a' has the title 'Solar insolation (1 month). January 1, 2012 00:00 – January 31 2012 23:59'. It is a global map using normal cylindrical projection, faintly showing the outlines of the continents. The map is coloured using a scale ranging from very dark red, which represents zero W/m superscript 2, through shades of red to orange, which represents 275 W/m superscript 2, through shades of yellow to very light yellow (almost white), which represents 550 W/m superscript 2. The colouring of the map is in horizontal bands covering both land and sea that merge from one colour to next. These bands are not straight and the transition of colours is too complex to describe in detail. The approximate pattern is as follows: The Arctic regions are dark red. North America, Europe and Asia are red. Central America, Africa and Australia are yellow. Southern oceans are orange and there is a thin band of red covering the Antarctic Ocean. Antarctica is light yellow. Map 'b' has the title 'Solar insolation (1 month). June 1, 2012 00:00 – June 30 2012 23:59'. The map is the same format as map 'a' i.e. a global map using normal cylindrical projection faintly showing the outlines of the continents. The map is coloured using the same scale as map 'a'. The colouring of the map is in horizontal bands covering both land and sea that merge from one colour to next. These bands are not straight and the transition of colours is too complex to describe in detail. However, this time the colouring is almost the inverse of map 'a'. The approximate pattern is as follows: The Arctic is yellow. Canada, northern Europe and northern Asia are orange with some red. The U.S.A., northern Africa, southern Asia and Australasia are yellow. South America and the southern oceans are red. Antarctica and the Antarctic Ocean are dark red. Map 'c' has the title 'Yearly total of global horizontal irradiation [kWh/m superscript 2] UK and Ireland'. It is the normal cylindrical projection showing the outline of the countries and the major conurbations. There is a colour scale ranging from dark blue (750), through turquoise (875), green (950), yellow (1025) to dark orange (1100). The land area has been coloured as follows but note that the transition of colours is gradual: The very north of Scotland and Shetland Isles are dark blue. Scotland is blue. Northern England is green. The Midlands are light green. Wales, southern England and the coast of Norfolk are yellow. The South West of England is orange, getting darker towards Land's End. Northern Ireland and northern Eire is blue/green. Central Eire is green becoming yellow at the southern coastline.

 5.9 Why photovoltaics?