Page - 97 - in Clean Water Using Solar and Wind - Outside the Power Grid

Solar PV 97 The irradiance is quantified as Global Horizontal Irradiance (GHI) and is the total amount of solar energy incident on a horizontal surface, coming from both direct and scattered sunlight. GHI is a key parameter for solar PV applications. The GHI varies quite a lot depending on the geographical location: see Table 8.1. For most of the off-grid locations that we are focusing on – rural areas in Africa and developing Asia – the GHI is high. There are several sources of information of the solar irradiance around the world, for example the Global Solar Atlas, published by the World Bank Group (http://globalsolaratlas.info). Table 8.1 Annual Global Horizontal Irradiance (GHI) in various regions of the world. Region GHI Range kWh/m2 Per Year Africa 1,600–2,700+ Middle East & North Africa 1,700–2,700+ Latin America & Caribbean 1,000–2,700+ North America <700–2,600+ Europe <700–2,100 South and Central Asia 1,400–2,400 East Asia 1,000–2,300 South-East Asia & Pacific 900–2,600 Source: Data from WEC (2016, Chapter 8). The irradiation depends on the elevation angle α of the sun. For low elevation angles the direct solar radiation needs to cross a larger section of the atmosphere to reach any point on the ground, so the attenuation factor is larger. The length of the solar radiation path through the atmosphere compared to the shortest path is indicated as air mass (AM). AM1, i.e. one air mass, indicates a vertical path from sea level to the outer atmospheric layer at standard barometric pressure with the sun directly overhead. The AM is defined to be zero outside the atmosphere. A simplified, and widely reported, relationship links AM to the solar elevation α: AM = 1/sinα. This equation does not hold for very low values of the solar elevation α. Conventionally, AM is given a value of 38 for α ≈ 0. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user