Introduction Section 5.3 MONTHLY MEANS OF DAILY SOLAR RADIATION AND ITS VARIABILITY R.E. Schulze, M. Maharaj and R.D. Chapman The maps and statistics of solar radiation in this Section supersede the ones in the 1997 Atlas (Schulze, 1997) which were based on Clemence s (1992) equations. These daily estimates of solar radiation were derived using modifications for South African conditions of the Bristow and Campbell (1984) equation (cf. shaded box below and Section 5.2 of this Atlas). The daily values can be used as input in other equations such as the Penman-Monteith equation for potential crop evaporation (cf. Section 13.3). Determination of Monthly Means of Daily Solar Radiation and its Variability: A Summary The method of estimation of daily solar radiation loadings over South Africa and its verification have been presented in detail in Section 5.2. In summary the method is as follows: Based on the premise that clear sky solar radiation is determined essentially by extraterrestrial solar radiation modulated by an atmospheric extinction function, and dependent on high maximum temperatures associated with a high diurnal range in temperature, while cloudy/rainy conditions are associated with a low diurnal temperature range, the Bristow and Campbell (1984) equation was modified for South African conditions by regionally optimised expressions of clear sky depletion for atmospheric water vapour content, and by Determination of Monthly Means of Daily Solar Radiation and its Variability: A Summary (continued) month-by-month regionalised expressions for solar radiation extinction by cloudy/rainy conditions. Other than the optimised regional/monthly coefficients and the computation of extraterrestrial radiation, which is undertaken with trigonometrical geometry functions, the only other variables used were daily maximum and minimum temperatures. The latter were determined for the 50 year period 1950-1999 at each of 429 700 one arc minute (~ 1.7 x 1.7 km) raster points over South Africa by techniques outlined in Schulze and Maharaj (2004) and summarised in Section 2.1. Distribution Patterns over South Africa of Monthly Means of Daily Solar Radiation Over the course of a year, monthly means of daily solar radiation range from < 8 MJ/m 2 /day to > 28 MJ/m 2 /day. In mid-summer months highs in excess of 28 MJ/m 2 /day are found in the lower Orange River basin and the upper Karoo of the Northern Cape province, surrounded by a belt at 26-28 MJ/m 2 /day along the west coast, the remainder of the Northern Cape, the western half of the Free State, the north of Eastern Cape and the interior regions of the Western Cape - essentially in the rainless winter rainfall and semi-arid regions of South Africa. The lowest mid-summer monthly means of daily solar radiation are in the high-lying high rainfall areas of KwaZulu-Natal and Mpumalanga. A feature of mid-summer monthly means of daily solar radiation is that patterns display an east-west trend of low to high values. Transitional season months such as March and October display patterns of solar radiation largely parallel to the coast, at values of 12-22 MJ/km 2 /day. By midwinter the trend is much more latitudinal, with values of 14-16 MJ/m 2 /day in the north, 12-14 MJ/m 2 /day in the central areas of South Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 1
Africa and 8-10 in the winter rainfall region, but with < 8 MJ/m 2 /day in the extreme southwest of South Africa. Distribution Patterns over South Africa of Monthly Standard Deviations of Daily Solar Radiation Mid-summer month patterns of standard deviation are lowest (< 2 MJ/m 2 /day) in the winter rainfall region and the semi-arid west coast, as would be expected as a result of persistently clear sky days there in summer. Highest standard deviations in mid-summer months are in the relatively high rainfall coastal hinterland areas of the Eastern Cape and KwaZulu-Natal. The mid-winter month with the lowest standard deviation of daily solar radiation is June, with both the semi-arid west coast and sub-humid east coast in its non-rainy season with daily loadings varying by < 1.5 MJ/m 2 /day. The central parts of South Africa have standard deviations in excess of 2 MJ/m 2 /day in mid-winter months. References (In the sequence in which they appear in this Section, with the full references given in Section 22) 1. Schulze, R.E. (1997) 2. Bristow, K. L. and Campbell, G.S. (1984) 3. Schulze, R.E. and Maharaj, M. (2004) Citing from this Section of the Atlas When making reference to this Section of the Atlas, please cite as follows: Schulze, R.E. 2007. Monthly Means of Daily Solar Radiation and its Variability. In: Schulze, R.E. (Ed). 2007. South African Atlas of Climatology and Agrohydrology. Water Research Commission, Pretoria, RSA, WRC Report 1489/1/06, Section 5.3. Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 2
Monthly Means of Daily Solar Radiation (MJ/m 2 /day), January Limpopo 22.6 7 25.8 16.3 21.4 22.6 24.1 Mpumalanga 22.3 6 25.7 17.4 21.4 22.2 23.3 North West 25.0 6 27.6 21.8 23.8 24.6 26.5 Northern Cape 27.7 4 30.5 20.0 26.7 27.6 28.8 Gauteng 23.0 3 25.0 19.8 22.4 23.0 23.6 Free State 25.7 4 28.1 21.6 24.6 25.9 26.7 KwaZulu-Natal 21.6 10 27.0 13.7 19.9 21.6 23.5 Eastern Cape 24.4 11 29.0 13.4 22.1 24.8 26.8 Western Cape 25.7 9 30.6 10.4 24.3 26.2 27.4 Swaziland 21.3 5 23.9 18.2 20.4 21.5 22.1 Lesotho 25.0 3 27.0 21.7 24.3 25.1 25.7 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), April Limpopo 17.7 5 19.5 13.0 17.0 17.9 18.5 Mpumalanga 17.0 5 19.1 13.4 16.5 17.1 17.7 North West 17.8 4 19.3 15.6 17.1 17.8 18.5 Northern Cape 16.7 7 19.8 12.3 15.9 16.8 17.5 Gauteng 16.9 5 18.7 13.0 16.3 17.0 17.7 Free State 17.1 4 19.2 14.3 16.5 17.2 17.6 KwaZulu-Natal 16.0 10 19.5 10.5 14.5 16.1 17.4 Eastern Cape 15.3 9 18.0 9.2 14.3 15.5 16.5 Western Cape 13.8 9 16.8 4.6 12.9 13.9 14.9 Swaziland 16.3 5 17.8 13.9 15.6 16.4 17.1 Lesotho 16.9 4 18.8 14.5 16.4 16.9 17.4 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), February Limpopo 21.4 6 24.5 15.6 20.4 21.7 22.6 Mpumalanga 21.1 6 24.3 16.6 20.3 21.2 22.0 North West 22.6 5 25.3 19.9 21.7 22.5 23.6 Northern Cape 24.7 5 28.1 17.4 23.7 24.9 25.8 Gauteng 21.5 4 24.0 18.2 20.8 21.4 22.2 Free State 23.0 3 25.3 18.9 22.5 23.1 23.6 KwaZulu-Natal 20.3 10 25.8 13.1 18.8 20.4 22.0 Eastern Cape 22.0 10 25.8 12.1 20.5 22.4 23.9 Western Cape 23.0 10 27.5 7.4 21.7 23.5 24.6 Swaziland 20.4 4 22.4 17.5 19.6 20.4 21.1 Lesotho 22.9 3 24.8 19.2 22.5 22.9 23.3 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), May Limpopo 16.0 5 17.7 11.6 15.3 16.1 16.6 Mpumalanga 15.1 5 16.8 11.5 14.6 15.0 15.7 North West 15.6 4 16.9 14.0 15.0 15.6 16.1 Northern Cape 13.5 11 17.0 8.8 12.4 13.6 14.7 Gauteng 15.1 5 16.4 11.6 14.5 15.2 15.8 Free State 14.5 5 16.0 11.5 13.8 14.7 15.1 KwaZulu-Natal 13.7 8 16.0 10.1 12.7 13.9 14.8 Eastern Cape 12.4 9 14.7 7.8 11.5 12.6 13.3 Western Cape 10.5 10 12.9 6.3 9.6 10.5 11.5 Swaziland 14.5 4 15.7 12.4 13.9 14.6 15.1 Lesotho 13.8 3 15.0 12.3 13.4 13.8 14.2 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), March Limpopo 20.4 6 23.1 14.6 19.5 20.7 21.4 Mpumalanga 19.7 5 22.8 15.8 19.1 19.8 20.5 North West 20.7 4 22.3 18.4 19.9 20.8 21.5 Northern Cape 21.2 5 24.2 15.4 20.5 21.3 22.1 Gauteng 19.8 4 21.8 16.3 19.1 19.8 20.6 Free State 20.5 3 22.9 17.4 20.1 20.6 21.0 KwaZulu-Natal 18.8 10 23.0 11.7 17.2 18.9 20.4 Eastern Cape 19.0 9 21.9 10.9 17.8 19.2 20.3 Western Cape 18.4 10 22.8 5.8 17.1 18.8 19.8 Swaziland 19.0 5 20.9 15.8 18.2 19.0 19.8 Lesotho 20.6 3 22.4 17.6 20.3 20.7 21.1 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), June Limpopo 16.7 2 17.4 15.7 16.4 16.6 17.0 Mpumalanga 14.8 8 16.6 12.5 13.6 14.7 16.2 North West 14.4 6 16.4 12.8 13.6 14.1 15.0 Northern Cape 12.0 12 15.3 7.8 10.8 12.2 13.1 Gauteng 14.4 6 16.2 11.5 13.8 14.4 15.2 Free State 13.0 5 14.4 10.7 12.3 13.2 13.6 KwaZulu-Natal 12.6 7 14.2 9.6 11.8 12.6 13.4 Eastern Cape 10.9 9 13.0 6.7 10.2 11.1 11.7 Western Cape 9.0 12 11.6 5.9 8.1 8.8 10.2 Swaziland 13.6 5 15.6 11.6 13.0 13.5 14.1 Lesotho 12.3 3 13.1 11.2 12.0 12.4 12.7 Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 3
Monthly Means of Daily Solar Radiation (MJ/m 2 /day), July Limpopo 14.5 5 16.4 10.6 13.8 14.6 15.1 Mpumalanga 13.9 4 15.4 10.6 13.6 14.0 14.4 North West 14.4 4 15.6 12.8 13.9 14.4 14.8 Northern Cape 12.4 12 15.7 8.2 11.1 12.5 13.5 Gauteng 14.0 5 15.2 11.5 13.5 14.2 14.6 Free State 13.4 5 14.7 11.0 12.7 13.6 14.0 KwaZulu-Natal 13.0 8 14.9 9.6 12.1 13.2 14.0 Eastern Cape 11.6 8 13.8 6.5 10.8 11.8 12.3 Western Cape 9.7 10 12.1 6.4 8.8 9.7 10.6 Swaziland 13.9 4 15.1 11.8 13.4 14.0 14.4 Lesotho 13.0 3 13.9 11.7 12.6 13.0 13.4 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), October Limpopo 19.3 7 22.4 15.4 18.2 19.3 20.4 Mpumalanga 19.1 7 22.5 14.4 18.0 19.2 20.3 North West 21.8 5 24.4 19.0 20.8 21.6 23.0 Northern Cape 22.3 5 24.9 15.4 21.6 22.4 23.0 Gauteng 20.0 3 21.8 16.8 19.5 20.1 20.6 Free State 21.7 4 23.7 17.1 21.1 21.7 22.5 KwaZulu-Natal 17.8 11 22.9 10.9 16.0 17.8 19.7 Eastern Cape 19.1 10 22.7 10.8 17.9 19.5 20.5 Western Cape 19.6 8 23.9 8.1 18.8 19.8 20.8 Swaziland 18.0 4 19.7 15.9 17.4 18.1 18.7 Lesotho 20.7 3 22.1 17.3 20.2 20.7 21.2 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), August Limpopo 15.7 5 17.4 12.6 15.0 15.8 16.2 Mpumalanga 15.7 6 17.8 12.4 14.9 15.7 16.5 North West 16.9 4 18.4 14.7 16.1 16.9 17.5 Northern Cape 15.2 10 18.6 10.4 14.0 15.4 16.4 Gauteng 16.2 4 17.6 13.4 15.6 16.2 16.8 Free State 16.1 5 17.5 12.9 15.4 16.3 16.7 KwaZulu-Natal 14.5 9 17.0 10.1 13.4 14.7 15.7 Eastern Cape 13.6 8 16.0 7.7 12.9 13.8 14.5 Western Cape 12.1 9 14.9 7.5 11.1 12.1 13.1 Swaziland 15.2 4 16.5 13.4 14.7 15.3 15.8 Lesotho 15.1 4 16.3 13.2 14.6 15.1 15.6 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), November Limpopo 21.4 5 24.2 17.1 20.5 21.4 22.4 Mpumalanga 21.0 6 24.1 16.5 20.2 21.0 22.2 North West 24.5 5 26.6 20.9 23.2 24.5 25.9 Northern Cape 26.1 4 28.2 18.5 25.4 26.3 27.0 Gauteng 22.0 3 24.0 19.4 21.5 22.1 22.4 Free State 24.6 5 27.3 19.7 23.7 24.7 25.8 KwaZulu-Natal 19.7 11 25.8 12.3 17.8 19.5 21.8 Eastern Cape 22.2 11 26.6 12.2 20.1 22.7 24.4 Western Cape 23.5 9 28.4 10.0 22.3 24.0 25.1 Swaziland 19.4 4 21.2 17.0 18.5 19.5 20.1 Lesotho 23.1 3 24.9 19.7 22.5 23.2 23.7 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), September Limpopo 18.5 6 20.8 14.6 17.5 18.5 19.5 Mpumalanga 18.3 6 20.6 14.1 17.5 18.3 19.4 North West 19.9 3 21.5 17.7 19.3 19.9 20.5 Northern Cape 19.0 7 21.9 13.8 18.2 19.1 19.8 Gauteng 19.0 3 20.3 16.4 18.4 19.1 19.6 Free State 19.5 4 20.9 15.8 19.0 19.6 20.1 KwaZulu-Natal 16.6 10 20.2 10.7 15.1 16.7 18.3 Eastern Cape 16.8 8 19.5 10.1 15.9 17.0 18.0 Western Cape 15.9 8 18.9 9.1 14.8 16.0 16.9 Swaziland 17.2 4 18.6 15.5 16.7 17.3 17.8 Lesotho 18.3 3 19.8 16.0 17.8 18.3 18.9 Monthly Means of Daily Solar Radiation (MJ/m 2 /day), December Limpopo 22.5 5 24.7 17.9 21.5 22.5 23.5 Mpumalanga 23.3 8 27.7 18.6 22.0 23.1 25.1 North West 25.5 6 28.2 21.8 24.1 25.5 27.2 Northern Cape 28.1 4 30.7 19.0 27.4 28.3 29.0 Gauteng 22.8 3 24.9 20.1 22.2 22.8 23.4 Free State 26.9 4 29.8 22.5 25.9 27.2 27.8 KwaZulu-Natal 25.3 8 30.3 16.8 23.6 25.4 27.2 Eastern Cape 27.1 8 30.3 16.2 25.6 27.5 28.9 Western Cape 26.1 9 30.7 9.5 24.8 26.6 27.7 Swaziland 24.8 4 26.7 21.6 24.0 24.8 25.5 Lesotho 28.6 2 30.2 24.7 28.1 28.7 29.1 Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 4
Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 5
Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 6
Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), January Limpopo 4.9 12 6.9 3.8 4.3 4.9 5.3 Mpumalanga 4.8 9 6.4 3.4 4.5 4.8 5.1 North West 4.9 12 6.0 3.3 4.4 5.1 5.4 Northern Cape 3.2 30 6.3 1.0 2.4 3.3 4.1 Gauteng 4.8 7 5.8 4.0 4.5 4.8 5.1 Free State 4.7 11 5.8 3.1 4.2 4.8 5.2 KwaZulu-Natal 4.6 13 6.5 2.8 4.2 4.6 5.0 Eastern Cape 4.2 20 7.1 1.9 3.4 4.2 5.0 Western Cape 2.9 41 7.9 1.0 1.9 2.5 3.9 Swaziland 4.3 9 5.6 3.5 4.0 4.3 4.6 Lesotho 3.7 10 4.8 2.8 3.4 3.6 3.9 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), April Limpopo 3.3 13 4.9 2.4 2.9 3.2 3.6 Mpumalanga 3.3 10 4.4 2.5 3.0 3.3 3.6 North West 3.2 11 4.0 2.3 2.9 3.2 3.5 Northern Cape 2.9 18 4.3 1.2 2.5 3.1 3.3 Gauteng 3.3 7 4.0 2.7 3.1 3.4 3.5 Free State 3.3 7 3.9 1.9 3.1 3.3 3.5 KwaZulu-Natal 3.2 13 4.5 1.6 2.9 3.2 3.5 Eastern Cape 3.1 19 4.7 1.3 2.7 3.2 3.6 Western Cape 2.4 39 4.8 1.3 1.5 1.9 3.6 Swaziland 3.2 13 4.5 2.5 2.8 3.1 3.6 Lesotho 3.0 16 4.7 1.9 2.6 2.9 3.3 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), February Limpopo 4.4 8 5.9 3.5 4.1 4.3 4.6 Mpumalanga 4.6 9 5.7 3.3 4.2 4.6 4.9 North West 5.1 10 6.1 3.8 4.6 5.1 5.5 Northern Cape 3.7 26 6.6 1.2 3.0 3.8 4.6 Gauteng 4.8 7 5.7 3.7 4.5 4.8 5.0 Free State 4.9 9 5.7 2.8 4.7 5.0 5.2 KwaZulu-Natal 4.2 12 5.9 2.3 3.9 4.2 4.6 Eastern Cape 4.4 17 6.9 2.1 3.8 4.4 5.0 Western Cape 3.4 37 7.4 1.3 2.2 3.0 4.6 Swaziland 3.9 10 5.1 3.3 3.6 3.8 4.3 Lesotho 3.6 12 5.0 2.6 3.3 3.6 4.0 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), May Limpopo 2.3 20 3.9 1.5 1.9 2.2 2.6 Mpumalanga 2.2 14 3.7 1.5 2.0 2.2 2.4 North West 2.2 14 2.9 1.5 1.9 2.2 2.4 Northern Cape 2.2 18 3.2 1.0 1.8 2.2 2.5 Gauteng 2.1 12 2.7 1.7 1.9 2.1 2.4 Free State 2.2 12 3.0 1.1 2.0 2.2 2.4 KwaZulu-Natal 1.9 14 2.8 1.0 1.7 1.9 2.1 Eastern Cape 2.0 20 3.1 1.0 1.7 2.0 2.3 Western Cape 1.9 33 3.6 1.0 1.3 1.6 2.7 Swaziland 1.9 12 2.8 1.5 1.7 1.9 2.1 Lesotho 1.9 14 2.7 1.3 1.6 1.8 2.1 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), March Limpopo 3.9 11 5.6 2.9 3.6 3.8 4.2 Mpumalanga 4.1 8 5.2 2.9 3.8 4.1 4.3 North West 4.3 9 5.2 3.3 4.1 4.4 4.6 Northern Cape 3.4 22 5.9 1.4 2.9 3.4 4.1 Gauteng 4.2 6 5.0 3.3 4.0 4.2 4.4 Free State 4.3 8 4.8 2.5 4.1 4.4 4.5 KwaZulu-Natal 3.9 12 5.5 2.4 3.6 3.9 4.2 Eastern Cape 4.1 16 5.9 2.0 3.6 4.1 4.6 Western Cape 3.1 34 6.4 1.6 2.1 2.7 4.3 Swaziland 3.7 10 4.9 3.0 3.4 3.6 4.0 Lesotho 3.5 12 5.1 2.4 3.1 3.4 3.8 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), June Limpopo 0.6 46 2.4 0.3 0.4 0.5 0.7 Mpumalanga 1.0 39 1.9 0.3 0.6 1.0 1.4 North West 1.2 33 1.9 0.3 0.9 1.3 1.5 Northern Cape 1.5 21 2.6 0.7 1.3 1.5 1.7 Gauteng 1.0 32 1.7 0.3 0.7 1.0 1.2 Free State 1.5 15 2.2 0.6 1.3 1.4 1.6 KwaZulu-Natal 1.3 20 2.1 0.5 1.1 1.3 1.5 Eastern Cape 1.5 17 2.5 0.8 1.2 1.5 1.7 Western Cape 1.4 23 2.6 0.8 1.1 1.4 1.8 Swaziland 1.2 20 2.0 0.4 1.1 1.2 1.5 Lesotho 1.3 14 1.9 0.8 1.1 1.3 1.5 Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 7
Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), July Limpopo 1.9 25 3.3 1.0 1.4 1.8 2.2 Mpumalanga 1.8 18 2.8 1.1 1.5 1.9 2.1 North West 1.4 14 2.0 0.9 1.2 1.4 1.5 Northern Cape 1.6 19 2.7 0.9 1.4 1.6 1.8 Gauteng 1.4 13 2.0 1.1 1.3 1.4 1.6 Free State 1.6 11 2.4 0.9 1.4 1.6 1.8 KwaZulu-Natal 1.7 18 2.6 0.8 1.5 1.7 2.0 Eastern Cape 1.6 14 2.9 1.0 1.5 1.6 1.8 Western Cape 1.6 19 2.8 1.0 1.4 1.6 1.9 Swaziland 1.7 17 2.7 1.2 1.4 1.7 2.0 Lesotho 1.5 12 2.2 1.1 1.4 1.6 1.7 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), October Limpopo 4.3 19 6.5 2.8 3.5 4.3 5.1 Mpumalanga 4.6 12 6.5 2.8 4.2 4.5 4.9 North West 4.1 11 5.1 2.9 3.7 4.1 4.5 Northern Cape 3.5 17 6.3 1.5 3.0 3.7 4.0 Gauteng 4.3 8 5.1 3.2 4.0 4.3 4.6 Free State 4.1 10 5.1 2.8 3.7 4.1 4.5 KwaZulu-Natal 4.4 13 6.0 2.7 4.0 4.5 4.8 Eastern Cape 4.0 19 6.3 1.9 3.4 4.1 4.6 Western Cape 3.2 38 6.8 1.7 2.1 2.7 4.7 Swaziland 4.3 9 5.3 3.7 4.0 4.2 4.6 Lesotho 3.1 11 4.4 2.2 2.8 3.1 3.4 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), August Limpopo 1.9 22 3.2 1.2 1.5 1.9 2.3 Mpumalanga 2.2 14 3.1 1.3 1.9 2.2 2.5 North West 1.9 14 2.6 1.3 1.6 1.9 2.1 Northern Cape 2.3 17 3.7 1.3 2.0 2.3 2.6 Gauteng 1.9 10 2.6 1.5 1.7 1.9 2.0 Free State 2.3 11 3.1 1.7 2.1 2.2 2.5 KwaZulu-Natal 2.5 12 3.5 1.7 2.3 2.5 2.7 Eastern Cape 2.4 13 3.4 1.5 2.1 2.4 2.7 Western Cape 2.3 23 3.8 1.5 1.8 2.1 2.8 Swaziland 2.4 12 3.2 1.9 2.2 2.3 2.7 Lesotho 2.1 11 2.8 1.7 1.9 2.0 2.3 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), November Limpopo 4.7 13 6.7 3.5 4.1 4.6 5.3 Mpumalanga 4.8 10 6.7 3.5 4.4 4.7 5.1 North West 4.2 11 5.2 2.8 3.9 4.2 4.6 Northern Cape 3.2 16 6.5 1.4 2.8 3.2 3.6 Gauteng 4.6 7 5.5 3.8 4.3 4.7 4.9 Free State 4.1 12 5.3 2.7 3.7 4.1 4.6 KwaZulu-Natal 4.5 13 6.2 2.6 4.1 4.5 4.9 Eastern Cape 4.2 17 6.7 2.2 3.5 4.1 4.8 Western Cape 3.5 30 7.6 1.8 2.6 3.2 4.6 Swaziland 4.4 8 5.5 3.7 4.1 4.3 4.7 Lesotho 3.2 11 4.7 2.4 3.0 3.2 3.6 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), September Limpopo 3.6 19 5.6 2.2 2.9 3.6 4.2 Mpumalanga 3.5 16 5.5 2.2 3.0 3.5 3.9 North West 2.8 12 3.6 2.0 2.5 2.7 3.1 Northern Cape 2.6 13 3.9 1.5 2.4 2.6 2.9 Gauteng 2.9 9 3.8 2.4 2.7 3.0 3.2 Free State 2.8 11 3.9 2.2 2.5 2.8 3.0 KwaZulu-Natal 3.4 13 4.7 2.2 3.1 3.4 3.8 Eastern Cape 3.0 15 4.1 1.7 2.7 3.1 3.5 Western Cape 2.6 24 5.0 1.7 2.0 2.4 3.3 Swaziland 3.4 10 4.5 2.8 3.1 3.3 3.7 Lesotho 2.6 12 3.5 1.9 2.3 2.5 2.8 Standard Deviation of Daily Solar Radiation (MJ/m 2 /day), December Limpopo 4.1 13 6.2 3.1 3.7 4.0 4.6 Mpumalanga 4.4 11 5.8 2.9 4.0 4.4 4.8 North West 4.5 13 5.9 3.3 4.0 4.5 5.0 Northern Cape 3.4 22 6.9 1.1 2.8 3.5 4.0 Gauteng 4.7 9 5.7 3.4 4.3 4.7 5.1 Free State 4.3 12 5.4 2.0 4.0 4.3 4.7 KwaZulu-Natal 4.5 17 7.0 1.6 4.0 4.4 5.1 Eastern Cape 4.0 24 7.7 1.8 3.1 4.0 4.8 Western Cape 3.3 38 8.2 1.4 2.2 2.9 4.4 Swaziland 4.3 10 5.6 3.4 4.0 4.2 4.7 Lesotho 2.9 17 4.8 1.8 2.5 2.8 3.2 Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 8
Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 9
Section 5.3 Monthly Means of Daily Solar Radiation and its Variability 10