- Email: [email protected]
Estimation of global solar radiation
Solar E~lerg~' VoI 26. p. 279. 198I
04-)38 092X/030279 01 $020010 Pergamon Press L i d
Printed in Great Britain.
LETTER TO THE EDITORS Estimation of global solar radiation
Dear Sirs, In the paper entitled "A comparison of some simple models used to predict solar irradiance on a horizontal surface" by Goldberg et al. [1] the authors compared the estimates of global solar radiation (Rr) with different approaches for 30, 40 and 50 ° latitudes. These results have given me an opportunity to think where I had gone wrong. The formula developed by Reddy [2] for the estimation of global solar radiation (Rt) has been tested for many Indian locations [3] and was found to give a best fit. Using this formula R, has also been estimated for 70 locations in India [4]. However, the daylength term (N) was not adequately accounted in the formula because the data used in developing and testing the model was pertaining to Indian stations only, where the change in N was not wide. This is clearly evident from the above paper where the estimates of Rt from Reddy [2] model are very close to observed data in the case of 30 ° latitude. However, when the term K is multiplied by N (i.e. K = K × N/12), the estimates of Rt for 30, 40 and 50 ° latitudes are very close to that of Barbaro et al. [5] and observed data; hence the modified equation can be written as:
The terms in this equation are the same as explained in Reddy and Rao [3]. ICRISAT Patancheru P.O. Andhra Pradish 502324 India
S.J. R~!DDY
REFERENCES
1. B. Goldberg, W. H. Klein and R. D. McCarmey, A comparison of some simple models used to predict solar irradiance on a horizontal surface. Solar Energy 23, 81-83 (1979). 2. S. J. Reddy, An emFtirical method for the estimation of total solar radiation: Solar Energy 13, 289-290 (1971). 3. S. J. Reddy and K.. R. Rao, An empirical method of estimation of evaporation from free surface of water. Indian d. Met. Geophys. 24, 137 152 (1973). 4. S. J. Reddy and K. R. Rao, Radiation and evaporation distribution over India. Natl. Geograph. J. India XXII, 54 63 (1976). 5. S. Barbaro, S. Coppolingo, C. Leona and E. Sinagra, Global solar radiation in Italy. Solar Energy 20, 431~435 (1978).
R, = (K x N/12) (1.0 + 0.8s) (1.0 - 0.2t)/O.l\h. [3]
279
04-)38 092X/030279 01 $020010 Pergamon Press L i d
Printed in Great Britain.
LETTER TO THE EDITORS Estimation of global solar radiation
Dear Sirs, In the paper entitled "A comparison of some simple models used to predict solar irradiance on a horizontal surface" by Goldberg et al. [1] the authors compared the estimates of global solar radiation (Rr) with different approaches for 30, 40 and 50 ° latitudes. These results have given me an opportunity to think where I had gone wrong. The formula developed by Reddy [2] for the estimation of global solar radiation (Rt) has been tested for many Indian locations [3] and was found to give a best fit. Using this formula R, has also been estimated for 70 locations in India [4]. However, the daylength term (N) was not adequately accounted in the formula because the data used in developing and testing the model was pertaining to Indian stations only, where the change in N was not wide. This is clearly evident from the above paper where the estimates of Rt from Reddy [2] model are very close to observed data in the case of 30 ° latitude. However, when the term K is multiplied by N (i.e. K = K × N/12), the estimates of Rt for 30, 40 and 50 ° latitudes are very close to that of Barbaro et al. [5] and observed data; hence the modified equation can be written as:
The terms in this equation are the same as explained in Reddy and Rao [3]. ICRISAT Patancheru P.O. Andhra Pradish 502324 India
S.J. R~!DDY
REFERENCES
1. B. Goldberg, W. H. Klein and R. D. McCarmey, A comparison of some simple models used to predict solar irradiance on a horizontal surface. Solar Energy 23, 81-83 (1979). 2. S. J. Reddy, An emFtirical method for the estimation of total solar radiation: Solar Energy 13, 289-290 (1971). 3. S. J. Reddy and K.. R. Rao, An empirical method of estimation of evaporation from free surface of water. Indian d. Met. Geophys. 24, 137 152 (1973). 4. S. J. Reddy and K. R. Rao, Radiation and evaporation distribution over India. Natl. Geograph. J. India XXII, 54 63 (1976). 5. S. Barbaro, S. Coppolingo, C. Leona and E. Sinagra, Global solar radiation in Italy. Solar Energy 20, 431~435 (1978).
R, = (K x N/12) (1.0 + 0.8s) (1.0 - 0.2t)/O.l\h. [3]
279