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Measurement of solar energy radiation at Nsukka and the determination of the regression coefficients

1988; Elsevier BV; Volume: 28; Issue: 4 Linguagem: Inglês

10.1016/0196-8904(88)90050-7

1879-2227

I.R.N. Awachie, C.E. Okeke,

Solar Thermal and Photovoltaic Systems

Solar radiation for Nsukka, latitude 6.8°N, longitude 7.35°E, located 488 m above sea level, was collected for 11 yr using a Gunn-Bellani instrument, and the data obtained were restandardized using an Eppley precision pyranometer. The sunshine data during this period were also obtained using a Campbell-Stokes sunshine recorder. It is observed that the insolation level for the month of November during the period of measurement is the highest, with an average of 17.50 MJ/m2. The level of insolation during this month varied sinusoidally with an amplitude of 3.84 MJ/m2. The clearness index, kT, is 0.53, and there is an indication that the atmosphere was persistently laden with dust. August has the least insolation level with an average of 11.86 MJ/m2 and a kT of 0.32. The atmosphere during this month was always covered with cloud. This work confirmed the assertion by Awachie and co-workers that dust and haze attenuate insolation less than cloud cover. The Nsukka weather is rated to be heavily overcast, and over 90% of the total solar radiation is diffuse, with an average kT value of 0.43. The average regression coefficients a and b for Nsukka are 0.21 and 0.51 respectively. These values do not agree with the general relations and values already quoted by some workers. The predicted insolation values for Nsukka using these coefficients in the Angstrom type of formula agree with the measured data with an error of 0.7%. This level of accuracy compares well with those obtained when the insolation values are predicted for each year using the values of a and b deduced for the respective year. Furthermore, there was an indication that the level of accuracy obtained using average values of a and b might increase if a longer period is considered. Thus, with reliable average values of a and b obtained over a reasonably long period, and knowledge of the bright sunshine hours, the measurement of solar radiation in a location, for design purposes, may not be necessary.