Determining Angstrom Constants for Estimating Solar Radiation in Malawi

Affiliation(s)

Department of Mechanical Engineering, University of Malawi—The Polytechnic, Blantyre, Malawi.

Department of Civil Engineering, University of Malawi—The Polytechnic, Blantyre, Malawi.

Department of Mechanical Engineering, University of Malawi—The Polytechnic, Blantyre, Malawi.

Department of Civil Engineering, University of Malawi—The Polytechnic, Blantyre, Malawi.

ABSTRACT

This paper discusses a procedure that was adopted for the development of a linear regression model for estimating solar radiation in Malawi. By making use of sunshine-hours data recorded at six selected meteorological stations in the country, namely: Salima, Makoka, Karonga, Bolero, Chileka and Mzimba over the period 1991-1995, a set of Angstrom constants were obtained and averaged in order to develop the linear regression model. This model has potential for generating ground observation data of solar radiation at any given location in the country using sunshine hours as the only required input. The Gunn-Bellan Spherical Pyranometer and the Campbell Stokes Sunshine Recorder were respectively used in the measurement of incident radiation (I_{b}) in J·cm^{–2}/day (converted to MJ·m^{–2}·day^{–1}) and sunshine hours. An Angstrom model of monthly average Clearness Index with normalized sunshine duration was then developed for each of the six meteorological stations. The resulting linear regression model was applied in estimating monthly average daily solar radiation. Regression analysis between computed and measured radiation data was applied to assess the reliability of the generated Angstrom constants. The results generally show a high degree of agreement between the two variables, with correlation coefficients ranging from 0.63 to 0.90. Angstrom constants obtained at the six meteorological stations were thereafter averaged in order to develop a linear regression model for estimating solar radiation in Malawi. Solar radiation values obtained using this model were noted to be in good agreement with those developed for each of the six meteorological stations.

This paper discusses a procedure that was adopted for the development of a linear regression model for estimating solar radiation in Malawi. By making use of sunshine-hours data recorded at six selected meteorological stations in the country, namely: Salima, Makoka, Karonga, Bolero, Chileka and Mzimba over the period 1991-1995, a set of Angstrom constants were obtained and averaged in order to develop the linear regression model. This model has potential for generating ground observation data of solar radiation at any given location in the country using sunshine hours as the only required input. The Gunn-Bellan Spherical Pyranometer and the Campbell Stokes Sunshine Recorder were respectively used in the measurement of incident radiation (I

Cite this paper

G. Salima and G. M. S. Chavula, "Determining Angstrom Constants for Estimating Solar Radiation in Malawi,"*International Journal of Geosciences*, Vol. 3 No. 2, 2012, pp. 391-397. doi: 10.4236/ijg.2012.32043.

G. Salima and G. M. S. Chavula, "Determining Angstrom Constants for Estimating Solar Radiation in Malawi,"

References

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[2] Government of Malawi, “Malawi State of Environment and Outlook: Environment for Sustainable Economic Growth,” Malawi Government , 2010.

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[1] Government of Malawi, “Malawi Biomass Energy Strategy,” Department of Energy, Lilongwe, 2009.

[2] Government of Malawi, “Malawi State of Environment and Outlook: Environment for Sustainable Economic Growth,” Malawi Government , 2010.

[3] J. A. Duffie and W. A. Beckman, “Solar Engineering of Thermal Processes,” 2nd Edition, John Wiley, New York, 1994.

[4] A. Angstrom, “Solar and Terrestrial Radiation,” Quarterly Journal of the Royal Meteorological Society, Vol. 50, No. 210, 1924, pp. 121-125. doi: 10.1002/qj.49705021008

[5] A. K. Som, “Solar Utilization Potential in Malawi,” Malawi Journal of Science, Vol. 3, 1979, pp. 103-104.

[6] B. Zingano, “An Appraisal for Solar Water Heating in Malawi,” MSc. Thesis, University of Malawi, Zomba, 1986.

[7] B. Zingano, “A Discussion on Thermal Comfort with Reference to Bath Water Temperature to Deduce a Midpoint of the Thermal Comfort Zone,” Renewable Energy, Vol. 23, 2001, pp. 41-47.

[8] A. Madhlopa, “Evaluation of Piecewise Polynomial Models for Computation of Daily Diffuse Radiation in Malawi,” Proceedings of the 2001 ISES Solar World Congress, 2001, pp. 2183-2189.

[9] A. Madhlopa, “Solar Radiation Climate in Malawi,” Solar Energy, Science Direct, University of Malawi, Zomba, 2005.

[10] S. Griffin, “Spatial and Temporal Solar Radiation Distribution and Solar Energy Collection Potential in Malawi,” M.Sc. Dissertation, University of Zimbabwe, Harare, 2007.

[11] L. Diabate, Ph. Blanc and L. Wald, “Solar Climate in Africa,” Solar Energy, Vol. 76, No. 6, 2004, pp. 733-744. doi:10.1016/j.solener.2004.01.002