SOLAR-RADIATION RESOURCE ASSESSMENT BY MEANS OF SILICON CELLS

To provide an accurate solar resource assessment, radiometric stations measuring global, diffuse, and direct irradiance must be widespread. Nevertheless, the high capital costs of thermopile instruments, usuall y used in pyranometry, represent an important obstacle. Therefore, sil icon photovoltaic sensors have emerged as a more accessible alternativ e than standard thermopile sensors. However, their temperature and spe ctral responses must be taken into account in order to match silicon c ells and thermopile responses. Global and diffuse irradiance have been measured from early 1990 to the end of 1992 in Almeria, southeastern Spain. by means of thermopile and photovoltaic sensor. Polar axis shad owbands were employed to measure the diffuse irradiance. These 10-minu te coincident data sets, covering a complete range of atmospheric cond itions, have been used to develop a correction procedure for the silic on detector measurements. Before the correction procedure was applied severe discrepancies were found, especially for the diffuse irradiance measurements performed under clear skies. Results of the correction m ethod applied to an independent data set show a remarkable improvement . After correction, the comparison of silicon cell measurements with t hose obtained by means of thermopile pyranometers leads to a root mean square deviation of about 4% and 5% over the mean Value of global and diffuse horizontal irradiance, respectively.