Retrospective Calculation of Irradiation Incident on Inclined Solar

Generators, Using Global Radiation Readings on the Horizontal Plane

Подпись: Examples: 1. The December reading in Kloten was H — 1.10kWh/m2 in lieu of H — 0.70kWh/m2. Hence, to calculate HG retrospectively for December, H — 1.1kWh/m2, HD — 0.60kWh/m2 and HB — 0.50kWh/m2 were used. 2. If, on the other hand, the December Kloten reading was only H — 0.50kWh/m2 in lieu of 0.70kWh/m2, the calculation would be performed using H — 0.50kWh/m2, HD — 0.42kWh/m2 and HB — 0.08 kWh/m2.

In any given year, mean monthly irradiation readings can deviate considerably from the long-term mean values indicated in this book, particularly during the winter. However, such discrepancies mainly relate to direct beam irradiation HB. When the H values that differ considerably from the mean values are converted to HG values on the solar generator plane using the R(b, g) factor (see Section 2.4), a major error arises because R factors are determined by the ratio of HB to HD. In such cases as well, using the three-component model (see above) in conjunction with the following simple method allows for a far realistic determination of the HG values that actually occur: 80% of the H value exceedances relative to mean monthly values in the tables is allocated to direct beam irradiation HB, while only 20% is allocated to diffuse irradiation HD. The H values that fall short of the tabular values are evenly divided between direct beam irradiation HB and diffuse irradiation HD. In cases where the H values fall far short of the tabular values, HB can of course never be negative, and in extreme cases HD — H would occur.

Updated: August 3, 2015 — 4:48 am