Direct Normal Data Research Articles

Texas Solar Radiation Database (TSRDB)

Solar radiation data have been acquired over approximately a five to six year period (1996–2002) at 15 sites in Texas (Texas Solar Radiation DataBase—TSRDB). These data are compared with comparable sites in the National Solar Radiation DataBase (NSRDB). Comparisons of the TSRDB and NSRDB data for eleven (11) coincident or nearby locations show reasonably good agreement between their global horizontal values. The monthly average differences range from −18 to +13%, and the annual average differences vary from −10 to +8%. The differences are ratioed to TSRDB values and positive differences represent larger TSRDB values. Across the sites, the TSRDB global horizontal annual data are about 3% lower than the NSRDB. However, there are considerable differences in the direct normal values, with TSRDB generally being higher. Monthly average differences range from −17 to +41%, and the average annual differences range from −10 to +20%. Across the sites, the TSRDB direct normal annual data are about 6% higher than the NSRDB. The greatest deviations for direct normal data are for coastal locations in the winter, with the three compared coastal locations exhibiting an average difference of about +29% for the combined months of December and January. Also, the TSRDB data for the Trans-Pecos region in west Texas exhibits significantly higher direct normal solar radiation throughout the year (22%) than does the NSRDB.

Ground- and satellite-based meteo-data for solar thermal power stations in Jordan

Meteorological Parameters play an important role in the design and operation as well as in the economic assessment of solar thermal power stations. Beside the usual climatic data, quantity and quality of the direct normal solar irradiation are of particular importance, because they considerably affect the electricity production cost. An extensive literature search for Jordan resulted in vast quantities of conventional meteorological data, such as global horizontal irradiation, air temperature, rainfall, humidity, sunshine duration and wind speed. All these data are highly valuable but of limited use for the design and operation of solar power stations, because: - No direct normal irradiation data are available (there are only some measured data available on the global and very few on the diffuse irradiation, which have been converted into direct normal data) - For quality analysis the time resolution is not sufficient. - The measured meteodata in general do not cover well potential sites for solar power stations. Therefore, within the frame of the PHOEBUS-project (30 MW-solar power station), a specific meteo measurement campaign was started in the middle of 1989 in the South of Jordan. The preliminary equipment installed in 1989 was completed in January 1990 by adding the main equipment (PC-data acquisition system, extra sensors, etc.) At the time one meteo-station (reference station) developed by Paul Scherrer Institute, PSI and two smaller, so-called satellite-meteostations developed by Deutsche Forschungsanstalt für Luft- und Raumfahrt, DLR are in operation. Parallel to these three ground-stations, an evaluation of other potential sites in Jordan based on METEOSAT-data was performed. First measurements of the direct-normal irradiation in Quwairah confirm the high values calculated for Jubeiha-Amman station of the Royal Scientific Society, RSS. For the periode July 89 to June 90 a yearly sum of 2668 kWh/m 2 for the direct-normal irradiation and 3501 kWh/m 2 for the global-normal irradiation was registered. The direct normal monthly sums correspond well to irradiation data measured at Barstow, California. For a reliable site evaluation it is important to know the spatial solar irradiation distribution. However, the few meteo stations do not sufficiently cover the territory of Jordan. One promising way to get information about the spatial distribution is the analysis of image data taken by earth remote sensing satellites. Based on 1985 data of the visible channel of the geostationary satellite METEOSAT, it was possible to estimate monthly values for the global-horizontal and the diffuse-horizontal irradiation with a longitude and latitude resolution of 0.5°, respectively (i.e. the spatial resolution for Jordan is about 45km × 55km). The model used has been developed by the Institute for Geophysics and Meteorology of the University of Cologne (Germany) in the framework of the European research program SUNSAT. These data have been combined with irradiation data of the meteo station at Jubeiha-Amman leading to the monthly and yearly spatial distribution of the direct normal component. The contour plots show that favourite sites can be found in the south of the country as well as south-east of the mountain Jabal al Arab whereas in the Wadi as Saharan the conditions are less promising.