Forecast of energy received by solar collectors
2008
Pelece, I., Latvia Univ. of Agriculture, Jelgava (Latvia) | Iljins, U., Latvia Univ. of Agriculture, Jelgava (Latvia) | Ziemelis, I., Latvia Univ. of Agriculture, Jelgava (Latvia)
Align with others environment – friendly renewable energy sources the solar energy is widely used in the world. Also in Latvia solar collectors are used. However, in Latvia because of its geographical and climatic conditions are some features in comparison with the traditional solar energy using countries. One of them is rather large cloudiness. Effort to forecast the energy sum, received by several solar collectors, taking into account the cloudiness, is done in this article. The energy sum, received by the solar collector, consists of the direct radiation and diffused one. The clear sky direct radiation can be calculated from the position of the sun at every moment and of the receiving surface. Then the received energy depends only on the lucidity of the atmosphere, which can be considered as constant. For calculations of the direct radiation received at real conditions the influence of the cloudiness has to be taken into account. The diffused radiation depends on the direct one and on the cloudiness, and it increases with increasing of the cloudiness (besides very thick, dark clouds). In order to verify such calculations calculated values are compared with measured for flat receiving surface tracking the sun (always perpendicular). It has been established that the difference between calculated and measured values of seasonal energy sum is approximately 4%. Measurements of received energy were carried out in Riga at 2005 from April till October and at 2006 from March till October. Data on cloudiness in this period are taken from Latvia Agency of Environment Meteorology and Geology. For the forecasting data on cloudiness from 2003 to 2007 are used.
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