Influence of nebulosity on use of solar energy in Latvia
2008
Pelece, I., Latvia Univ. of Agriculture, Jelgava (Latvia). Faculty of Information Technologies. Dept. of Physics
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 often is large nebulosity. Therefore it is important to study influence of the nebulosity on possibility of use of solar energy. There are daily sums of the received hemi-spherical solar energy of two surfaces - fixed, at noon perpendicular to the sun rays, and tracking the sun - in dependence on the nebulosity studied in this article. Data on the nebulosity from State agency 'Latvian Environment, geology and meteorology agency' are obtained. Nebulosity has been evaluated in grades five times daily, after ever three hours. Measurements of the received hemi-spherical energy of both fixed and tracking the sun receivers after every 15 min were performed. These measurements have been performed in Riga at 2005 from April 1 till October 31 and at 2006 from March 1 till October 31. Daily sums of received hemispherical energy of both fixed and tracking the sun surfaces have been compared with each other and with theoretically calculated clear-day hemi-spherical energy sum for corresponding surface. There was in this period 53, or 12 %, clear days (with nebulosity 0 to 2 grades), 182 (40 %) partly sunny days (nebulosity 3 to 7 grades) and 222 (48 %) overcast (nebulosity greater than 7 grades) days. It has been found out that at medium nebulosity (3 to 7 grades) 60 to 85 % from theoretical energy sum can be received. At fully clear-sky conditions all 100 % from theoretical energy sum can be received, but at fully overcast only 20 %. At all season summary approximately 55 % from theoretical energy sum can be received by both tracking the sun and fixed receivers.
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