Tilt angles for optimizing energy reception by fixed and periodically adjusted solar-irradiated surfaces in Nigeria

Abstract

The insolation received on a solar collecting surface is maximized by ensuring the beam component of solar radiation which is normal to the surface. In this study, optimum tilt angles for fixed and periodically adjusted south-facing solar collecting surfaces have been estimated for different periods of the year, for locations in Nigeria (Lat. 4–14 $${^{\circ }}$$ N and Lon. 2–15 $${^{\circ }}$$ E). The spatial domain of interest was discretized into a grid of 1 $${^{\circ }}$$ latitude by 1 $${^{\circ }}$$ longitude cells; and for each cell, monthly average data of daily horizontal irradiation were obtained from the web-based NASA-SSE meteorological data services. These were used as inputs to an anisotropic tilt radiation model to search for the collector tilts that maximized incident radiation. A fixed collector tilt scheme and five periodic tilt angle adjustment schemes: adjustments of tilt angles (i) twice, (ii) thrice, (iii) four times, (iv) six times, and (v) twelve times in the year, were considered. Negative optimum tilt angles were obtained during the rainy season (April–August), indicating that for those periods, north-facing collector orientations will result in higher solar energy collection. Adjusting solar collectors twelve times per year, yielded the most annual irradiation, which was 3.4–6.7% more than the annual irradiation received by collectors with optimum angles fixed all year round. However, of the five periodic adjustment schemes, adjusting three times in the year is recommended as ideal, based on a comparison between the gains in the obtainable solar energy and the complexity/inconvenience associated with implementing the scheme.