The performance of solar collector systems is optimized for the Beirut climate with respect to the following parameters: angle of tilt and orientation, plate emissivity and number of glass covers. The Beirut hourly ambient temperature, wind speed, wind direction and the monthly averaged hourly and daily global, beam and diffuse radiation are used in the calculation of the useful harnessed energy, collector's efficiency, storage-tank temperature and other relevant parameters. The optimal thermal performance of the solar collector in Beirut is obtained for a south-facing collector all the year with a slope angle equal to latitude +15° in winter and latitude -15° in the summer. The use of a selective surface of low emissivity in the collector gives a higher useful energy gain of about 25% in summer and 10% in winter as compared with a nonselective plate surface. The collector's daily efficiency, under optimal conditions, varies from 55 to 65% depending upon the month of the year.
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