Correlation between Solar Intensity and Relative Humidity and its Influence on the Performance of Solar Stills

Abstract

Solar stills are thermal devices that can be used in far distant areas or rural communities with freshwater deficits due to their ease of construction and relative cheap costs. Nonetheless, climatic factors can significantly affect performance of these devices and the technical feasibility for their usage. This research assesses solar intensity behavior, relative humidity, cloud cover and the existing correlations between these climatic factors in addition to how they influence a solar still production and performance. Tests were carried out in the city of Misantla, Veracruz State, Mexico; therefore, results cannot be extrapolated to a different latitude. It was found that there is a negative linear correlation between solar intensity and relative humidity of the monitoring site, depending on cloudiness. This negative correlation varies from moderate to high when cloud cover is between 46 and 55%. However, for less than 10% cloud cover, negative linear correlation was very high, with a correlation coefficient higher than -0.90. It was verified that performance of solar stills depends fundamentally on the average solar radiation, cloud cover and duration of the shadow at the test site.