The Relationship Between Incoming Solar Radiation And Daily Air Temperature

ABSTRACT

Solar radiation is the ultimate source of energy for the planet. To predict the values of temperature and instant solar radiation when equipment are not readily available from obtained equations, a good knowledge and understanding of the disposition and distribution of solar radiation is a requirement for modelling earth’s weather and climate change variables. A pyranometer (CM3) in series with a PHYWE amplifier and a voltmeter were experimentally set up and used to study the amount of solar radiation received at the Physics Department of the University of Ghana during the day. The temperature of the study area, as well as the Relative Humidity, was also recorded. Data was collected over a period of one month (from 2nd to 24th April, 2012). Days for which rain was recorded were ignored because rain could damage the pyranometer. The data obtained by the set-up were therefore used to compare with data obtained by a wireless weather station (Davis Vintage Pro). The data from these separate set-ups indicated that a perfect correlation existed between the solar radiation and temperature of the place. The data obtained by the experimental set-up was split into two separate sessions as morning and evening sessions. It was observed that the experimental set-up had a good correlation with that of the weather station on a particular day 11th April, 2012. The various Regression Coefficient (𝑅 2 ) values for morning session were respectively 𝑅 2 = 0.96 and 𝑅 2 = 0.95 with their respective equations as 𝐼𝑊 = 136.22𝑇𝑊 − 40623 and 𝐼𝑝 = 2.3198𝑇𝑃 − 678.14. The evening session also had good Regression Coefficient values of 𝑅 2 = 0.81 𝑎𝑛𝑑 𝑅2 = 0.97 with equations of 𝐼𝑃 = 2.1098𝑇𝑃 − 625 and 𝐼𝑊 = 161.31𝑇𝑊 − 48769. Similar analysis of the data from the separate set-ups gave a better correlation for that of the experimental set-up than that of the wireless station. The range of values of Regression Coefficient (𝑅 2 ) for the experimental set-up was between 0.82 − 0.99 for the morning and 0.45 − 0.98 for the evening while the wireless station had 0.10 − 0.95 for the morning and 0.18 − 0.98 for the evening sessions. Analysis performed on the data set for the entire period indicated that a strong correlation existed between the mean solar radiation (𝐼𝑚) and the mean temperature (𝑇𝑚). The equations obtained for both set-ups for the morning and evening sessions were found to be; 𝐼𝑚 = 2.417𝑇𝑚 − 713 with a Regression Coefficient (𝑅 2 ) value of 0.98 and 𝐼𝑚 = 3.265𝑇𝑚 − 974 with a Regression Coefficient (𝑅 2 ) value of 0.97.