Evaluation of rotating shadowband radiometer measurements in desert conditions

Ground meas urement of s olar radiation is the mos t accurate way to evaluate and quantify the available s olar res ources at any specific s ite. This is particularly important for s olar energy projects. The acquis ition of high quality s olar radiation data requires the ins tallation of a s olar radiation monitoring s tation with thermoelectric type of s ensors s uch as pyranometers and pyrheliometer, mounted on a s un-tracker s ystem. This type of station allows the collection of reliable s olar radiation data, but it is cos tly and requires continuous maintenance. An alternative method for on-site measurements of solar radiation is the use of a rotating s hadow band irradiometer (RSI) bas ed on a photodiode s ensor. The s ystem is les s expensive and requires les s frequent maintenance; however, the collected data are les s accurate. A s tudy of the data measured by an RSI operating in desert conditions is pres ented here; This RSI has been calibrated and corrections have been applied by the manufacturer, but not for the local conditions at the s ite of this s tudy. The res ults s how the es timated uncertainties of s olar components derived by RSI, when compared to the ones acquired by the thermopilebas ed s ensors; the relative root mean s quare errors for GHI are les s than 3 % and they are larger for the diffuse and direct components. The largest deviations are found for the direct component, which is computed by the RSI from the global and diffuse components, and not measured.