THE EFFECT OF TIME ERRORS ON THE ACCURACY OF SOLAR-RADIATION MEASUREMENTS

There is a need to focus on the accuracy of the time that is attached to solar radiation measurements. In this paper the effect of time errors on the calculation of the clearness index is investigated. An approximate expression for the error in clearness index due to time errors is derived. Using instantaneous solar radiation measurements from Townsville, Australia, the effect of time errors is illustrated with cumulative probability distribution curves. It is shown that even relatively small time errors (10 min) can substantially change the distribution curves. Time errors can be caused by drifts or inaccuracies of the data recording device's clock.