Evaluation of solar radiation energy as a first-hand option in the preliminary evaluation of PV pumping systems

Daily average global solar radiation data of Addis Ababa, Ethiopia, station from year 1970-1994 was taken in the evaluation. The percentage ratio of the solar radiation energy below 3 kWh/m²/d based on the number of consecutive days, and the probability density and the cumulative frequency distribution of the solar radiation energy were calculated for each month. The evaluation shows that the cost of PV systems can be reduced by carefully evaluating the consecutive bad solar radiation days and the daily water balance. The consecutive negative water balance values are summed, and the lowest value from the series of values is the worst consecutive bad solar radiation days. This lowest value is exactly the amount of the extra water required to fulfil the water demand, and is equal to the size of the water tank. This is the optimum tank size that makes the PV system operating at full capacity