The first BIPV system of Turkey was installed on the facade and two towers of the Staff's Block of Education Faculty building of Mugla Sitki Kocman University in February 2008. The PV systems cover 405 m(2) (60 tilted surface and two vertical towers on east and west sides of the building) with single and triple junction amorphous (3j-aSi) photovoltaic modules. The total installed power of the BIPV system is 40.3 kWp. Total cumulative produced electricity of the BIPV system at the end of 2014 from the start up is exceeding 200,000 kW h. In this work, the shading effect on the performance of two PV systems based on 3j-aSi photovoltaic modules on the facade is analysed. There are 5 rows on the facade of the building and two identical strings' energy rating values are compared. One string has only row shading but the second string has smaller shading. In this comparison it is found that energetic performances so called energy rating (kW h/kWp) values of the arrays differ 16% for an annual average between 10% and 24% monthly intervals. In winter months the shading effect is caused by the tree is less than 1% in the electricity yield where there is no row shading in winter months. But in summer months (because of the height of the sun) the calculated energy yield difference is about 15%. In 21st of June between 9.00 and 13.00 it is calculated that the output between the inverters is 15% where there is no shading because of the tree all shading is from the upper rows. PV data is collected with a Sunlog data logger. Daily power and electricity production values and the shading effect on different seasons are also analysed. (C) 2015 Elsevier Ltd. All rights reserved.