Performance and degradation analyses of two different pv modules in central anatolia

Ankara (latitude: around 40°N) is in Central Anatolia and the climate is dry continental. Due to the rapid transition to renewable energy policies of Turkey it is now a must to complete truthful feasibility analyses for solar power systems countrywide. Long term performance and degradation analyses have been carried out by the authors for three different arrays and many research results appearing in the literature are summarized. Present research analyzes the outdoor testing results of two PV modules monthly data. One of the modules has multi crystalline silicon (Poly-Si) cells and the other is thin film silicon (amorphous Si / microcrystalline Si tandem structure - a-Si/μc-Si) cells. The results showed that in five years the average yearly efficiency decreases from 14% to 11% for Poly-Si (14.72% is the nameplate Standard Test Condition (STC) efficiency) and from 8% to 6% for thin film modules (9.15% is STC efficiency). Our calculations are based on measured solar global-horizontal irradiance from which we calculated plane-of-array irradiation using an anisotropic sky model. We present the details of these analyses and degradation rates for the two types of modules to be used in long term feasibility analyses.