P artial shadowing of photovoltaic arrays with different system configurations : literature review and field test results

Partial shadowing has been identified as a main cause for reducing energy yield of grid-connected photovoltaic systems. The impact of the applied system configuration on the energy yield of partially shadowed arrays has been widely discussed. Nevertheless, there is still much confusion especially regarding the optimal grade of modularity for such systems. A 5-kWp photovoltaic system was installed at K.U. Leuven. The system consists of three independent subsystems: central inverter, string inverter, and a number of AC modules. Throughout the year, parts of the photovoltaic array are shadowed by vegetation and other surrounding obstacles. The dimensions of shadowing obstacles were recorded and the expectable shadowing losses were estimated by applying different approaches. Based on the results of almost 2 years of analytical monitoring, the photovoltaic system is assessed with regard to shadowing losses and their dependence on the chosen system configuration. The results indicate that with obstacles of irregular shape being close to the photovoltaic array, simulation estimates the shadowing losses rather imprecise. At array positions mainly suffering from a reduction of the visible horizon by obstacles far away from the photovoltaic array, a simulation returns good results. Significant differences regarding shadow tolerance of different inverter types or overproportional losses with long module strings could not be confirmed for the system under examination. The negative impact of partial shadowing on the array performance should not be underestimated, but it affects modular systems as well as central inverter systems.  2003 Elsevier Ltd. All rights reserved. 1 . Introduction reductions in energy yield (Decker and Jahn, 1997; Erge et al., 1998). The Japanese field test programme that was In the industrialised countries, grid-connected photoinitiated in 1992 returned similar results (Kurokawa et al., voltaic (PV) systems are mainly installed on buildings. 1997b; Otani et al., 2001). Up to then, partial shadowing The integration of these systems into the built environment had mainly been considered a problem with regard to offers a large potential for cost reduction and can contribthermal destruction of solar cells due to hot spots. Now, ute to the overall value of urban architecture. A well overproportional losses due to partial shadowing of PV designed PV facade expresses the reconciliation of modern arrays became an issue. technology and environmental concern, and thus is well In the meantime, the impact of partial shadowing on the suited for application in contemporary urban design. energy yield of PV has been widely discussed. NevertheWide experience with PV on buildings became available less, there is still much confusion, especially regarding the in the early 1990s. In the German 1000-Roofs-PV-Prooptimal grade of modularity of the system configuration. gramme that was started in 1990, partial shadowing of PV arrays turned out to be one of the main reasons for 2 . Review and discussion of previous research *Corresponding author. Tel.: 132-16-321-020; fax: 132-162 .1. Partial shadowing of photovoltaic devices 321-985. E-mail address: [email protected] (A. Woyte). ISES member. Shadowing of a single cell in a series string of solar 0038-092X/03/$ – see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0038-092X(03)00155-5 218 A. Woyte et al. / Solar Energy 74 (2003) 217–233