Impacts of large scale photovoltaic systems on the low voltage network

To investigate the reaction of the low voltage network as well as the associated medium high voltage network under the influence of roof integrated photovoltaic plants, a concrete low voltage network and 30 kV network of a village with some 1000 nodes were imaged. The simulation was required to model load curves for each household, as well as for commercial enterprises in the village. The time resolution for the ultimate load curve for the model is 5 min. The next step assumed photovoltaic plants on the roofs of buildings, taking building size into account. The plant capacities were varied in four scenarios. For the run of the irradiation we used a summer day with maximal irradiation. With the assistance of a load flow program we calculated the voltages of every nodes in the low and medium high voltage network, the observance of the permissible currents and the balance of losses. In scenarios using a major part of the suitable roof areas voltage excess the limits in some branches of the low voltage network (U-nominal+10%). Voltages were always within the tolerance range in the medium high voltage network. Improvements can be realised by strengthening the lines, optimal adjustment of low voltage transformers and regulation of the medium voltage transformers based on active power. (C) 1997 Elsevier Science Ltd.