In the European countries renewable and decentralised electric power generation is continuously gaining in importance. More than one half of the total worldwide installed capacity of wind power plants is located in Europe. Furthermore the electric power generation of small hydro power plants and biomass fired cogeneration plants increases steadily, not least encouraged by legislation. However, especially during off-peak load conditions, a high penetration by decentralised electric power generation can cause significant problems for a stable power system operation and establishes new responsibilities for system operators. A EU-Project has been initiated to investigate the development of renewable energy sources especially for the Western Balkan Countries (WBC), including an analysis of the impact on the grid. The effects of decentralised electric power generation on the grid of the WBC are analysed, aiming for the development of a general methodology to identify critical system configurations. The limits of the feed-in into the existing transmission and distribution systems of decentralised power generation units, not taking part in power system control services, are analysed for steady state conditions. Together with matching approaches of the other project partners, corresponding problems can be addressed already within the planning phase. (c) 2008 Elsevier Ltd. All rights reserved.