Before revision:  Furthermore, a spot market analysis based on the assumption that renewable energy sources (RES ) units have to feed-in with their assumed true marginal costs, i.e., operation and maintenance costs, is performed.
After revision:  Furthermore, a spot market analysis based on the assumption that renewable energy sources (RES ) units have to feed-in with their assumed true marginal costs, i.e., operation , maintenance and balancing costs, is performed.