Renewable energy support schemes implementation increases the significance of renewable energy power plants (REPPs) in studying power market characteristics. In this paper, an analytical approach is presented to investigate the impact of REPPs on transmission lines congestion. For this purpose, considering REPPs, social welfare maximization problem corresponding to the spot electricity market should be solved by the independent system operator (ISO). A closed-form expression of the Lagrange multiplier (LM) of each congested line is presented to analytically demonstrate the role of the power system structure and strategic behaviour of conventional generation companies (GenCos) on the network congestion. The structural part of LM expression is decomposed into four components to distinguish the impact of GenCos from the impact of REPPs. The GenCos’ strategic behaviour in the spot market bidding problem is simulated using well-known Q-Learning (QL) algorithm. The results confirm that REPPs deployment can remarkably affect both the structural and behavioural parts of the LM and emphasize the significance of the GenCos strategic behaviour on the occurrence of congestion. The results illustrate that since renewable energy support schemes may increase the possibility of congestion and GenCos’ strategic behaviour, it is essential to take power system characteristics into account in their design.

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