The roles of transmission and distribution networks in integrating variable renewable electricity generation

Sammanfattning: Emission reduction targets, together with other factors, such as security of supply, are driving the expansion of variable renewable energy sources for electricity generation, mainly solar and wind power. Trading across the transmission grid is an important measure to handle the increased variability and to balance supply with demand. Connecting generation capacity at the distribution level as distributed generation may confer benefits on the system, although it could also impose new requirements on distribution systems. This work applies a cost-minimising investment model together with several economic dispatch models to study how transmission and distribution grids can be used in future scenarios with high penetration levels of solar and wind power. We show that new congestion patterns arise in the European transmission system as a result of expansion of wind and solar power capacities, due to the low marginal costs of electricity at times of high output from these technologies. Furthermore, our results show that such instances of congestion may be difficult to handle with alternative variation management strategies, such as demand-side management (DSM), whereas for peak-load congestion, DSM may be an alternative to grid capacity expansion. We also find that rapid expansion of solar power generation within Europe could have a significant impact on marginal costs of electricity and could cause significant congestion during sunny seasons if its geographical distribution is uneven. However, we also show that distributed solar power can help to reduce losses if installations are optimised to maximise local consumption.