Available technical flexibility for balancing variable renewable energy sources: case study in Belgium

The world is facing a historical increase in energy demand and energy consumption. Renewable energy sources are considered as a solution to both environmental issues and increasing energy demand, but present high variability and low predictability.
Variability and uncertainty are familiar aspects of all power systems. However, the increase of the share of renewable sources leads to new needs in terms of flexible resources. These resources can be provided by four different means:
1. Dispachable power plants (i.e with ramp up and ramp down capabilities)
2. Storage systems, mainly in the form of pumping stations.
3. Grid interconnections between countries
4. Demand side management.
The present work focuses on the high voltage transmission grid, and assesses the amount of technical flexibility available to balance the fluctuations of Variable Renewable Energy (VRE) sources. The model is based on a dynamic programming unit commitment algorithm (i.e. accounting for each individual power plant on the grid) and focuses more particularly on the flexibility potential of power plants and of energy storage. The selected time resolution is one hour. Residual load curves are established on the basis of actual consumption for the year 2012 and on different scenarios of solar and wind penetration.
The method is applied to the case of Belgium, based on actual disaggregated power consumption curves throughout the year, and on the current power generation park. Due to the difficulty to assess the flexible resource available through interconnections, the Belgian grid is considered isolated. It should also be noted that this work does not address the voltage stability issue: it focuses on balancing issues only (i.e. time constants varying between minutes and days).
Simulation results show the VRE penetration potential is higher than usually considered. Bottlenecks therefore seems to be related to improper or inefficient market mechanisms, unable to take full profit of the technical flexible resource available.