The place beyond the lines - Efficient storage allocation in a spatially unbalanced power system with a high share of renewables

In electricity grids with high shares of solar and wind, storage technologies, such as electric batteries, are suitable to complement renewable generation. Renewable generation is unequally distributed both temporally and spatially. Storage can offset the temporal volatility of wind and photovoltaic (PV) by shifting generation or load if it they do not coincide temporally. In Germany, the power system is additionally affected by a spatial mismatch between load and renewable generation. While wind power generation is predominantly located in the North of Germany, demand is centred in the more densely populated West and South.  Due to insufficient transmission capacity, North-South transmission lines are frequently overloaded in situations with high wind generation. As a result, wind generation is curtailed while fossil fired generation is used to supply loads south of the transmission bottleneck, thus jeopardizing German efforts to increase renewable generation and reducing greenhouse gases. Installing storage capacities can address this spatial mismatch to achieve a more balanced transmission line utilization, thus increasing overall transmission grid utilization, decreasing curtailment and reducing the use of fossil-fuel combustion.  To do so, the allocation of storage within the electricity grid is critical. To investigate the relationship between storage, renewable generation, and the transmission grid, we employ a linear optimization model that allows to analyse optimal allocation of storage and generation technologies within Germany. Our model simulations use high resolution reanalysis meteorological data from the COSMO-REA6 data set developed by the Hans-Ertel-Centre for Weather Research, Climate Monitoring and Diagnostics, and a detailed depiction of electricity grid constraints of Germany. We find that an allocation of storage close to grid bottlenecks is optimal to facilitate wind generation replacing fossil fired generation, thus making efficient use of renewable generation. If grid bottlenecks are not accounted for in the storage allocation, storage cannot be used to relieve grid congestion. Consequently, we find an increase of up to 10% in the overall system operational costs and higher curtailment rates for wind and solar power compared to having storage installed at optimal locations.