Underground Gas Storage Linear Modeling: Application to the European Union

The European Union (EU) has a natural gas storing capacity of approximately 1100 TWh in underground reservoirs. This energy capacity, in the form of natural gas, is one million times larger than the world's largest electricity battery project. Underground gas storage (UGS) facilities offer large-scale, long-duration energy storage solutions that aid in balancing supply and demand, stabilizing gas and electricity prices, and enhancing the overall EU energy security. Energy modelers frequently rely on simplified model formulations for UGS facilities, which are akin to electrochemical battery models. In this paper, we emphasize the importance of employing appropriate UGS formulations in energy system models. First, we introduce the primary characteristics of UGS. Subsequently, we develop an optimization problem to estimate the optimal set of linear equations for adjusting the non-convex operating capacity limits of UGS. We present numerical results for various approximations and specific EU countries with UGS facilities. The findings reveal that generic battery-like models are insufficiently representative of gas storage facilities, with errors as large as 90% of the total withdrawal capacity. However, a simple two-segment piecewise linear approximation results in negligible or very low approximation errors.