Underground Gas Storage Linear Modeling: Application To The European Union

The European Union (EU) has a working capacity for storing natural gas in underground reservoirs of about 1100 TWh. The energy capacity stored, in form of natural gas, is one million times larger than the biggest electricity battery project in the world. Underground gas storage (UGS) facilities provide a large-scale, long-duration energy storage solution that helps to balance supply and demand, smooth gas and electricity prices, and improve the overall EU energy security.

Energy modelers constantly resort to simplified model formulations of UGS facilities, resembling electrochemical battery models. In this paper, we rise the importance of using adequate UGS formulations in energy system models. First, we introduce the main features of UGS. Then we develop an optimization problem for the estimation of the best set of linear equations for adjusting the non-convex operating capacity limits of UGS. We provide numerical results for various approximations and some countries in the EU with UGS. The results show that generic battery-like models are far from being representative of gas storage facilities. Errors can be as large as 90% of the total withdrawal capacity for most of the EU countries. However, a simple two-segment piecewise linear approximation has negligible or very low approximation errors.