Study of a 100% renewable electricity system for Western Europe : an EROI-based analysis

Renewable energies are going to become the dominant means of electricity generation during and after the energy transition. In Europe, wind and solar energies are the main sources to be exploited. Their production being inherently intermittent, more frequent unbalances are expected on the grid. In order to balance it, the flexibility of the remaining power plants, imports and exports, the storage and the curtailment of renewable energies will all have an important role. This study analyses the case of Western Europe and determines the types, the locations and the sizes of the storage needed, taking into account the power exchange capacities between countries, the curtailment and the flexibility of the power plants. A model, in the form of a large optimisation problem, has been specifically developed for this study. It balances the grid every hour while maximising the Energy Return On Investment (EROI) of the electricity production and storage. It also optimises the renewable energy and storage assets. The EROI is used as a metric because it is not biased by subsidy policies, interest rates or lobbies. The study highlights the key role of storage in Western Europe. To reach an EROI-optimal 100% RE electricity system, 4.8 TWh of batteries and 152 TWh of gas storage coupled with a PtG power of 522 GW are needed. From the total production, 38% is stored before being consumed leading to a loss of 17% of the production. A doubling of the transmission capacities between countries leads to a decrease of 2.5% of the total energy invested with a decrease of 17% of the energy invested in the storage.