The complexity of bottom-up energy system models has progressively grown to enhance the representativeness of the system under analysis. Among them, whole-energy system models aim at representing the energy resources, conversion technologies, and energy demands of regions (i.e., a country) in its entirety. Despite this effort leading to an increased number of conversion processes modeled, the typologies of the end-use demand have remained limited to three categories: electricity, heat, and transportation. A fourth category, herein addressed as the non-energy demand, has widely been neglected. Being associated with the production of chemicals (i.e., plastics and fertilizers), the non-energy demand represents 10% of the world’s total end-use demand. Its relevance becomes fundamental in analyses that define the optimal defossilization pathways of energy systems with high dependence on fossil resources. This contribution introduces a schematic representation of the conversion processes involved in the satisfaction of the non-energy demand. Through its implementation in a bottom-up whole-energy system model, it evaluates the impact of this additional end-use in the configuration of the optimal energy system. In this study, the Belgian energy system, characterized by a penetration of the chemical and the petrochemical industries up to 20% of its total end-use demand, is taken as a reference case. The transition to a defossilized energy system is enforced through a snapshot analysis with a progressively more restrictive emissions cap. The results emphasize the role of renewable carriers (i.e., methanol and ammonia) in the defossilization of the energy system, otherwise hindered when the non-energy demand is neglected. The 100% import of these carriers at the lowest emissions cap highlights the potential dependence of the country under analysis, with limited availability of renewable resources, from countries exporting renewable methanol and ammonia.

Energy crops on marginal lands are seen as an interesting option to increase biomass contribution to the primary energy mix. However, in the literature there is currently a lack of integrated assessments of margin land availability, energy crop production potential and supply chain optimisation. Assessing the potential and the cost of these resources in a given region is therefore a difficult task. This work also emphasises the importance on a clear definition and discussion about marginal lands and the related ethical issues embedded in the concept to ensure positive societal impacts of the results. This study proposes a methodology to estimate and analyse, in terms of economic costs, the potential of miscanthus grown on marginal lands from the production to the final point of use. Different datasets are assembled and a supply chain optimisation model is developed to minimize the total cost of the system. Miscanthus is used as a representative energy crop for the Belgian and French case studies. High temperature heat demand is considered as final use. The miscanthus can be traded by truck either in the form of chips or pellets. The results show that the miscanthus on marginal lands could supply high temperature heat up to 38 TWh in France and 1.4 TWh in Belgium with an average cost of around 50 €/t. The different sensitivity analyses showed that the yield variation has the strongest influence on the final cost, together with the distances and the cost of production of miscanthus. The main pattern observed is the local consumption of miscanthus chips and export of the surplus (if any) to the neighbouring regions. Pellets are only of marginal interest for France and are never observed for Belgium. Distances and availability of sufficient feedstocks are the two main parameters impacting the production of pellets.

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