The energy return on investment of whole energy systems: application to Belgium

Planning the defossilization of energy systems by facilitating high
penetration of renewables and maintaining access to abundant and affordable
primary energy resources is a nontrivial multi-objective problem. However, so
far, most long-term policies to decrease the carbon footprint of our societies
consider the cost of the system as the leading indicator in the energy system
models. This paper is the first to develop a novel approach by adding the
energy return on investment (EROI) to a whole energy system optimization model.
We built the database with all EROI technologies and resources considered. In
addition, moving away from fossil-based to carbon-neutral energy systems raises
the issue of the uncertainty of low-carbon technologies and resource data.
Thus, we conducted a global sensitivity analysis to identify the main
parameters driving the variations in the EROI of the system. This novel
approach can be applied to any energy system, and we use a real-world case
study to illustrate the model: the 2035 Belgian energy system for several
greenhouse gas emissions targets.
The main results are threefold: (i) the EROI of the system decreases from 8.9
to 3.9 when greenhouse gas emissions are reduced by 5; (ii) the renewable fuels
- mainly imported renewable gas - represent the largest share of the system
primary energy mix; (iii) in the sensitivity analysis, the renewable fuels
drive 67% of the variation of the EROI of the system for low greenhouse gas
emissions scenarios. The decrease in the EROI raises questions about meeting
the climate targets without adverse socio-economic impact. Most countries rely
massively on fossil fuels, and they could encounter an EROI decline when
shifting to carbon neutrality. Thus, this study demonstrates the importance of
considering other criteria, such as EROI, in energy system models.