Life cycle assessment of Power-to-X integration in renewable energy systems

Power-to-X (PtX) is a key technology for the decarbonization of energy systems. It can provide carbon-free energy carriers, but the supply chain of this technology also generates greenhouse gas emissions. As such, estimating the environmental impacts of PtX requires the use of life cycle assessments (LCA). We contribute to current literature by coupling LCA with the EnergyPLAN energy system modelling tool and by using consequential LCA to provide relevant decision-support in a national context. The paper contributes with a novel and systematic approach for system expansion of heat and power in local settings which is central for the energy transition towards a smart energy system, where large-scale flexible consumers, such as PtX systems, are expected to vastly increase power consumption. This study presents a novel framework considering the system impacts of full or partial PtX integration into an energy system by accounting for changes to marginal suppliers. This is based on energy modelling in EnergyPLAN with an hourly temporal resolution and by accounting for avoided impacts connected to sector integration enabling waste heat utilization. The framework is demonstrated on a planned, Danish Power-to-Ammonia plant. The results show the importance of applying systems thinking to PtX integration, as delimiting the assessment to the specific supply chain risks missing important trade-offs and burden shifting. Our findings highlight that impacts on the broader energy system should be included when determining optimal integration pathways for PtX plants, as global warming impacts from electricity production almost double when using an average mix compared to the marginal mix from EnergyPLAN. Power-to-Ammonia can lead to emissions reductions of 89 % and 73 % depending on the use case, but impact trade-offs of land use and respiratory inorganics were found due to the increased demand for renewable electricity. The results show the indispensability of the modelling approach if local conditions are relevant, as the impacts vary significantly from more general systems, and demonstrate a methodology that can be used for decision-support when determining optimal PtX integration pathways into an energy system.