Life cycle assessment of heat production from grape marc pellets

In an international context characterised by the promotion of renewable sources to face an increasing energy demand, grape marc is an organic co-product of the vinification process whose potential as an energy source has been underexploited. This study analysed the production chain of grape marc pellets and evaluated, through an attributional Life Cycle Assessment based on primary data from field experiments, the overall environmental performance of using grape marc pellets for heat production, as well as its comparison with alternative fossil and renewable energy resources. A sensitivity analysis was carried out concerning the type of fuel used for drying, the methodological approach to solve multi-functionality, as well as the influence of the water content of grape marc. The combustion and drying of pellets were found to be the main contributors to the environmental impacts, although a crucial influence of methodological choices on co-products management was observed. The use of wood chips for drying and an optimization of the pellets loading rate in the combustion process are the main improvement recommendations. Overall, results showed that the production of pellets from grape marc for heat production purposes is a promising technology from an environmental perspective, which is always superior to alternative fuels at the endpoint impact level. Compared to fossil fuels, its main advantage lies in the reduced contribution to climate change. When compared to mixed wood chips, it has an advantage regarding the contribution of agricultural land occupation. For policy support purposes, however, this study should be complemented by further analyses focussing, for instance, on market-driven consequences of large scale implementation. The results were shown to be dependent on the midpoint and endpoint impact categories. Their comprehensive interpretation led to the overarching clear recommendation to adapt the impact assessment categories and models and the approach to deal with multi-functionality to the geographical and market specificities features and to assure maximum transparency in the communication of results.