Dynamic modelling of cut-and-store systems for year-round deliveries of short rotation coppice willow

Short rotation coppice willow (SRCW) is a high-yielding energy crop that can be used to produce solid, liquid or gaseous biofuels. The crop is harvested during the winter, when the leaves have dropped. For economic reasons, however, most fuel processing plants require continuous year-round delivery of raw material. Thus, SRCW should be harvested as stems or in larger pieces in order to be storable, and not chipped directly at harvest for immediate use in large-scale heating plants, which is common practice at present. The aim of the project within which this study was conducted is to find cost-effective whole-stem harvesting and handling systems for year-round deliveries of natural-dried SRCW. A discrete event simulation model for such systems was developed in this study, taking weather, soil trafficability, geographical conditions, natural drying of the material and storage losses into account. The model was applied to a fictitious processing plant in Uppsala, Sweden. Machine performance and costs for a system with one stem harvester and up to three in-field shuttles, together with one chipper truck for chipping and transport, were investigated. The simulations showed that field trafficability had a crucial impact on total quantity harvested. The total cost was € 40 t−1 dry matter. Yield of SRCW and harvest productivity were important factors regarding costs. The model can be used to design cost-effective harvesting and handling systems for year-round deliveries of SRCW.