Feasibility of Solar-Enhanced Drying of Woody Biomass

Sustainable biomass resources are limited and their utilization therefore needs to be more efficient. In addition, there is an urgent need for low-cost energy storage, particularly for solar energy. Drying considerably increases the calorific value of woody biomass, and the resulting dried biomass provides easy seasonal energy storage. The drying both improves the quality of the biomass and extends its storage life. To investigate the technology and feasibility of solar-enhanced drying, several drying experiments were conducted on wood chips in VTT’s 12 kWpeak convective dryer in Jyväskylä, Finland. Drying times varied from 3.5 to 27 h and the final moistures from 12 to 32 w-%. VTT’s experiments show that solar heat can be successfully applied to thermal drying of biomass. The moderate drying temperatures used (typically 20–50 °C) are advantageous for ensuring homogenous drying of wood particles and for preventing changes to the physical structure of the biomass and loss of volatiles. Due to the low efficiency of the system, still in its prototype phase, the calculated payback times were not highly attractive to the entrepreneur. In the experiments, best profitability was achieved by drying seasoned wood, for which a payback time of 12–17 years was estimated for a large scale system such as a biomass terminal. Based on the assumptions that technical improvements are made, the best drying efficiency reached in our experiments is achieved, and some investment subsidy is secured; scale-up is feasible. With these criteria met, the payback time of such a dryer could be brought below 10 years. This requires, however, that drying increases the selling price of wood chips.