Carly Whittaker

Status and prospects for renewable energy using wood pellets from the southeastern United States

The ongoing debate about costs and benefits of wood‐pellet based bioenergy production in the southeastern United States (SE USA) requires an understanding of the science and context influencing market decisions associated with its sustainability. Production of pellets has garnered much attention as US exports have grown from negligible amounts in the early 2000s to 4.6 million metric tonnes in 2015. Currently, 98% of these pellet exports are shipped to Europe to displace coal in power plants. We ask, ‘How is the production of wood pellets in the SE USA affecting forest systems and the ecosystem services they provide?’ To address this question, we review current forest conditions and the status of the wood products industry, how pellet production affects ecosystem services and biodiversity, and what methods are in place to monitor changes and protect vulnerable systems. Scientific studies provide evidence that wood pellets in the SE USA are a fraction of total forestry operations and can be produced while maintaining or improving forest ecosystem services. Ecosystem services are protected by the requirement to utilize loggers trained to apply scientifically based best management practices in planning and implementing harvest for the export market. Bioenergy markets supplement incomes to private rural landholders and provide an incentive for forest management practices that simultaneously benefit water quality and wildlife and reduce risk of fire and insect outbreaks. Bioenergy also increases the value of forest land to landowners, thereby decreasing likelihood of conversion to nonforest uses. Monitoring and evaluation are essential to verify that regulations and good practices are achieving goals and to enable timely responses if problems arise. Conducting rigorous research to understand how conditions change in response to management choices requires baseline data, monitoring, and appropriate reference scenarios. Long‐term monitoring data on forest conditions should be publicly accessible and utilized to inform adaptive management.

Life cycle assessment of biofuels in the European Renewable Energy Directive: a combination of approaches?

The European Renewable Energy Directive (RED) was produced by the European Parliament and the Council of the European Union to promote the uptake of energy from renewable resources by participating member states. It sets greenhouse gas (GHG) saving targets for renewable transport fuels and dictates the method by which this should be calculated. This study examines the life cycle assessment (LCA) methodology set out in the RED and compares it to attributional and consequential assessments. A case study of wheat-based bioethanol is used to illustrate how differences in methodology affect the GHG emission results. The results show that GHG emissions from wheat bioethanol are lowest when calculated under the RED, and highest when substitution credits are applied. The RED has been shown to not only combine attributional LCA and consequential LCA approaches but also to contain rules for specific co-products. For example, cereal residues are not allocated GHG emissions from cultivation, and exported electricity is awarded a credit based on similar electricity generation from the same source. It is suggested that these rules may be a reaction to concerns over indirect global land use change, and therefore these methodological anomalies in the RED place artificial biases in GHG emission results.

Dry matter losses and quality changes during short rotation coppice willow storage in chip or rod form

This study compares dry matter losses and quality changes during the storage of SRC willow as chips and as rods. A wood chip stack consisting of approximately 74 tonnes of fresh biomass, or 31 tonnes dry matter (DM) was built after harvesting in the spring. Three weeks later, four smaller stacks of rods with an average weight of 0.8 tonnes, or 0.4 tonnes DM were built. During the course of the experiment temperature recorders placed in the stacks found that the wood chip pile reached 60 °C within 10 days of construction, but the piles of rods remained mostly at ambient temperatures. Dry matter losses were calculated by using pre-weighed independent samples within the stacks and by weighing the whole stack before and after storage. After 6 months the wood chip stack showed a DM loss of between 19.8 and 22.6%, and mean losses of 23.1% were measured from the 17 independent samples. In comparison, the rod stacks showed an average stack DM loss of between 0 and 9%, and between 1.4% and 10.6% loss from the independent samples. Analysis of the stored material suggests that storing willow in small piles of rods produces a higher quality fuel in terms of lower moisture and ash content; however, it has a higher fine content compared to storage in chip form. Therefore, according to the two storage methods tested here, there may be a compromise between maximising the net dry matter yield from SRC willow and the final fine content of the fuel.

Biomass Harvesting, Processing, Storage, and Transport

Abstract This chapter focuses on the typical stages of biomass supply chains that occur between the point of harvesting and final consumption. Firstly, the harvesting methods depend on the feedstock; in many supply chains, there are options to harvest in whole or chipped form, with there being trade-offs further down the supply chain in regard to how they are stored, processed, and finally transported. This chapter also provides some typical fuel consumption figures for harvesting, processing, and storing biomass. Finally, the GHG emissions of road, rail, and marine transport of transporting different biomass types are compared.