Enviva’s Sustainable Supply Chain: The Voyage from Low-Value Wood to Low-Carbon Bioenergy
To understand how sustainable wood pellets help our customers reduce the greenhouse gas (GHG) intensity of energy generation, it is helpful to illustrate the carbon impact of Enviva’s product over its full lifecycle, from the forest all the way to the customer.
Using the new Drax Biomass Carbon Calculator—a user-friendly, transparent platform that calculates biomass lifecycle emissions—the graphic below shows the estimated emissions associated with each of the steps in Enviva’s supply chain, from our Northampton site in North Carolina to Drax’s power station in Selby, U.K. Because our supply area in the Southeast U.S. has stable or increasing carbon stocks, following the standard practice for carbon accounting we can assume that the GHG emissions released during combustion are offset by the carbon stored in the biomass as it grew. Read more about the scientific basis for this in our recent white paper, Seeing the Forest: Sustainable Wood Bioenergy in the Southeast United States.
Biomass supply chain emissions are typically reported to regulators using an approved calculator, and for regulatory purposes they must fall below certain prespecified thresholds. The U.K. requires that supply chain emissions from biomass be under 55 grams of CO2 equivalent per megajoule of power (gCO2e/MJ) from 2020 to 2025 for existing biomass generators. When we deliver wood pellets from Northampton to Drax’s facility, we find that the embodied life cycle emissions from production of our wood pellets total 9.7 gCO2e per MJ of energy in the pellets. This means that the GHG emissions associated with our biomass supply chain to Drax total 26 gCO2e per MJ of power, which is well below this regulatory threshold.
Of that total, the step-by-step breakdown is as follows:
- Harvest activities (5%) – emissions from cultivating, collecting, and processing biomass feedstock at the harvest site
- Feedstock transportation to the mill (9%) – vehicle emissions from transporting products from the harvest site to the pellet mill
- Pelletizing (51%) – emissions from processing feedstock into pellet form, which includes onsite chipping, hammering, drying, and milling
- Pellet transportation to the end user (32%) – emissions from transporting products to a port facility and emissions from marine transportation to the end user
- Product use (3%) – small amounts of non-carbon dioxide emissions from biomass combustion, like methane and nitrogen oxides, that do not have sinks in forest carbon cycling
The GHG emissions from shipping pellets across the ocean comprise only about a third of the supply chain emissions, because bulk shipping greatly enhances the efficiency of the trans-Atlantic journey. The emissions from electricity used in the manufacturing process – in the Southeast U.S. where the electric grid is especially coal-heavy – are responsible for the largest portion of the total, at just over half of the total supply chain emissions.
The graphic also shows the carbon intensity of wood pellets compared to coal and natural gas. With an apples-to-apples comparison such that the supply chain emissions associated with coal and natural gas are also included, we find that the embodied emissions in wood pellets per unit of energy output are 91% lower than the embodied emissions from coal and 85% lower than from natural gas.
We continue to seek opportunities to further reduce our carbon impact and improve the emissions intensity of biomass in our supply chain. Read more here.