This post includes an excerpt of the feature article in the June/July/August edition of Wood Bioenergy US (WBUS) written by Amanda Lang, Brooks Mendell, and Will Caldwell. The article compares estimates of wood-to-energy conversions from industry and academic research across wood energy types: pellets, ethanol, and electricity.
Press releases, public filings (such as 10-Ks), and company websites frequently report the energy-generating capacity of bioenergy plants. However, wood consumption requirements remain less commonly reported as they vary by feedstock type, moisture content, bark content, and production efficiency. Forisk compares estimates of wood-to-energy conversions from industry and academic research across energy types: pellets, ethanol, and electricity. Findings on wood pellets and electricity production suggest 10% to 20% more green wood is needed per unit of output than often reported or assumed in previous projections. Available research confirms conversions applied to liquid fuel projects.
Previous Wood Bioenergy US (WBUS) projections assumed 1 US short ton of pellets requires 2 green short tons of pulpwood roundwood (including bark). This 2-to-1 assumption is widely used for presentations, models, and back-of-the-envelope estimates; however, published and industry research indicates that the actual conversion rate is 2.2 green short tons per short ton of pellets. Bark content critically affects the conversions for pellets, and is often not explicitly noted when conversions are reported, leaving the reader to assume if bark is included or excluded in the estimate. Bark content of delivered roundwood often accounts for anywhere between 10-13%. Bark is often collected during the debarking process and used to fuel boilers in biofuel production if feedstock arrives as roundwood, but not often used in biofuel production due to chemical composition. For pellet projects, most newly announced pellet capacity in the US assumes roundwood pulpwood feedstock as a primary component, for which the 2.2-to-1 conversion applies.
Forisk assumes 40 gallons of ethanol out for every 1 green short ton in, and industry research suggests similar conversion rates. Forisk previously assumed 10,000 green short tons per 1 MW of electricity; however, published and industry research suggests that actual conversions average 12,000 green short tons per 1 MW.
Revised conversion rates for pellets and electricity/CHP projects resulted in wood use projections that are 9% (10.7 million tons) higher by 2023 for total wood use from bioenergy and are 9% (7.0 million tons) higher for volumes that pass screening criteria. The updated wood use conversions affect logging residues to a greater degree (11% increase), followed by hardwood pulpwood (10%) for projects that passed viability screens. These impacts affect projections in the North the most on a percentage basis (10.4% increase across feedstocks), and they affect the South the most in absolute terms (3.5 million ton increase across feedstocks).
WBUS Market Update: As of July/August 2014, WBUS counts 448 announced and operating wood bioenergy projects in the U.S. with total, potential wood use of 135.6 million tons per year by 2023. Based on Forisk analysis, 293 projects representing potential wood use of 88.0 million tons per year pass basic viability screening. To download the free WBUS summary, click here.