Carbon Debt Payback Time for a Biomass Fired CHP Plant—A Case Study from Northern Europe

Kristian Madsen,Niclas Bentsen

doi:10.3390/en11040807

Abstract

The European Union (EU) has experienced a large increase in the use of biomass for energy in the last decades. In 2015, biomass used to generate electricity, heat, and to a limited extent, liquid fuels accounted for 51% of the EU’s renewable energy production. Bioenergy use is expected to grow substantially to meet energy and climate targets for 2020 and beyond. This development has resulted in analyses suggesting the increased use of biomass for energy might initially lead to increased greenhouse gas (GHG) emissions to the atmosphere, a so-called carbon debt. Here, we analyze carbon debt and payback time of substituting coal with forest residues for combined heat and power generation (CHP). The analysis is, in contrast to most other studies, based on empirical data from a retrofit of a CHP plant in northern Europe. The results corroborate findings of a carbon debt, here 4.4 kg CO2eq GJ−1. The carbon debt has a payback time of one year after conversion, and furthermore, the results show that GHG emissions are reduced to 50% relative to continued coal combustion after about 12 years. The findings support the use of residue biomass for energy as an effective means for climate change mitigation.

Highlights

The recent decades, have seen a massive increase in the use of biomass for energy [1]. The majority of this increase has occurred in the European Union (EU), where bioenergy currently (2015) accounts for 51% of renewable energy production [2] and it is expected to increase further to meet the targets on renewable energy by 2020 [3,4]
A number of studies find that increased use of bioenergy creates a so-called carbon debt [5,6,7,8], which implies a period with larger greenhouse gas (GHG) emissions as compared to a continued fossil fuel use scenario
This study shows that the use of biomass for energy is not carbon neutral in absolute terms

Summary

Introduction

The recent decades, have seen a massive increase in the use of biomass for energy [1]. The majority of this increase has occurred in the European Union (EU), where bioenergy currently (2015) accounts for 51% of renewable energy production [2] and it is expected to increase further to meet the targets on renewable energy by 2020 [3,4]. Studies reporting long carbon debt payback times in general assume that the biomass is utilized for electricity production with low conversion efficiencies and that the woody biomass originates from the dedicated harvest of trees for energy from long rotation forestry [13]. Looking at the current use of bioenergy in the EU, there is little evidence that such supply chains dominate [14]

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