In the article, we used 3 time periods to describe the marginal electricity mix:
- 2020: coal-dominated, at 1000 gCO2-eq kWh-1
- 2030: coal and natural gas mix, at 500 gCO2-eq kWh-1
- 2040: efficient natural gas, at 250 gCO2-eq kWh-1).
All these values are higher than the current average emission factor for electricity in Sweden, which is around 40-50 gCO2-eq kWh-1.
This was based on a report from Hagberg (2017) and their specific methodology. Altough both the modelling and the time frame suggested can be discussed, the conclusion that remains is that biochar is rarely preferable over conventional bioenergy in a fossil energy system. Despite carbon sequestration, it does not achieve as much climate-change mitigation as an efficient combined heat and power plant introduced in a fossil energy system.
Later, we recalculated these results with the current Swedish average mix for electricity (dominated by nuclear and hydro power). The climate-relevance of the energy-biochar trade-off is in that case much less important. This led to the following general conclusions for energy utilities.
Investing in biochar production capacity is a rather suitable climate decision if the four following conditions are met:
- in both the short- and long-term, you foresee that energy services (e.g. heat and electricity) will have a climate change impact well-below the one from natural gas energy generation,
- if you foresee that sustainable biomass is available in sufficient amounts, considering also other potential uses of biomass under development,
- if you are confident that the biochar production process selected will lead to a form of biochar that is highly stable in soils,
- if you can ensure that biochar will be used in applications that provide tangible socio-environmental benefits.