GGR pathways require different amount of biophysical and financial resources, while interacting with the energy systems (consuming and/or producing energy) in various steps of their supply chain. For instance, DACCS captures CO2 from ambient air with chemicals with subsequent CO2 storage, imposing high demands for energy upon the system. In comparison, other options, such as BECCS, can produce more energy than they require, but the availability of biophysical resources such as land and water represent a crucial barrier to their scale up.
The system integration and scale up potential of GGR practices is also the result of their supply chain configuration (e.g., access to low carbon energy), process specifications (e.g., energy efficiency), and the counterfactual scenario considered, among others.
This guide establishes a framework for evaluating the systems integration and scale up potential of GGR projects, based on their compatibility with current/future technical regimes, their resource efficiency – in terms of land, water and energy use, and costs.
The set of indicators should allow a comparison of the relative ease by which GGR can be integrated into existing technical and biophysical regimes and the key enabling factors for their scale up over time.
A key enabling factor for energy intensive GGR is the possibility to access low carbon energy sources. Enhanced weathering (EW), biochar and tree planting entail energy-intensive steps such as material grinding and transport for EW, transport and application for biochar, and forest management (e.g., fertilizer application) for afforestation. The availability of low carbon energy is also a pre-condition for energy intensive direct air capture (DAC) technologies.
Similarly, it is important to quantify the resource intensity/efficiency of these options, given that the access to natural resources (water, land, energy) might hinder the deployment and, ultimately the scale up, of these technologies in given locations.
Compatibility with the wider technical regime
We measure the compatibility of a given GGR with the wider technical system via the carbon intensity of its energy use (fuels, electricity, thermal energy) over its full GGR life cycle. The completeness of the GGR life cycle is determined as per guidelines described in the Quality of reporting indicators. As the wider system decarbonises, the carbon intensity of fuels will decrease over time, hence we suggest measuring and reporting these carbon intensities of energy annually, over the full duration of the project.
An indicator of GGR efficiency is the amount of physical resources, i.e., water, land and energy, consumed within the supply chain of GGR per tonne of CO2 removed. The CO2 removed is the net life cycle GHG emissions over the life cycle of the GGR, as described in the Removal indicators of the CO2RE evaluation framework.
The table below describes various resource efficiency indicators which should be evaluated for each GGR. The lower the consumption of resources is per tonne CO2 removed, the more efficient the GGR is.
Land use associated with:
|ha / tCO2 removed
|Land quality/type not considered here
Water use associated with:
|m3 / tCO2 removed
|Impact on water availability for other purposes (e.g., livelihoods or food production) not considered here
Net amount of energy consumed within each supply chain step:
|MJ / tCO2 removed
|Should be calculated as (Energy use – Energy produced) to account for coproduction of electricity/heat in BECCS and biochar pathways
A good indicator of the removal cost is the annual capital and operating expenses associated with a given GGR project. To allow for a consistent comparison across different GGR projects, these costs should be normalised on the net amount of annual CO2 removed, estimated as described in the Removal indicators.
Prof Niall Mac Dowell
Imperial College London
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