Greenhouse gas emissions projections: phase 1 and phase 2 modelling results

10. Negative Emission Technologies (NETs)

10.1 Sector Overview

10.1.1 Sector Background

Scotland is unlikely to meet its CO₂ reduction targets without the implementation of some form of Negative Emissions Technologies (NETs), including direct air carbon capture and storage (DAC) and bioenergy with carbon capture and storage (BECCS). BECCS applications include BECCS power, BECCS hydrogen, BECCS in industry, BECCS biofuels and biogas, and BECCS energy from waste (EfW). The importance of BECCS and DACCS for Scotland to achieve net zero targets has been highlighted by the CCC's Sixth Carbon Budget. BECCS and DACCS are needed in Scotland to balance residual emissions in 2030 and 2045.^[54]

The CCPu NETs envelopes are 3.8 Mt CO₂e/year in 2030 and 5.7 Mt CO₂e/year in 2032. The majority of the 5.7 Mt CO₂e/year target comes from BECCS with around 0.5 CO₂e/year coming from DACCS. This shows the importance of bioenergy with carbon capture and storage for Scotland as a NET. Increased interest in NETs in Scotland is evident. For example, the Acorn CCS project will explore the potential to develop a large-scale DACCS facility in Scotland. Partners in the Acorn project have announced a further £1bn in investment^[55] and as of spring 2023 the Scottish Government has pushed the UK Government for additional funding.^[56] However, policies to encourage the development of NETs are needed in Scotland in order to reduce revenue uncertainty and promote investment.

10.1.2 Subsectors Considered

The NETs sector was disaggregated into two subsectors, BECCS and DAC. There are other sectors which fall under NETs such as afforestation, reforestation and forest management. The CCPu considers DACCS and BECCS within the NETs sector; natural sequestration methods such as afforestation which may result in negative emissions are covered by the LULUCF sector.

10.1.3 Data Sources

The baseline energy consumption and associated emissions for the NETs sector are zero, as there are currently no NETs plants in Scotland. Hence, there is no baseline energy consumption data required for this subsector. In order to carry out the calculations described in the 'Underlying drivers of energy and emissions' section, the following data sources and documents were utilised:

10.1.4 Underlying Drivers of Energy & Emissions

The underlying driver of energy consumption within the NETs sector consists of the operation of the NETs plants. The form of BECCS considered is BECCS power, as this the technology with one of the highest TRLs at the current time. Other forms of BECCS, such as BECCS biomethane, may also progress quickly due to the high purity CO₂ streams that are produced, however less data is currently available in literature to incorporate these into the model. The energy consumption for BECCS power and DAC is predominantly in the form of electricity. The emissions factor utilised for electricity within the model is zero, and hence, no additional emissions are expected to arise from the operation of the NETs plants.

BECCS

A calculation was undertaken to estimate the capacity of a plant required to allow for 5.2 MtCO₂ to be captured per year. The calculation is based on a reference case plant of biomass post combustion with CCS for power generation. Assumption figures have been based on a comprehensive benchmarking CCS report^[57]. It is common practice within BECCS for power generation to operate the CCS plants with electricity diverted from the electricity produced onsite, hence the electricity would be diverted from the electricity to the NETs sector. However, for the sake of simplifying the model, it is assumed that additional electricity from external sources will be utilised on the NETs plants, and hence this subsector. The calculated figures and assumptions are outlined in the table below.

DAC

The reference plant utilised for DAC calculations is one which utilises liquid solvent for CO₂ capture. This is because there is more data available on this type of plant than others, such as solid sorbent. An estimated figure based on existing literature^[59] was used for the approximate energy consumption per unit of CO₂ captured.

10.2 Policy Measures and outcomes Modelled

10.2.1 Phase 1 – Policy Measures

The key policy for developing the NETs sector is to 'Support the development of NETs within Scotland', which falls within Outcome 2: CCUS (Carbon Capture, Usage and Storage): the continued development of CCUS technologies and systems is prioritised to ensure these can be rolled out commercially and at scale by the late 2020s. All other policy proposals within outcome 2, and all policy proposals within outcome 1 are considered to be supporting measures towards the key policy of supporting the development of NETs technologies within Scotland. These supporting policy proposals are outlined in Table 10‑4 below.

The remaining policies fall under Outcome 3 and are shown in Table 10‑5 below and are also considered to be supporting measures.

The NETs sector in Scotland is acknowledged to still be within its infancy. As previously mentioned, NETs is an important sector in Scotland to contribute towards net zero targets. Many of the policies within this sector are therefore aimed at accelerating the development of NETs in Scotland, through measures including feasibility studies and developing appropriate support mechanisms. Detailed feasibility studies will need to consider:

• Identifying key policy enablers and potential actions based on emerging national GGR support mechanisms
• Assessment of build-out rates and supply chain limitations to understand whether deployment rates are reasonable
• Plant specific feasibility studies to prioritise short term efforts as well as creating the relevant literature on NETs and gathering necessary data, technology assessment and limitations, permitting requirements
• Bioresource availability
• Evaluation of costs

Although these supporting policies will not lead to a direct reduction in emissions, actions such as these are crucial to inform future policies that will provide a mechanism for NETs to develop in Scotland, and hence contribute to the NETs targets outlined within the CCPu.

Targets

The potential negative emissions reduction of the policies is modelled to reach the CCPu target for NETs. It was agreed with Scottish Government that the timeline for reaching the targets is expected to be revised, therefore the policy start date is 2033, and the expected completion date to reach the targets is 2040 It is then assumed that approximately 90% of this target is attributed to BECCS and the remaining 10% is attributed to DAC. The figures are as shown in the table below.

Calculations were then carried out to estimate the associated electricity consumption of BECCS and DAC plants that would achieve the targets shown in Table 10‑6.

10.2.2 Phase 2 – Policy Outcomes

No additional modelling was carried out for Phase 2 of this work, as no further quantifiable policies/targets could be identified.

10.2.3 Summary of Policy Packages

The table below indicates which policies were found to have the biggest potential impact within each package, which policies overlap with (or reinforce) each other, and which policies act as supporting measures.^[60]

For the NETs sector, one key policy was identified, with two supporting measures.

10.2.4 Variation across scenarios

The policy measure identified for each subsector, BECCS and DAC, includes supporting the development of NETs in Scotland, through the SIETF and EETF. An indication of how they are expected to change under each scenario is outlined below.

NETs are required for Scotland to reach its net zero targets, therefore, even in a low growth scenario, medium growth of NETs can still be expected. In a high growth scenario, there will be more emissions and hence more NETs will be required to balance residual emissions, resulting in high NETs growth in a high growth scenario. NETs are expected to be deployed in sectors which are harder to decarbonise, such as in industry. NETs are also expected in the power sector where it can be retrofitted onto existing biomass and EfW sites.

In a low hydrogen scenario, it is likely that hydrogen would not be predominantly produced through BECCS due to biomass resource availability and would more likely come from other sources such as renewables including solar PV and wind, or CCUS from fossil fuels. Hence in a low hydrogen scenario, low NETs growth is expected. In a high hydrogen scenario, there is a higher likelihood of hydrogen BECCS; however it can still be expected that hydrogen is predominately produced through other sources. Therefore, medium NETs growth can be expected in a high hydrogen scenario.

10.3 Emissions Projections

10.3.1 Phase 1 results

Figure 10‑1 below represents the emissions in the NETs sector, should the targets be realised. As can be observed in Figure 10‑1 below, the total emissions from the NETs sector in all scenarios (high, central, low) is expected to be zero until 2032. This acknowledges that several years are required to build a BECCS or DAC plant, as all of the emissions reduction in the sector is driven by the introduction of NETs plants which are capturing emissions from fuel sources or directly from the air. After 2032, NETs plants will begin to come online resulting in negative emissions from the sector, increasing up until 2040 when the NETs targets are expected to be reached. Emissions in the baseline scenario are zero all through to 2050, where it is assumed in this scenario that there is no growth in the NETs sector and hence no reduction in emissions associated with NETs.

Note: The results from the three growth scenarios are visibly almost indistinguishable from each other because of the small magnitude of differences between them.

The central scenario follows the same trends as the low scenario. The reason for this is that, as explained previously, it is already widely understood that NETs are needed to balance residual emissions and hence reach net zero targets. Therefore, the NETs targets within the CCPu must be met in both cases in order for Scotland to reach net zero by 2045. In the high scenario, it has been assumed that there will be further growth in all sectors, some of which will already be low carbon and some which will not. Hence, further emissions reduction from the NETs sector will be required to balance residual emissions in sectors which are hardest to decarbonise.

As explained in the underlying drivers of energy and emissions section, the predominant energy use in the NETs sector consists of electricity, to operate the NETs plants. The energy profile of the sector follows a similar trend to the emissions, where electricity use is forecasted to increase from 2032 onwards once NETs plants begin to come online. Once the target is reached in 2040, the electricity use stabilises as there are no further NETs plants coming online.

10.3.2 Phase 2 results

As stated previously, no additional modelling was undertaken.

10.3.3 Comparison of Phases 1 & 2

The table below provides a comparison of the projected emissions for Phase 1 and Phase 2 (in ktCO₂e) and by scenario.

10.3.4 Emissions reduction by policy package (2032) – Phase 1 & 2

Only one policy package was modelled for the NETs sector and, as impacts are only seen in later years, there are no emissions reductions associated with this package in 2032.

10.4 Uncertainties

The calculations for BECCS and DAC are based on one type of plant alone for each. For BECCS, there are several different end applications, all of which can use a variation of biomass feedstocks, conversation technologies and CO₂ capture technologies. Hence depending on the type of BECCS plant operating, final figures for emissions captured and electricity usage will vary, resulting in uncertainties in the modelled figures. The calculation for electricity consumption per tCO₂ captured is also based off of one large plant. In reality, it is likely that this would be through multiple, smaller plants, and hence creates additional uncertainty in the modelled figures. Implementation of BECCS in different applications will also result in variances in the inputs and hence result in further differences to the modelled emissions.

For DAC, there are several different CO₂ capture technologies, such as liquid solvent and solid adsorbent. The calculations for electricity consumption are only based on one technology, and hence this will also lead to uncertainties in the modelled figures.

As most NETs are still not commercially mature, the future landscape for implementation will likely depend on several factors which are not considered within the model. The current targets for BECCS and DAC, as outlined in Section 10.2.1, may shift depending on factors such as views on the sustainability of biomass and use of biomass imports, as well as the importance of BECCS by-products such as heat, power and hydrogen. The use of biochar for greenhouse gas removals is also gaining increasing importance, hence this is a further sensitivity to this analysis since biochar is not considered within the model.

10.5 Sensitivities

Emissions projections for NETs would normally be sensitive to the carbon intensity of the grid, but as the emissions from electricity generation are modelled under the Electricity sector, this is not visible in these results.