(368g) Determining the Role of Negative Emission Technologies (NETs) in the Electricity System in the UK

In line with the 2015 Paris Climate Accord¹, the Inter-governmental panel for Climate Change (IPCC) highlighted the crucial role of negative emission technologies (NETs). In particular, bioenergy with carbon capture and storage (BECCS) is inevitable to meet the 1.5^oC target above pre-industrial levels, but presents technical, sustainable and political challenges² which need to be assessed. Also, only a few studies have been looking into NETs synergies as part of a broader NETs portfolio. Moreover, it is essential to model regional granularity to integrate NET’s key deployment parameters, such as biomass supply chain for BECCS³ or climate ecological zones for Afforestation (AF). Meanwhile, the UK global economy, including the power sector, is required to reach net-zero emissions in 2050, with an estimated 90 MtCO₂/year of Greenhouse Gas Removal (GGR) in 2050 (Committee on Climate Change, 2020). However, no studies mentioned the eventuality of a national net-negative electricity sector, implying substantially more BECCS deployment and a profound impact on the design and operation of the electricity system. Whereas there are works modelling and optimising the UK electricity system⁴, also including BECCS and DACCS, none of them studied the impact of nature-based NETs deployment on the electricity capacity mix.

To fill these gaps, our contribution is double. First the implementation of the Modelling and Optimisation of Negative Emission Technology (MONET-UK) that integrates three NETs (BECCS, AF and Direct Air Capture (DACCS)) and accounts for national bio-geophysical resources at a regional level. Second, the combination of the Electricity System Optimisation (ESO) -a pre-existing model⁴- and MONET-UK in a joint system. These two models allow the system to find the global minimum of the total system cost under technological and national CDR constraints. The joint system is optimised by successively optimising MONET and ESO, until a global minimum is reached. The interaction terminates if a convergence criterion verifying the stability of total system capacity is satisfied. (see Fig. 1)

Our results show a typical UK NET optimal portfolio for delivering 90 MtCO₂ of GGR in 2050 (see Fig. 2). AF, the cheapest solution (105 $/tCO₂) is fully deployed and is limited by national forest expansion rate. BECCS, slightly more expensive (155 $/tCO₂), is deployed until available national biomass and imported pellet are out of stock. As a last resort DACCS is deployed as it is the most expensive technology (529 $/tCO₂).

Then, in figure 3, we compare the path to follow for a net-zero and a carbon negative electricity system in 2050. The coloured dots show the associated optimal NET portfolio responsible for other sector’s emissions removal estimated to 90 MtCO₂ by 2050. The net-zero electricity system presents a high share of renewables but also requires firm thermal generation (natural gas, biomass), as renewables are not flexible and require additional storage that is not available. We notice a progressive build of renewable capacity (solar, wind), due to the need of low-carbon electricity generation, as well as a system demand increase (+15%) caused by significant DACCS deployment. In contrast, a carbon negative electricity system is achieved through substantially more BECCS capacity, 17.5GW in 2050 (versus 2.5GW in the net-zero scenario) displacing renewable capacity and firm low-carbon generation. These results confirm that the use of intermittent renewable technologies is not sufficient, although important, to deliver required CDR targets. Moreover, they also show that, in order to meet these targets, having a net-zero electricity system and relying on other NETs (AF and DACCS) is drastically more expensive (+33%) than aiming at a net-negative electricity sector, which requires less external removal (AF and DACCS).

Finally, we studied how nature-based solutions affect the power system and total system cost. For example, if we increase biomass availability, average cost of carbon removal decreases due to DACCS share replaced by BECCS. Simultaneously, it increases BECCS share in the electricity sector, which proves cheaper than further IRES growth which requires further energy storage and grid flexibility. In figure 4, a cost analysis shows that increasing biomass availability from 100 to 200TWh decreases total investment of 12% per year, however further increase doesn’t change much. We recognize that heavy dependence on imported pellet poses global security concerns, making the power sector vulnerable to the instability of global supply chains. In our next steps, we will focus on other natural based solutions -other NETs e.g. biochar, afforestation potential increase- to avoid such a dependence.

References
1. IPCC, 2018: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels. In Press.

2. Galik, C. S. (2020, January 1). A continuing need to revisit BECCS and its potential. Nature Climate Change. Nature Research.
3. Fajardy, M., Chiquier, S., & Mac Dowell, N. (2018). Investigating the BECCS resource nexus: Delivering sustainable negative emissions. Energy and Environmental Science, 11(12), 3408–3430.
4. Heuberger, C. F., Rubin, E. S., Staffell, I., Shah, N., & Mac Dowell, N. (2017). Power capacity expansion planning considering endogenous technology cost learning. Applied Energy, 204, 831–845.