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New Working Paper: Role of NETs in Deep Decarbonisation of Energy in Ireland

posted Mar 31, 2019, 10:27 AM by Barry McMullin   [ updated Mar 31, 2019, 10:28 AM ]

The IE-NETs project is pleased to release a new working paper, the detailed report on Work Package 4: Investigating the Role of Negative Emissions Technologies in Deep Decarbonisation Pathways for the Irish Energy System (Barry McMullin and Paul Price, March 2019).


As indicated by the IENETS WP1 assessment of National Carbon Quota (MCQ) pathways for Ireland (Price et al.2018, Chapter 8) and largely borne out by the modelling developed in this work package, Ireland’s (prudent, minimally equitable) NCQ is likely to be exhausted by 2023-2025, tacitly committing to some level of NCQ overshoot dependent on nett cumulative CO₂ emissions thereafter. The overall structure and evolution of Ireland’s energy system will therefore need to change and decarbonise very rapidly to limit the scale and duration of such overshoot, lest effective reversal of it becomes infeasible. This is the essential physical consequence of good faith commitment to the Paris Agreement. Sufficient carbon dioxide removal (CDR) using negative emissions technologies (NETs) would then be needed to return to the NCQ level within a very few decades (assumed in this report to be by 2100 at the latest). Cost effectiveness analysis of alternative energy system transition options for national energy and climate plans should therefore account for the full aggregate costs of long-term strategies toward fulfilling the Paris temperature objective (EU 2018, Article 15:3(b)). These costs need to include risk averse estimates of projected negative emissions reliance in terms of technology and the uncertainty attached to policy reliance on NETs such as BioEnergy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS) that are not yet proven or available at scale. Carbon commitment analysis of policy and modelled energy system pathways to evaluate their likely cumulative CO2 outcomes (nett and gross) is therefore essential to economic and feasibility assessment of the alternatives that do plausibly meet the Paris-aligned NCQ.

This work package investigated modelling options that could complement energy system models currently used to guide policy-making in Ireland and potentially provide useful additional insights into Paris-aligned energy system decarbonisation. The outputs from such coarse-grained modelling are not comprehensive and all quantified results presented should be treated with due caution as outputs that are only indicative of the overall mitigation outcomes of the particular scenarios. Nonetheless, the modelling outputs clearly indicate serious carbon commitment concerns and critical risks related to alternative scenarios and sketched the possibility-space of energy system change constrained by a Paris-aligned carbon quota, with or without use of Carbon Cpture and Storage (CCS) or NETs.

Using a newly developed spreadsheet-based modelling tool, Anthem, the strong effect of CCS on primary energy options is made evident – both in limiting fossil carbon combustion emissions and in enabling permanent CDR via BECCS and DACCS to limit and potentially reverse NCQ overshoot – as are the associated tradeoffs in CCS energy penalty and requirements for large scale infrastructure investment to capture and store such large amounts of CO2. Incorporating the potential backstop economic costs of CCS options into decarbonisation analysis may well militate in favour of other mitigation options: near-term supply-side constraint (rationing, in effect) of unabated fossil fuel energy to drive more rapid deployment of non‑bio renewables and planned reductions in societal energy demand; or early deployment of other NETs including land carbon storage and Enhanced Weathering (EW) and ocean carbon storage.

These findings are potentially highly policy relevant for near-term choices that will now determine the availability of energy to society within an equitable Paris-aligned cumulative carbon constraint. The over-riding advice to policy makers, and society at large, from this analysis is to act on these options without delay. A plan for sustained and substantial reductions in absolute system CO₂ emissions is required, aiming for nett-zero CO₂ emissions from aggregate energy, cement and land-use, including a period of significant nett negative emissions to cancel accumulated carbon debt following overshoot.

The work package included an initial assessment of a range of freely available energy modelling tools, following which two were selected for detailed model development – EnergyPLAN and the Ireland 2050 Pathways Calculator (IE2050). These were used to examine the carbon commitment of scenarios in terms of annual and cumulative CO pathways relative to the NCQ. Despite differing limitations of EnergyPLAN and IE2050, and some technical difficulties encountered in extending them usefully, it was worthwhile to examine how the “possibility space” of an energy system model is bounded by its design. In particular, working with these models was effective in assessing the embodied expert assumptions regarding deployment extent, transition timing and the inherent risks of making essentially ad hoc user choices (including our own) that may be questionable in themselves and need to be very clearly identified and logged in presenting findings. EnergyPLAN is focused on achieving an energy system based on 100% renewables (excluding nuclear), predominantly reliant for primary energy supply on variable renewables (VRE), wind and solar, with limited availability of bioenergy, enabled by access to large scale system flexibility via heat and chemical (electrofuel) energy storage at multi‑TWh y‑1 level. CCS is only relatively simplistically supported in the most recent EnergyPLAN release and BECCS is not explicitly represented. In contrast, IE2050 is designed with the intention of being agnostic toward energy system outcome, using a range of user choices for supply and demand ambition levers (including nuclear energy). However, its detailed internal design means that, in addressing any given mitigation target, it tends to favour unabated bioenergy (assuming unproblematic carbon neutrality for all bioenergy fuels), and implicitly excluding the high VRE+electrofuel alternative configurations that EnergyPLAN accommodates. Our work with these models showed EnergyPLAN’s usefulness in examining energy supply options (assuming nuclear energy is excluded) and in exploring system design whereas IE2050’s usefulness was more limited to examining demand options, particularly through changing the internal effect of some high ambition levers to find potential opportunities for plausibly increased ambition.

EnergyPLAN was used to validate the Green Plan Ireland data and findings of Connolly and Mathiesen (2014) and explore the implementation of the specified transition steps in a hypothetical scenario, whereby each step was fully completed in 5-year stages. This indicated that the earlier delivery of all steps, but particularly early investment in ensuring availability of electrofuel infrastructure in combination with very large scale deployment of offshore wind energy are critical to limiting NCQ overshoot while still maintaining access to levels of final energy consumption comparable to the current system.

Although useful in giving a limited assessment of the speed and extent of overshoot relative to different supply and demand policies, in the different ways discussed for each, neither EnergyPLAN nor IE2050 proved adequate to investigating substantive NCQ overshoot scenarios requiring significant and prolonged CDR from NETs. A new modelling tool, Anthem was created to provide specific additional insight on this question. Anthem is coarse-grained and schematic, based primarily on the thermal combustion emissions of hydrocarbon fuel pathways through time and any nett capture rate to storage. Despite this comparatively schematic approach, it proved effective in providing rapid carbon commitment analysis (CCA) for a variety of scenarios of carbon-based primary energy supply, with or without CCS and NETs. It yielded high-level, but correspondingly robust, insights into the annual and cumulative outcomes for energy availability to society, CO (nett value, gross emissions and gross removals) and quasi-permanent CO storage requirements for CDR and for CCS used for capture of emissions from cement production and continued fossil fuel combustion (FFCCS). Anthem was also specifically used to assess the energy system scenarios presented in the Draft National Energy and Climate Plan (NECP) for Ireland (DCCAE 2018). All of these scenarios indicate steadily increasing total primary energy supply (up to an horizon of 2040), without a committed or quantified use of CCS. Accordingly, they do not show a significant reduction in annual emissions, and would lead to overshoot of the Paris-aligned NCQ by 600 MtCO2 to 750 MtCO2 already by 2040. Separately, Anthem was applied to assess a Long Term Resilience Study of the Irish Energy system (GNI and Eirgrid 2018). This study envisaged increased use of lower carbon intensity methane (mainly natural gas, but including some limited biomethane), to replace the other fossil fuels currently used in the Irish energy system. The Anthem analysis shows that this would have a relatively minimal effect on emission reduction unless and until large scale CCS is also applied.

Climate mitigation is usually described in policy terms of “reducing emissions” within a “low carbon transition” but this framing is becoming progressively less useful as NCQ overshoot is approached. Within good faith commitment to the Paris Agreement, the overriding climate action objective and narrative is arguably now better focused on: radical, near-term and sustained reductions in unabated carbon combustion (fossil and bio‑energy) usage to near-zero as soon as possible; and, in parallel, investing in development of sufficient gross CDR capability, made available as soon as possible, to offset ongoing gross CO emissions and, in excess of that, to progressively cancel carbon debt within a very few decades by achieving nett negative emissions at least until returning to the NCQ level.

BECCS and DACCS remain highly speculative technologies with uncertain costs, energy input or output, and CO₂ removal capability. Therefore, their early delivery by 2030 shown in the various scenarios assessed, represents a likely upper bound on what might be technically feasible; in that sense the outputs of this research are coarsely informative in indicating the most optimistic relative availability of carbon-based energy and associated annual and cumulative emissions between scenarios over time. Continued high, near-term fossil fuel emissions and delayed negative emissions (gross removals) will inevitably tend to lock in progressively more cumulative CO₂ overshoot relative to the NCQ limit. In all of the scenarios, the ambitious but highly uncertain assumptions of a substantial indigenous supply of bioenergy of about 40 TWh y‑1 by 2050 while meeting stringent sustainability criteria and CCS availability, allows a supply of nett-negative-CO energy from BECCS which theoretically also enables a far slower reduction in fossil energy supply. However, as for the tradeoff between early unabated FF and later FFCCS, high levels of BECCS may therefore require limiting near-term harvest of forestry biomass, particularly avoiding its relative emissions-inefficient use in unabated bioenergy production, so that it can be conserved to allow much greater total carbon-based energy if or when harvest can be allocated to use in BECCS. DACCS is currently even more speculative than BECCS, likely requires large nett energy input (i.e., is not in itself a source of energy supply, but rather would result in a reduction in energy supply to conventional societal needs as DACCS deployment ramps up).

Ideally, all carbon removed from atmosphere into biomass should be prevented from re-release to atmosphere. So, specifically, in biomethane pathways, the CO that is present in the raw biogas, and separated during "upgrading for grid injection" should not simply be re-released to atmosphere. It can either be directly consigned to geo-storage, or used as a feedstock for P2M (producing "synthetic natural gas" or SNG by combining CO with H from water electrolysis using excess variable renewable energy (VRE) sources, especially wind; but in the latter case, the produced SNG should still be routed to some CCS combustion pathway to minimise CO release to atmosphere.

Unlike current energy projections, or energy system modelling results underpinningIreland’s National Mitigation Plan, the research in this report clearly indicates that an escalating level of climate action and intensive energy system planning is now appropriate in the very near-term to limit NCQ overshoot and deliver socio-politically manageable decarbonisation in accord with the Paris Agreement. As a matter of urgency, Irish society and its policy makers need to address very challenging near-term energy and climate planning decisions that could deeply affect economic and societal planning, with rapidly escalating future CDR costs for every year that required reduction pathways are not met. 

Key Policy Recommendations

Across all modelling frameworks studied, Paris-aligned mitigation, without national CO quota overshoot, would equate to achieving extremely rapid and immediate absolute reductions in near-term fossil fuel usage, at a year-on-year rate of c. 20%, falling effectively to zero within 10-15 years (c. 2030-2035). Due to the time lag of large scale infrastructure turnover and deployment, this finding remains robust even with the fastest technically plausible roll-out of fossil fuel carbon capture and storage (FFCCS). That is, a CCS “bridge” strategy would no longer be able to avoid overshoot; at best, FFCCS deployment can now contribute only to limiting the scale and duration of overshoot.

In fact, on current projections and policies, including those included in its Draft National Energy and Climate Plan [NECP] (DCCAE 2018), Ireland is likely to overshoot its prudent maximum Paris-aligned CO quota (estimated as 378 MtCO from 2015, here denoted LowGCB:pop) as early as 2023-25, representing a tacit commitment to carbon debt and implying significant future energy system costs for large scale carbon dioxide removal [CDR] via Negative Emissions Technologies [NETs]. Due to the low current Technology Readiness Level [TRL] of proposed NETs, these costs are subject to high uncertainty. Nonetheless, prudential estimates of such costs should now properly be included in any notional cost effectiveness analyses of future energy policy interventions.

In all scenarios with significant quota overshoot, deployment of NETs then becomes unavoidable to reverse such overshoot (assuming continued good faith participation in the Paris Agreement). The feasibility of doing this at required scale is highly uncertain and is likely sharply constrained by absolute cost. Indigenous territorial potential is further severely limited by bioenergy resource availability for bioenergy with CCS [BECCS], total low/zero-carbon energy availability for direct air capture (of CO) with CCS [DACCS] or enhanced weathering [EW], and relatively very limited total territorial CO geo-storage potential (required for all forms of CCS deployment).

Accordingly, even in the (likely) quota overshoot scenarios, near-term deep reduction in unabated fossil fuel use to limit the extent and duration of overshoot remains a key national risk management imperative. This suggests that, even in the short term, the finalised NECP (to be properly Paris-aligned) should show a national annual CO emissions pathway to nett zero with minimum quota overshoot: that is to say, achieving nett-zero annual CO emissions much earlier than 2050.

Coupled with rapid reductions in fossil fuel CO emissions, early deployment of BECCS could, in principle, contribute to achieving nett-zero and then nett-negative total energy system CO emissions (to reverse accumulated quota overshoot). However, this would inter alia imply early prioritising of bioenergy fuel use into BECCS in preference to unabated end use in transport and small or medium scale heating. Of course this does not dilute the requirement for deep decarbonisation of the latter energy use sectors; rather it points at the need to focus primarily on strategies for those sectors which are not based on unabated bioenergy use (e.g., direct electrification and/or end use substitution with non-carbon electrofuels such as hydrogen).

Projected cumulative nett CO emissions in the LULUCF sector significantly impacts on quota available for energy (or, conversely, requires significantly greater cumulative nett-negative emissions in the energy sector to compensate).

In parallel, early demand reduction in all sectors, and early investment in low-regret or no-regret mitigation options are likely needed to achieve sustained reductions in nett absolute emissions.

Low regret energy system decarbonisation options, including large scale wind and solar energy development, non-carbon electrofuels produced at periods of excess variable renewable energy as large scale energy storage, for grid backup and direct end use in heat and transport, and limited CCS + NETs are likely all now essential components to prudent and effective climate mitigation action.

WP4 Report Full Text (PDF)