BECCS and DACCS as Negative Emission Providers in an Intermittent Electricity System: Why Levelized Cost of Carbon May Be a Misleading Measure for Policy Decisions

Carbon dioxide removal (CDR) from the atmosphere is likely to be needed to limit global warming to 1.5 or 2\ub0C and thereby for meeting the Paris Agreement. There is a debate which methods are most suitable and cost-effective for this goal and thus deeper understanding of system effects related to CDR are needed for effective governance of these technologies. Bio-Energy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS) are two CDR methods, that have a direct relation to the electricity system—BECCS via producing it and DACCS via consuming. In this work, we investigate how BECCS and DACCS interact with an intermittent electricity system to achieve net negative emissions in the sector using an energy system model and two regions with different wind and solar resource conditions. The analysis shows that DACCS has a higher levelized cost of carbon (LCOC) than BECCS, implying that it is less costly to capture CO2 using BECCS under the assumptions made in this study. However, due to a high levelized cost of electricity (LCOE) produced by BECCS, the total system cost is lower using DACCS as negative emission provider as it is more flexible and enables cheaper electricity production from wind and solar PV. We also find that the replacement effect outweighs the flexibility effect. Since variations in solar-based systems are more regular and shorter (daily cycles), one could assume that DACCS is better suited for such systems, whereas our results point in the opposite direction showing that DACCS is more competitive in the wind-based systems. The result is sensitive to the price of biomass and to the amount of negative emissions required from the electricity sector. Our results show that the use of the LCOC as often presented in the literature as a main indicator for choosing between different CDR options might be misleading and that broader system effects need to be considered for well-grounded decisions

Biomass in the electricity system: A complement to variable renewables or a source of negative emissions?

Biomass is often assigned a central role in future energy system scenarios as a carbon sink, making negative greenhouse gas emissions possible through carbon capture and storage of biogenic carbon dioxide from biomass-fuelled power plants. However, biomass could also serve as a strategic complement to variable renewables by supplying electricity during hours of high residual load. In this work, we investigate the role of biomass in electricity systems with net zero or negative emissions of carbon dioxide and with different levels of biomass availability. We show that access to biomass corresponding to ca. 20% of the electricity demand in primary energy terms, is of high value to the electricity system. Biomass for flexibility purposes can be a cost-efficient support to reach a carbon neutral electricity system with the main share of electricity from wind and solar power. Biomass-fired power plants equipped with carbon capture and storage in combination with natural gas combined cycle turbines are identified as being the cost-effective choice to supply the electricity system with flexibility if the availability of biomass within the electricity system is low. In contrast, in the case of excess biomass, flexibility is supplied by biomethane-fired combined cycle turbines or by biomass-fired power plants

The Potential Role of Ammonia as Marine Fuel-Based on Energy Systems Modeling and Multi-Criteria Decision Analysis

To reduce the climate impact of shipping, the introduction of alternative fuels is required. There is a range of different marine fuel options but ammonia, a potential zero carbon fuel, has recently received a lot of attention. The purpose of this paper is to assess the prospects for ammonia as a future fuel for the shipping sector in relation to other marine fuels. The assessment is based on a synthesis of knowledge in combination with: (i) energy systems modeling including the cost-effectiveness of ammonia as marine fuel in relation to other fuels for reaching global climate targets; and (ii) a multi-criteria decision analysis (MCDA) approach ranking marine fuel options while considering estimated fuel performance and the importance of criteria based on maritime stakeholder preferences. In the long-term and to reach global GHG reduction, the energy systems modeled indicate that the use of hydrogen represents a more cost-effective marine fuel option than ammonia. However, in the MCDA covering more aspects, we find that ammonia may be almost as interesting for shipping related stakeholders as hydrogen and various biomass-based fuels. Ammonia may to some extent be an interesting future marine fuel option, but many issues remain to be solved before large-scale introduction

WHAT FUTURE FOR ELECTROFUELS?

Transport sector is seen as the most difficult sector to decarbonise. In recent years so called electrofuels have been proposed as one option for emissions reduction. Electrofuels – fuels made from electricity and carbon dioxide - can potentially help to manage variations in electricity production and reducethe need for biofuels as well as make use of current infrastructure and can be used in sectors where fuel switch is difficult such as aviation. We investigate the cost-effectiveness of electrofuels under climate mitigation constraint and find that electrofuels are unlikely to become cost-effective unless options for storing carbon are very limited

The role of negative carbon emissions in reaching the Paris climate targets: The impact of target formulation in integrated assessment models

Global net-negative carbon emissions are prevalent in almost all emission pathways that meet the Paris temperature targets. In this paper, we generate and compare cost-effective emission pathways that satisfy two different types of climate targets. First, the common approach of a radiative forcing target that has to be met by the year 2100 (RF2100), and, second, a temperature ceiling target that has to be met over the entire period, avoiding any overshoot. Across two integrated assessment models (IAMs), we found that the amount of net-negative emissions - when global net emissions fall below zero - depends to a large extent on how the target is represented, i.e. implemented in the model. With a temperature ceiling (no temperature overshoot), net-negative emissions are limited and primarily a consequence of trade-offs with non-CO2 emissions, whereas net-negative emissions are significant for the RF2100 target (temperature overshoot). The difference becomes more pronounced with more stringent climate targets. This has important implications: more stringent near-term emission reductions are needed when a temperature ceiling is implemented compared to when an RF2100 target is implemented. Further, in one IAM, for our base case assumptions, the cost-effective negative carbon emissions (i.e. gross anthropogenic removals) do not depend to any significant extent on how the constraint is implemented, only, largely, on the ultimate stringency of the constraint. Hence, for a given climate target stringency in 2100, the RF2100 target and the temperature ceiling may result in essentially the same amount of negative carbon emissions. Finally, it is important that IAM demonstrate results for diverse ways of implementing a climate target, since the implementation has implications for the level of near-term emissions and the perceived need for net-negative emissions (beyond 2050)

Reviewing the development of alternative aviation fuels and aircraft propulsion systems

Alternative aviation fuels such as bio-jet fuels, liquid natural gas (LCH4), hydrogen (H2), electro-jet fuels and direct electricity use play an important role in decarbonizing the aviation sector. New aircraft propulsion systems are being developed but low-blending of fuels is possible for some options. It is imperative to understand the technical, environmental and economic performance of the different alternative aviation fuels and the new engine and propulsion technologies for the utilization of these fuels. We have reviewed various literature to map the current status of development on alternative aviation fuels and related aircraft propulsion systems in relation to different perspective such as their cost and technical maturity. There are several challenges related to the design and implementation of the fuels and new propulsion systems. For instance, the volumetric energy content of alternative fuels is lower than the conventional aviation fuels which requires larger fuel storage tanks. Despite the advantageous environmental performance, both the bio-jet and electro-jet fuels are currently not economically competitive. Yet, studies forecast that increased use of alternative aviation fuels is possible after modifications of engines, fuel storage tanks and improvements of the aerodynamics of aircraft and by introducing subsidies and/or carbon taxes on conventional jet fuels

What Future for Electrofuels in Transport? Analysis of Cost Competitiveness in Global Climate Mitigation

The transport sector is often seen as the most difficult sector to decarbonize. In recent years, so-called electrofuels have been proposed as one option for reducing emissions. Electrofuels-here defined as fuels made from electricity, water, and carbon dioxide-can potentially help manage variations in electricity production, reduce the need for biofuels in the transportation sector while utilizing current infrastructure, and be of use in sectors where fuel switching is difficult, such as shipping. We investigate the cost-effectiveness of electrofuels from an energy system perspective under a climate mitigation constraint (either 450 or 550 ppm of CO2 in 2100), and we find the following: (i) Electrofuels are unlikely to become cost-effective unless options for storing carbon are very limited; in the most favorable case modeled-an energy system without carbon storage and with the more stringent constraint on carbon dioxide emissions-they provide approximately 30 EJ globally in 2070 or approximately 15% of the energy demand from transport. (ii) The cost of the electrolyzer and increased availability of variable renewables appear not to be key factors in whether electrofuels enter the transport system, in contrast to findings in previous studies

Actuating the European Energy System Transition: Indicators for Translating Energy Systems Modelling Results into Policy-Making

In this paper, we define indicators, with a focus on the electricity sector, that translate the results of energy systems modelling to quantitative entities that can facilitate assessments of the transitions required to meet stringent climate targets. Such indicators, which are often overlooked in model scenario presentations, can be applied to make the modelling results more accessible and are useful for managing the transition on the policy level, as well as for internal evaluations of modelling results. We propose a set of 13 indicators related to: 1) the resource and material usages in modelled energy system designs; 2) the rates of transition from current to future energy systems; and 3) the energy security in energy system modelling results. To illustrate its value, the proposed set of indicators is applied to energy system scenarios derived from an electricity system investment model for Northern Europe. We show that the proposed indicators are useful for facilitating discussions, raising new questions, and relating the modelling results to Sustainable Development Goals and thus facilitate better policy processes. The indicators presented here should not be seen as a complete set, but rather as examples. Therefore, this paper represents a starting point and a call to other modellers to expand and refine the list of indicators

Nuclear Power as a Climate Change Mitigation Option: a Modelling Approach

Although nuclear power can provide electricity with very low life cycle carbon emissions and thus reduce the cost of climate change mitigation, it also brings along many specific challenges: accident risk, need for radioactive waste management and nuclear weapons proliferation risk. Due to this controversial nature nuclear power, among other energy forms, has been relatively little studied in a climate mitigation context. This thesis aims to provide some insight into the possible role of nuclear power in climate change mitigation.In the first paper we assess the impact of potential nuclear expansion and advanced nuclear cycles on climate change mitigation cost and reflect on this expansion’s relation to nuclear weapons proliferation risk. We find that nuclear power can reduce the mitigation cost around 20%, and new reactor types and advanced uranium extraction methods provide a significant part of the savings (10%). To materialize those savings however the number of reactors would need to increase tenfold by 2070, which implies an increase in enrichment and/or reprocessing facilities, technologies that are directly related to proliferation risk. We show that even if reprocessing can be made proliferation safe as some scientists believe, the switch to a closed fuel cycle that does not need enrichment will take more than the remainder of this century under a cost minimising condition, and therefore proliferation risk cannot be eliminated.In the second paper we investigate further the mitigation cost reducing ability of nuclear power by subjecting our model to numerous parameter variations and a Monte Carlo analysis. We observe that nuclear power can provide significant cost savings in almost all cases and that the expansion of nuclear power is dependent on climate policy. In addition we discovered that the capacity for carbon capture and storage plays a significant role in cases of a nuclear phase out and high climate sensitivity but is inconsequential if nuclear expansion is allowed

Modelling the Role of Nuclear Power and Variable Renewables in Climate Change Mitigation

As the number of people on Earth and our energy needs have increased the system for providing this energy has become ever more complex and complicated and thus the need for more systematic understanding of it has grown. However, change in energy system is slow and many of the challenges that we face such as mitigating climate change need global solutions. Energy system models with long time span and global reach provide a way to analyse questions related to these challenges. This thesis focuses on capturing the role of nuclear power and variable renewables in global long term energy models.Papers I, II and IV assess the potential role nuclear power can play in global climate mitigation as well as identify the determining factors of this contribution whereas Paper III looks at the possible effects of phase out of Swedish nuclear power on European CO2 emissions and electricity prices. We show that nuclear power can reduce the climate change mitigation cost if allowed to remain or expand. The main factors determining the cost reduction potential are availability and cost of carbon capture and storage and cost of renewable and nuclear technologies. However, to decide whether to allow for a large scale expansion of nuclear power, the observed cost savings must be weighed against increased risks of accidental radiation releases from reactor operation, waste storage and nuclear weapons proliferation. To make this decision economic as well as non-economic factors should also be considered.To analyse such concerns we use post analysis of model scenarios in Paper I to assess the nuclear power expansion’s effect on nuclear weapons’ proliferation and apply the multi-criteria model analysis (MCMA) method in Paper IV to actively include criteria such as proliferation concern and energy security into optimisation. We find that MCMA method significantly improves the analysis of attainability of multiple simultaneous goals such in large-scale energy-systems models compared to simple scenario analysis that is presented in Paper I. The approach is more intuitive and requires minimal mathematical skills on the part of the user. MCMA method also avoids infeasible or dominated solutions that are caused by the stringent constraints applied in parametric optimisation.Paper V presents a method for capturing the effects of intermittency induced by variable renewables into the power system. Our results show that this approach manages to capture many aspects such as need for flexible generation capacity and curtailment at high penetration levels. We also find optimal electricity production mixes to vary significantly between regions due to different endowments of solar and wind resources. We show that adding electricity storage to the system will favour solar power but has only a minor effect on wind and nuclear power