Imperial College London

DrNiallMac Dowell

Faculty of Natural SciencesCentre for Environmental Policy

Reader in Energy Systems
 
 
 
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Contact

 

+44 (0)20 7594 9298niall Website

 
 
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Location

 

16 Prince's GardensSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

110 results found

Cabral RP, Bui M, Dowell NM, 2019, A synergistic approach for the simultaneous decarbonisation of power and industry via bioenergy with carbon capture and storage (BECCS), International Journal of Greenhouse Gas Control, Vol: 87, Pages: 221-237, ISSN: 1750-5836

There is a need for a rapid and large scale decarbonisation to reduce CO2 emissions by 45% within 12 years. Thus, we propose a method that accelerates decarbonisation across multiple sectors via a synergistic approach with bioenergy with CCS (BECCS), which is able to remove 740 kgCO2 from air per MWh electricity generated. Industry is a hard-to-decarbonise sector which presents a unique set of challenges where, unlike the power sector, there are no obvious alternatives to CCS. One of these challenges is the significant variation of CO2 concentration, which directly influences CO2 capture costs, ranging from $10/tCO2 to over $170/tCO2 for high (95–99% CO2) and low CO2 concentration (4% CO2) applications, respectively. Re-purposing the existing coal-fired power plant fleet into BECCS displaces CO2 emissions from coal-use and enables a just transition, i.e., avoiding job loss, providing a supportive economic framework that does not rely on government subsidies. Negative emissions generated from capturing and storing atmospheric CO2 can be converted into negative emission credits (NECs) and auctioned to hard-to-decarbonise sectors, thus providing another revenue stream to the power plant. A levelised cost of electricity (LCOE) between $70 and $100 per MWh can be achieved through auctioning NECs at $90–$135 per tCO2. Offsetting the global industrial CO2 emissions of 9 GtCO2 would require 3000 BECCS plants under this framework. This approach could jumpstart industrial decarbonisation whilst giving this sector more time to develop new CCS technologies.

Journal article

Hankin A, Guillen Gosalbez G, Kelsall G, Mac Dowell N, Shah N, Weider S, Brophy Ket al., 2019, Assessing the economic and environmental value of carbon capture and utilisation in the UK, Briefing paper, 3

• As a signatory to the 2015 Paris Climate Change Agreement, the UK has committed to an ambitious transformation of its economy.• Decarbonisation of the UK’s economy must be a priority, but carbon-based fuels and platform chemicals will remain important to the global economy; their production from captured carbon dioxide and renewable energy can support this industrial need.• In this Briefing Paper, we report on results of a systematic procedure developed to assess the viability of different carbon capture and utilisation (CCU) pathways.• Our findings on three CCU pathways show that proposed CCU projects should always be assessed on a case-by-case basis, using detailed, UK centric, cradle-to-grave life cycle analyses.• CCU cannot provide the emission mitigation rate of carbon capture and storage (CCS), but as the UK’s entire geological storage capacity is offshore, CCU could mitigate emissions from inland point sources.• Of the considered CCU pathways, presently the production of polyurethane is the most promising for the UK and could provide an immediate short-term mitigation solution for greenhouse gas (GHG) emissions. Currently, methanol production does not appear to be a viable solution.

Report

Hankin A, Guillen Gosalbez G, Kelsall G, Mac Dowell N, Shah N, Weider S, Brophy Ket al., 2019, Assessing the economic and environmental value of carbon capture and utilisation in the UK, Briefing Note – summary of Briefing Paper No 3

• As a signatory to the 2015 Paris Climate Change Agreement, the UK has committed to an ambitious transformation of its economy.• Decarbonisation of the UK’s economy must be a priority, but carbon-based fuels and platform chemicals will remain important to the global economy; their production from captured carbon dioxide and renewable energy can support this industrial need.• In this Briefing Paper, we report on results of a systematic procedure developed to assess the viability of different carbon capture and utilisation (CCU) pathways.• Our findings on three CCU pathways show that proposed CCU projects should always be assessed on a case-by-case basis, using detailed, UK centric, cradle-to-grave life cycle analyses.• CCU cannot provide the emission mitigation rate of carbon capture and storage (CCS), but as the UK’s entire geological storage capacity is offshore, CCU could mitigate emissions from inland point sources.• Of the considered CCU pathways, presently the production of polyurethane is the most promising for the UK and could provide an immediate short-term mitigation solution for greenhouse gas (GHG) emissions. Currently, methanol production does not appear to be a viable solution.

Report

Daggash HA, Mac Dowell N, 2019, The implications of delivering the UK’s Paris Agreement commitments on the power sector, International Journal of Greenhouse Gas Control, Vol: 85, Pages: 174-181, ISSN: 1750-5836

Through the 2015 Paris Agreement, the UK committed to keeping average global temperature rise to “well below 2 °C”. Integrated Assessment Models show that this will require extensive greenhouse gas removal (GGR) from the atmosphere. For the EU, it is estimated that 20–70 GtCO2 of cumulative GGR by 2100 is required, all from bioenergy with carbon capture and storage (BECCS). Depending on how the burden of GGR is shared, the UK would need to remove 2–6 GtCO2 from the atmosphere. We apply a power systems planning model to determine how the electricity system would need to transition from 2015 to 2100 to meet the UK’s Paris Agreement commitments. We find that until 2050, increased penetration of renewables, interconnection capacity and energy storage, alongside 15–17 GW of CCGT−CCS, is sufficient to stay on the required emissions trajectory. Between 2050 and 2100, however, the deployment of 7–26 GW of BECCS and 2–5 GW of direct air capture and storage (DACS) is crucial to provide the GGR required. A Paris-compliant UK electricity system will require £620–700 billion of capital and operational expenditure by 2100, 3–16% greater than the cost of achieving a decarbonised system. For the upper-bound GGR target, local biomass supply is insufficient, so imports are necessary. By 2100, up to 26% of annual demand is met by imported biomass. Such heavy dependence on imports may raise energy security concerns. Also, should biomass imports not be available in the required quantities, alternative (and more expensive) GGR methods will be necessary thereby increasing the cost of delivering a Paris-compliant system.

Journal article

Cabral RP, Heldebrant DJ, Mac Dowell N, 2019, A Techno-Economic Analysis of a Novel Solvent-Based Oxycombustion CO <inf>2</inf> Capture Process, Industrial and Engineering Chemistry Research, ISSN: 0888-5885

Copyright © 2019 American Chemical Society. The gas processing unit (GPU) has previously been identified as the least thermodynamically efficient element of an oxycombustion process. A marginal improvement of this unit operation can provide a greater decrease of the parasitic power to the oxycombustion process than an equivalent improvement in the air separation unit (ASU). Hence, capturing CO 2 from oxycombustion using an alternative method than the conventional cryogenic process has potential to reduce the parasitic power consumption of the GPU. In this work, the authors present an initial evaluation of a new process concept; a hybrid oxycombustion process that uses a solvent-based GPU to capture CO 2 from the flue gas. N-Ethyldiethanolamine (EDEA) is a tertiary alkanolamine that captures CO 2 by forming a zwitterionic ammonium alkylcarbonate ionic liquid in the absence of water as a cosolvent. The new solvent-based GPU proposed herein demonstrates a clear potential to improve the net power efficiency by 1%, a 9% CAPEX reduction, and up to 5% LCOE reduction of an oxycombustion process if the price of EDEA is below $270/kg. Both lower CAPEX and the potential of reduced LCOE demonstrates that alternative CO 2 capture methods for oxycombustion can be more economical.

Journal article

Daggash HA, Mac Dowell N, 2019, Structural evolution of the UK electricity system in a below 2°C World, Joule, ISSN: 2542-4351

We employ an electricity system model to determine the least-cost transition necessary to meet a given carbon dioxide removal (CDR) burden in the UK. The results show that, while sufficient in the medium term, a system dominated by intermittent renewable energy technologies (IRES) cannot deliver CDR at the scale required in a cost-effective manner. The marginal value of IRES for climate change mitigation diminishes with time, especially in the context of the Paris Agreement. Deeper decarbonization precipitates a resurgence of thermal generation from bioenergy and gas (with carbon capture and storage) and nuclear. Such a system is inherently centralized and will require maintenance of existing transmission and distribution infrastructure. Current policy direction, however, encourages the proliferation of renewables and decentralization of energy services. To avoid locking the power system into a future where it cannot meet climate change mitigation ambitions, policy must recognize and adequately incentivize the new technologies (CCS) and services (CDR) necessary.

Journal article

Lee R, Homan S, Mac Dowell N, Brown Set al., 2019, A closed-loop analysis of grid scale battery systems providing frequency response and reserve services in a variable inertia grid, APPLIED ENERGY, Vol: 236, Pages: 961-972, ISSN: 0306-2619

Journal article

Daggash H, Heuberger C, Mac Dowell N, 2019, The role and value of negative emissions technologies in decarbonising the UK energy system, International Journal of Greenhouse Gas Control, Vol: 81, Pages: 181-198, ISSN: 1750-5836

The UK is committed to the Paris Agreement and has a legally-binding target to reduce economy-wide greenhouse gas emissions by 80% relative to 1990 levels by 2050. Meeting these targets would require deep decarbonisation, including the deployment of negative emissions technologies. This study, via a power supply capacity expansion model, investigates the potential role of bio-energy with carbon capture and storage (BECCS) and direct air capture and storage (DACS) in meeting the UK's emissions reduction targets. We show that to achieve power sector decarbonisation, a system dominated by firm and dispatchable low-carbon generators with BECCS or DACS to compensate for their associated emissions is significantly cheaper than a system dominated by intermittent renewables and energy storage. By offsetting CO2 emissions from cheaper thermal plants, thereby allowing for their continued utilisation in a carbon-constrained electricity system, BECCS and DACS can reduce the cost of decarbonisation by 37–48%. Allowing some this value transferred to accrue to NETs offers a potential route for their commercial deployment.

Journal article

Harraz AA, Freeman J, Wang K, Mac Dowell N, Markides CNet al., 2019, Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-γ Mie, Energy Procedia, Vol: 158, Pages: 2360-2365, ISSN: 1876-6102

Diffusion-absorption refrigeration (DAR) is a clean thermally-powered refrigeration technology that can readily be activated by low- to medium-grade renewable heat. There is an ongoing interest in identifying or designing new working fluids for performance improvement, particularly in solar applications with non-concentrating solar collectors providing heat at temperatures < 150 °C. In this work, the state-of-the-art statistical associating fluid theory (SAFT) is adopted for predicting the thermodynamic properties of suitable DAR working fluids. A first-law thermodynamic analysis is performed in the software environment gPROMS for a DAR cycle using ammonia as the refrigerant, water as the absorbent and hydrogen as the auxiliary gas. The simulation results show good agreement with experimental data generated in a prototype DAR system with a nominal cooling capacity of 100 W. In particular, at a charge pressure of 17 bar and when delivering cooling at 5 °C, the model results agree with experimental COP data to within ± 7 % over a range of heat inputs from 150 to 500 W. The maximum coefficient of performance (COP) is estimated to be 0.24 at a heat input of 250 W. The group-contribution SAFT-γ Mie equation of state is of particular interest as it offers good agreement with experimental data and provides flexibility in extending the model to test different working fluids with a high degree of fidelity. A methodology is also presented that allows the DAR thermodynamic analysis and working-fluid modelling to be integrated into a more general technology optimisation framework.

Journal article

Algunaibet I, Pozo Fernandez C, Galan Martin A, Huijbregts M, Mac Dowell N, Guillen Gosalbez Get al., Powering sustainable development within planetary boundaries, Energy and Environmental Science, ISSN: 1754-5692

The concept of planetary boundaries identifies a safe space for humanity. Current energy systems are primarily designed with a focus on total cost minimization and bounds on greenhouse gas emissions. Omitting planetary boundaries in energy systems design can lead to energy mixes unable to power our sustainable development. To overcome this conceptual limitation, we here incorporate planetary boundaries into energy systems models, explicitly linking energy generation with the Earth’s ecological limits. Taking the United States as a testbed, we found that the least cost energy mix that would meet the Paris Agreement 2 degrees Celsius target, still transgresses five out of eight planetary boundaries. It is possible to meet seven out of eight planetary boundaries concurrently by incurring a doubling of the cost compared to the least cost energy mix solution (1.3% of the United States gross domestic product in 2017). Due to the stringent downscaled planetary boundary on biogeochemical nitrogen flow, there is no energy mix in the United States capable of satisfying all planetary boundaries concurrently. Our work highlights the importance of considering planetary boundaries in energy systems design and paves the way for further research on how to effectively accomplish such integration in energy related studies.

Journal article

Patrizio P, Leduc S, Kraxner F, Fuss S, Kindermann G, Mesfun S, Spokas K, Mendoza A, Mac Dowell N, Wetterlund E, Lundgren J, Dotzauer E, Yowargana P, Obersteiner Met al., 2018, Reducing US Coal Emissions Can Boost Employment, JOULE, Vol: 2, Pages: 2633-2648, ISSN: 2542-4351

Journal article

Al-Saqlawi J, Madani K, Mac Dowell N, 2018, Techno-economic feasibility of grid-independent residential roof-top solar PV systems in Muscat, Oman, Energy Conversion and Management, Vol: 178, Pages: 322-334, ISSN: 0196-8904

Oman is a country characterised by high solar availability, yet very little electricity is produced using solar energy. As the residential sector is the largest consumer of electricity in Oman, we develop a novel approach, using houses in Muscat as a case study, to assess the potential of implementing roof-top solar PV/battery technologies, that operate without recourse to the electricity grid. Such systems target the complete decarbonisation of electricity demand per household and are defined in this study as grid-independent systems. The approach adopted starts with a technical assessment of grid-independent systems that evaluates the characteristics of the solar panel and the battery facility required to provide grid-independence. This is then compared to a similar grid-connected system and any techno-economic targets necessary to enhance the feasibility of residential roof-top PV systems in Muscat are identified. Such an analysis was achieved through developing a detailed techno-economic mathematical model describing four sub-systems; the solar panel DC source, the grid-independent sub-system, the grid-connected sub-system and the economic sub-system. The model was implemented in gPROMS and uses real hourly weather and climate conditions matched with real demand data, over a simulated period of 20 years. The results indicate that, in the context of the system studied, grid-independent PV systems are not feasible. However, combined with a sufficiently high electricity price, grid-independent systems can become economically feasible only with significant reductions in battery costs (>90% reductions).

Journal article

Bui M, Tait P, Lucquiaud M, Mac Dowell Net al., 2018, Dynamic operation and modelling of amine-based CO2 capture at pilot scale, International Journal of Greenhouse Gas Control, Vol: 79, Pages: 134-153, ISSN: 1750-5836

This study combines pilot plant experiments and dynamic modelling to gain insight into the interaction between key process parameters in producing the dynamic response of an amine-based CO2 capture process. Three dynamic scenarios from the UKCCSRC PACT pilot plant are presented: (i) partial load stripping, (ii) capture plant ramping, and (iii) reboiler decoupling. These scenarios are representative of realistic flexible operation of non-baseload CCS power stations. Experimental plant data was used to validate a dynamic model developed in gCCS. In the capture plant ramping scenario, increased liquid-to-gas (L/G) ratio resulted in higher CO2 capture rate. The partial load stripping scenario demonstrated that the hot water flow directly affects reboiler temperature, which in turn, has an impact on the solvent lean loading and CO2 capture rate. The reboiler decoupling scenario demonstrates a similar relationship. Turning off the heat supply to the reboiler leads to a gradual decline in reboiler temperature, which increases solvent lean loading and reduces CO2 capture rate. The absorber column temperature profile is influenced by the degree of CO2 capture. For scenarios that result in lower solvent lean loading, the absorber temperature profile shifts to higher temperature (due to the higher CO2 capture rate).

Journal article

Budinis S, Krevor S, Mac Dowell N, Brandon N, Hawkes Aet al., 2018, An assessment of CCS costs, barriers and potential, Energy Strategy Reviews, Vol: 22, Pages: 61-81, ISSN: 2211-467X

© 2018 Elsevier Ltd Global decarbonisation scenarios include Carbon Capture and Storage (CCS) as a key technology to reduce carbon dioxide (CO2) emissions from the power and industrial sectors. However, few large scale CCS plants are operating worldwide. This mismatch between expectations and reality is caused by a series of barriers which are preventing this technology from being adopted more widely. The goal of this paper is to identify and review the barriers to CCS development, with a focus on recent cost estimates, and to assess the potential of CCS to enable access to fossil fuels without causing dangerous levels of climate change. The result of the review shows that no CCS barriers are exclusively technical, with CCS cost being the most significant hurdle in the short to medium term. In the long term, CCS is found to be very cost effective when compared with other mitigation options. Cost estimates exhibit a high range, which depends on process type, separation technology, CO2transport technique and storage site. CCS potential has been quantified by comparing the amount of fossil fuels that could be used globally with and without CCS. In modelled energy system transition pathways that limit global warming to less than 2 °C, scenarios without CCS result in 26% of fossil fuel reserves being consumed by 2050, against 37% being consumed when CCS is available. However, by 2100, the scenarios without CCS have only consumed slightly more fossil fuel reserves (33%), whereas scenarios with CCS available end up consuming 65% of reserves. It was also shown that the residual emissions from CCS facilities is the key factor limiting long term uptake, rather than cost. Overall, the results show that worldwide CCS adoption will be critical if fossil fuel reserves are to continue to be substantively accessed whilst still meeting climate targets.

Journal article

Fajardy M, Chiquier S, Mac Dowell N, 2018, Investigating the BECCS resource nexus: delivering sustainable negative emissions, Energy and Environmental Science, ISSN: 1754-5692

Bioenergy with carbon capture and storage (BECCS), and other negative emissions technologies (NETs), are integral to all scenarios consistent with meeting global climate ambitions. BECCS's ability to promptly remove CO2 from the atmosphere in a resource efficient manner, whilst being a net energy generator to the global economy, remains controversial. Given the large range of potential outcomes, it is crucial to understand how, if at all, this technology can be deployed in a way which minimises its impact on natural resources and ecosystems, while maximising both carbon removal and power generation. In this study, we present a series of thought experiments, using the Modelling and Optimisation of Negative Emissions Technologies (MONET) framework, to provide insight into the combinations of biomass feedstock, origin, land type, and transport route, to meet a given CO2 removal target. The optimal structure of an international BECCS supply chain was found to vary both quantitatively and qualitatively as the focus shifted from conserving water, land or biomass, to maximising energy generated, with the water use in particular increasing threefold in the land and biomass use minimisation scenario, as compared to the water minimisation scenario. In meeting regional targets, imported biomass was consistently chosen over indigenous biomass in the land and water minimisation scenarios, confirming the dominance of factors such as yield, electricity grid carbon intensity, and precipitation, over transport distance. A pareto-front analysis was performed and, in addition to highlighting the strong trade-offs between BECCS resource efficiency objectives, indicated the potential for tipping points. An analysis of the sensitivity to the availability of marginal land and agricultural residues showed that (1) the availability of agricultural residues had a great impact on BECCS land, and that (2) water use and land use change, two critical sustainability indicators for BECCS, were neg

Journal article

Iruretagoyena Ferrer D, Sunny N, Chadwick D, Mac Dowell N, Shah Net al., Towards a low carbon economy via sorption enhanced water gas shift and alcohol reforming

Book chapter

Najjaran Kheirabadi A, Harraz AA, Freeman J, Mac Dowell N, Markides CNet al., 2018, Numerical and experimental investigations of diffusion absorption refrigeration systems for use with low temperature heat sources, ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS

he diffusion absorption refrigeration (DAR) cycle is a technology of increasing interest thanks to its suitabilityfor providing cooling from a thermal energyinputin a range of applications. Itcan bedistinguished from other absorption refrigeration cycles by its employment of a thermally-driven bubble pump to circulate the working fluid, which gives it anability to operate entirely off-gridwithout an electricity input. In this work,we present results from an experimentalcampaign aimed atcharacterisingthe performance of aprototypeammonia-water-hydrogen DAR system with a nominal cooling capacity of 100 W,over a range of operating conditions, specifically with a view ofadaptingthe system for use in low-temperature applications. In the experiments, the heat input to the DAR generator is provided over a range of temperatures from175to215°Cby using electrical cartridge heaters. The system is charged to 22 bar, and the ammonia mass concentration of the working fluid mixture is 30%. The resulting coefficient of performance (COP) of the system is measured in the range 0.12to 0.26. A new methodology for the selection of optimal working-fluid mixtures using the state-of-the-art, statistical associating fluid theory (SAFT) approach implemented within the process modelling software gPROMS®is also presented. The experimental results will be used for futurevalidation of a thermodynamic model of the cycle. Finally,the performance of the system in a solar application is investigated, with a thermal inputprovided by an array of evacuated tube heat pipe solar collectors. The system pressure and condensation temperature are found to be key factors in determining the performance of solar-DAR systems.

Conference paper

Heuberger CF, Rubin ES, Staffell L, Shah N, Mac Dowell Net al., 2018, Power capacity expansion planning considering endogenous technology cost learning (vol 204, pg 831, 2017), APPLIED ENERGY, Vol: 220, Pages: 974-974, ISSN: 0306-2619

Journal article

Schnellmann MA, Heuberger CF, Scott SA, Dennis JS, Mac Dowell Net al., 2018, Quantifying the role and value of chemical looping combustion in future electricity systems via a retrosynthetic approach, International Journal of Greenhouse Gas Control, Vol: 73, Pages: 1-15, ISSN: 1750-5836

Carbon capture and sequestration of CO2from the combustion of fossil fuels in thermal power plants is expected to be important in the mitigation of climate change. Deployment however falls far short of what is required. A key barrier is the perception by developers and investorsthat these technologies are too inefficient, expensive and risky. To address these issues, we have developed a novel retrosynthetic approach to evaluate technologies and their design based on the demands of the system in which they would operate. We have applied it to chemical looping combustion (CLC), a promising technology, which enables carbon dioxide emissions to be inherently captured from the combustion of fossil fuels. Our approach has provided unique insight into the potential role and value of different CLC variants in future electricity systems and the likely impact of their integration on the optimal capacity mix, the operational and system cost, and dispatch patterns. The three variants investigated couldall provide significant value by reducing the total investment and operational cost of a future electricity system. The minimisation of capital cost appears to be key for the attractiveness of CLC, rather than other factors such as higher efficiency or loweroxygen carrier costs.

Journal article

Mac Dowell N, Hallett JP, 2018, Challenges and opportunities for the utilisation of ionic liquids as solvents for CO2 capture, Molecular Systems Design & Engineering, Vol: 3, Pages: 560-571, ISSN: 2058-9689

Ionic Liquids have been extensively investigated as promising materials for several gas separationprocesses, including CO2capture. They have the potential to outperform traditional solvents, interms of their capacity, selectivity, regenerability and stability. In fact, hundreds of ionic liquidshave been investigated as potential sorbents for CO2capture. However, most studies focus onenhancing equilibrium capacity, and neglect to consider other properties, such as transport prop-erties, and hence ignore the effect that the overall set of properties have on process performance,and therefore on cost. In this study, we propose a new methodology for their evaluation using arange of monetised and non-monetised process performance indices. Our results demonstratethat whilst most research effort is focused on improving CO2solubility, viscosity, a transport prop-erty, and heat capacity, a thermochemical property, might preclude the use of ionic liquids, eventhose which are highly CO2-philic, and therefore increased effort on addressing the challengesassociated with heat capacity and viscosity is an urgent necessity. This work highlights a rangeof potential challenges that ionic liquids will face before they can be applied at process scale, andidentifies some key research opportunities.

Journal article

Daggash HA, Patzschke CF, Heuberger CF, Zhu L, Hellgardt K, Fennell PS, Bhave AN, Bardow A, Mac Dowell Net al., 2018, Closing the carbon cycle to maximise climate change mitigation: Power-to-Methanol vs Power-to-Direct Air Capture, Sustainable Energy and Fuels, Vol: 2, Pages: 1153-1169, ISSN: 2398-4902

It is broadly recognised that CO2 capture and storage (CCS) and associated negative emissions technologies (NETs) are vital to meeting the Paris agreement target. The hitherto failure to deploy CCS on the required scale has led to the search for options to improve its economic return. CO2 capture and utilisation (CCU) has been proposed as an opportunity to generate value from waste CO2 emissions and improve the economic viability of CCS, with the suggestion of using curtailed renewable energy as a core component of this strategy. This study sets out to quantify (a) the amount of curtailed renewable energy that is likely to be available in the coming decades, (b) the amount of fossil CO2 emissions which can be avoided by using this curtailed energy to convert CO2 to methanol for use as a transport fuel – power-to-fuel, with the counterfactual of using that curtailed energy to directly remove CO2 from the atmosphere via direct air capture (DAC) and subsequent underground storage, power-to-DAC. In 2015, the UK curtailed 1277 GWh of renewable power, or 1.5% of total renewable power generated. Our analysis shows that the level of curtailed energy is unlikely to increase beyond 2.5% until renewable power accounts for more than 50% of total installed capacity. This is unlikely to be the case in the UK before 2035. It was found that: (1) power-to-DAC could achieve 0.23–0.67 tCO2 avoided MWh−1 of curtailed power, and (2) power-to-Fuel could achieve 0.13 tCO2 avoided MWh−1. The power-to-fuel concept was estimated to cost $209 tCO2 avoided−1 in addition to requiring an additional $430–660 tCO2 avoided−1 to finally close the carbon cycle by air capture. The power-to-DAC concept was found to cost only the $430–660 tCO2 avoided−1 for air capture. For power-to-fuel to become profitable, hydrogen prices would need to be less than or equal to $1635 tH2−1 or methanol prices must increase to $960 tMeOH−1. Absent this ch

Journal article

Fajardy M, Mac Dowell N, 2018, The energy return on investment of BECCS: is BECCS a threat to energy security?, Energy and Environmental Science, Vol: 11, Pages: 1581-1594, ISSN: 1754-5692

Compliance with long term climate targets whilst maintaining energy security is understood to relyheavily on the large-scale deployment of negative emissions technologies (NETs). One option,Bioenergy with Carbon Capture and Storage (BECCS) is prominent in Integrated AssessmentModels (IAMs), with projected annual contributions of 8 – 16.5 GtCO2/yr of atmospheric carbondioxide removal whilst contributing 150 – 300 EJ/yr, or 14 to 20% of global primary energy supply,in 2100. Implicit in these scenarios is the assumption that BECCS is a net producer of energy.However, relatively energy intensive biomass supply chains and low power generation efficiencycould challenge this ubiquitous assumption. Deploying an energy negative technology at thisscale could thus represent a threat to energy security. In this contribution, we evaluate the energyreturn on investment (EROI) of an archetypal BECCS facility. In order to highlight the importanceof biomass sourcing, two feedstock scenarios are considered: use of domestic biomass pellets(UK) and import of biomass pellets from Louisiana, USA. We use the Modelling and Optimisationof Negative Emissions Technologies (MONET) framework to explicitly account for growing, pre-treating, transporting and converting the feedstock in a 500 MW BECCS facility. As an example,we illustrate how the net electricity balance (NElB) of a UK-based BECCS facility can be eitherpositive or negative, as a function of supply chain decisions. Power plant efficiency, fuel efficiencyfor transport, transport distance, moisture content, drying method, as well as yield were identifiedas key factors that need to be carefully managed to maximise BECCS net electricity balance. Akey insight of this contribution is that, given an annual carbon removal target, increasing BECCS’power generation efficiency by using a more advanced biomass conversion and CO2capturetechnology could improve BECCS net electricity balance, but at the cos

Journal article

Heuberger CF, Staffell I, Shah N, Mac Dowell Net al., 2018, Impact of myopic decision-making and disruptive events in power systems planning., Nature Energy, ISSN: 1520-8524

The delayed deployment of low-carbon energy technologies is impeding energy system decarbonization. The continuing debate about the cost-competitiveness of low-carbon technologies has led to a strategy of waiting for a ‘unicorn technology’ to appear. Here, we show that myopic strategies that rely on the eventual manifestation of a unicorn technology result in either an oversized and underutilized power system when decarbonization objectives are achieved, or one that is far from being decarbonized, even if the unicorn technology becomes available. Under perfect foresight, disruptive technology innovation can reduce total system cost by 13%. However, a strategy of waiting for a unicorn technology that never appears could result in 61% higher cumulative total system cost by mid-century compared to deploying currently available low-carbon technologies early on.

Journal article

Heuberger C, Mac Dowell N, 2018, Real-world challenges with a rapid transition to 100 % renewable power systems, Joule, Vol: 2, Pages: 367-370, ISSN: 2542-4351

Journal article

Bui M, Adjiman CS, Bardow A, Anthony EJ, Boston A, Brown S, Fennell PS, Fuss S, Galindo A, Hackett LA, Hallett JP, Herzog HJ, Jackson G, Kemper J, Krevor S, Maitland GC, Matuszewski M, Metcalfe IS, Petit C, Puxty G, Reimer J, Reiner DM, Rubin ES, Scott SA, Shah N, Smit B, Trusler JPM, Webley P, Wilcox J, Mac Dowell Net al., 2018, Carbon capture and storage (CCS): the way forward, Energy and Environmental Science, Vol: 11, Pages: 1062-1176, ISSN: 1754-5692

Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

Journal article

Galán-Martín A, Pozo C, Azapagic A, Grossmann IE, Mac Dowell N, Guillén-Gosálbez Get al., 2018, Time for global action: an optimised cooperative approach towards effective climate change mitigation, Energy and Environmental Science, Vol: 11, Pages: 572-581, ISSN: 1754-5692

The difficulties in climate change negotiations together with the recent withdrawal of the U.S. from the Paris Agreement call for new cooperative mechanisms to enable a resilient international response. In this study we propose an approach to aid such negotiations based on quantifying the benefits of interregional cooperation and distributing them among the participants in a fair manner. Our approach is underpinned by advanced optimisation techniques that automate the screening of millions of alternatives for differing levels of cooperation, ultimately identifying the most cost-effective solutions for meeting emission targets. We apply this approach to the Clean Power Plan, a related act in the U.S. aiming at curbing carbon emissions from electricity generation, but also being withdrawn. We find that, with only half of the states cooperating, the cost of electricity generation could be reduced by US$41 billion per year, while simultaneously cutting carbon emissions by 68% below 2012 levels. These win–win scenarios are attained by sharing the emission targets and trading electricity among the states, which allows exploiting regional advantages. Fair sharing of dividends may be used as a key driver to spur cooperation since the global action to mitigate climate change becomes beneficial for all participants. Even if global cooperation remains elusive, it is worth trying since the mere cooperation of a few states leads to significant benefits for both the U.S. economy and the climate. These findings call on the U.S. to reconsider its withdrawal but also boost individual states to take initiative even in the absence of federal action.

Journal article

Kolster C, Masnadi MS, Krevor S, Dowell NM, Brandt ARet al., 2017, CO2 enhanced oil recovery: a catalyst for gigatonne-scale carbon capture and storage deployment?, Energy and Environmental Science, Vol: 10, Pages: 2594-2608, ISSN: 1754-5692

Using carbon dioxide for enhanced oil recovery (CO2-EOR) has been widely cited as a potential catalyst for gigatonne-scale carbon capture and storage (CCS) deployment. Carbon dioxide enhanced oil recovery could provide revenues for CO2 capture projects in the absence of strong carbon taxes, providing a means for technological learning and economies of scale to reduce the cost of CCS. We develop an open-source techno-economic Model of Iterative Investment in CCS with CO2-EOR (MIICE), using dynamic technology deployment modeling to assess the impact of CO2-EOR on the deployment of CCS. Synthetic sets of potential CCS with EOR projects are created with typical field characteristics and dynamic oil and CO2 production profiles. Investment decisions are made iteratively over a 35 year simulation period, and long-term changes to technology cost and revenues are tracked. Installed capacity at 2050 is used as an indicator, with 1 gigatonne per year of CO2 capture used as a benchmark for successful large-scale CCS deployment. Results show that current CO2 tax and oil price conditions do not incentivize gigatonne-scale investment in CCS. For current oil prices ($45 per bbl–$55 per bbl), the final CO2 tax must reach $70 per tCO2 for gigatonne-scale deployment. If oil price alone is expected to induce CCS deployment and learning, oil prices above $85 per bbl are required to promote the development of a gigatonne-scale CCS industry. Nonlinear feedbacks between early deployment and learning result in large changes in final state due to small changes in initial conditions. We investigate the future of CCS in five potential ‘states of the world’: an optimistic ‘Base Case’ with a low CO2 tax and low oil price, a ‘Climate Action’ world with high CO2 tax, a ‘High Oil’ world with high oil prices, a ‘Depleting Resources’ world with an increasing deficit in oil supply, and a ‘Forward Learning’ world where mechan

Journal article

Kolster C, Agada S, Mac Dowell N, Krevor Set al., 2017, The impact of time-varying CO2 injection rate on large scale storage in the UK Bunter Sandstone, International Journal of Greenhouse Gas Control, Vol: 68, Pages: 77-85, ISSN: 1750-5836

Carbon capture and storage (CCS) is expected to play a key role in meeting targets set by the Paris Agreement and for meeting legally binding greenhouse gas emissions targets set within the UK (Energy and Climate Change Committee, 2016). Energy systems models have been essential in identifying the importance of CCS but they neglect to impose constraints on the availability and use of geologic CO2 storage reservoirs. In this work we analyse reservoir performance sensitivities to varying CO2 storage demand for three sets of injection scenarios designed to encompass the UK's future low carbon energy market. We use the ECLIPSE reservoir simulator and a model of part of the Southern North Sea Bunter Sandstone saline aquifer. From a first set of injection scenarios we find that varying amplitude and frequency of injection on a multi-year basis has little effect on reservoir pressure response and plume migration. Injectivity varies with site location due to variations in depth and regional permeability. In a second set of injection scenarios, we show that with envisioned UK storage demand levels for a large coal fired power plant, it makes no difference to reservoir response whether all injection sites are deployed upfront or gradually as demand increases. Meanwhile, there may be an advantage to deploying infrastructure in deep sites first in order to meet higher demand later. However, deep-site deployment will incur higher upfront cost than shallow-site deployment. In a third set of injection scenarios, we show that starting injection at a high rate with ramping down, a low rate with ramping up or at a constant rate makes little difference to the overall injectivity of the reservoir. Therefore, such variability is not essential to represent CO2 storage in energy systems models resolving plume and pressure evolution over decadal timescales.

Journal article

Bui M, Fajardy M, Mac Dowell N, 2017, Bio-energy with carbon capture and storage (BECCS): Opportunities for performance improvement, Fuel, Vol: 213, Pages: 164-175, ISSN: 0016-2361

This study evaluates the performance of a 500 MW pulverised fuel BECCS system. A performance matrix is developed to assess the opportunities for BECCS performance improvement in terms of: energy efficiency, carbon intensity, and pollutant emissions. The effect of fuel properties was analysed for variable (i) coal type (high/medium sulphur content), (ii) biomass type (wheat straw and wood chips), (iii) moisture content, and (iv) biomass co-firing proportion %. It was observed that the co-firing of biomass increased the quantity and quality of waste heat available for recovery from the exhaust gas. The opportunities to improve energy efficiency in the BECCS system include enhancing heat recovery and using high performance solvents for CO2 capture, such as biphasic materials. Implementing these approaches increased the power generation efficiency from 31%HHV (conventional MEA system) to 38%HHV (using an advanced biphasic solvent with heat recovery). Furthermore, power generation efficiency was found to influence the carbon intensity on an annual basis and annual capacity (load factor) of the BECCS system. Significant reductions to SOX emissions were achieved by increasing biomass co-firing % or using low sulphur coal.

Journal article

Mac Dowell N, Hallett J, Mota Martinez M, 2017, Solvent selection and design for CO2 capture - how we might have been missing the point, Sustainable Energy & Fuels, Vol: 1, Pages: 2078-2090, ISSN: 2398-4902

Carbon capture and storage (CCS) is a vital technology for the cost-effective mitigation of anthropogenic CO2 emissions. However, a key obstacle to its deployment on a large scale remains its cost – both capital and operating costs. In this context, the development of improved sorbents is a key research priority. Consequently, there is a vast global effort to develop new materials for this purpose, with literally thousands of new materials having been proposed since the beginning of the millennium. One common element of these contributions is that they focus on the equilibrium capacity of the material to absorb CO2 and rarely, if ever, other key factors such as transport properties. To date, the majority of this effort has cost significant amounts of time and resources and has almost exclusively focused on developing sorbents with increased CO2 capacity and/or reduced heat of regeneration. Given that sorbent regeneration largely dictates operational cost, this would, on the surface, appear rational. However, it is vital to recall that the cost structure of $ per MWh of electricity generated is composed of contributions from both capital and operational costs. Consequently, this single-minded focus on equilibrium CO2 capacity and heat of regeneration excludes the contribution of transport and kinetic properties which determine the equipment size and thus the capital cost. Therefore, in order to develop sorbents which will result in a non-negligible cost reduction, it is essential to move beyond equilibrium-based metrics of sorbent performance. In this paper, we present a new methodological approach for sorbent screening which explicitly includes rate-based phenomena. Our approach uses both monetised and non-monetised performance indicators. Our results suggest that whilst equilibrium CO2 capacity is a key determinant of process performance, transport properties (e.g., viscosity) and other thermophysical properties (e.g., heat capacity) have a significant effect

Journal article

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