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
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102 results found

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, Pages: 961-972, ISSN: 0306-2619

© 2018 With increasing penetration of wind and solar generation the deployment of fast response plant, principally batteries, is currently considered necessary to mitigate reduced system inertia and the possibility of demand-supply imbalances. In this work the impact of these factors on battery cycling rates, taking into account the input from the batteries themselves, are analysed by applying the swing equation to a future inertia based on forecast generation mix. The operational capacity of batteries is a determining factor in their cycling rate, though the depth of discharge appears to be less well correlated. It is found that reducing system inertia does not, of itself, significantly impact on frequency volatility where the volatility of the generation to load imbalance is unchanged. However, the potential for a reduction in the damping of frequency deviations as a result of an increase in inverter connected motor drives may have a large impact on battery cycling characteristics. Provision of reserve services from battery systems requires a more complex operational strategy to ensure services are always deliverable and results in a significantly different cycling profile that may lead to greater battery degradation and consequently higher operational costs.

JOURNAL ARTICLE

Daggash HA, Heuberger CF, 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

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

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

JOURNAL ARTICLE

Fajardy M, Chiquier S, Mac Dowell N, 2018, Investigating the BECCS resource nexus: delivering sustainable negative emissions, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 3408-3430, ISSN: 1754-5692

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

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, Vol: 3, Pages: 634-640, ISSN: 2058-7546

JOURNAL ARTICLE

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

Harraz AA, Freeman J, Wang K, Mac Dowell N, Markides CNet al., Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-γ Mie, 10th International Conference on Applied Energy (ICAE2018), Publisher: Elsevier, 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 aprototype 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 250W. The group-contribution SAFT-γ Mie equation of state is of particular interest as it offers good agreement with experimental data and providesflexibility inextendingthe model to test different working fluids witha high degree of fidelity. A methodology is also presented that allowsthe DAR thermodynamic analysis and working-fluid modelling to be integrated intoa more general technology optimisation framework.

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

Mota-Martinez MT, Brandl P, Hallett JP, Mac Dowell Net al., 2018, Challenges and for the utilisation of ionic liquids as solvents for CO2 capture, MOLECULAR SYSTEMS DESIGN & ENGINEERING, Vol: 3, Pages: 560-571, ISSN: 2058-9689

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

JOURNAL ARTICLE

Fajardy M, Mac Dowell N, 2018, The energy return on investment of BECCS: is BECCS a threat to energy security?, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 1581-1594, ISSN: 1754-5692

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 & FUELS, Vol: 2, Pages: 1153-1169, ISSN: 2398-4902

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 & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 1062-1176, ISSN: 1754-5692

JOURNAL ARTICLE

Heuberger CF, 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

Galan-Martin A, Pozo C, Azapagic A, Grossmann IE, Mac Dowell N, Guillen-Gosalbez Get al., 2018, Time for global action: an optimised cooperative approach towards effective climate change mitigation, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 572-581, ISSN: 1754-5692

JOURNAL ARTICLE

Bui M, Fajardy M, Mac Dowell N, 2018, Bio-energy with carbon capture and storage (BECCS): Opportunities for performance improvement, FUEL, Vol: 213, Pages: 164-175, ISSN: 0016-2361

JOURNAL ARTICLE

, 2018, Towards a low carbon economy via sorptionenhanced water gas shift and alcohol reforming, Computer Aided Chemical Engineering, Pages: 1729-1734

© 2018 Elsevier B.V. Hydrogen (H2) is one of the most important raw materials in the chemical and refinery industries. H2 is also regarded as a future “energy vector” due to its potential to act as an ultraclean fuel in the heat, power, and transport sectors. Therefore, development of efficient, low carbon routes to produce H2 is essential to meet its current and growing demand. In particular, this has placed an imperative on improving the efficiency of steam reforming of hydrocarbons (SRH), this process being considered the most feasible and economic route to large scale H2 production. The water gas shift reaction (WGS) is one of the most important stages of SRH, but is equilibrium limited and requires improvements in energy efficiency. In this study, we demonstrate that the overall efficiency of the WGS can be improved by removing CO2 in situ and co-feeding alcohols such as methanol and ethanol. The feasibility of this novel concept is investigated by conducting thermodynamic analyses of the alcohol reforming/WGS (alcohol-to-shift) reactions for H2 production alone and with simultaneous CO2 adsorption (sorption-enhanced, SEalcohol-to-shift). To this end, a non-stoichiometric approach based on the minimisation of the Gibbs free energy is used. The results show that adding alcohols to the feed facilitates autothermal operation of the shift unit and significantly increases the amount of H2 produced. The H2 productivity can be further enhanced by adsorbing CO2 in situ. The theoretical studies presented here are carried out under relevant operating conditions for SRH and aim to serve as a guideline for future work on alcohol-to-shift processes enhanced by adsorption.

BOOK CHAPTER

Kolster C, Agada S, Mac Dowell N, Krevor Set al., 2018, 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

JOURNAL ARTICLE

Heuberger CF, Staffell I, Shah N, Mac Dowell Net al., 2017, A systems approach to quantifying the value of power generation and energy storage technologies in future electricity networks, COMPUTERS & CHEMICAL ENGINEERING, Vol: 107, Pages: 247-256, ISSN: 0098-1354

JOURNAL ARTICLE

Mota-Martinez MT, Hallett JP, Mac Dowell N, 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

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 & ENVIRONMENTAL SCIENCE, Vol: 10, Pages: 2594-2608, ISSN: 1754-5692

JOURNAL ARTICLE

Cabral RP, Mac Dowell N, 2017, A novel methodological approach for achieving pound/MWh cost reduction of CO2 capture and storage (CCS) processes, APPLIED ENERGY, Vol: 205, Pages: 529-539, ISSN: 0306-2619

JOURNAL ARTICLE

Heuberger CF, Rubin ES, Staffell I, Shah N, Mac Dowell Net al., 2017, Power capacity expansion planning considering endogenous technology cost learning, APPLIED ENERGY, Vol: 204, Pages: 831-845, ISSN: 0306-2619

JOURNAL ARTICLE

Agada S, Jackson S, Kolster C, Mac Dowell N, Williams G, Vosper H, Williams J, Krevor Set al., 2017, The impact of energy systems demands on pressure limited CO2 storage in the Bunter Sandstone of the UK Southern North Sea, INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL, Vol: 65, Pages: 128-136, ISSN: 1750-5836

JOURNAL ARTICLE

Fajardy M, Mac Dowell N, 2017, Can BECCS deliver sustainable and resource efficient negative emissions? (vol 10, 1389, 2017), ENERGY & ENVIRONMENTAL SCIENCE, Vol: 10, Pages: 2267-2267, ISSN: 1754-5692

JOURNAL ARTICLE

Psarras P, Krutka H, Fajardy M, Zhang Z, Liguori S, Mac Dowell N, Wilcox Jet al., 2017, Slicing the pie: how big could carbon dioxide removal be?, WILEY INTERDISCIPLINARY REVIEWS-ENERGY AND ENVIRONMENT, Vol: 6, ISSN: 2041-8396

JOURNAL ARTICLE

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