Imperial College London

ProfessorChristosMarkides

Faculty of EngineeringDepartment of Chemical Engineering

Professor of Clean Energy Technologies
 
 
 
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Contact

 

+44 (0)20 7594 1601c.markides Website

 
 
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Location

 

404ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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478 results found

He Y, Song J, Guo S, Zhou J, Markides CNet al., 2024, Profitability analysis and sizing-arbitrage optimisation of retrofitting coal-fired power plants for grid-side energy storage, Journal of Energy Storage, Vol: 84

In the context of global decarbonisation, retrofitting existing coal-fired power plants (CFPPs) is an essential pathway to achieving sustainable transition of power systems. This paper explores the potential of using electric heaters and thermal energy storage based on molten salt heat transfer fluids to retrofit CFPPs for grid-side energy storage systems (ESSs), along with an investigation of the energy arbitrage profitability. Sizing and scheduling co-optimisation of CFPP-retrofitted ESSs is formulated as a bi-level framework, in which the upper-level sizing model aims to achieve the maximum net present value (NPV) and the lower-level scheduling model maximises the annual arbitrage profit. The co-optimisation problem is solved by the teaching-learning-based optimisation algorithm coupled with the mixed integer linear programming optimiser. Furthermore, the initial state of charge (SOC) factor is innovatively considered as a decision variable in the scheduling optimisation, which is co-optimised with the charging/discharging power of ESSs. Taking a CFPP with the realistic annual electricity tariff profile in Zhejiang Province, China from 12/2022 to 11/2023 as a case study (annual average peak-valley tariff gap of 132 USD/MWh and peak duration of 6/8 h), the results show that the CFPP-retrofitted ESS is profitable via energy arbitrage. The initial SOC factor is found to have a significant impact on the profitability of the CFPP retrofitting scheme, and the optimal value (24 %) enables the full operational cycle of energy arbitrage and increases the NPV by 16 % compared to the default value (50 %). The levelised cost of storage of the CFPP-retrofitted ESS is also evaluated and compared with those of Li-ion and Lead-acid batteries, with results indicating that the CFPP-retrofitted ESS is more cost-effective than batteries in energy arbitrage applications. Finally, sensitivity analyses of electricity tariff profiles are conducted to explore the profitability with diffe

Journal article

Li W, Zeng M, Wang B, Chen Y, Markides CNet al., 2024, Characteristic analysis of lithium–oxygen batteries considering the discontinuous deposit and electrolyte degradation effects during discharge, Journal of Energy Storage, Vol: 82

The modeling research plays a crucial role in grasping the reaction mechanisms and forecasting the performance of lithium‑oxygen (Li[sbnd]O2) batteries. A transient Li[sbnd]O2 battery model including continuity, transportation, and reaction kinetics by simultaneously considering the discontinuous deposit of discharge product Li2O2 and the formation of by-product Li2CO3 due to electrolyte degradation, is developed to reveal the discharge phenomena. The effects of operating conditions and electrolyte and electrode properties on the discharge behaviors including voltage-capacity curve, energy density, profiles of O2 concentration (CO2) and porosity (ɛ) at the cathode are quantitatively studied. It is found that enhancing O2 solubility (SO2) and diffusivity (DO2) significantly improves discharge capacity and voltage plateau; the promotion of voltage plateau will be inconspicuous as electrolyte conductivity (κ) is enlarged over 1 S/m. With the rise of ɛ from 0.73 to 0.93, the specific capacity is boosted from 874 to 6122 mAh/g‑carbon, and the corresponding specific energy upgrades from 2260 to 15,610 mWh/g‑carbon. Shortening cathode thickness (Lca) facilitates the efficient utilization of carbon cathode material but this comes at the expense of lowering the mass loading of carbon, the practical energy drops 59.4 % as Lca reduces from 750 μm to 100 μm. After 20 consecutive charge-discharge cycles, the capacity retention obtained is 36.884 %, accompanied by a 13.8 % volume fraction of Li2CO3 formation inside the cathode. This work may guide in designing electrodes and electrolytes and provide performance regulation strategies for Li[sbnd]O2 batteries.

Journal article

Olympios AV, Song J, Ziolkowski A, Shanmugam VS, Markides CNet al., 2024, Data-driven compressor performance maps and cost correlations for small-scale heat-pumping applications, Energy, Vol: 291, ISSN: 0360-5442

The performance of vapour-compression heat pumps depends crucially upon compressor selection and design. In this work, a unified modelling framework is developed to enable technoeconomic comparisons of compressors intended for small-scale heating applications (<30 kWth). Published information on 120 commercially available compressors is analysed and used to develop performance maps that predict isentropic efficiency over a wide range of working conditions. Additionally, cost correlations are established to predict price as a function of nominal compressor inlet volumetric flowrate. When rotary-vane compressors are an available option (i.e., for inlet volumetric flowrates up to 5 ∙ 10−3 m3/s), they consistently achieve a high isentropic efficiency (∼70 %) for the investigated pressure ratios (1.5–9.5). Scroll compressors have an even higher isentropic efficiency (∼75 %) at pressure ratios below 5.5, but this drops to 50 % at higher pressure ratios, while the isentropic efficiency of reciprocating-piston compressors is best (∼75 %) at higher pressure ratios (5.5–7.5). Utilising an air-source heat pump model, the compressor types are compared for countries with different weather characteristics and electricity prices. Rotary-vane compressors are associated with the lowest levelised cost of heat, but the comparison largely depends on location and heating requirements.

Journal article

Roy D, Zhu S, Wang R, González-Pino I, Herrando M, Markides CN, Roskilly APet al., 2024, Techno-economic and environmental analyses of a solar-assisted Stirling engine cogeneration system for different dwelling types in the United Kingdom, Energy Conversion and Management, Vol: 302, ISSN: 0196-8904

In this study, a hybrid cogeneration system that combines photovoltaic-thermal (PV-T) collectors with a Stirling engine, and a battery-pack-based energy option is proposed for residential applications. The system's purpose is to fulfil the electrical and heating requirements of different types of houses in the United Kingdom, including detached, semi-detached and mid-terraced houses. This study includes a comprehensive assessment of the techno-economic feasibility and environmental impact of the proposed integrated energy system, after determining the appropriate sizing of the system's components for the three different house types. The exergy efficiency of the integrated system for detached houses (with a 1 kWe-Stirling engine plus 28 m2 of PV-T collector array) is found to be higher compared to that for the semi-detached and mid-terraced house configurations, with the highest efficiency of 22 %. In terms of economic performance, detached houses have the lowest levelized cost of electricity (0.622 £/kWh), levelized cost of heat (0.147 £/kWh), and levelized cost of total energy (0.205 £/kWh). Furthermore, the system demonstrates the maximum potential reduction in CO2 emissions in detached houses. The achieved CO2 emissions reduction rates for different house configurations fall within the range of 30 % to 45 %. The proposed hybrid cogeneration system shows promise as an effective and sustainable solution to meet the energy demands of various residential house types in the United Kingdom, offering improved efficiency, cost-effectiveness, and substantial reductions in carbon emissions for detached houses.

Journal article

Municchi F, Markides CN, Matar OK, Magnini Met al., 2024, Computational study of bubble, thin-film dynamics and heat transfer during flow boiling in non-circular microchannels, Applied Thermal Engineering, Vol: 238, ISSN: 1359-4311

Flow boiling in multi-microchannel evaporators is one of the most efficient thermal management solutions forhigh-power-density applications. However, there is still a lack of understanding of the governing two-phaseheat and mass transfer processes that occur in these devices, which has resulted in a limited availability ofapplicable boiling heat transfer prediction methods based on first principles, and of reliable thermal designtools. This article presents a systematic analysis of the dynamics of bubbles and the surrounding liquid filmduring flow boiling in three-side-heated non-circular microchannels. The study is performed using a customversion of ESI OpenFOAM v2106 with a geometric volume-of-fluid method to capture the interface dynamics, also incorporating conjugate heat transfer through the evaporator walls. The hydraulic diameter of the channel is fixed to 𝐷ℎ = 0.229 mm and the range of width-to-height aspect ratios 𝜖 = 0.25−4 is examined. We investigate different fluids, namely water, HFE7100, R1233zd(E), R1234ze(E), and evaporator materials, namely copper, aluminium, silicon, stainless steel, with base heat fluxes in the range 𝑞𝑏 = 50 − 200 kW∕m2. The results show that conjugate heat transfer acts to make the temperature distributions around the perimeter of the channel cross-section more uniform, and that the topography of the lubricating film and the extension of the dry vapour patches that develop while the film is depleted both depend on the cross-sectional channel shape and influence the heat transfer performance significantly. For highly wetting conditions, channels with 𝜖 = 0.25 tend to allow enhanced heat transfer rates, with a spatially-averaged Nusselt number that is 50% higher than that obtained for 𝜖 = 1 (square channels) and 10% higher than that for 𝜖 = 4. This arises thanks to an extended evaporating film that covers the vertical walls which, owing to the three-side-heated configuration, contribute twice to the spatially-ave

Journal article

A I, Kumar C S S, Chougule SS, Markides CN S Jet al., 2024, Enhanced electrolytic immersion cooling for thermal crisis mitigation in high-energy–density systems, Energy Conversion and Management, Vol: 300, ISSN: 0196-8904

Motivated by the increasing need for effective cooling solutions in high-energy–density systems, this experimental study presents the two-phase cooling of a superheated SS 316L sample via immersion quenching in saturated deionized (DI) water at atmospheric pressure conditions with and without a DC electric field. We investigate the effect of the applied electric field, electrode polarity, and in-situ oxidation on quenching characteristics such as the cooling profile, vapour layer behaviour, minimum film boiling temperature (Tmin), and heat transfer rate. The cooling curves of samples quenched with the application of an electric field shift towards the left compared to the sample quenched without an electric field. The cathode sample at 200 V exhibits 33 % faster cooling than the bare sample (0 V). Overall, the in-situ oxidised SS 316L cathode sample at 200 V exhibits a 55 % reduction in film boiling duration, and Tmin increased from 268 °C to 322 °C compared to the bare sample (0 V). The visualisation studies highlight that the liquid–vapour interface experiences a series of oscillations followed by temporal collapse due to electrostatic attraction and electrolytic activity. The obtained results show that hydrogen-rich vapour bubbles increase heat transfer performance. The evolution of hydrogen and its adsorption at the sample surface reduces the activation energy for bubble nucleation and improves the bubble density via liquid pumping. These insights open the pathway for employing hydrogen bubbles for handling ultra-high thermal loads in high-energy density systems, and the specific case of a revised design of concentrating solar receiver is considered based on the present findings.

Journal article

Fan G, Song J, Zhang J, Fu Z, Gong X, Dai Y, Markides CNet al., 2024, Thermo-economic assessment and systematic comparison of combined supercritical CO2 and organic Rankine cycle (SCO2-ORC) systems for solar power tower plants, Applied Thermal Engineering, Vol: 236, ISSN: 1359-4311

Solar power towers (SPTs) integrated with thermal energy storage are promising solutions for solar energy utilisation. Supercritical CO2 power cycles are acknowledged as an attractive option for dry-cooling SPT plants. However, abundant low-grade waste heat exists in the SCO2 gas cooler, which is directly dissipated to the ambient. In order to further improve the performance of SCO2-based SPT plants, organic Rankine cycle (ORC) systems can be introduced as a bottoming cycle subsystem. In this paper, an ORC subsystem is added to four different SCO2 cycle layouts, i.e., recuperated (RE), recompression (RC), intercooling (IC), and partial cooling (PC) cycles, to form combined cycle systems for SPT applications. A parametric study reveals that the thermal efficiency of the power block (i.e., the whole power cycle system), and the salt temperature difference across the receiver are the determining factors of the thermo-economic performance of SPT-SCO2-ORC plants. Design optimisation and annual performance evaluations are implemented using actual weather data in Delingha, China. Compared to the SPT plant with a standalone recuperated SCO2 cycle system, the annual electricity generation is increased by 19 % by integrating a bottoming ORC subsystem. The SPT-RC-ORC system produces the maximum electricity generation of 123 GW·h/year, while the SPT-RE-ORC system achieves the lowest levelised cost of electricity (LCOE) of 0.12 $/kW·h and the minimum payback time of 8.8 years. A wide range of solar irradiance conditions is further considered to generalise the performance evaluation of such combined cycle systems, with results showing that with the highest solar irradiance investigated (3700 sunshine hours, 1000 W/m2·h), the LCOE of the SPT-RE-ORC plant can be as low as 0.07 $/kW·h and the payback time is as short as 6 years. This study investigates optimal SCO2-ORC configurations for SPT applications based on annual performance evaluations, and presen

Journal article

Li W, Wang B, Chen Y, Deng Y, Markides CN, Zeng Met al., 2024, Discharge characteristic analysis of lithium-sulfur batteries considering the discontinuous deposit and transport-limited effects, Journal of Cleaner Production, Vol: 436, ISSN: 0959-6526

The modeling research plays a crucial role in grasping the reaction mechanisms and forecasting the performance of lithium-sulfur (Li–S) batteries. A transient Li–S battery model including continuity, transportation, and reaction kinetics by simultaneously considering the discontinuous deposit of discharge product Li2S and the transport limitation in the concentrated electrolyte, is developed to reveal the discharge phenomena. The effects of operating conditions and electrolyte and electrode properties on the discharge behaviors including voltage-capacity curve, energy density, profiles of solid product (ɛLi2S) and porosity (ɛ) at the cathode are quantitatively studied. It is found that low discharge rate is beneficial to the discharge capacity and utilization of cathode sulfur. Enhancing precipitate (S8) solubility Ksp, S8 and ionic diffusivity Di improves voltage plateau and specific energy to varying degrees; the promotion of voltage plateau will be inconspicuous as electrode conductivity σ is enlarged over 0.1 S/m. With the rise of ɛ from 0.5 to 0.9, the specific capacity and the specific energy are expanded by around 5 times. When lengthening Lca from 20 μm to 60 μm, the specific capacity ascends from 944.5 to 991.5 mAh/g-S, whereas the growth rate of specific capacity and specific energy decreases gradually; the practical total energy almost increases linearly with thickness, yielding a 218.75% enhancement. With a certain period of relaxation, the recovered cell capacity after the high discharge rate is higher than that after the low discharge rate. This work may guide in designing electrodes and electrolytes and provide performance regulation strategies for Li–S batteries.

Journal article

Li W, Markides CN, Zeng M, Peng Jet al., 2024, 4E evaluations of salt hydrate-based solar thermochemical heat transformer system used for domestic hot water production, Energy, Vol: 286, ISSN: 0360-5442

A critical step toward the widespread use of renewables is the development of effective energy storage technology. An impressive solution for energy storage and heat upgrade is the salt hydrate-based solar thermochemical heat transformer (THT). The article aims at the temperature lift effects of pressurization-assisted THT systems employing different salts to fulfill the heat requirements of domestic hot water (DHW) generation. To grasp the sustainability of the GJ-level THT systems, energy, exergy, economic, and environmental (4E) assessments are performed under various working conditions. Results manifest that the majority of THT systems enable discharging temperatures (Tdis) to surpass 65 °C, matching regular DHW production. Tdis can be further boosted by the two-stage pressurization whereas at the expense of lowering thermodynamic properties. The SrBr2-based system almost exhibits the best 4E performances with a Tdis of 74.3 °C, although its levelized energy cost (LEC) of 0.1162 $/kWh is slightly higher than that of the LiOH-based system (0.1147 $/kWh). Both systems yield great useable heat, up to 11,667 MJ and 11,140 MJ, respectively, with maximum exergy efficiency of 89.16 % and 63.41 %. Albeit capable of generating higher temperature DHW (≥90 °C), the useable heat and thermodynamic performances of the FeCl2 and CaCl2 based systems are unsatisfactory. By contrast, the K2CO3 and LiOH based systems render higher temperature DHW while ensuring acceptable thermodynamic properties and useable heat. Targeting the regular and higher temperature DHW productions, the lowest CO2 emissions are separately achieved by the SrBr2 and LiCl based systems, i.e., 15 kg/MWh and 56.2 kg/MWh; and the former shows the slowest growth rate in carbon emission with increased Tdis. Augmenting solar irradiation and duration contributes to reducing LEC, and the ideal operating conditions in thermo-economic performance may differ from system to system.

Journal article

Alkharusi T, Huang G, Markides CN, 2024, Characterisation of soiling on glass surfaces and their impact on optical and solar photovoltaic performance, Renewable Energy, Vol: 220

Photovoltaic (PV) module soiling, i.e., the accumulation of soil deposits on the surface of a PV module, directly affects the amount of solar energy received by the PV cells in that module and can also give rise to additional heating, leading to significant power generation losses. In this work, we present results from an extensive outdoor experimental testing campaign of soiling, apply detailed characterisation techniques, and consider the resulting losses. Soil from sixty low-iron glass coupons was collected at various tilt angles over a study period of 12 months to capture monthly, seasonal and annual variations. Transmittance measurements showed that the horizontal coupons experienced the highest degree of soiling. The horizontal wet-season, dry-season and full-year samples experienced a relative transmittance decrease of 65 %, 68 %, and 64 %, respectively, which corresponds to a predicted relative decrease of 67 %, 70 %, and 66 % in electrical power generation. An analysis of the soiling matter using an X-ray diffractometer and a scanning electron microscope showed the presence of particulate matter with diameters <10 μm (PM10), which was the most prevalent in the studied region.

Journal article

Varallo N, Mereu R, Besagni G, Markides CNet al., 2024, Computational fluid dynamics modelling of the regular wave flow regime in air-water downwards annular flows, Chemical Engineering Research and Design, Vol: 201, Pages: 631-644, ISSN: 0263-8762

Although the global flow characteristics of annular gas-liquid flows have been studied experimentally for more than 50 years, the spatiotemporally-resolved details of these flows have remained relatively unexplored until recently, with data provided via advanced experimental methods based, e.g., on optical techniques. Similarly, the numerical modelling of annular flows is still an immature process. The present work aims to provide a computational fluid dynamics (CFD) model based on the volume of fluid (VOF) method for simulating annular gas-liquid flows, setting the stage for a deeper investigation of these flows at global and local scales. The work focuses on the most common downwards annular flow (DAF) flow pattern: the regular wave regime. 3-D and 2-D axisymmetric transient simulations have been performed using a commercial code (ANSYS Fluent 2021 R1). The code is validated through available experimental data regarding topological flow properties, mainly film thickness and wave statistics. The validation results suggest that 3-D simulations are needed to provide predictions that agree with the experimental data, highlighting strong 3-D features in the flow.

Journal article

Li L, Liu K, Tian H, Cai J, Markides CN, Wang J, Shi L, Wang X, Ma Y, Liang X, Shu Get al., 2023, A low-carbon CO2 ice rink technology for the Winter Olympics, Science Bulletin, Vol: 68, Pages: 2877-2880, ISSN: 2095-9273

Journal article

Aunedi M, Olympios AV, Pantaleo AM, Markides CN, Strbac Get al., 2023, System-driven design and integration of low-carbon domestic heating technologies, Renewable and Sustainable Energy Reviews, Vol: 187, ISSN: 1364-0321

This research explores various combinations of electric heat pumps (EHPs), hydrogen boilers (HBs), electric boilers (EBs), hydrogen absorption heat pumps (AHPs) and thermal energy storage (TES) to assess their potential for delivering cost-efficient low-carbon heat supply. The proposed technology-to-systems approach is based on comprehensive thermodynamic and component-costing models of various heating technologies, which are integrated into a whole-energy system optimisation model to determine cost-effective configurations of heating systems that minimise the overall cost for both the system and the end-user. Case studies presented in the study focus on two archetypal systems: (i) the North system, which is characterised by colder climate conditions and abundant wind resource; and (ii) the South system, which is characterised by a milder climate and higher solar energy potential. The results indicate a preference for a portfolio of low-carbon heating technologies including EHPs, EBs and HBs, coupled with a sizable amount of TES, while AHPs are not chosen, since, for the investigated conditions, their efficiency does not outweigh the high investment cost. Capacities of heat technologies are found to vary significantly depending on system properties such as the volume and diversity of heat demand and the availability profiles of renewable generation. The bulk of heat (83–97%) is delivered through EHPs, while the remainder is supplied by a mix of EBs and HBs. The results also suggest a strong impact of heat demand diversity on the cost-efficient mix of heating technologies, with higher diversity penalizing EHP relatively more than other, less capital-intensive heating options.

Journal article

Zhu S, Wang T, Jiang C, Wu Z, Yu G, Hu J, Markides C, Luo Eet al., 2023, Experimental and numerical study of a liquid metal magnetohydrodynamic generator for thermoacoustic power generation, Applied Energy, Vol: 348, ISSN: 0306-2619

Combining a thermoacoustic cycle engine with a liquid metal magnetohydrodynamic (LMMHD) generator will result in a thermal power generation system with no mechanical moving parts and high reliability. This disruptive technology has drawn much attention in space nuclear power generation, especially in recent years. It requires an LMMHD generator to work at a higher frequency than conventional LMMHD generators targeted for ocean wave energy conversion. However, the operating characteristics and loss mechanisms of LMMHD generators at high operating frequencies remain poorly understood, and experimental characterization of such a generator is lacking. In this work, a three-dimensional transient numerical analysis of a high-frequency LMMHD generator is performed based on multi-physics field simulation software COMSOL, to understand the operating characteristics of the generator, and the effects of inlet velocity, load resistance, and operating frequency on the generator’s performance. Furthermore, an LMMHD generator prototype was designed, constructed, and tested under different inlet velocities, load resistances, and frequencies by using a linear compressor for the first time. When the operating frequency and inlet velocity are 15 Hz and 4.3 m/s, the output voltage and current of the generator prototype reached 113 mV and 1720 A, with an output power of 68 W at a corresponding acoustic-to-electric efficiency of 24 %. A discrepancy between the numerical predictions and the experimental results was found, which gave insight into where further improvements can be made. This work reveals the operating characteristics and losses mechanism of LMMHD generators operating at higher frequencies and contributes to the development of high-efficiency generators for thermoacoustic power generation.

Journal article

Georgiev AG, Bottarelli M, Besagni G, Markides CNet al., 2023, Editorial/ preface of VSI:ATE_AESMT'22, APPLIED THERMAL ENGINEERING, Vol: 233, ISSN: 1359-4311

Journal article

Maghrabi AM, Song J, Markides CN, 2023, How can industrial heat decarbonisation be accelerated through energy efficiency?, Applied Thermal Engineering, Vol: 233, ISSN: 1359-4311

The ongoing energy transition necessitates commitments from various sectors to utilise resources more efficiently. Amongst these, the industrial sector, which is associated with high energy and resource consumption and emissions, has been attracting attention specifically aimed at performance enhancements and continuous progress in energy utilisation. The continued evolution of industrial operations and performance requires energy efficiency measures to be developed and implemented. Diverse portfolios of products, wide-ranging types of equipment, processes and, subsequently, plants, are adopted in the industrial sector, such that energy efficiency measures vary widely, along with their effectiveness, technological maturity, technical and economic impact. It remains a challenge to select the optimal energy efficiency measure(s) for a specific industry, plant and process, given the specific asset requirements. In this context, the development of systematic approaches for identifying optimal energy efficiency measures is of great interest. In this vision paper, we present an assembly of available systematic tools for advancing the energy efficiency of plants and sites in the industrial sector. The contribution of this work to the field of industrial heat decarbonisation arises from developing and proposing the use of a new holistic framework as a guide for the continuous performance improvement of thermal-energy-intensive industries through a series of energy efficiency measures and actions. Specifically, the framework suggests initiating efforts from a proposed top-down peer benchmarking practice aimed at identifying gaps in energy-efficiency performance across products, plants, processes and equipment. In a second stage, recommendations are made in form of a list of steps to close these gaps, starting with conducting equipment gap closure analyses, followed by design improvement studies at the process, plant and site levels using tools such as pinch analysis, steam s

Journal article

Maghrabi A, Song J, Sapin P, Markides CNet al., 2023, Electricity demand reduction through waste heat recovery in olefins plants based on a technology-agnostic approach, Energy Conversion and Management: X, Vol: 20, Pages: 1-18, ISSN: 2590-1745

Developing systematic approaches for the identification of optimal WHR options in industrial applications is key to reducing plant-scale energy demands. In particular, electricity consumption accounts for more than half of industrial energy use, and its share is expected to grow with progressive electrification. In this paper, industrial WHR technologies including organic Rankine cycle (ORC) and absorption systems are investigated, and tools are developed to understand the sustainability and techno-economic impact of integrating these technologies within industrial processes and facilities. We specifically propose a data-driven technology-agnostic approach to evaluate the use of heat engines, which can in practice be ORC systems, and thermally-driven (i.e., absorption) heat pumps in the context of industrial WHR for plant-scale electricity demand reduction. The aim of this work is to explore three pathways for achieving efficiency improvements in bulk chemicals plants, represented here by olefins production facilities: (i) direct onsite power generation; (ii) enhancement of existing power generation processes; and (iii) reduction in power consumption by compressor efficiency improvements through waste-heat-driven cooling. The techno-economic performance of these technologies is assessed for five different countries representing a diverse portfolio of climates, technical and economic parameters (including utility prices), using fine-tuned thermodynamic and market-based costing models. The results reveal that the proposed approach has the potential to reduce emissions by between 5,000 tCO2(eq.)/year and 101,500 tCO2(eq.)/year depending on the scenario. The marginal abatement cost of the proposed solutions ranges from -1,200 $/tCO2(eq.) to -35 $/tCO2(eq.), with a payback time between 1.5 and 8 years depending on the scenario considered.

Journal article

Jamil MA, Shahzad MW, Bin Xu B, Imran M, Ng KC, Zubair SM, Markides CN, Worek WMet al., 2023, Energy-efficient indirect evaporative cooler design framework: an experimental and numerical study, Energy Conversion and Management, Vol: 292, ISSN: 0196-8904

A remarkable surge in cooling demand is observed in the last decades. Currently, the cooling market is dominated by mechanical vapor compression chillers which are energy intensive and use harmful chemical refrigerants. Therefore, the current focus of the current research in cooling is the development of unconventional, sustainable cooling systems. In this regard, indirect evaporative coolers have shown significant potential (particularly under hot-dry climates) with high energy efficiency, low cost, water-based sustainable operation, and benign emissions. However, these systems are in the development stage and have not yet been fully commercialized because of certain design challenges. An innovative indirect evaporative cooler is proposed, fabricated, and experimentally tested in this study. Particularly, the study is focused on the development of heat transfer coefficient correlation for the system for commercial-scale design and expansion. This is because the earlier available correlation is based on simple airflow between parallel plates assumption and does not incorporate the effect of the evaporative potential of the system resulting in under/over-estimation of the heat transfer characteristics. The results showed that the proposed system achieved a temperature drop of 20 °C, a cooling capacity of around 180 W, and an overall heat transfer coefficient of up to 30 W/m2K. Moreover, the study presents an experiment-regression-based heat transfer coefficient correlation that satisfactorily captures the effect of outdoor air temperature and airflow rate ratio which are critical in the design of evaporative coolers. The proposed correlation showed a high (±5%) with experimental data thus making it suitable for the future design of IEC systems over assorted operating scenarios.

Journal article

Hoseinpoori P, Hanna R, Woods J, Markides C, Shah Net al., 2023, Comparing alternative pathways for the future role of the gas grid in a low-carbon heating system, Energy Strategy Reviews, Vol: 49, Pages: 1-25, ISSN: 2211-467X

This paper uses a whole-system approach to examine different strategies related to the future role of the gas grid in alow-carbon heat system. A novel model of integrated gas, electricity and heat systems, HEGIT, is used to investigate fourkey sets of scenarios for the future of the gas grid using the UK as a case study: a) complete electrification of heating; b)conversion of the existing gas grid to deliver hydrogen; c) a hybrid heat pump system; and d) a greener gas grid. Ourresults indicate that although the infrastructure requirements, the fuel or resource mix, and the breakdown of costs varysignificantly over the complete electrification to complete conversion of the gas grid to hydrogen spectrum, the total systemtransition cost is relatively similar. This reduces the significance of total system cost as a guiding factor in policy decisionson the future of the gas grid. Furthermore, we show that determining the roles of low-carbon gases and electrification fordecarbonising heating is better guided by the trade-offs between short- and long-term energy security risks in the system,as well as trade-offs between consumer investment in fuel switching and infrastructure requirements for decarbonisingheating. Our analysis of these trade-offs indicates that although electrification of heating using heat pumps is not thecheapest option to decarbonise heat, it has clear co-benefits as it reduces fuel security risks and dependency on carboncapture and storage infrastructure. Combining different strategies, such as grid integration of heat pumps with increasedthermal storage capacity and installing hybrid heat pumps with gas boilers on the consumer side, are demonstrated toeffectively moderate the infrastructure requirements, consumer costs and reliability risks of widespread electrification.Further reducing demand on the electricity grid can be accomplished by complementary options at the system level, suchas partial carbon offsetting using negative emission technologies

Journal article

Aunedi M, Al Kindi AA, Pantaleo AM, Markides CN, Strbac Get al., 2023, System-driven design of flexible nuclear power plant configurations with thermal energy storage, Energy Conversion and Management, Vol: 291, Pages: 1-14, ISSN: 0196-8904

Nuclear power plants are expected to make an important contribution to the decarbonisation of electricity supply alongside variable renewable generation, especially if their operational flexibility is enhanced by coupling them with thermal energy storage. This paper presents a system modelling approach to identifying configurations of flexible nuclear plants that minimise the investment and operation costs in a decarbonised energy system, effectively proposing a system-driven design of flexible nuclear technology. Case studies presented in the paper explore the impact of system features on plant configuration choices. The results suggest that cost-efficient flexible nuclear configurations should adapt to the system they are located in. In the main low-carbon scenarios and assuming standard-size nuclear power plants (1,610 MWel), the lowest-cost system configuration included around 500 MWel of additional secondary generation capacity coupled to the nuclear power plants, with 4.5 GWhth of thermal storage capacity and a discharging duration of 2.2 h. Net system benefits per unit of flexible nuclear generation for the main scenarios were quantified at £29-33 m/yr for a wind-dominated system and £19-20 m/yr for a solar-dominated system.

Journal article

Li Q, Jiang L, Huang G, Wang D-W, Shepherd J, Daiyan R, Markides CN, Taylor RA, Scott Jet al., 2023, A ternary system exploiting the full solar spectrum to generate renewable hydrogen from a waste biomass feedstock, Energy and Environmental Science, Vol: 16, Pages: 3497-3513, ISSN: 1754-5692

A solar-driven system is proposed capable of hydrogen production from waste biomass with low carbon and water footprints. The ternary system consists of a membrane-based waste biomass concentrator (WBC), a biomass preconditioning reactor (BPR) integrated with an array of hybrid PV-thermal (PVT) collectors, and a flow electrolysis cell (FEC) equipped with a custom, high-performance electrode – NiMo alloy deposited onto Ni foam. An innovative full-solar-spectrum hybrid PVT reflector-concentrator was constructed to confirm performance; this enabled a thermal efficiency of up to ∼50% to be achieved when operating the BPR at 120–150 °C, while also converting ∼8% of the solar flux to electricity for the FEC. The solar-thermal BPR can reform recovered waste biomass (i.e., a sugar-containing liquid feedstock) into a bio-alcohol (5-hydroxymethylfurfural) with a yield of 25 mol%, with the transformed biomass then used to feed the anodic compartment of the FEC. Within the FEC, biomass electrolysis using the NiMo catalyst facilitated hydrogen production, offering a low energy consumption of 40–53 kW h kg−1, which is 16–28% more efficient than alkaline water splitting using Ni foam electrodes. The ternary system achieved a 7.5% overall solar-to-hydrogen efficiency, additional revenue from clean water production (with >80% water reclaimed), and a value-added chemical by-product (2,5-furandicarboxylic acid at a 3–10% yield from the waste sugar stream). This work presents a new route towards efficient and economically feasible renewable hydrogen production—a system which can underpin a circular economy.

Journal article

Nemati H, Moghimi MA, Markides CN, 2023, Heat transfer characteristics of thermally and hydrodynamically developing flows in multi-layer mini-channel heat sinks, International Journal of Heat and Mass Transfer, Vol: 208, Pages: 1-12, ISSN: 0017-9310

In this study, a novel type of air-cooled heat sink is proposed, which consists of several layers of mini-channels. In this design, the hydraulic diameter is smaller than in conventional types of heat sinks, such as plate-fin heat sinks, and consequently, the achievable heat transfer rates are higher. To predict the cooling performance of this heat sink, an innovative analytical method is proposed, results from which are complemented by an extensive number of numerical simulations of the simultaneously developing flows, thermally and hydrodynamically, inside a rectangular channel of the heat sink. The results of the analytical method are compared against two- and three-dimensional simulations and good agreement is found, while from the simulations, correlations are proposed for the Nusselt number in these flows. Finally, the performance of the proposed heat sink is compared to a plate-fin heat sink. This comparison reveals that entropy generation in the latter is around 27% higher than in the former, and suggests a promising advantage of the proposed heat sink design.

Journal article

Herrando M, Wang K, Huang G, Otanicar T, Mousa OB, Agathokleous RA, Ding Y, Kalogirou S, Ekins-Daukes N, Taylor RA, Markides CNet al., 2023, A review of solar hybrid photovoltaic-thermal (PV-T) collectors and systems, Progress in Energy and Combustion Science, Vol: 97, Pages: 1-74, ISSN: 0360-1285

In this paper, we provide a comprehensive overview of the state-of-the-art in hybrid PV-T collectors and the wider systems within which they can be implemented, and assess the worldwide energy and carbon mitigation potential of these systems. We cover both experimental and computational studies, identify opportunities for performance enhancement, pathways for collector innovation, and implications of their wider deployment at the solar-generation system level. First, we classify and review the main types of PV-T collectors, including air-based, liquid-based, dual air–water, heat-pipe, building integrated and concentrated PV-T collectors. This is followed by a presentation of performance enhancement opportunities and pathways for collector innovation. Here, we address state-of-the-art design modifications, next-generation PV cell technologies, selective coatings, spectral splitting and nanofluids. Beyond this, we address wider PV-T systems and their applications, comprising a thorough review of solar combined heat and power (S–CHP), solar cooling, solar combined cooling, heat and power (S–CCHP), solar desalination, solar drying and solar for hydrogen production systems. This includes a specific review of potential performance and cost improvements and opportunities at the solar-generation system level in thermal energy storage, control and demand-side management. Subsequently, a set of the most promising PV-T systems is assessed to analyse their carbon mitigation potential and how this technology might fit within pathways for global decarbonization. It is estimated that the REmap baseline emission curve can be reduced by more than 16% in 2030 if the uptake of solar PV-T technologies can be promoted. Finally, the review turns to a critical examination of key challenges for the adoption of PV-T technology and recommendations.

Journal article

Tafuni A, Giannotta A, Mersch M, Pantaleo AM, Amirante R, Markides CN, De Palma Pet al., 2023, Thermo-economic analysis of a low-cost greenhouse thermal solar plant with seasonal energy storage, Energy Conversion and Management, Vol: 288, Pages: 1-11, ISSN: 0196-8904

Reduction of greenhouse gas emissions is today mandatory to limit the increase of ambient temperature. This paper provides a numerical study of a thermal solar plant using a seasonal dual-media sensible heat thermal energy storage system for supplying the total energy demand of a greenhouse located in the South of Italy, avoiding the use of the gas boiler. The aim of the work is to assess the technical and economic performance of a low-cost pit storage system, made of gravel and water, placed under the greenhouse to save surface. The study provides an original analysis of the charging and discharging phases during one year of operation on the basis of the real hourly heating demand and on real weather data. A sensitivity analysis of the levelized cost of heat is carried on with respect to the solar-collector area and to the storage-pit volume. The analysis shows that a minimum-cost design solution exists to cover 100% of the heat demand with an estimated levelized cost of heat of 153.3 EUR/MWh. The results demonstrate that dual-media thermal energy storage systems with solar thermal collectors represent a viable solution for reducing the environmental impact of greenhouses.

Journal article

Mersch M, Sapin P, Olympios AV, Ding Y, Mac Dowell N, Markides CNet al., 2023, A unified framework for the thermo-economic optimisation of compressed-air energy storage systems with solid and liquid thermal stores, Energy Conversion and Management, Vol: 287, Pages: 1-15, ISSN: 0196-8904

Compressed-air energy storage is an attractive option for satisfying the increasing storage demands of electricity grids with high shares of renewable generation. It is a proven technology that can store multiple gigawatt hours of electricity for hours, days and even weeks at a competitive cost and efficiency. However, compressed–air energy storage plants need to be designed carefully to deliver these benefits. In this work, a consistent thermo-economic optimisation framework is applied to assess the performance and costs of different compressed–air energy storage configurations across different scales. Special attention is paid to the thermal energy stores, with both solid packed-bed stores and liquid stores examined as viable options for advanced compressed–air energy storage plants and different storage materials proposed for both options. The comprehensive thermo-economic optimisation, considering different system layouts, thermal energy storage technologies and storage materials, and system scales is a key novelty of the presented work. A configuration with two packed–bed thermal energy stores using Basalt as the storage material is found to perform best, achieving an energy capital cost of 140 $/kWh, a power capital cost of 970 $/kW and a roundtrip efficiency of 76% at a nominal discharge power of 50 MW and a charging / discharging duration of 6 h. The best-performing liquid storage material is solar salt, which is associated with an energy capital cost of 170 $/kWh and a power capital cost of 1,230 $/kW. Systems with liquid thermal energy stores however are found generally to perform worse than systems with packed–bed thermal energy stores both in terms of cost and efficiency across all scales.

Journal article

Huang G, Xu J, Markides C, Huang G, Markides C, Xu Jet al., 2023, High-efficiency bio-inspired hybrid multi-generation photovoltaic leaf, Nature Communications, Vol: 14, ISSN: 2041-1723

Most solar energy incident (>70%) upon commercial photovoltaic panelsis dissipated as heat, increasing their operating temperature, and leading to significant deterioration in electrical performance. The solar utilization efficiency of commercial photovoltaic panels is typically below 25%. Here, we demonstrate a hybrid multi-generation photovoltaic leaf concept that employs a biomimetic transpiration structure made of eco-friendly, low-cost and widely-available materials for effective passive thermal management and multi-generation. We demonstrate experimentally that bio-inspired transpiration can remove~590 W/m2 of heat from a photovoltaic cell, reducing the cell temperature by ~26 °C under an irradianceof 1000 W/m2, and resulting in a 13.6% increase in electrical efficiency. Furthermore, the photovoltaic leaf is capable of synergistically utilizing the recovered heat to co-generate additional thermal energy and freshwater simultaneously within the same component, significantly elevating the overall solarutilization efficiency from 13.2% to over 74.5%, along with over 1.1 L/h/m2 of clean water.

Journal article

Kamel MA, Lobasov AS, Lakshmi Narayanan SN, Pervunin KS, Markides CNet al., 2023, Hydrate growth over a sessile drop of water in cyclopentane, Crystal Growth and Design, Vol: 23, Pages: 4273-4284, ISSN: 1528-7483

Liquid cyclopentane is frequently used in hydrate formation studies as an analogue of natural gas because cyclopentane hydrates are stable above the ice melting point at ambient pressure. In this study, hydrate growth was established on a sessile water drop of 11 mm in diameter and 4.5 mm in height (volume of 0.25 mL) immersed in liquid cyclopentane. The hydrate formation mechanism and growth processes were observed optically over an extended range of subcooling temperatures from 5.1 to 15.2 °C, with the cyclopentane bulk temperature maintained in different experimental runs between 2.6 and −7.5 °C. Qualitative and quantitative comparisons were performed to confirm the absence of ice freezing during hydrate formation, and thus, the lack of contamination of the latter from the former in the experiments. Different transformations in the hydrate film morphology were registered from macroscopic observation over the considered range of subcooling temperatures, with the hydrate crystals composing the film taking the form of polyhedral, dendritic, or spherulitic structures. It was also found that the hydrate growth rate varied depending on the subcooling temperature, with the variation of the growth rate as a function of this temperature changing from a power to an (approximately) linear law with an increase in the degree of subcooling. We postulate that hydrate film growth can be governed by different mechanisms, whose roles change over the range of explored subcooling temperatures.

Journal article

Iqbal Q, Fang S, Zhao Y, Yao Y, Xu Z, Gan H, Zhang H, Qiu L, Markides CN, Wang Ket al., 2023, Thermo-economic assessment of sub-ambient temperature pumped-thermal electricity storage integrated with external heat sources, Energy Conversion and Management, Vol: 285, Pages: 1-14, ISSN: 0196-8904

Thermally integrated pumped-thermal electricity storage (TI-PTES) offers the opportunity to store electricity as thermal exergy at a large scale, and existing studies are primarily focused on TI-PTES systems based on high-temperature thermal energy storage. This paper presents a thermo-economic analysis of a “cold TI-PTES” system which converts electricity into cold energy using a vapor compression refrigeration (VCR) unit and stores it at sub-ambient temperatures during the charging process, and generates electricity by using an organic Rankine cycle (ORC) working between the sub-ambient temperature and an external low-grade heat source during the discharging process. The effects of key parameters, i.e., mass flowrate and temperature of the storage medium, ORC evaporation temperature, component efficiencies, and pinch-point temperature differences, on the system performance are evaluated based on a whole-system thermo-economic model. The results reveal that the roundtrip efficiency and levelized cost of storage (LCOS) of the system increases while the electrical energy storage capacity decreases as the temperatures of the two cold storage tanks approach each other. When the temperature of the cold storage tank 1 rises from 1 °C to 8 °C while the cold storage tank 2 remains as 13 °C, there is an increase of 25% and 20% in the roundtrip efficiency and LCOS respectively while the energy storage capacity decreases by 69%. A roundtrip efficiency of 0.74 and LCOS of 0.32 $/kWh are achieved with a heat source temperature of 85 °C, using a mass flowrate and temperature of the cold storage medium of 50 kg/s and 1 °C. Furthermore, any change in cold storage medium mass flowrate changes both electrical energy storage capacity and power output by the same proportions. With a continuous high-flowrate external heat source, the LCOS can be as low as 0.17 $/kWh. By providing sufficient heat from an external heat source, the proposed system possesses

Journal article

Zhu S, Wang K, González-Pino I, Song J, Yu G, Luo E, Markides Cet al., 2023, Techno-economic analysis of a combined heat and power system integrating hybrid photovoltaic-thermal collectors, a Stirling engine and energy storage, Energy Conversion and Management, Vol: 284, ISSN: 0196-8904

This paper presents a comprehensive analysis of the energetic, economic and environmental performance of a micro-combined heat and power (CHP) system that comprises 29.5 m2 of hybrid photovoltaic-thermal (PVT) collectors, a 1-kWe Stirling engine (SE) and energy storage. First, a model for the solar micro-CHP system, which includes a validated transient model for the SE micro-CHP unit, is developed. Parametric analyses are performed throughout a year to evaluate the effects of key component sizes and operating parameters, including collector flow rate, storage tank size, SE micro-CHP flow rate, and battery capacity, on the energetic, economic and environmental performance of the proposed system using real hourly weather data, and thermal and electrical energy demand profiles of a detached house located in London (UK). The optimum component sizes and operating parameters are determined accordingly. The daily and monthly operating characteristics of the system are evaluated, and its annual performance is compared to those of a reference system (gas boiler plus grid electricity), as well as of other alternative solar-CHP systems including a PVT-assisted heat pump system and a standalone PVT system. The results indicate that the installation of such a system can achieve an annual electricity self-sufficiency of 87% and an annual thermal energy demand coverage of 99%, along with annual primary energy savings and carbon emission reduction rate of 35% and 37% relative to the reference system. Over 30 years of operation, the net present value (NPV) of the proposed system is £1990 and the discounted payback period is 28 years. The economics of the proposed system is very sensitive to utility prices, especially the electricity purchase price. Relative to the alternative solar systems, the proposed system offers greater environmental benefits but has a longer payback period. This implies that although the energy saving and emission reduction potential of the proposed syst

Journal article

Wieland C, Schifflechner C, Braimakis K, Kaufmann F, Dawo F, Karellas S, Besagni G, Markides CNet al., 2023, Innovations for organic Rankine cycle power systems: Current trends and future perspectives, Applied Thermal Engineering, Vol: 225, Pages: 1-17, ISSN: 1359-4311

Since the early 2000s, organic Rankine cycle (ORC) technology has experienced rapid development and market uptake. More than 4.5 GW of total ORC power plant capacity has been installed since then. Due to its flexibility, suitability for small- to medium-scale installations, its applicability to low- to medium-temperature heat sources, and compact design, ORC technology is already considered as state-of-the-art. However, to further increase the technical and economic potential of this technology, significant research is needed to further improve efficiency and other key performance indicators, as well as to address environmental and safety aspects. Therefore, it is important to research new technologies and to foster innovations for improving performance; but it is of similar importance to resolve operational challenges with applied research that focuses closer to the market, and the technology provider and user needs. This vision article outlines the current state-of-the-art and presents current research trends. Parts of this article summarize the research progress reported at the 6th International Seminar on ORC Power Systems (ORC2021) and accompanies the associated special issue published following this event. The article highlights research trends at the concept level, but also at the component and system levels and, therefore, provides a holistic overview for the interested reader regarding the current challenges and potential future research activities in this area. Beyond the variety of cycle concepts in Section 2.1, the different heat sources and applications in Section 2.2, rotating device and turbomachinery (pumps and expansion devices) options in Section 2.3, current R&D trends for working fluids are presented in Section 2.4. This editorial concludes with a more applied perspective on ORC systems, covering process control and a general perspective on the technology in Section 2.5. With an increasing number of ORC plants operating in the field, their in

Journal article

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