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Journal articleYe Y, Qiu D, Wu X, et al., 2020,
Model-Free Real-Time Autonomous Control for A Residential Multi-Energy System Using Deep Reinforcement Learning
, IEEE Transactions on Smart Grid, Vol: 11, Pages: 3068-3068, ISSN: 1949-3053Multi-energy systems (MES) are attracting increasing attention driven by its potential to offer significant flexibility in future smart grids. At the residential level, the roll-out of smart meters and rapid deployment of smart energy devices call for autonomous multi-energy management systems which can exploit real-time information to optimally schedule the usage of different devices with the aim of minimizing end-users’ energy costs. This paper proposes a novel real-time autonomous energy management strategy for a residential MES using a model-free deep reinforcement learning (DRL) based approach, combining state-of-the-art deep deterministic policy gradient (DDPG) method with an innovative prioritized experience replay strategy. This approach is tailored to align with the nature of the problem by posing it in multi-dimensional continuous state and action spaces, facilitating more cost-effective control strategies to be devised. The superior performance of the proposed approach in reducing end-user’s energy cost while coping with the MES uncertainties is demonstrated by comparing it against state-of-the-art DRL methods as well as conventional stochastic programming and robust optimization methods in numerous case studies in a real-world scenario.
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Journal articleGeorgiou S, Aunedi M, Strbac G, et al., 2020,
On the value of liquid-air and Pumped-Thermal Electricity Storage systems in low-carbon electricity systems
, Energy, Vol: 193, ISSN: 0360-5442We consider two medium-to-large scale thermomechanical electricity storage technologies currently under development, namely ‘Liquid-Air Energy Storage’ (LAES) and ‘Pumped-Thermal Electricity Storage’ (PTES). Consistent thermodynamic models and costing methods based on a unified methodology for the two systems from previous work are presented and used with the objective of integrating the characteristics of the technologies into a whole-electricity system assessment model and assessing their system-level value in various scenarios for system decarbonization. It is found that the value of storage depends on the cumulative installed capacity of storage in the system, with storage technologies providing greater marginal benefits at low penetrations. The system value of PTES was found to be slightly higher than that of LAES, driven by a higher storage duration and efficiency, although these results must be seen in light of the uncertainty in the (as yet, not demonstrated) performance of key PTES components, namely the reciprocating-piston compressors and expanders. At the same time, PTES was also found to have a higher power capital cost. The results indicate that the complexity of the decarbonization challenge makes it difficult to identify clearly a ‘best’ technology and suggest that the uptake of either technology can provide significant system-level benefits.
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Journal articleGiannelos S, Djapic P, Pudjianto D, et al., 2020,
Quantification of the energy storage contribution to security of supply through the F-factor methodology
, Energies, Vol: 13, Pages: 826-826, ISSN: 1996-1073The ongoing electrification of the heat and transport sectors is expected to lead to a substantial increase in peak electricity demand over the coming decades, which may drive significant investment in network reinforcement in order to maintain a secure supply of electricity to consumers. The traditional way of security provision has been based on conventional investments such as the upgrade of the capacity of electricity transmission or distribution lines. However, energy storage can also provide security of supply. In this context, the current paper presents a methodology for the quantification of the security contribution of energy storage, based on the use of mathematical optimization for the calculation of the F-factor metric, which reflects the optimal amount of peak demand reduction that can be achieved as compared to the power capability of the corresponding energy storage asset. In this context, case studies underline that the F-factors decrease with greater storage power capability and increase with greater storage efficiency and energy capacity as well as peakiness of the load profile. Furthermore, it is shown that increased investment in energy storage per system bus does not increase the overall contribution to security of supply.
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Journal articleGardiner D, Schmidt O, Heptonstall P, et al., 2020,
Quantifying the impact of policy on the investment case for residential electricity storage in the UK
, Journal of Energy Storage, Vol: 27, ISSN: 2352-152XElectrical energy storage has a critical role in future energy systems, but deployment is constrained by high costs and barriers to ‘stacking’ multiple revenue streams. We analyse the effects of different policy measures and revenue stacking on the economics of residential electricity storage in the UK. We identify six policy interventions through industry interviews and quantify their impact using a techno-economic model of a 4kWh battery paired with a 4kW solar system. Without policy intervention, residential batteries are not currently financially viable in the UK. Policies that enable access to multiple revenue streams, rather than just maximising PV self-consumption, improve this proposition. Demand Load-Shifting and Peak Shaving respectively increase the net present value per unit of investment cost (NPV/Capex) by 30% and 9% respectively. Given projected reductions in storage costs, stacking these services brings forward the break even date for residential batteries by 9 years to 2024, and increases the effectiveness of policies that reduce upfront costs, suggesting that current policy is correctly focused on enabling revenue stacking. However, additional support is needed to accelerate deployment in the near term. Combining revenue stacking with a subsidy of £250 per kWh or zero-interest loans could make residential storage profitable by 2020.
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Journal articlePawlak J, Imani AF, Sivakumar A, 2020,
A microeconomic framework for integrated agent-based modelling of activity-travel patterns and energy consumption
, Procedia Computer Science, Vol: 170, Pages: 785-790, ISSN: 1877-0509The sophistication in the demand management approaches in both transport and energy sectors and their interaction call for modelling approaches that consider both sectors jointly. For agent-based microsimulation models of travel demand and energy consumption, this implies the necessity to ensure consistent representation of user behaviour with respect to mobility and energy consumption behaviours across the model components. Therefore this paper proposes a microeconomic framework, termed the HOT model (Home, Out-of-home, Travel) grounded in the goods-leisure paradigm, but extended to incorporate emerging activity-travel behaviour patterns and their energy consumption implications. We discuss how the model can be operationalised and embedded within agent-based frameworks with a case study using time use and energy consumption data from the UK.
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Journal articleKadivar MR, Moghimi MA, Sapin P, et al., 2019,
Annulus eccentricity optimisation of a phase-change material (PCM) horizontal double-pipe thermal energy store
, Journal of Energy Storage, Vol: 26, ISSN: 2352-152XThe application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce air-conditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times
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Conference paperRomanos P, Pantaleo A, Markides C, 2019,
Energy management and enhanced flexibility of power stations via thermal energy storage and secondary power cycles
, 11th International Conference on Applied EnergyThe operation of power plants must meet a series of requirements in order to enable the increasing penetration of intermittent renewable energy and the consequent intensifying demand for flexible generation. It is proposed here that during off-peak demand, steam can be extracted from Rankine-cycle power stations for the charging of thermal storage tanks that contain suitable phase-change materials (PCMs); during peak demand time, these thermal energy storage (TES) tanks can act as the heat sources of secondary thermal power plants in order to generate power, for example as evaporators of organic Rankine cycle (ORC) plants that are suitable for power generation at reduced temperatures and smaller scales. This type of solution offers greater flexibility than TES-only solutions that store thermal energy and then release this back to the base power station, in that it allows both derating andover-generation compared to the base power-station. The approach is here applied to a case study of a 670-MW rated nuclear power station, since nuclear power stations are generally suitable for baseload generation and the proposed system configuration could increase the operational flexibility of such plants.
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Journal articleChen X, Liu X, Ouyang M, et al., 2019,
Electrospun composite nanofibre supercapacitors enhanced with electrochemically 3D printed current collectors
, Journal of Energy Storage, Vol: 26, Pages: 100993-100993, ISSN: 2352-152XCarbonised electrospun nanofibres are attractive for supercapacitors due to their relatively high surface area, facile production routes and flexibility. With the addition of materials such as manganese oxide (MnO), the specific capacitance of the carbon nanofibres can be further improved through fast surface redox reactions, however this can reduce the electrical conductivity. In this work, electrochemical 3D printing is used as a novel means of improving electrical conductivity and the current collector-electrode interfacial resistance through the deposition of highly controlled layers of copper. Neat carbonised electrospun electrodes made with a 30 wt% manganese acetylacetonate (MnACAC) and polyacrylonitrile precursor solution have a hydrophobic nature preventing an even copper deposition. However, with an ethanol treatment, the nanofibre films can be made hydrophilic which enhances the copper deposition morphology to enable the formation of a percolating conductive network through the electrode. This has the impact of increasing electrode electronic conductivity by 360% from 10 S/m to 46 S/m and increasing specific capacitance 110% from 99 F/g to 208 F/g at 5 mV/s through increased utilisation of the pseudocapacitive active material. This novel approach thus provides a new route for performance enhancement of electrochemical devices using 3D printing, which opens new design possibilities.
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Journal articlePantaleo A, Simpson M, Rotolo G, et al., 2019,
Thermoeconomic optimisation of small-scale organic Rankine cycle systems based on screw vs. piston expander maps in waste heat recovery applications
, Energy Conversion and Management, Vol: 200, ISSN: 0196-8904The high cost of organic Rankine cycle (ORC) systems is a key barrier to their implementation in waste heat recovery (WHR) applications. In particular, the choice ofexpansion device has a significant influence on this cost, strongly affecting the economic viabilityof an installation. In this work, numerical simulations and optimisation strategies are used to compare the performance and profitability of small-scale ORC systems using reciprocating-piston orsingle/two-stage screw expanders whenre covering heat from the exhaust gases of a 185-kWinternal combustion engine operating in baseload mode. The study goes beyond previous work by directly comparingthese small-scaleexpanders fora broad range of working fluids, and by exploring the sensitivity of project viability to key parameters such as electricity price and onsite heat demand.For the piston expander, a lumped-massmodel and optimisation based on artificial neural networks are used to generate performance maps, while performance and cost correlations from the literature are used for the screw expanders. The thermodynamic analysisshows that two-stage screw expanders typically deliver more power than either single-stage screw or piston expanders due to their higher conversion efficiencyat the required pressure ratios. The best fluids areacetone and ethanol, as these provide a compromise between the exergy losses in the condenser and in the evaporatorin this application. The maximum net power output isfound to be 17.7kW, from an ORC engine operating withacetone anda two-stage screw expander. On the other hand, the thermoeconomic optimisation shows that reciprocating-piston expandersshow a potential for lowerspecific costs, and sincesuchan expander technology is not mature, especially at these scales, this finding motivates further consideration of this component. A minimum specific investment cost of 1630€/kW is observed for an ORC engine with a pisto
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Conference paperAunedi M, Kuriyan K, Pantaleo AM, et al., 2019,
Multi-scale modelling of interactions between heat and electricity networks in low-carbon energy systems
, 14th Conference on Sustainable Development of Energy, Water and Environment Systems – SDEWES Conference, Publisher: SDEWESDecarbonisation of the heating and cooling sector is critical for achieving long-term energy and climate change objectives. Closer integration between heating/cooling and electricity systems can provide additional flexibility required to support the integration of variable renewables and other low-carbon energy sources. This paper proposes a framework for identifying cost-efficient solutions for supplying district heating systems within both operation and investment timescales, while considering local and national-level interactions between heat and electricity infrastructures. The proposed approach cost-optimises the portfolio of heating technologies, including Combined Heat and Power (CHP) and polygeneration systems, large-scale heat pumps (HPs), gas boilers and thermal energy storage (TES). It is implemented as a mixed-integer linear programming (MILP) optimisation model that minimises net cost of heat supply, taking into account investment and operation cost of heat supply and storage options as well as the impact of local and wider interactions with the electricity system.
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Journal articleKozarcanin S, Andresen GB, Staffell I, 2019,
Estimating country-specific space heating threshold temperatures from national gas and electricity consumption data
, Energy and Buildings, Vol: 199, Pages: 368-380, ISSN: 0378-7788 -
Journal articleTomaszewska A, Chu Z, Feng X, et al., 2019,
Lithium-ion battery fast charging: A review
, eTransportation, Vol: 1, Pages: 1-28, ISSN: 2590-1168In the recent years, lithium-ion batteries have become the battery technology of choice for portable devices, electric vehicles and grid storage. While increasing numbers of car manufacturers are introducing electrified models into their offering, range anxiety and the length of time required to recharge the batteries are still a common concern. The high currents needed to accelerate the charging process have been known to reduce energy efficiency and cause accelerated capacity and power fade. Fast charging is a multiscale problem, therefore insights from atomic to system level are required to understand and improve fast charging performance. The present paper reviews the literature on the physical phenomena that limit battery charging speeds, the degradation mechanisms that commonly result from charging at high currents, and the approaches that have been proposed to address these issues. Special attention is paid to low temperature charging. Alternative fast charging protocols are presented and critically assessed. Safety implications are explored, including the potential influence of fast charging on thermal runaway characteristics. Finally, knowledge gaps are identified and recommendations are made for the direction of future research. The need to develop reliable in operando methods to detect lithium plating and mechanical degradation is highlighted. Robust model-based charging optimisation strategies are identified as key to enabling fast charging in all conditions. Thermal management strategies to both cool batteries during charging and preheat them in cold weather are acknowledged as critical, with a particular focus on techniques capable of achieving high speeds and good temperature homogeneities.
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Journal articlePollet BG, Kocha SS, Staffell I, 2019,
Current status of automotive fuel cells for sustainable transport
, Current Opinion in Electrochemistry, Vol: 16, Pages: 90-95, ISSN: 2451-9103Automotive proton-exchange membrane fuel cells (PEMFCs) have finally reached a state of technological readiness where several major automotive companies are commercially leasing and selling fuel cell electric vehicles, including Toyota, Honda, and Hyundai. These now claim vehicle speed and acceleration, refueling time, driving range, and durability that rival conventional internal combustion engines and in most cases outperform battery electric vehicles. The residual challenges and areas of improvement which remain for PEMFCs are performance at high current density, durability, and cost. These are expected to be resolved over the coming decade while hydrogen infrastructure needs to become widely available. Here, we briefly discuss the status of automotive PEMFCs, misconceptions about the barriers that platinum usage creates, and the remaining hurdles for the technology to become broadly accepted and implemented.
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Journal articleChakrabarti A, Proeglhoef R, Bustos-Turu G, et al., 2019,
Optimisation and analysis of system integration between electric vehicles and UK decentralised energy schemes
, Energy, Vol: 176, Pages: 805-815, ISSN: 0360-5442Although district heat network schemes provide a pragmatic solution for reducing the environmental impact of urban energy systems, there are additional benefits that could arise from servicing electric vehicles. Using the electricity generated on-site to power electric vehicles can make district heating networks more economically feasible, while also increasing environmental benefits. This paper explores the potential integration of electric vehicle charging into large-scale district heating networks with the aim of increasing the value of the generated electricity and thereby improving the financial feasibility of such systems. A modelling approach is presented composed of a diverse range of distributed technologies that considers residential and commercial electric vehicle charging demands via agent-based modelling. An existing district heating network system in London was taken as a case study. The energy system was modelled as a mixed integer linear program and optimised for either profit maximisation or carbon dioxide emissions minimisation. Commercial electric vehicles provided the best alternative to increase revenue streams by about 11% against the current system configuration with emissions effectively unchanged. The research indicates that district heating network systems need to carefully analyse opportunities for transport electrification in order to improve the integration, and sustainability, of urban energy systems.
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Journal articleYin C, Liu X, Wei J, et al., 2019,
“All-in-Gel” design for supercapacitors towards solid-state energy devices with thermal and mechanical compliance
, Journal of Materials Chemistry A, Vol: 7, Pages: 8826-8831, ISSN: 2050-7488Ionogels are semi-solid, ion conductive and mechanically compliant materials that hold promise for flexible, shape-conformable and all-solid-state energy storage devices. However, identifying facile routes for manufacturing ionogels into devices with highly resilient electrode/electrolyte interfaces remains a challenge. Here we present a novel all-in-gel supercapacitor consisting of an ionogel composite electrolyte and bucky gel electrodes processed using a one-step method. Compared with the mechanical properties and ionic conductivities of pure ionogels, our composite ionogels offer enhanced self-recovery (retaining 78% of mechanical robustness after 300 cycles at 60% strain) and a high ionic conductivity of 8.7 mS cm−1, which is attributed to the robust amorphous polymer phase that enables facile permeation of ionic liquids, facilitating effective diffusion of charge carriers. We show that development of a supercapacitor with these gel electrodes and electrolytes significantly improves the interfacial contact between electrodes and electrolyte, yielding an area specific capacitance of 43 mF cm−2 at a current density of 1.0 mA cm−2. Additionally, through this all-in-gel design a supercapacitor can achieve a capacitance between 22–81 mF cm−2 over a wide operating temperature range of −40 °C to 100 °C at a current density of 0.2 mA cm−2.
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Journal articleStrbac G, Pudjianto D, Aunedi M, et al., 2019,
Cost-effective decarbonization in a decentralized market the benefits of using flexible technologies and resources
, IEEE Power and Energy Magazine, Vol: 17, Pages: 25-36, ISSN: 1540-7977 -
Journal articleBalcombe P, Brierley J, Lewis C, et al., 2019,
How to decarbonise international shipping: Options for fuels, technologies and policies
, Energy Conversion and Management, Vol: 182, Pages: 72-88, ISSN: 0196-8904International shipping provides 80–90% of global trade, but strict environmental regulations around NOX, SOX and greenhouse gas (GHG) emissions are set to cause major technological shifts. The pathway to achieving the international target of 50% GHG reduction by 2050 is unclear, but numerous promising options exist. This study provides a holistic assessment of these options and their combined potential to decarbonise international shipping, from a technology, environmental and policy perspective. Liquefied natural gas (LNG) is reaching mainstream and provides 20–30% CO2 reductions whilst minimising SOX and other emissions. Costs are favourable, but GHG benefits are reduced by methane slip, which varies across engine types. Biofuels, hydrogen, nuclear and carbon capture and storage (CCS) could all decarbonise much further, but each faces significant barriers around their economics, resource potentials and public acceptability. Regarding efficiency measures, considerable fuel and GHG savings could be attained by slow-steaming, ship design changes and utilising renewable resources. There is clearly no single route and a multifaceted response is required for deep decarbonisation. The scale of this challenge is explored by estimating the combined decarbonisation potential of multiple options. Achieving 50% decarbonisation with LNG or electric propulsion would likely require 4 or more complementary efficiency measures to be applied simultaneously. Broadly, larger GHG reductions require stronger policy and may differentiate between short- and long-term approaches. With LNG being economically feasible and offering moderate environmental benefits, this may have short-term promise with minor policy intervention. Longer term, deeper decarbonisation will require strong financial incentives. Lowest-cost policy options should be fuel- or technology-agnostic, internationally applied and will require action now to ensure targets are met by 2050.
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Journal articleSchmidt O, Melchior S, Hawkes A, et al., 2019,
Projecting the future levelized cost of electricity storage technologies
, Joule, Vol: 3, Pages: 81-100, ISSN: 2542-4351The future role of stationary electricity storage is perceived as highly uncertain. One reason is that most studies into the future cost of storage technologies focus on investment cost. An appropriate cost assessment must be based on the application-specific lifetime cost of storing electricity. We determine the levelized cost of storage (LCOS) for 9 technologies in 12 power system applications from 2015 to 2050 based on projected investment cost reductions and current performance parameters. We find that LCOS will reduce by one-third to one-half by 2030 and 2050, respectively, across the modeled applications, with lithium ion likely to become most cost efficient for nearly all stationary applications from 2030. Investments in alternative technologies may prove futile unless significant performance improvements can retain competitiveness with lithium ion. These insights increase transparency around the future competitiveness of electricity storage technologies and can help guide research, policy, and investment activities to ensure cost-efficient deployment.
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