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  • Journal article
    García Kerdan I, Giarola S, Hawkes A, 2019,

    A novel energy systems model to explore the role of land use and reforestation in achieving carbon mitigation targets: A Brazil case study

    , Journal of Cleaner Production, Vol: 232, Pages: 796-821, ISSN: 0959-6526

    Due to its low global share of direct energy consumption and greenhouse gas emissions (1–2%), the implications of technological transitions in the agricultural and forestry sector on the energy system have been overlooked. This paper introduces the Agriculture and Land Use Sector module part of the ModUlar energy System Environment (MUSE), a novel energy system simulation model. The study presents a generalisable method that enables energy modellers to characterise agricultural technologies within an energy system modelling framework. Different mechanisation processes were characterised to simulate intensification/extensification transitions in the sector and its wider implications in the energy and land use system aiming at providing reliable non-energy outputs similarly to those found in dedicated land use models. Additionally, a forest growth model has been integrated to explore the role of reforestation alongside decarbonisation measures in the energy system in achieving carbon mitigation pathways. To illustrate the model's capabilities, Brazil is used as case study. Outputs suggest that by 2030 under a 2 °C mitigation scenario, most of Brazil agricultural production would move from ‘transitional’ to ‘modern’ practices, improving productivity and reducing deforestation rates, at the expense of higher energy and fertiliser demand. By mid-century Brazil has the potential to liberate around 24.4 Mha of agricultural land, where large-scale reforestation could have the capacity to sequester around 5.6 GtCO2, alleviating mitigation efforts in the energy system, especially reducing carbon capture and storage technology investments in the industry and power sector.

  • Journal article
    Sachs J, Moya D, Giarola S, Hawkes Aet al., 2019,

    Clustered spatially and temporally resolved global heat and cooling energy demand in the residential sector

    , Applied Energy, Vol: 250, Pages: 48-62, ISSN: 0306-2619

    Climatic conditions, population density, geography, and settlement structure all have a strong influence on the heating and cooling demand of a country, and thus on resulting energy use and greenhouse gas emissions. In particular, the choice of heating or cooling system is influenced by available energy distribution infrastructure, where the cost of such infrastructure is strongly related to the spatial density of the demand. As such, a better estimation of the spatial and temporal distribution of demand is desirable to enhance the accuracy of technology assessment. This paper presents a Geographical Information System methodology combining the hourly NASA MERRA-2 global temperature dataset with spatially resolved population data and national energy balances to determine global high-resolution heat and cooling energy density maps. A set of energy density bands is then produced for each country using K-means clustering. Finally, demand profiles representing diurnal and seasonal variations in each band are derived to capture the temporal variability. The resulting dataset for 165 countries, published alongside this article, is designed to be integrated into a new integrated assessment model called MUSE (ModUlar energy systems Simulation Environment)but can be used in any national heat or cooling technology analysis. These demand profiles are key inputs for energy planning as they describe demand density and its fluctuations via a consistent method for every country where data is available.

  • Journal article
    Guo Y, Hawkes A, 2019,

    Asset stranding in natural gas export facilities: An agent-based simulation

    , ENERGY POLICY, Vol: 132, Pages: 132-155, ISSN: 0301-4215
  • Journal article
    Vijay A, Hawkes A, 2019,

    Demand side flexibility from residential heating to absorb surplus renewables in low carbon futures

    , Renewable Energy: An International Journal, Vol: 138, Pages: 598-609, ISSN: 0960-1481

    Higher penetration of renewable sources of energy is essential for mitigating climate change. This introduces problems related to the balance of supply and demand. Instances in which the generation from intermittent and inflexible sources is in excess of system load are expected to increase in low carbon futures. Curtailment is likely to involve high constraint payments to renewable sources, and failing to curtail threatens the stability of the system. This work investigates a solution that makes use of residential heating systems to absorb the excess generation. Consumers are incentivised to increase consumption via a demand turn up mechanism that sets the electricity price to zero when excess generation occurs. The reduction in electricity price significantly weakens the economic case of dwelling-scale micro-cogeneration units. But technologies that use electricity are able to charge the thermal store when free electricity is available and discharge it when electricity prices are high. Such actions reduce the equivalent annual cost by 50 percent for a resistive heater and by 60 percent for a heat pump. Without disincentives, resistive heaters are likely to be chosen over heat pumps since they are easy to install, do not involve high upfront costs and can provide significant economic benefits.

  • Journal article
    Realmonte G, Hawkes A, Gambhir A, Tavoni M, Glynn J, Koberle A, Drouet Let al., 2019,

    An inter-model assessment of the role of direct air capture in deep mitigation pathways

    , Nature Communications, Vol: 10, ISSN: 2041-1723

    The feasibility of large-scale biological CO2 removal to achieve stringent climate targets remains unclear. Direct Air CarbonCapture and Storage (DACCS) offers an alternative negative emissions technology (NET) option. Here we conduct the firstinter-model comparison on the role of DACCS in 1.5 and 2°C scenarios, under a variety of techno-economic assumptions.Deploying DACCS significantly reduces mitigation costs, and it complements rather than substitutes other NETs. The key factorlimiting DACCS deployment is the rate at which it can be scaled up. Our scenarios’ average DACCS scale-up rates of 1.5GtCO2/yr would require considerable sorbent production and up to 300 EJ/yr of energy input by 2100. The risk of assumingthat DACCS can be deployed at scale, and finding it to be subsequently unavailable, leads to a global temperature overshoot ofup to 0.8°C. DACCS should therefore be developed and deployed alongside, rather than instead of, other mitigation options.

  • Journal article
    Cooper J, Balcombe P, Hawkes A, 2019,

    Life cycle environmental impacts of natural gas drivetrains used in UK road freighting and impacts to UK emission targets

    , Science of the Total Environment, Vol: 674, Pages: 482-493, ISSN: 0048-9697

    Using natural gas as a fuel in the road freight sector instead of diesel could cut greenhouse gas and air quality emissions but the switch alone is not enough to meet UK climate targets. A life cycle assessment (LCA) has been conducted comparing natural gas trucks to diesel, biodiesel, dimethyl ether and electric trucks on impacts to climate change, land use change, air quality, human health and resource depletion. This is the first LCA to consider a full suite of environmental impacts and is the first study to estimate what impact natural gas could have on reducing emissions form the UK freight sector. If LNG is used, climate change impacts could be up to 33% lower per km and up to 12% lower per kWh engine output. However, methane emissions will eliminate any benefits if they exceed 1.5–3.5% of throughput for typical fuel consumption. For non-climate impacts, natural gas exhibits lower emissions (11–66%) than diesel for all indicators. Thus, for natural gas climate benefits are modest. However, emissions of CO, methane and particulate matter are over air quality limits set for UK trucks. Of the other options, electric and biodiesel trucks perform best in climate change, but are the worst with respect to land use change (which could have significant impacts on overall climate change benefits), air quality, human toxicity and metals depletion indicators. Natural gas could help reduce the sector's emissions but deeper decarbonization options are required to meet 2030 climate targets, thus the window for beneficial utilisation is short.

  • Journal article
    Crow DJG, Balcombe P, Brandon N, Hawkes ADet al., 2019,

    Assessing the impact of future greenhouse gas emissions from natural gas production

    , Science of the Total Environment, Vol: 668, Pages: 1242-1258, ISSN: 0048-9697

    Greenhouse gases (GHGs) produced by the extraction of natural gas are an important contributor to lifecycle emissions and account for a significant fraction of anthropogenic methane emissions in the USA. The timing as well as the magnitude of these emissions matters, as the short term climate warming impact of methane is up to 120 times that of CO 2 . This study uses estimates of CO 2 and methane emissions associated with different upstream operations to build a deterministic model of GHG emissions from conventional and unconventional gas fields as a function of time. By combining these emissions with a dynamic, techno-economic model of gas supply we assess their potential impact on the value of different types of project and identify stranded resources in various carbon price scenarios. We focus in particular on the effects of different emission metrics for methane, using the global warming potential (GWP) and the global temperature potential (GTP), with both fixed 20-year and 100-year CO 2 -equivalent values and in a time-dependent way based on a target year for climate stabilisation. We report a strong time dependence of emissions over the lifecycle of a typical field, and find that bringing forward the stabilisation year dramatically increases the importance of the methane contribution to these emissions. Using a commercial database of the remaining reserves of individual projects, we use our model to quantify future emissions resulting from the extraction of current US non-associated reserves. A carbon price of at least 400 USD/tonne CO 2 is effective in reducing cumulative GHGs by 30–60%, indicating that decarbonising the upstream component of the natural gas supply chain is achievable using carbon prices similar to those needed to decarbonise the energy system as a whole. Surprisingly, for large carbon prices, the choice of emission metric does not have a significant impact on cumulative emissions.

  • Journal article
    García Kerdan I, Morillón Gálvez D, Sousa G, Suárez de la Fuente S, Silva R, Hawkes Aet al., 2019,

    Thermodynamic and thermal comfort optimisation of a coastal social house considering the influence of the thermal breeze

    , Building and Environment, Vol: 155, Pages: 224-246, ISSN: 0360-1323

    Tropical coastal areas are characterised by high levels of wind and solar resources with large potentials to be utilised for low-energy building design. This paper presents a multi-objective optimisation framework capable of evaluating cost-efficient and low-exergy coastal building designs considering the influence of the thermal breeze. An integrated dynamic simulation tool has been enhanced to consider the impacts of the sea-land breeze effect, aiming at potentiating natural cross-ventilation to improve occupant's thermal comfort and reduce cooling energy demand. Furthermore, the technological database considers a wide range of active and passive energy conservation measures. As a case study, a two-storey/two-flat detached social house located in the North-Pacific coast of Mexico has been investigated. The optimisation problem has considered the minimisation of: i. annual exergy consumption, ii. life cycle cost, and iii. thermal discomfort. Optimisation results have shown that adequate building orientation and window opening control to optimise the effects of the thermal breeze, combined with other passive and active strategies such as solar shading devices, an improved envelope's physical characteristics, and solar assisted air source heat pumps have provided the best performance under a limited budget. Compared to the baseline design, the closest to utopia design has increased thermal comfort by 93.8% and reduced exergy consumption by 10.3% whilst increasing the life cycle cost over the next 50 years by 18.5% (from US$39,864 to US$47,246). The importance of renewable generation incentives is further discussed as a counter effect measure for capital cost increase as well as unlocking currently high-cost low-exergy technologies.

  • Journal article
    Guo Y, Hawkes A, 2019,

    The impact of demand uncertainties and China-US natural gas tariff on global gas trade

    , Energy, Vol: 175, Pages: 205-217, ISSN: 0360-5442

    The uncertainties in gas demand levels and geopolitical issues may lead to significant changes in global gas trade. This paper uses an agent-based model to simulate the alternative market futures under two demand trajectories: a baseline following current policy pledges until 2060 and another where demand shifts to a lower level in 2030. Endogenously generated capacity investments are driven by long-term bilateral contracts between importers and exporters, where investors are assumed to evaluate the potential risks of demand changes while making their decisions. The results suggest that, when the demand decreases in 2030, the Middle East takes the dominant position in Eastern Asia, whereas this role is occupied by North America in the current policy scenario. In addition, the impacts of a 25% tariff by China on U.S. natural gas are studied for both scenarios. The revenue of North American gas trade is only marginally affected by this tariff. Under the normal demand trajectory, the tariff influences the Chinese market more notably in the longer term when global supply is tightened by decommissioning. In the case of lower global gas demand, the market share of Russia in Western Europe could be threatened by increasing North American export there.

  • Journal article
    Cooper J, Balcombe P, 2019,

    Life cycle environmental impacts of natural gas drivetrains used in road freighting

    , Procedia CIRP, Vol: 80, Pages: 334-339, ISSN: 2212-8271
  • Journal article
    Sachs J, Meng Y, Giarola S, Hawkes Aet al., 2019,

    An agent-based model for energy investment decisions in the residential sector

    , Energy, Vol: 172, Pages: 752-768, ISSN: 0360-5442

    Energy-related investment decisions in the buildings sector are heterogeneous in that the outcome for each individual varies according to budget, values, and perception of a technology, even if an apparently identical decision task is faced. In particular, the rate of adoption of new energy-efficient technologies is often hard to model and underlines the need for an advanced approach to capture diversity in decision-making, and enable the inclusion of economic, comfort, environmental and social aspects. This paper presents an enhanced agent-based model that captures several characteristics of consumer behaviour that influence investment decisions. Multiple agents with different objectives, search strategies, and decision methods are implemented. A case study is presented which illustrates the benefits of the approach for the residential sector in the UK. The agent-based method shows diversity in investment decisions, without requiring the constraints on uptake needed in many models. This leads to a range of technologies in the market during a transition phase, continuous investment in low capital cost technologies, and eventually the emergence of a low carbon system based on new mass market technologies. The system that emerges is vastly different from one observed when economically rational investment is assumed and uptake constraints are applied.

  • Journal article
    Napp TA, Few S, Sood A, Bernie D, Hawkes A, Gambhir Aet al., 2019,

    The role of advanced demand-sector technologies and energy demand reduction in achieving ambitious carbon budgets

    , Applied Energy, Vol: 238, Pages: 351-367, ISSN: 0306-2619

    Limiting cumulative carbon emissions to keep global temperature increase to well below 2 °C (and as low as 1.5 °C) is an extremely challenging task, requiring rapid reduction in the carbon intensity of all sectors of the economy and with limited leeway for residual emissions. Addressing residual emissions in ‘challenging-to-decarbonise’ sectors such as the industrial and aviation sectors relies on the development and commercialization of innovative advanced technologies, currently still in their infancy. The aim of this study was to (a) explore the role of advanced technologies in achieving deep decarbonisation of the energy system and (b) provide technology-specific details of how rapid and deep carbon intensity reductions can be achieved in the energy demand sectors. This was done using TIAM-Grantham – a linear cost optimization model of the global energy system with a detailed representation of demand-side technologies. We find that the inclusion of advanced technologies in the demand sectors, together with energy demand reduction through behavioural changes, enables the model to achieve the rapid and deep decarbonisation of the energy system associated with limiting global warming to below 2 °C whilst at the same time reduces reliance on negative emissions technologies by up to ∼18% compared to the same scenario with a standard set of technologies. Realising such advanced technologies at commercial scales, as well as achieving such significant reductions in energy demand, represents a major challenge for policy makers, businesses and civil society. There is an urgent need for continued R&D efforts in the demand sectors to ensure that advanced technologies become commercially available when we need them and to avoid the gamble of overreliance on negative emissions technologies to offset residual emissions.

  • Journal article
    Balcombe P, Brierley J, Lewis C, Skatvedt L, Speirs J, Hawkes A, Staffell Iet al., 2019,

    How to decarbonise international shipping: Options for fuels, technologies and policies

    , Energy Conversion and Management, Vol: 182, Pages: 72-88, ISSN: 0196-8904

    International 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.

  • Journal article
    Staffell I, Scamman D, Velazquez Abad A, Balcombe P, Dodds PE, Ekins P, Shah N, Ward KRet al., 2019,

    The role of hydrogen and fuel cells in the global energy system

    , Energy and Environmental Science, Vol: 12, Pages: 463-491, ISSN: 1754-5692

    Hydrogen technologies have experienced cycles of excessive expectations followed by disillusion. Nonetheless, a growing body of evidence suggests these technologies form an attractive option for the deep decarbonisation of global energy systems, and that recent improvements in their cost and performance point towards economic viability as well. This paper is a comprehensive review of the potential role that hydrogen could play in the provision of electricity, heat, industry, transport and energy storage in a low-carbon energy system, and an assessment of the status of hydrogen in being able to fulfil that potential. The picture that emerges is one of qualified promise: hydrogen is well established in certain niches such as forklift trucks, while mainstream applications are now forthcoming. Hydrogen vehicles are available commercially in several countries, and 225,000 fuel cell home heating systems have been sold. This represents a step change from the situationof only five years ago. This review shows that challenges around cost and performance remain, and considerable improvements are still required for hydrogen to become truly competitive. But such competitiveness in the medium-term future no longer seems anunrealistic prospect, which fully justifies the growing interest and policy support for these technologies around the world.

  • Report
    Speirs J, Balcombe P, Blomerus P, Stettler M, Brandon N, Hawkes Aet al., 2019,

    Can natural gas reduce emissions from transport?: Heavy goods vehicles and shipping

  • Journal article
    Schmidt O, Melchior S, Hawkes A, Staffell Iet al., 2019,

    Projecting the future levelized cost of electricity storage technologies

    , Joule, Vol: 3, Pages: 81-100, ISSN: 2542-4351

    The 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.

  • Conference paper
    Santarelli M, Gandiglio M, Acri M, Hakala T, Rautanen M, Hawkes Aet al., 2019,

    Results from industrial size biogas-fed SOFC plant (DeMosofC project)

    , Pages: 107-116, ISSN: 1938-6737

    The EU-funded DEMOSOFC project demonstrates the technical and economic feasibility of operating a 174 kWe (+ 100 kWth) SOFC system in a wastewater treatment plant, fed by biogas. The integrated biogas-SOFC plant includes three main units: 1) the biogas clean-up and compression section; 2) the SOFC power modules, and 3) the heat recovery loop. The present work is related to the results of the operation of the SOFC system. More than 7000 hours of operation have been reached onsite. Biogas raw composition is daily measured: starting form values of around 50 ppm (Sulphur equivalent) and 1.0-1.5 ppm (siloxanes equivalent) downstream the results show zero H2S and zero siloxanes. Measured SOFC efficiency from biogas to AC power has always been higher than 52-53%, with peaks of 56%. A dedicated emissions measurements campaign shows NOx < 20 mg/m3, SO2 < 8 mg/m3 and particulate lower than ambient air values (0.01 mg/m3).

  • Journal article
    Oluleye G, Wigh D, Shah N, Napoli M, Hawkes Aet al., 2019,

    A framework for biogas exploitation in Italian waste water treatment plants

    , Chemical Engineering Transactions, Vol: 76, Pages: 991-996

    Copyright © 2019, AIDIC Servizi S.r.l. Effective utilisation of biogas is an important step in increasing usage of renewable energy, due to the great flexibility that solar and wind power in particular lacks. Biogas generated through anaerobic digestion (AD) of sewage sludge addresses environmental concerns together with creating electricity generation potential. There is currently no optimisation-based decision-support framework to determine the best use of biogas from a Waste Water Treatment Plant (WWTP), and provide a market outlook for each of the options. This work proposes a novel multi-period Mixed Integer Linear Program (MILP) model for dispatch and selection of technologies capable of exploiting biogas produced from sludge. The novelty is also highlighted by extrapolating the optimised results to a broader analysis of 855 Italian WWTPs with Population Equivalent (P.E.) > 20,000. The use of real input data provides a unique added value to the work. The modelling framework is applied to several case studies. Results show that 7–23 % savings in operating costs are possible from integrating three systems to exploit biogas, and the trade-offs between capital and operating costs affect the optimal system choice. Furthermore, market driven scenarios are used to analyse how to improve the economic performance.

  • Journal article
    Parkinson B, Balcombe P, Speirs JF, Hawkes AD, Hellgardt Ket al., 2019,

    Levelized cost of CO2 mitigation from hydrogen production routes

    , Energy and Environmental Science, Vol: 12, Pages: 19-40, ISSN: 1754-5692

    Different technologies produce hydrogen with varying cost and carbon footprints over the entire resource supply chain and manufacturing steps. This paper examines the relative costs of carbon mitigation from a life cycle perspective for 12 different hydrogen production techniques using fossil fuels, nuclear energy and renewable sources by technology substitution. Production costs and life cycle emissions are parameterized and re-estimated from currently available assessments to produce robust ranges to describe uncertainties for each technology. Hydrogen production routes are then compared using a combination of metrics, levelized cost of carbon mitigation and the proportional decarbonization benchmarked against steam methane reforming, to provide a clearer picture of the relative merits of various hydrogen production pathways, the limitations of technologies and the research challenges that need to be addressed for cost-effective decarbonization pathways. The results show that there is a trade-off between the cost of mitigation and the proportion of decarbonization achieved. The most cost-effective methods of decarbonization still utilize fossil feedstocks due to their low cost of extraction and processing, but only offer moderate decarbonisation levels due to previous underestimations of supply chain emissions contributions. Methane pyrolysis may be the most cost-effective short-term abatement solution, but its emissions reduction performance is heavily dependent on managing supply chain emissions whilst cost effectiveness is governed by the price of solid carbon. Renewable electrolytic routes offer significantly higher emissions reductions, but production routes are more complex than those that utilise naturally-occurring energy-dense fuels and hydrogen costs are high at modest renewable energy capacity factors. Nuclear routes are highly cost-effective mitigation options, but could suffer from regionally varied perceptions of safety and concerns regarding prolife

  • Journal article
    Bosch J, Staffell I, Hawkes A, 2018,

    Temporally explicit and spatially resolved global offshore wind energy potentials

    , Energy, Vol: 163, Pages: 766-781, ISSN: 0360-5442

    Several influential energy systems models (ESMs) indicate that renewable energy must supply a large share of the world's electricity to limit global temperature increases to 1.5 °C. To better represent the costs and other implications of such a transition, it is important that ESMs can realistically characterise the technical and economic potential of renewable energy resources. This paper presents a Geospatial Information System methodology for estimating the global offshore wind energy potential, i.e. the terawatt hour per year (TWh/yr) production potential of wind farms, assuming capacity could be built across the viable offshore area of each country. A bottom-up approach characterises the capacity factors of offshore wind farms by estimating the available wind power from high resolution global wind speed data sets. Temporal phenomena are retained by binning hourly wind speeds into 32 time slices per year considering the wind resource across several decades. For 157 countries with a viable offshore wind potential, electricity generation potential is produced in tranches according to the distance to grid connection, water depth and average annual capacity factor. These data can be used as inputs to ESMs and to assess the economically viable offshore wind energy potential, on a global or per-country basis.

  • Journal article
    Budinis S, Krevor S, Mac Dowell N, Brandon N, Hawkes Aet al., 2018,

    An assessment of CCS costs, barriers and potential

    , Energy Strategy Reviews, Vol: 22, Pages: 61-81, ISSN: 2211-467X

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

  • Journal article
    Oluleye OO, Allison J, Hawker G, Kelly N, Hawkes Aet al., 2018,

    A two-step optimization model for quantifying the flexibility potential of power-to-heat systems in dwellings

    , Applied Energy, Vol: 228, Pages: 215-228, ISSN: 0306-2619

    Coupling the electricity and heat sectors is receiving interest as a potential source of flexibility to help absorb surplus renewable electricity. The flexibility afforded by power-to-heat systems in dwellings has yet to be quantified in terms of time, energy and costs, and especially in cases where homeowners are heterogeneous prosumers. Flexibility quantification whilst accounting for prosumer heterogeneity is non-trivial. Therefore in this work a novel two-step optimization framework is proposed to quantify the potential of prosumers to absorb surplus renewable electricity through the integration of air source heat pumps and thermal energy storage. The first step is formulated as a multi-period mixed integer linear programming problem to determine the optimal energy system, and the quantity of surplus electricity absorbed. The second step is formulated as a linear programming problem to determine the price a prosumer will accept for absorbing surplus electricity, and thus the number of active prosumers in the market.A case study of 445 prosumers is presented to illustrate the approach. Results show that the number of active prosumers is affected by the quantity of absorbed electricity, frequency of requests, the price offered by aggregators and how prosumers determine the acceptable value of flexibility provided. This study is a step towards reducing the need for renewable curtailment and increasing pricing transparency in relation to demand-side response.

  • Journal article
    Balcombe P, Speirs JF, Brandon NP, Hawkes ADet al., 2018,

    Methane emissions: choosing the right climate metric and time horizon

    , Environmental Science: Processes and Impacts, Vol: 20, Pages: 1323-1339, ISSN: 2050-7895

    Methane is a more potent greenhouse gas (GHG) than CO2, but it has a shorter atmospheric lifespan, thus its relative climate impact reduces significantly over time. Different GHGs are often conflated into a single metric to compare technologies and supply chains, such as the global warming potential (GWP). However, the use of GWP is criticised, regarding: (1) the need to select a timeframe; (2) its physical basis on radiative forcing; and (3) the fact that it measures the average forcing of a pulse over time rather than a sustained emission at a specific end-point in time. Many alternative metrics have been proposed which tackle different aspects of these limitations and this paper assesses them by their key attributes and limitations, with respect to methane emissions. A case study application of various metrics is produced and recommendations are made for the use of climate metrics for different categories of applications. Across metrics, CO2 equivalences for methane range from 4–199 gCO2eq./gCH4, although most estimates fall between 20 and 80 gCO2eq./gCH4. Therefore the selection of metric and time horizon for technology evaluations is likely to change the rank order of preference, as demonstrated herein with the use of natural gas as a shipping fuel versus alternatives. It is not advisable or conservative to use only a short time horizon, e.g. 20 years, which disregards the long-term impacts of CO2 emissions and is thus detrimental to achieving eventual climate stabilisation. Recommendations are made for the use of metrics in 3 categories of applications. Short-term emissions estimates of facilities or regions should be transparent and use a single metric and include the separated contribution from each GHG. Multi-year technology assessments should use both short and long term static metrics (e.g. GWP) to test robustness of results. Longer term energy assessments or decarbonisation pathways must use both short and long-term metrics and where this has a lar

  • Journal article
    Guo Y, Hawkes A, 2018,

    Simulating the game-theoretic market equilibrium and contract-driven investment in global gas trade using an agent-based method

    , Energy, Vol: 160, Pages: 820-834, ISSN: 0360-5442

    To understand how the alternative US liquefied natural gas exportation strategies may affect future global gas market dynamics, a global-scale model Gas-GAME is developed using an agent-based framework. This is the first model having explicit contract-driven capacity expansion process, allowing investors to hold imperfect foresights, and simulating market power in global gas trade. With these features, Gas-GAME can analyse market development subject to the incentives and perspectives of each market player. The model simulates short-term game-theoretical market equilibrium with Mixed Complementarity Problem approach. For long-term investment decisions, bilateral contracting processes considering both import requests and export profitability are modelled. A base case is presented and validated, followed by a case study considering US export strategy. When the US stays conservative in export expansion, gas supply tightness occurs, leading to continuing European dependence on Russian gas, and a shift to pipeline-based import in the Chinese market. Conversely, when the US invests aggressively, Middle East and Australia both see significant revenue losses, and Western Europe constructs more regasification plants to provide alternatives to Russian supply. Gas-GAME captures the essential dynamics between market power, short-term prices and long-term contracts to provide a more nuanced view of global gas market.

  • Journal article
    Crow DJG, Anderson K, Hawkes AD, Brandon Net al., 2018,

    Impact of drilling costs on the US gas industry: prospects for automation

    , Energies, Vol: 11, ISSN: 1996-1073

    Recent low gas prices have greatly increased pressure on drilling companies to reduce costs and increase efficiency. Field trials have shown that implementing automation can dramatically reduce drilling costs by reducing the time required to drill wells. This study uses the DYNamic upstreAm gAs MOdel (DYNAAMO), a new techno-economic, bottom-up model of natural gas supply, to quantitatively assess the economic impact of lower drilling costs on the US upstream gas industry. A sensitivity analysis of three key economic indicators is presented, with results quoted for the most common field types currently producing, including unconventional and offshore gas. While all operating environments show increased profitability from drilling automation, it is found that conventional onshore reserves can benefit to the greatest extent. For large gas fields, a 50% reduction in drilling costs is found to reduce initial project breakevens by up to 17 million USD per billion cubic metres (MUSD/BCM) and mid-plateau breakevens by up to 8 MUSD/BCM. In this same scenario, additional volumes of around 160 BCM of unconventional gas are shown to become commercial due to both the lower costs of additional production wells in mature fields and the viability of developing new resources held in smaller fields. The capital efficiency of onshore projects increases by 50%-100%, with initial project net present value (NPV) gains of up to 32%.

  • Journal article
    Miu LM, Wisniewska N, Mazur C, Hardy J, Hawkes Aet al., 2018,

    A simple assessment of housing retrofit policies for the UK: what should succeed the energy company obligation?

    , Energies, Vol: 11, ISSN: 1996-1073

    Despite the need for large-scale retrofit of UK housing to meet emissions reduction targets, progress to date has been slow and domestic energy efficiency policies have struggled to accelerate housing retrofit processes. There is a need for housing retrofit policies that overcome key barriers within the retrofit sector while maintaining economic viability for customers, funding organizations, and effectively addressing UK emission reductions and fuel poverty targets. In this study, we use a simple assessment framework to assess three policies (the Variable Council Tax, the Variable Stamp Duty Land Tax, and Green Mortgage) proposed to replace the UK’s current major domestic retrofit programme known as the Energy Company Obligation (ECO). We show that the Variable Council Tax and Green Mortgage proposals have the greatest potential for overcoming the main barriers to retrofit policies while maintaining economic viability and contributing to high-level UK targets. We also show that, while none of the assessed schemes are capable of overcoming all retrofit barriers on their own, a mix of all three policies could address most barriers and provide key benefits such as wide coverage of property markets, operation on existing financial infrastructures, and application of a “carrot-and-stick” approach to incentivize retrofit. Lastly, we indicate that the specific support and protection of fuel-poor households cannot be achieved by a mix of these policies and a complementary scheme focused on fuel-poor households is required.

  • Journal article
    Balcombe P, Speirs J, Johnson E, Martin J, Brandon N, Hawkes Aet al., 2018,

    The carbon credentials of hydrogen gas networks and supply chains

    , Renewable and Sustainable Energy Reviews, Vol: 91, Pages: 1077-1088, ISSN: 1364-0321

    Projections of decarbonisation pathways have typically involved reducing dependence on natural gas grids via greater electrification of heat using heat pumps or even electric heaters. However, many technical, economic and consumer barriers to electrification of heat persist. The gas network holds value in relation to flexibility of operation, requiring simpler control and enabling less expensive storage. There may be value in retaining and repurposing gas infrastructure where there are feasible routes to decarbonisation. This study quantifies and analyses the decarbonisation potential associated with the conversion of gas grids to deliver hydrogen, focusing on supply chains. Routes to produce hydrogen for gas grids are categorised as: reforming natural gas with (or without) carbon capture and storage (CCS); gasification of coal with (or without) CCS; gasification of biomass with (or without) CCS; electrolysis using low carbon electricity. The overall range of greenhouse gas emissions across routes is extremely large, from − 371 to 642 gCO 2 eq/kW h H2 . Therefore, when including supply chain emissions, hydrogen can have a range of carbon intensities and cannot be assumed to be low carbon. Emissions estimates for natural gas reforming with CCS lie in the range of 23–150 g/kW h H2 , with CCS typically reducing CO 2 emissions by 75%. Hydrogen from electrolysis ranges from 24 to 178 gCO 2 eq/kW h H2 for renewable electricity sources, where wind electricity results in the lowest CO 2 emissions. Solar PV electricity typically exhibits higher emissions and varies significantly by geographical region. The emissions from upstream supply chains is a major contributor to total emissions and varies considerably across different routes to hydrogen. Biomass gasification is characterised by very large negative emissions in the supply chain and very large positive emissions in the gasification process. Therefore, improvements in total emissions are large if even small i

  • Journal article
    Vijay A, Hawkes A, 2018,

    Impact of dynamic aspects on economics of fuel cell based micro co-generation in low carbon futures

    , Energy, Vol: 155, Pages: 874-886, ISSN: 0360-5442

    This article evaluates the impact of a range of dynamic performance parameters on the techno-economics of fuel cell based micro co-generation. The main novelties in methodology are: (1) Analysis in the context of future power system decarbonisation, (2) Use of the Long Run Marginal Cost of electricity, (3) Combination of the above with dynamic aspects such as start-up cost, ramping limit, turn down ratio, minimum up time and minimum down time and (4) Identification of sensitive parameters for future research. To this end it combines a national level energy systems model with an individual heating system model. A case study of the United Kingdom is considered for the year 2035. Economic viability of fuel cell based micro co-generation hinges upon the use of an optimized control strategy. With such a control strategy, a hot start-up approach offers much greater economic potential than a cold start-up approach. The best case ratio of maximum allowable hot standby power to the nominal value is 4.2 while the ratio for cold start is only 1.1. Combinations involving low ramping limits less than 70 W/min and limited turn down ratios above 35% need to be avoided as they seriously hinder economic performance.

  • Journal article
    Jalil Vega FA, Hawkes A, 2018,

    The effect of spatial resolution on outcomes from energy systems modelling of heat decarbonisation

    , Energy, Vol: 155, Pages: 339-350, ISSN: 0360-5442

    Spatial resolution is often cited as a crucial determinant of results from energy systems models. However, there is no study that comprehensively analyses the effect of spatial resolution. This paper addresses this gap by applying the Heat Infrastructure and Technology heat decarbonisation optimisation model in six UK Local Authorities representing a range of rural/urban areas, at three levels of spatial resolution, in order to systematically compare results. Results show the importance of spatial resolution for optimal allocation of heat supply technologies and infrastructure across different urban/rural areas. Firstly, for the studied cases, differences of up to 30% in heat network uptake were observed when comparing results between different resolutions for a given area. Secondly, for areas that generally exhibit the high and low extremes of linear heat density, results are less dependent on spatial resolution. Also, spatial resolution effects are more significant when there is higher variability of linear heat density throughout zones. Finally, results show that it is important to use finer resolutions when using optimisation models to inform detailed network planning and expansion. Higher spatial resolutions provide more detailed information on zones that act as anchors that can seed network growth and on location of network supply technologies.

  • Journal article
    Allison J, Bell K, Clarke J, Cowie A, Elsayed A, Flett G, Oluleye G, Hawkes A, Hawker G, Kelly N, de Castro MMM, Sharpe T, Shea A, Strachan P, Tuohy Pet al., 2018,

    Assessing domestic heat storage requirements for energy flexibility over varying timescales

    , Applied Thermal Engineering, Vol: 136, Pages: 602-616, ISSN: 1359-4311

    © 2018 The Authors This paper explores the feasibility of storing heat in an encapsulated store to support thermal load shifting over three timescales: diurnal, weekly and seasonal. A building simulation tool was used to calculate the space heating and hot water demands for four common UK housing types and a range of operating conditions. A custom sizing methodology calculated the capacities of storage required to fully meet the heat demands over the three timescales. Corresponding storage volumes were calculated for a range of heat storage materials deemed suitable for storing heat within a dwelling, either in a tank or as an integral part of the building fabric: hot water, concrete, high-temperature magnetite blocks, and a phase change material. The results indicate that with low temperature heat storage, domestic load shifting is feasible over a few days. Beyond this timescale, the very large storage volumes required make integration in dwellings problematic. Supporting load shifting over 1–2 weeks is feasible with high temperature storage. Retention of heat over periods longer than this is challenging, even with significant levels of insulation. Seasonal storage of heat in an encapsulated store appeared impractical in all cases modelled due to the volume of material required.

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