Evaluating the regional potential for emissions reduction using energy storage

Energy storage is an enabler of low carbon electricity generation, however several studies have shown that its use can cause a non-trivial increase in carbon emissions even if the storage has 100% round-trip efficiency. To understand the impact of storage operation and demand response on emissions, it is necessary to determine the marginal emissions factor (MEF) at the time the storage or demand response was operated. This paper presents statistical approaches to determining regional MEFs using data on regional electricity demand and generation by fuel type, with a simple power flow model used to determine consumption emissions by region. The technique is applied to the electricity system in Great Britain in 2018. It is found that the impact of storage varies widely by location and operating mode, with the greatest emissions reductions achieved when storage is used to reduce wind curtailment in areas which consume high levels of fossil fuel generation, and the greatest emissions increases occurring where storage is used for wind balancing in areas where wind is not curtailed. The difference between the highest emissions reduction and highest emissions increase is found to be significant, at 785 gCO2 per kWh that passes through storage

Technical benefits of energy storage and electricity interconnections in future British power systems

There are concerns that the GB (Great Britain) electricity system may not be able to fully absorb increasing levels of variable renewables with consequent implications for emission reduction targets. This study considers the technical benefits of additional energy storage and interconnections in future GB electricity systems. Initially a reference model of the GB electricity system was developed using the EnergyPLAN tool. The model was validated against actual data and was confirmed to accurately represent the GB electricity system. Subsequently, an analysis of four possible scenarios, for the years 2020 and 2030, has been performed and the maximum technically feasible wind penetration calculated. Finally, the level of interconnection and energy storage has been varied to assess the technical benefits to the operation of a 2030 GB electricity system. We conclude that increasing levels of interconnection and energy storage allow a further reduction in the primary energy supply and an increase in maximum technically feasible wind penetration, permitting the system emissions intensity to be reduced from 483 gCO/kWh in 2012 to 113 gCO/kWh in 2030. Increasing the levels of interconnection and energy storage has significant technical benefits in the potential future GB systems considered

Energy system requirements of fossil-free steelmaking using hydrogen direct reduction

The iron and steel industry is one of the world's largest industrial emitters of greenhouse gases. One promising option for decarbonising the industry is hydrogen direct reduction of iron (H-DR) with electric arc furnace (EAF) steelmaking, powered by zero carbon electricity. However, to date, little attention has been given to the energy system requirements of adopting such a highly energy-intensive process. This study integrates a newly developed long-term energy system planning tool, with a thermodynamic process model of H-DR/EAF steelmaking developed by Vogl et al. (2018), to assess the optimal combination of generation and storage technologies needed to provide a reliable supply of electricity and hydrogen. The modelling tools can be applied to any country or region and their use is demonstrated here by application to the UK iron and steel industry as a case study. It is found that the optimal energy system comprises 1.3 GW of electrolysers, 3 GW of wind power, 2.5 GW of solar, 60 MW of combined cycle gas with carbon capture, 600 GWh/600 MW of hydrogen storage, and 30 GWh/130 MW of compressed air energy storage. The hydrogen storage requirements of the industry can be significantly reduced by maintaining some dispatchable generation, for example from 600 GWh with no restriction on dispatchable generation to 140 GWh if 20% of electricity demand is met using dispatchable generation. The marginal abatement costs of a switch to hydrogen-based steelmaking are projected to be less than carbon price forecasts within 5–10 years

The value of electricity storage to large enterprises: A case study on Lancaster University

Co-locating electricity storage with demand has significant potential to increase consumption of locally-generated electricity, defer infrastructure investments, and contribute to the task of balancing supply and demand on the wider network. In the UK, unlike domestic consumers, large enterprises are already incentivised to reduce peak demand through exposure to time- and demand-dependent network charges. This paper considers the potential of electricity storage to reduce the bills of large enterprises, focusing on Lancaster University as a case study. Through analysis of Lancaster University's recent demand and generation data and current and future charges, it is shown that recent widening of red distribution charge time bands has reduced the value of electricity storage to enterprises, and that in 2015 an enterprise such as Lancaster University could have expected electricity storage to deliver annual savings of around £27 per kWh of storage capacity, by reducing network charges. An analysis of these charges around Great Britain shows that the opportunity for storage to provide savings to enterprises is greatest in the south-west (at least £70/kWh.yr in 2017) and lowest in the north of Scotland (at least £20/kWh.yr). Whether investment in storage provides positive value to enterprises is shown to be strongly dependent upon location

Reducing the life cycle environmental impact of electric vehicles through emissions-responsive charging

Electric vehicles (EVs) are currently being promoted to reduce transport emissions. We present a life cycle assessment of EV charging behaviours based on marginal emissions factors. For Great Britain, we find that electricity consumption accounts for the highest proportion of life cycle carbon emissions from EVs. We highlight the potential life cycle carbon emissions reduction brought by charging during periods when the grid mix produces relatively low emissions. While our study focuses on Great Britain, we have applied our methodology to several European countries with contrasting electricity generation mixes. Our analysis demonstrates that countries with a high proportion of fossil energy will have reduced benefits from deploying EVs, but are likely to achieve increased benefits from smart charging approaches. We conclude that using marginal emissions factors is essential to understanding the greenhouse gas impacts of EV deployment, and that smart charging tied to instantaneous grid emissions factors can bring benefits

Using electricity storage to reduce greenhouse gas emissions

While energy storage is key to increasing the penetration of variable renewables, the near-term effects of storage on greenhouse gas emissions are uncertain. Several studies have shown that storage operation can increase emissions even if the storage has 100% turnaround efficiency. Furthermore, previous studies have relied on national-level data and given very little attention to the impacts of storage on emissions at local scales. This is an important omission, as carbon intensities can vary very significantly at sub-national scales. We introduce a novel approach to calculating regional marginal emissions factors, based on a validated power system model and regression analysis. The techniques are used to investigate the impacts of storage operation on CO2 emissions in Great Britain in 2019, under a range of operating scenarios. It is found that there are significant regional differences in storage emissions factors, with storage tending to increase emissions when used for wind balancing in areas with little wind curtailment. In contrast, the greatest emissions reductions are achieved when charging storage with otherwise-curtailed renewables and discharging to reduce peak demands in areas consuming high volumes of fossil fuel power. Over all regions and operating modes studied, the difference between the highest reduction in emissions and the highest increase in emissions is considerable, at 741 gCO2 per kWh discharged. We conclude that power system regulators should pay increased attention to the impact of storage operation on system CO2 emissions

Community energy storage: A case study in the UK using a linear programming method

In this paper, we investigate how energy storage can be used to increase the value of community energy schemes through cost reductions, infrastructure support, increased scheme membership, and reduced carbon emissions. A linear programming optimisation framework is developed to schedule the operation of behind-the-meter energy storage such that costs are minimised, while keeping peak demands within allowable limits. This is also extended to model generation-integrated energy storage systems, where the storage is located in the flow of energy from primary source (e.g. wind) to a usable form (e.g. electricity). To demonstrate the potential of energy storage within a real community energy scheme, we present a case study of a community hydro scheme in North Wales, considering both battery storage and a reservoir-based storage system. It is found that either system can be used to substantially increase the membership of the scheme while avoiding impacts on the electricity network, but that storage remains prohibitively expensive when used for self-consumption of renewables and arbitrage. We also investigate the impacts of energy storage on the community's carbon emissions, showing that storage operation appears to provide very little additional reduction in emissions when grid average emissions factors are used

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

X-ray emission from the Sombrero galaxy: discrete sources

We present a study of discrete X-ray sources in and around the bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival Chandra observations with a total exposure of ~200 ks. With a detection limit of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30 kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray binaries (LMXBs). We quantify the differential luminosity functions (LFs) for both the detected GC and field LMXBs, whose power-low indices (~1.1 for the GC-LF and ~1.6 for field-LF) are consistent with previous studies for elliptical galaxies. With precise sky positions of the GCs without a detected X-ray source, we further quantify, through a fluctuation analysis, the GC LF at fainter luminosities down to 1E35 erg/s. The derived index rules out a faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent findings in several elliptical galaxies and the bulge of M31. On the other hand, the 2-6 keV unresolved emission places a tight constraint on the field LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101 sources in the halo of Sombrero. The presence of these sources cannot be interpreted as galactic LMXBs whose spatial distribution empirically follows the starlight. Their number is also higher than the expected number of cosmic AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray surveys. We suggest that either the cosmic X-ray background is unusually high in the direction of Sombrero, or a distinct population of X-ray sources is present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres