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Environmental impacts of high penetration renewable energy scenarios for Europe

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2016 Environ. Res. Lett. 11 014012

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Environ. Res. Lett. 11 (2016) 014012 doi:10.1088/1748-9326/11/1/014012

LETTER

Environmental impacts of high penetration renewable energyscenarios for Europe

Peter Berrill1, AndersArvesen1, Yvonne Scholz2, HansChristianGils2 andEdgarGHertwich1,3

1 Industrial Ecology Programme andDepartment of Energy and Process Engineering, NorwegianUniversity of Science andTechnology(NTNU), Sem Sælands vei 7,NTNU,NO-7491 Trondheim,Norway

2 Institute of Engineering Thermodynamics, GermanAerospace Center (DLR), Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany3 Center for Industrial Ecology, School of Forestry &Environmental Studies, YaleUniversity, NewHaven, CT 06511,USA

E-mail: anders.arvesen@ntnu.no

Keywords: life cycle assessment (LCA), electricity scenarios, power system, THEMIS, REMix

AbstractThe prospect of irreversible environmental alterations and an increasingly volatile climate pressurisessocieties to reduce greenhouse gas emissions, therebymitigating climate change impacts. As globalelectricity demand continues to grow, particularly if considering a futurewith increased electrificationof heat and transport sectors, the imperative to decarbonise our electricity supply becomesmoreurgent. This letter implements outputs of a detailed power systemoptimisationmodel into aprospective life cycle analysis framework in order to present a life cycle analysis of 44 electricityscenarios for Europe in 2050, including analyses of systems based largely on low-carbon fossil energyoptions (natural gas, and coal with carbon capture and storage (CCS)) as well as systemswith highshares of variable renewable energy (VRE) (wind and solar). VRE curtailments and impacts caused byextra energy storage and transmission capabilities necessary in systems based onVRE are taken intoaccount. The results show that systems based largely onVRE performmuch better regarding climatechange and other impact categories than the investigated systems based on fossil fuels. The climatechange impacts fromEurope for the year 2050 in a scenario using primarily natural gas are 1400 TgCO2-eqwhile in a scenario usingmostly coal withCCS the impacts are 480 TgCO2-eq. Systems basedon renewables with an evenmix of wind and solar capacity generate impacts of 120–140 TgCO2-eq.Impacts arising as a result of wind and solar variability do not significantly compromise the climatebenefits of utilising these energy resources. VRE systems requiremore infrastructure leading tomuchlargermineral resource depletion impacts than fossil fuel systems, and greater land occupationimpacts than systems based on natural gas. Emissions and resource requirements fromwind powerare smaller than from solar power.

1. Introduction

The provision of electricity has become an indispen-sable part of our society. Countless human activitiesare founded upon a reliable, abundant and affordableelectricity supply. Today’s electricity system still usesfossil fuels for the majority of power generation [1]. Asa result, the electricity sector causes significant con-tributions to greenhouse gas (GHG) emissions. Forinstance, 27% of GHG emissions in EU-27 in 2012came from the electricity sector [2]. In the comingyears the electricity sector is expected to shoulder themajority of energy-related GHG emission reductions,

while potentially undergoing increases in demand ifwe see large scale electrification of the heat andtransport sectors [3]. In its roadmap for a competitivelow carbon economy, the European Commissionprojects almost zero GHG emissions from the powersector by 2050 [4]. As renewable sources displacefossil fuels in the generation portfolio, the magnitudeand types of impacts will change. Impacts fromelectricity are not limited to GHGs; various studieshave demonstrated the other environmental burdenscaused by the electricity sector, such as resourcedepletion, human health impacts, and land occupa-tion [5–8]. Quantifying the impacts of a changing

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generation mix, including direct effects (e.g. powerplant emissions) and indirect effects (e.g. emissionsfrom fuel extraction, infrastructure creation), requiresa life cycle approach. Numerous life cycle assessment(LCA) studies exist examining environmental impactsof particular parts of the electricity system, includingelectricity generation technologies (e.g., [9–12], orliterature reviews [13, 14]) and electricity transmissionor distribution infrastructure [15–18]. Relatively fewstudies have attempted to analyse the electricity systemas a whole [5, 6, 19], and to our knowledge no LCAstudies of electricity systems have taken into accountthe impacts of energy storage and grid extensions inscenarios with high penetrations of variable renewableenergy (VRE).

The present study uses an integrated, hybrid LCAmodelling framework [20] to examine 44 different sce-narios for the provision of electricity in Europe in theyear 2050, explicitly considering additional require-ments to accommodate the variability of wind andsolar power. The LCA model incorporates the effectsof a changing electricity generation mix on electricityinputs to production processes. In this way feedbackeffects of a cleaner electricity mix are included. The 44scenarios of European power supply structures in theyear 2050 are generated by REMix, a high resolutionenergy system optimisation model [21, 22]. Amongthe numerous models that have been used to analysepower systems incorporating large amounts of VREsources [23, 24], REMix is particularly suitable for thepresent analysis due to its explicit description ofenergy storage technologies and transmission gridextensions required in each scenario, in addition to itsdetailed geographical resolution covering the whole ofEurope.

2.Models and scenarios

2.1. Technology hybridized environmental-economicmodel with integrated scenarios(THEMIS)THEMIS is a multi-regional, integrated hybrid LCAmodelling framework [20]. The current version ofTHEMIS makes use of the LCA database Ecoinvent[25] and the multi-regional input–output databaseEXIOBASE [26]. Further, it incorporates prospectivelife cycle inventory (LCI) data for electricity generationtechnologies, and integrates these data into all life cyclesupply chain descriptions in the model, followingeither a baseline or a climate change mitigationscenario. In addition to changes in electricity supply,the model includes projected changes in key para-meters of industrial production, such as reducedenergy inputs to clinker production.

THEMIS has been used previously in analysis ofpower generation technologies [6]. LCI data forenergy storage and transmission technologies areadded in the present study, as is described in

section 3. In this study, expected technology forEurope for the year 2050 in a climate change mitiga-tion scenario [20] is used. Environmental impactsfor six impact categories are examined using theReCiPe impact assessment method [27]: climatechange, particulate matter formation, freshwaterecotoxicity, freshwater eutrophication, land occupa-tion andmineral resource depletion.

2.2. REMixREMix is a least-cost energy system optimisationmodel that determines installed capacities of powergeneration, transmission and storage units and simu-lates the operation of these system components[21, 22]. For the present study, the model wasparameterised with projections of electricity demandand technical and economic parameters for powergeneration, transmission and storage technologies forthe year 2050 [28, 29]. Investment costs are assumed todecrease due to future technical change in accordancewith typical learning rates of large-scale integratedassessmentmodels [29].

Total input of VRE (before curtailment), corresp-onding share of solar and wind production and theCO2 price are further input parameters. The input ofVRE varies from 0% to 140%. Input can exceed 100%because of curtailment effects, which prevent the totalelectricity generated from being used. Thus, after cur-tailment, actual input of VRE to electricity productionis always less than 100%. The following VRE splits areexplored for each VRE penetration level: 80% wind20% solar, 50% wind 50% solar, and 20% wind 80%solar. The VRE technologies considered in the REMixassessment are concentrating solar power, roof-mounted and ground-mounted solar photovoltaic(PV), as well as onshore and offshore wind power.Potentials for each technology are quantified in [22].Residual electricity production is determined by eco-nomic optimisation. The costs to beminimised are thetotal system costs, i.e. the sum of all investment, fixedand variable operation costs.

Results are presented here for scenarios with twoCO2 prices, €50/t and €150/t. These values represent2050 price levels that deliver significant degrees of cli-mate change mitigation in mitigation scenario litera-ture. The €150/t price is roughly consistent with the2050 carbon price of the most ambitious referencemitigation scenario (the ‘RCP2.6’) considered by theIPCC Fifth Assessment Report [30, 31]. In €50/t sce-narios the model selects natural gas combined cyclewithout carbon capture and storage (CCS) as the base-load technology, while in €150/t scenarios coal withCCS is selected. Notably, there is no input fromnuclear, biomass or coal without CCS in any scenario.This is not a conscious modelling decision but ratheran outcome of themodel.

Three storage technologies are considered inREMix: pumped hydro storage (PHS), battery storage

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and hydrogen storage. While other technologies forstoring energy exist, the three just-mentioned optionsare assumed to be overall representative in terms ofmain technical and economic characteristics. Loadshifting measures are not considered in this work, butcould further reduce the system costs and replace sto-rage to some extent [32]. The scenarios presented hereshow zero utilisation of hydrogen storage. The repre-sentation of power transmission is in this study limitedtoDC links between neighbouring countries.

2.3. CombinedmodelThe environmental performance of the electricitysystems described by each REMix scenario, incorporat-ing electricity generationmixes, energy storage capacitycreation and utilisation, and transmission grid exten-sions, are analysed using THEMIS. Technologicalcharacteristics (i.e. inputs and emissions of eachtechnology at each life cycle stage) of the requiredtechnologies aredefined inTHEMIS. Expected technol-ogy for Europe in 2050 is used, including expectedpower plant technologies and efficiencies. For example,electricity generation from coal is provided by a mix oftechnologies (integrated gasification combined cycle,supercritical generation and subcritical generation)which is more developed than today. Similarly, the

electricity generation from solar PV is provided by amix of PV types (polycrystalline silicon, cadmiumtelluride and copper indium gallium selenide), and inaddition a distinction is made between ground-mounted (about 40% of total) and rooftop installations(60%). All such assumptions about specific breakdownsof electricity generation technologies are adopted from[6], and are shown in table S1.

2.4. ScenariosThe REMix scenarios described above total 22 for eachCO2 price. Figure 1 summarises results for all scenar-ios. Scenarios based on VRE have considerably largerinstalled capacities than scenarios based on conven-tional thermal generation. This is more pronouncedfor solar power than wind power, because of thesmaller capacity factors for solar power. There is aconstant capacity of PHS in almost all scenarios, andlarge creation of battery storage capacity in scenarioswith high solar production. Hydrogen storage is notvisible as this technology is never invested in by REMixin these scenarios. Curtailment levels rise with increas-ing penetration of VRE, becoming a significantproportion of total generation. Grid extensions alsoincrease with higher input of renewables, especiallywind. Transmission losses vary by scenario within the

Figure 1.Annual electricity generation (TWh yr−1), installed electricity generation capacity (GW), installed energy storage capacities(GWh), annual curtailment of electricity generation (TWh/year) and required transmission grid extension (GWkm) for all scenarios.Left column: €50/t scenarios. Right column: €150/t scenarios. Scenario labels: the first number indicates the total theoretical input ofwind and solar power as a percentage of total power generation; the second two numbers are the percentage split betweenwind andsolar, in that order (e.g., 60%20W:80S has 60%of total theoretical input of wind and solar, of which 20% iswind and 80% solar). Fromleft to right within each panel, the total share of wind and solar energy increases.

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range of 0.1%–2% of total generation (note that thisonly includes losses in DC connections betweencountries; other transmission losses are not consid-ered). The scenarios are labelled as follows: the firstnumber indicates the total theoretical input of VRE asa percentage of total generation; the second twonumbers are the percentage split between wind andsolar, in that order. So, scenario 60%20W:80S has 60%of total theoretical input of VRE; 20% of that is fromwind and 80% from solar.

3. LCI data

Life cycle inventories are presented for grid infrastruc-ture and storage technologies added to the model forthis study. Electricity generation processes alreadyexisting in THEMIS are described in supplementaryinformation to [6] and [20]. Table S1 in the supportinginformation provides an overview of all individualtechnologiesmodelled in THEMIS for this study.

3.1. Energy storageIn the present study, installed capacities for eachstorage technology (PHS and battery) and aggregatestored energy amounts (combined PHS and battery)are obtained from REMix, and further it is assumedthat the amount of energy storage performed by eachtechnology is proportional to the installed capacity ofthe technology. The following subsections describe theLCI data for energy storage technologies.

3.1.1. BatteryMaterial inputs and emissions for battery storage areadapted from a study of Li-ion battery packs for use inelectric vehicles [33]. Sodium-sulfur (NaS) batteriesmay be a superior technological solution for grid scalestorage [34, 35], but LCI data are not currentlyavailable. Li-ion technology is not without its merits,including high energy density and high efficiencies[34]. Adaptations of the source data for use in thisstudy involve removal of battery tray and batteryretention, which are only needed for vehicle installa-tion. After the adaptations, the 220 kg battery packprovides an energy storage capacity of 26.6 kWh. Thelifetime of the battery is 10 years. Operational impactsfor all storage technologies arise solely from extraelectricity production to compensate for losses andare determined by the efficiency of the conversioncycle. A round trip efficiency of 90% is assumed forbattery storage [36].

3.1.2. Pumped hydroFollowing the approach in Ecoinvent [37], the con-struction of PHS reservoirs is assumed to be identicalto construction of hydroelectric reservoir powerplants. Following consideration of a review of biogenicemissions from hydropower and PHS plants [38],biogenic emissions are not considered due to the lackof a proper understanding of the way PHS develop-ments affect biogenic GHG emissions. Round tripefficiency for PHS is 70%.

3.2. Electricity transmissionInputs to high voltage direct current (HVDC) trans-mission grid extension encompass HVDC lines andcables, gas insulated substations and AC–DC conver-ter stations. LCI data sources and the approach forincorporating inputs to grid extension are detailed inthe following subsections.

3.2.1. Lines and cablesLines and cables are comprised of overhead lines, land(subterranean) cables and subsea cables. ENTSO-E[39] reports that 75% (of length) of HVDC networkextensions in the coming decade will be sea cables,20%will be overhead lines, and 5%will be land cables.This breakdown is adopted in this study. Materialrequirements for overhead lines come from a state-ment by theDanish transmission systemoperator for a400 kV overhead DC line [40]. The power transmis-sion capacity of the line is not explicitly mentioned;based on specifications of a 350 kV HVDC line with acapacity of 300MW [41] and applying an assumptionof future technology development, a capacity of500MW is assumed. Land occupation figures foroverhead lines are added using a conservative assump-tion of 50 m required ground clearance area, based onfigures from [42].

Material requirements for land cables come from adescription of the 600MW connection between Ger-many andDenmark [43]. Subsea cable data is based ondata from the 700MWNordNed link [44] and utilisesmaterial assumptions outlined in [45]. The lifetime ofall lines and cables is 40 years. Input coefficients to gridextension for all lines and cables are summarised intable 1.

3.2.2. Electrical equipmentWe include analysis of DC to AC converter substationsand conventional voltage substations which convertfrom high voltage to lower voltage, creating the linkbetween the transmission and distribution levels. DC

Table 1. Input coefficients forHVDC lines and cables to 1 GWkmgrid extension.

Component Data source Capacity (GW) Percentage input to extensions Lifetime (years) Input to 1 GW km

Overhead line [40] 0.5 20% 40 0.01

Land cable [43] 0.6 5% 40 0.002

Sea cable [44, 45] 0.7 75% 40 0.027

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to AC current converter station equipment data iscurrently not available, and is approximated with ACpower transformer data [46, 47]. Material require-ments for the site structure are assumed to be similarto those for a gas insulated substation [16], and arescaled by the expected quantity of concrete in HVDCconverter sites [48]. The lifetime of transformers is 35years [46, 47], and the lifetime of the structure is 70years (own assumption). It is assumed that there existsone converter station for every 100 GWkm. Taking anaverage transmission grid capacity of 0.65 GW, thatcorresponds approximately to one substation for every150 kmof transmission grid.

Voltage substations are assumed to be gas insu-lated (as opposed to air insulated). Site structural datais from [16] and gas insulated switchgear material andemission data is from an environmental productdeclaration of gas insulated switchgear [49]. One sub-station contains 10 bays of switchgear. Equipment life-time is 40 years and it is assumed there is onesubstation for every 100 GWkm of grid extension. SF6leakages are 22 kg per unit switchgear over the 40 yearlifespan, or roughly 0.1% per annum, a suitable upperlimit for future leakages [50].

4. Results and discussion

4.1.Overall system impactsFigure 2 depicts total life cycle impacts for all 44scenarios in the six impact categories.

4.1.1. Climate changeClimate change impacts reduce considerably withincreasing inputs of renewable energy. Lowest impactsfor both €50/t and €150/t scenarios are in the140%80W:20S scenario, where generation comesalmost exclusively (99%) from renewables. IncreasingVRE input from0% to 140%with a CO2 price of €50/treduces impacts by 78% (140%20W:80S) or 93%(140%80W:20S). Similar increases with a €150/t CO2

price reduce impacts by 57% or 81%. It is seen thatsystems with large inputs of solar energy have higherimpacts than those with large inputs of wind. Themarginal benefit of increasing VRE penetrationdecreases when moving beyond 100%: Taking €50/tscenarios with a 50:50 wind solar split, impacts are0.19, 0.15 and 0.14 Pg CO2-eq in 100%, 120% and140% scenarios, respectively. Such reductions are less

significant than in 50:50 scenarioswithVRE increasingfrom 60% to 80% and 100%, where impacts are0.56 Pg CO2-eq, 0.33 Pg CO2-eq and 0.19 Pg CO2-eqrespectively.

As for the effects of CO2 price, impacts in €150/tscenarios are smaller than impacts in €50/t scenarios,largely due to coal power with CCS replacing naturalgas power without CCS as baseload technology. Themagnitude of impact reductions as input of renew-ables increases is therefore smaller in €150/t scenariosthan in €50/t scenarios, although considerable reduc-tions are still visible, especially in systems dominatedbywind power.

4.1.2. Freshwater eutrophicationEutrophication impacts from coal overshadowimpacts from all other technologies. These impactsfrom coal are primarily caused by leaching of phos-phates from landfill disposal of spoil from coalmining.Eutrophication impacts increase as natural gas isdisplaced by renewables in €50/t scenarios—this ismainly due to leaching of phosphates from tailingsproduced during processing of copper used in solarand battery storage. These increases are negligible incomparisonwith impacts from coal, however. Increas-ing inputs of wind and solar from 0% to 100%–140%in €150/t scenarios reduces impacts by 91%–97%.

4.1.3. Freshwater ecotoxicityToxic impacts are closely related to coal and naturalgas supply chains, arising from metal pollutants(nickel and magnesium) in ground water from dis-posed coal mine spoil, pollutants to river water fromcoal power plants, and emissions (particularly ofbromine) towater during natural gas extraction. Thereare significant impacts from solar PV, due to disposalof sulfidic tailings during copper processing andchlorine emissions to water during silicon refinement.Still, impacts are lowered with increasing input ofrenewables. The largest reductions are seen in €150/tscenarios, where impacts from a system with highinput of wind power (120%80W:20S) show reductionsof 92% compared with a system based largely on coal(0%VRE).

4.1.4. Particulatematter formationNatural gas is the prime cause of particulate matterformation, owing to SO2 releases during gas

Table 2. Input coefficients for substations and substation equipment to 1 GWkmgrid extension.

Component Data source

Input to one

station

Distance between sta-

tions (GWkm) Lifetime (years) Input to 1 GWkm

Converter substation [16] — 100 70 0.0001

500 MVA transformer [46] 4/3 — 35 0.0004

250 MVA transformer [47] 2/3 — 35 0.0002

Voltage substation [16] — 100 40 0.0002

Gas insulated switchgear [49] 10 — 40 0.0025

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extraction. Impacts from coal are smaller but stillconsiderable, and arise from tailpipe emissions aftercombustion as well as emissions during blasting athard coal mines. Impacts are therefore higher inscenarios with high input of fossil fuels (particularlynatural gas), and lower as input of renewablesincreases. Scenarios with lowest impact are those withhigh inputs of wind. The CO2 price makes littledifference to impacts in scenarios with high renewableinput. Solar PV production causes notable emissions;this is attributable to production ofmetallurgical gradesilicon.

4.1.5.Mineral resource depletionMineral resource depletion is the only examinedcategory in which impacts consistently increase withincreasing input of VRE. Figures 2(E) and (K) showthat impacts arise mainly from creation of wind andsolar capacity, although some impacts results fromenergy storage and grid extensions. Manganese andcopper, followed by iron, nickel and chromium, areresources which lead to high depletion impacts.Comparing a system based on natural gas (0% VRE,€50/t CO2) with a system based almost entirely on

Figure 2.Annual environmental impacts for all scenarios, broken down into contributions fromvarious power generationtechnologies, DC grid losses, energy storage andDC transmission grid extensions. Left column: €50/t scenarios. Right column: €150/t scenarios. Scenario labels: thefirst number indicates the total theoretical input of wind and solar power as a percentage of total powergeneration; the second two numbers are the percentage split betweenwind and solar, in that order (e.g., 60%20W:80S has 60%of totaltheoretical input of wind and solar, of which 20% iswind and 80% solar). From left to right within each panel, the total share of windand solar energy increases.

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renewables (140%50W:50S, €50/t CO2), impactsincrease by a factor of 36 from2.1 to 75 Pg Fe-eq.

4.1.6. Land occupationCoal is the most intensive electricity technologyregarding land occupation, due to timber require-ments in coal mines as well as dumping and extractionat themining site. Groundmounted solar systems alsocause large impacts. Comparing a system largely basedon natural gas (0%VRE)with a predominantly renew-able system in €50/t scenarios, factor 3.0 (140%80W:20S) or 4.7 (140%20W:80S) increases in landoccupation are visible. The corresponding comparisonwith a €150/t CO2 price between a system based oncoal with CCS (0% VRE) and a largely renewablesbased system results in reductions of 63% (140%80W:20S) or 40% (140%20W:80S) in land occupation.Thus the effect of increased renewables on landoccupation depends on which kind of system youtransition from. It is worth noting that the direct landuse of wind farms is measured as the area occupied bywind turbines and other infrastructure, excluding theland between infrastructure elements, as the windfarm does not prevent this land from fulfilling otherfunctions such as agriculture [6].

4.2. Impacts of grid extension, storage and lossesThe combined impacts of DC grid extensions, energystorage and losses for scenarios with a €150/t CO2

price are shown in figure 3. Corresponding figures for€50/t CO2 price scenarios are broadly similar. Thefigures are arranged according to theoretical input ofwind and solar to the electricity mix, so for examplethe bottom left point shows the 0% renewablescenario, and the top-most point shows the 140%20W:80S scenario, corresponding to 28%(20%·140%=28%) theoretical input of wind and112% (80%·140%=112%) theoretical input of solar.The rationale for presenting this figure is to show theinfluence of deployment of wind and solar on impactsfrom grid extension, storage and losses, and further toshow how these impacts vary depending on source ofVRE (i.e., the split betweenwind and solar). Impacts ofcurtailment are not considered here, owing to rela-tively small variations in curtailment depending onwind-solar splits (see figure 1), and difficulty indetermining consistent estimates of impacts asso-ciatedwith curtailment.

It is seen from figure 3 that for all impact categoriesexcepting land occupation, solar power leads to higherimpacts from grid extension, storage and losses. Forexample, climate change impacts in scenario 140%80W:20S are approximately 5 Tg CO2-eq, whereasimpacts in scenario 140%20W:80S are around 20 TgCO2-eq. The magnitude of the difference in impactsvaries for different scenarios and impacts categories.An exception to the norm is land occupation, wheredue to larger grid extensions being required for wind

power, marginally higher impacts occur in high windscenarios than in high solar scenarios. In general forthe results depicted in figure 3, impacts from storageand grid extension are dominant, while impacts frompower losses are negligible.

4.3. Summary of resultsThe main findings of the analysis are as follows: (i)increased penetration of wind and solar leads to largereductions in climate change impacts and co-benefitsin most other impact categories, excluding mineralresource depletion and in some cases land occupation.(ii) The additional impacts that arise as a result of thevariability of wind and solar energy do not significantlycompromise their climate benefits. (iii) Activitiesrelated to extraction of fossil fuels, particularlymethane and sulfur dioxide releases during natural gasextraction and disposal of spoil from coal mining, aresignificant polluting processes in many impact cate-gories. (iv) Copper is a prime cause of impacts in anumber of impact categories. Disposal of tailings fromcopper benefication causes toxic and eutrophyingemissions, and copper mining contributes signifi-cantly to mineral resource depletion. (v) The impactsof grid extension and energy storage are relativelyminor except in the case of mineral resource depletionand to a lesser extent land occupation. (vi) Solar poweris found to induce consistently larger impacts thanwind power; this is due to both higher impact intensityfor solar power and greater need for storage caused bysolar’s lower capacity factors.

4.4. Comparisonwith existing literatureResults that are in some ways similar to present resultshave been found in the small body of literatureanalysing impacts of electricity systems without con-sideration of additional impacts due to the variablenature of wind and solar energy [5, 6, 19]. The benefitsof renewable energy sources in reducing GHG emis-sions is a common finding across studies, and stillholds in this study after inclusion of grid extension andenergy storage requirements. In this respect, thecurrent study may be regarded as confirming theclimate benefits of replacing fossil power with windand solar power. The climate change impacts per kWhfound in 60% VRE scenarios with a €50/t CO2 price,0.146–0.163 kg CO2-eq, are comparable to the0.168 kg CO2-eq reported for the 2030-Green scenariowith 60% wind input reported by Turconi et al [19].Impacts in 60% VRE scenarios with a €150/t CO2

price are considerably lower, 0.064–0.077 kg CO2-eq.Much smaller impacts of 0.02 kg CO2-eq are reportedby Kouloumpis et al [5] in a scenario (B4) which usesapproximately 60% renewable energy and 40%nuclear power and does not consider impacts arisingfrom storage or transmission. Other common resultsacross studies are that the transition to a low carbonelectricity system invariably leads to greater material

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requirements, especially if that system relies mostly onrenewable energy [6, 45, 51], and that replacement oftraditional fossil fuel plants by their equivalent withCCS offers significantly less environmental benefitsthan replacement by renewables [6].

Aside from the inclusion of storage and grid exten-sion impacts in this study, some notable differencesexist between this and previous studies. Most notableis perhaps the inclusion of biomass, nuclear and netimports in other studies [5, 19]. The contribution ofnuclear to future electricity supply in Europe is uncer-tain, but unlikely to be zero. Based on current projectplans and shut-downs, ENTSO-E predicts a reductionof European nuclear capacity of up to 25 GW by 2030[39]. Extensive use of biomass for future electricity

generation is also a controversial issue. While theremay be energy security benefits and GHG reductionsassociated with biomass use (assuming that biogenicCO2 is carbon neutral), biomass can in some casescause significant environmental impacts regarding cli-mate change, acidification, eutrophication and landuse [5, 19]. It would be useful to include nuclear andbiomass in future scenarios if they are likely to play asignificant role. Regarding imports, as the region ofconcern in here is Europe, net electricity imports(which would be mostly with Russia, Turkey andpotentially North Africa) outside of this region areconsidered to be of limited magnitude compared withtotal production in Europe. This may turn out not bethe case if Turkey develops its vast potential for

Figure 3.Total annual environmental impacts and resource requirements associatedwith extension of transmission grid and storagecapacity andwith transmission and storage losses as a function of theoretical wind and solar input for scenarios with aCO2 price of€150/t.

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hydropower or if North Africa develops its vast solarpotential, and sufficient transmission interconnec-tions are constructed between those regions and theEuropean grid.

5. Conclusions

Future electricity system and energy scenario analysescan benefit from considering the life cycle impacts oftechnologies. This study represents an attempt tocombine life cycle and power system modellingtechniques, and is the first such study to examine thewhole European region. A further key novelty of thisLCA is the incorporation of the effects of renewableenergy curtailment and required energy storage andtransmission grid extensions. The results show thatdespite extra impacts being caused by energy storageand grid extensions, their relative magnitude are notlarge enough to undermine the environmental benefitsof switching to renewables and thus the case forswitching to renewables based on climate change andother environmental impacts is strengthened. Beyondthe energy storage and power transmission optionsconsidered in the present work, future research mayaddress the roles of balancing options such as electricvehicles and demand side management in the powersystem, as well as the environmental impacts arisingfrom their use.

An expanded system analysis would be required toanalyse the decarbonisation of the energy system as awhole, addressing important issues such as the techni-cal and material feasibility, and environmental impli-cations, of electrifying the heat and transport sectorswhile achievingGHG targets.

Acknowledgments

This letter builds on the MSc thesis of Berrill. Wegratefully acknowledge help with energy storage datapreparation fromEvert Bouman and LindaAger-WickEllingsen, and comments from two anonymousreviewers which helped to improve the letter. Theresearch leading to the REMix results used in this letterhas received funding from the European Union’sSeventh Programme FP7/2007-2013 under grantagreement number 308329 (ADVANCE). Arvesenacknowledges funding from the Research Council ofNorway through the Centre for Sustainable EnergyStudies (contract 209697).

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