Renewable Energy and Climate ChangeMitigation: An Overview of the IPCCSpecial Report

Ralph E. H. Sims

Abstract Renewable energy systems currently meet only around 7–8 % of thetotal global heating, cooling, electricity and transport end-use energy demands(Traditional biomass provides around 6.3 % of global primary energy and all otherrenewables around 6.7 %, but end-use energy is a more useful statistic used in thiscontext). However, rapid growth in renewable energy has been apparent in recentyears as a result of improved technology performance efficiencies and lower costsbeing demonstrated. Given appropriate support policies, renewables have theeconomic potential to significantly increase their share of total energy supply overthe next few decades. The IPCC Special Report on this subject released in May2011, covered cost trends, opportunities and barriers. This chapter summarises thefindings of that report (The author, who was a Co-ordinating Lead Author for‘‘Integration’’ of this IPCC report and co-author of the Summary for Policy Makers(SPM) and Technical Summary, acknowledges the inputs from around 150 co-authors and staff of the IPCC Technical Support Unit who contributed to writingthe report and producing the SPM on which this chapter is largely based. Seehttp://srren.org for the full report, list of authors, and extensive list of referencesthat support the assessment). Most renewable energy resources are dependent onthe local climate so there is a risk that they may be impacted by climate change.The size of the technical potentials of renewable energy resources and theirgeographic distribution could be affected, but there remains much uncertainty. Thepotential of renewable energy resources, even if significantly reduced, will still farexceed the projected global demand for primary energy, at least out to 2050. Allmitigation scenarios show that renewable energy could provide a large share ofenergy demand in all regions.

R. E. H. Sims (&)Centre for Energy Research, Massey University, Palmerston North, New Zealande-mail: R.E.Sims@massey.ac.nz

A. Troccoli et al. (eds.), Weather Matters for Energy,DOI: 10.1007/978-1-4614-9221-4_4,� Springer Science+Business Media New York 2014

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1 Introduction

An assessment was made by the Intergovernmental Panel on Climate Change(IPCC) on the scientific, technological, environmental, economic and socialaspects of renewable energy (RE) to climate change mitigation (IPCC 2011). TheSpecial Report (known as ‘‘SRREN’’) had six chapters on each of the maintechnologies (bioenergy, solar, hydro, geothermal, ocean and wind1) as well ascross-cutting chapters on mitigation potentials and costs, integration into presentand future energy systems, sustainable development, and policies and financing.

It is fully appreciated that as well as RE, there are several other options forreducing greenhouse gas (GHG) emissions arising from the energy system whilestill satisfying the demand for energy services. These include energy efficiency andconservation, fuel switching (for example, between coal and gas), nuclear elec-tricity and carbon dioxide capture and storage options. In addition, a number ofgeo-engineering technologies have been proposed to either remove GHGs from theatmosphere or manage the incoming solar radiation levels. Each of these mitiga-tion options can be evaluated in order to assess and compare their mitigationpotential, associated risks, costs and contribution to sustainable development. TheIPCC report findings as presented here focused on RE mitigation opportunitieswithin a portfolio of mitigation options.2

A wide range of evaluations have consistently found that the global technicalpotential3 for RE far exceeds the global energy demand. Solar energy has thehighest potential but all six major RE sources have substantial potential (Table 1).Even in regions where relatively low levels of technical potential have beenidentified using local resources, significant opportunities are normally present forincreased deployment compared to current RE supply levels. In the longer term,there are limits to some RE sources once their technical potential has been fullyrealised (for example, when all the high wind speed sites in a district have beencovered in wind turbines). Factors such as sustainability concerns, public accep-tance, economic factors and infrastructure constraints may limit future deploymentof some RE technologies. In such cases their socio-economic potential is lowerthan their technical potential.

Since the mid-nineteenth century, modern societies have increasingly dependedon the combustion of oil, gas and coal to provide heat, mobility and electricity.The ever-increasing demand for energy services is projected to continue in order to

1 In order of Chaps. 2 to 7 of the SRREN.2 An extensive literature list up to early 2011 is given in each chapter of the IPCC report shouldfurther details be required to substantiate any of the points addressed in this chapter.3 The technical potential is the amount of useful energy that can be obtained by the fullimplementation over time when using known technologies and practices relating to that specificRE resource. It excludes any impacts that competing costs, barriers and policies might have,though obvious practical constraints (such as the need for solar heated water to be produced inclose proximity to the hot water demand) are normally included.

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meet the basic human needs for welfare, comfort, lighting, cooking, mobility,communication and health of a growing global population, the aspirations fordevelopment of developing countries, and to drive productive processes. Shouldthis growing demand continue to be met mainly by fossil fuels, there are concernsof increasing environmental impacts, both local air pollution and increases inatmospheric concentrations of GHG, as well as future energy security issues. Thetransition to a low-carbon or ‘clean’ energy economy is therefore imperative—butthe promise is difficult to fulfil. The International Energy Agency, in its 2012Energy Technology Perspectives report (IEA 2012) stated that although rapidtechnology change is possible from deploying some renewable technologies,notably solar PV with 42 % annual average growth over the past decade and on-shore wind at 27 %, most clean energy technologies will require additional supportif they are to provide a more secure energy system and make the required con-tribution to reducing GHG emissions.

Current policies will not result in a sufficient increase in global RE shares tohelp meet the GHG mitigation ambitions necessary to achieve the 2 �C maximumglobal mean temperature rise above pre-industrial levels agreed by all nationalnegotiating teams at the fifteenth and sixteenth sessions of the Conference ofParties (held in Copenhagen in 2010 and Cancun in 2011) of the UNFCCC. Theadditional benefits of RE should also be considered by policy makers whenassessing their future potentials. If implemented properly, RE deployment can alsocontribute to social and economic development, security of energy supplies,improvements in environmental impacts and health, and provide energy access tothose currently without modern energy services.

2 Trends and Future Scenarios

Renewable energy accounted for almost 13 % of global primary energy in 2008(IEA 2010) of which around half was traditional solid biomass fuels used, as wellas some coal, for cooking and heating by 2.7 billion people in developing coun-tries (Fig. 1).

The share of RE is projected to increase significantly by most mitigation sce-nario analyses (as exemplified by a typical one shown in Fig. 2). This will requirepolicies (Sect. 7) to stimulate changes in the energy system by improving energy

Table 1 Indicative minimum and maximum technical potentials of primary energy for the mainRE resources can be compared with global primary energy demand in 2008 of 492 EJ

Biomass Direct solar Geothermal Hydropower Ocean Windpower

Minimum (EJ/yr) 50 1,500 250 50 10 100Maximum (EJ/yr) 500 50,000 2,500 100 500 600

Note The global end-use heat demand in 2008 was 164 EJ, and electricity demand was 61 EJAll energy data quoted here and in the SRREN is based on the direct equivalent accountingmethod which differs slightly from the physical accounting method as used by the IEA

Renewable Energy and Climate Change Mitigation 93

efficiency in all sectors; attracting the necessary increases in investments intechnologies and infrastructure; and reducing the current dependence on relativelycheap fossil fuels. This will involve removal of subsidies in many countries which,in 2010, totalled around $409 billion (IEA 2011).

Wind Energy 0.2%

Geothermal Energy 0.1%

Ocean Energy 0.002%

Direct Solar Energy 0.1%

Gas22.1%

Coal28.4%

RE12.9%

Oil34.6%

Nuclear Energy 2.0%

Hydropower 2.3%

Bioenergy10.2%

Fig. 1 Shares of total global primary energy (492 EJ) in 2008 with renewable energy at 12.9 %of which traditional biomass is almost half

2008 2035

Fig. 2 RE shares (green) of primary and final consumption energy in the transport, buildings(including traditional biomass for cooking and heating), industry and agriculture sectors in 2008and an indication of the projected increased RE shares needed by 2035 in order to be consistentwith a 450 ppm CO2eq stabilization target. Notes Areas of circles are approximately to scale.Energy system losses occur during the conversion, refining and distribution of primary energysources to produce energy services for final consumption. ‘Non-renewable’ energy (yellow)includes coal, oil, natural gas (with and without carbon dioxide capture and storage (CCS) by2035) and nuclear. Data based upon IEA World Energy Outlook 2010 (IEA 2010). Energyefficiency improvements above the 2008 baseline are included in the 2035 projection

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In the SRREN, 164 mitigation scenarios were assessed. More than 50 % pro-jected that the levels of global RE deployment by 2050 would more than triple the2008 level of around 33 EJ of primary energy supply (Fig. 2). The share of REcould rise from the current 12.9 % (including traditional biomass) to 17 % in 2030and to 27 % in 2050. The highest RE shares, as projected by one scenario, were43 % in 2030 and 77 % in 2050.

The lower GHG stabilisation level scenarios tend to have higher RE deploy-ment compared with their baselines (Fig. 3). As the RE shares increase, CO2

emissions from fossil fuels and industry decline, leading to lower stabilisationlevels. Most baseline scenarios assume continuing demand growth for energyservices this century and show a doubling of the RE share by 2030 due to con-strained future fossil fuel resource availability and the costs of RE continuing todecline as a result of improved performance and experience.

The scenarios confirmed that there are many low-carbon supply combinationspossible linked with end-use energy efficiency improvements to produce low GHGconcentration levels, but that in the majority of pathways, RE becomes thedominant technology alongside nuclear and carbon dioxide capture and storage(CCS). The range of assumptions made concerning future population growth, rateof economic development, fossil fuel reserves, policy approaches, carbon pricesand the ability to integrate renewables into energy supply systems (see Sect. 5),has led to a wide range of RE deployment projections but with the majorityincreasing above the current level.

There were good indications that growth in RE will be widespread, and althoughdistribution of RE deployment between regions varied between the scenarios,higher growth in the long term is more likely in developing (non-Annex 1)

Fig. 3 Global RE primary energy supply projections of 164 scenarios in 2030 and 2050. NotesColour-coding depicts baselines and categories I–IV of atmospheric carbon dioxide stabilisationconcentration levels. Crosses depict the relationship in 2007. Vertical bars show the REdeployment level range for each category

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countries than in OECD (Annex 1) countries, particularly for bioenergy and directsolar energy technologies (Fig. 4).

The primary energy shares between each of the RE technologies varies acrossthe scenarios, and between regions. No single technology is totally dominant,though geothermal and hydropower gave lower contributions to the total potentialthan wind, solar and bioenergy. All of the 164 scenarios confirmed that thetechnical potential of RE technologies is not a limiting factor to expanding globaldeployment. Based on four selected illustrative scenarios, only 2.5 % of theoverall global RE technical potential would need to be developed by 2050.

The four illustrative scenarios were selected to represent the range. Globalcumulative savings in CO2 emissions were around 70–90 % of the 1,530 Gt CO2

from fossil fuels and industry, as extrapolated from the IEA Reference scenario(IEA 2010) out to 2050. The attribution of this CO2 reduction to RE technologyuptake varies with assumptions made in each of the scenarios, including the energysources displaced by RE, and complex system behaviour.

3 Climate Change Impacts on Renewable Resources

The technical potentials of RE resources, their size and geographic distribution,could, in many regions, be impacted as climate change becomes more evident.Research into the possible effects is being undertaken but there remains muchuncertainty. The precise magnitude and nature of such impacts is not wellunderstood. RE resources are often dependent on the local climate so that futurechanges could affect that resource base, whether, for example, it results from anincrease or decrease of wind speeds or precipitation levels.

• Biomass resources. Impacts of climate change on biomass resources are moredifficult to assess than for other RE resources due to the large number offeedback mechanisms involved. Particularly for purpose-grown energy crops or

Fig. 4 Ranges of RE primary energy supply in 2030 and 2050 for bioenergy, hydropower, windpower, direct solar and geothermal technologies taken from 164 long-term mitigation scenarios.Note A1 Annex 1 countries. NA1 non-Annex 1 countries

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crop residues, climate change can impact on crop productivity due to changes insoil condition and moisture contents, solar irradiation, intensification of thehydrological cycle and changes in seasonal distribution such as snow melt.While positive ecophysiological effects on plant growth may result from ele-vated CO2 concentrations,4 the overall magnitude and pattern of impacts ofclimate change on plant growth remain uncertain. Some studies show that adoubling of atmospheric CO2 concentration levels could increase plant growthby up to 25 %, but other studies dispute this as, in the long term, the plants mayadapt to accommodate higher levels. In some locations, crop yields mightincrease, and in others they might decrease. While positive effects might occur,detrimental effects that offset these cannot be ruled out.Changes in precipitation levels can result in extremes (floods or droughts) thatimpact on crop production. At warmer temperatures, and particularly underhigher CO2 concentration levels, higher transpiration levels usually occur but,for some plant species, can be partially offset by greater water use efficiency (byincreased stomatal closure). Semi-arid lands in some regions may therefore beable to support energy crop production due to this improved water-use effi-ciency.Overall, it is considered that, if kept below 2 �C, a global mean temperatureincrease would have only a small effect on the technical potential of biomassproduction on a global basis. Agricultural management, plant breeding and theland area available are likely to have a greater impact. However, regionalvariations are expected and in tropical areas in particular, temperature increasesabove 2 �C may well result in declining crop productivity.

• Solar resources. Changes in the distribution and variability of atmospheric watervapour, cloud cover, rainfall and turbidity are likely to impact on solar systems insome locations. Some climate models have shown that, in some regions, variationin global monthly mean solar irradiance levels at the Earth’s surface do not varyby more than 1 % due to anthropogenic forcing. There is no current observationor other evidence to indicate a substantial impact of climate change on globalsolar resources. Some research on global dimming and global brightening indi-cates probable impacts on solar irradiation but to date there is no evidence. Ifsome regions receive lower solar radiation levels than at present, they maypossibly benefit from a resulting lower demand for cooling services. The overalleffect on the technical potential for solar energy is expected to be small.

• Hydro resources. The resource potential depends upon the volume, variabilityand seasonal distribution of water availability (run-off) which varies withtopography and size of water catchment. Run-off could be affected by climatechange due to changes in river-flows as a result of variations in precipitation;seasonal variations in rainfall and snow melt; glaciers receding; extreme

4 Greenhouse growers often use ‘‘CO2 fertilisation’’ whereby they artificially increase the CO2

levels in the enclosed atmosphere using bottled CO2 or un-flued combustion heating plants, toenhance crop productivity.

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weather events causing floods and risks to dams; extreme droughts giving risksto generation system reliability; and sediment loads increasing due to changinghydrology and extreme events. This could lead to dams silting up, therebyreducing water storage volumes, and cause turbine blades to wear out fasterfrom increased abrasion.Models have projected large-scale changes in water run-off for hydropowerplants this century with probable increases in high latitudes and the wet tropics,decreases in mid-latitudes and some drier regions of the tropics, uncertainties indesert regions, and uncertain variations in the monsoon regions at lower lati-tudes. Many discrepancies exist when comparing outputs from the models whichleads to high uncertainty. Significant seasonal variations are also expectedbetween regions. An increase in climate variability, even with no change inaverage run-off, can lead to reduced hydropower generation unless more storagecapacity is built or the operation of the plant modified to suit the new hydrology.Indirect effects of water availability on hydropower generation may result fromincreased competition for irrigation and drinking due to projected fresh waterdeficiencies, but the impacts of this are difficult to assess.Overall, the impacts through changes to annual precipitation volumes and run-off are expected to be slightly positive. As one indicator, the total output from allhydropower plants that were operating worldwide in 2005 (when they generated2,931 TWh) is likely to be around 1 % higher by 2050. By that time however,there will probably be substantial regional variations in changes to precipitation,with most of the increases probably occurring in Asia, decreases expected inEurope and few other major changes expected elsewhere. Local effects andvariations may be significant, so some hydropower plants may be impactedmore than others, even within the same national borders.

• Wind energy. The distribution, annual variability and quality of the windresource could be impacted by climate change but climate models are unable toconfirm the extent (IPCC 2007). Some research suggests that multi-year meanannual wind speed averages will change by no more than ±25 % this centuryover most of North America and Europe, although other studies have shown thiscould be as high as ±50 % in northern Europe. The west coast of South Americacould experience an increase in mean annual wind speeds of around 15 %. Fewother regions have been analysed and overall, wind resource change projectionsfor a given location remain uncertain. Wind turbines and their operation couldbe impacted by extreme weather effects where more frequent, extremely high,gale force winds could cause increased stresses and ultimately damage mayoccur from structural fatigue.Changes in seasonal and decadal variations in long-term average wind speedscould occur. At present, for example, northern Europe and the north-eastAtlantic have higher wind speeds in the winter than the summer. Climate modelsare, as yet, unable to reproduce these conditions so future projections cannot bemade with any degree of accuracy. Similarly, any historic changes in near-surface wind speeds cannot be attributed specifically to climate change as otherfactors may have played a role.

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Overall, the global technical potential of wind resources used for power gen-eration is unlikely to be greatly impacted by climatic change, but changes in theregional distribution of the wind energy resource may occur. In addition, sealevel rise could impact on the foundation and anchoring costs of future designsof deep-water, off-shore wind turbines.

• Ocean energy. Several prototype wave technologies have already experienceddamage during extreme weather events. Therefore designing devices that havegreater reliability under such extreme conditions in an already challengingenvironment is critical, but they can add significantly to the capital costs. Futuresea level rise should be accounted for when designing tidal range systems oranchored wave devices. Tidal ranges, ocean currents and ocean thermal systemsare less likely to be impacted by climate change but no detailed analysis hasbeen conducted to date.

• Geothermal systems. These are unlikely to be affected by climate changeimpacts, other than through the possible temperature rise of river water used forcooling at a power generation plant.

Water availability can influence choice of RE technology as is the similar casefor water-cooled thermal power and nuclear power plants. Such plants couldbecome vulnerable to changing water supply conditions should climate change addto water scarcity or average temperatures. Dry cooling systems are already used inareas where water scarcity is already a concern, so technical solutions are feasible.Hydropower and bioenergy depend on good water supply availability as do solarPV and concentrating solar power (CSP) systems for cleaning the panels.

Life cycle analysis (LCA) is a useful tool for assessing the full climate changemitigation potential of an RE technology. A full LCA also includes other indi-cators such as water use, materials consumption, levels of local air pollution, etc.For electricity generation, most LCAs indicate that the GHG emissions from REtechnologies are usually lower than those associated with fossil fuel use, evenwhen associated with CCS (Fig. 5). Under present climatic conditions, typicalaverage values for all RE systems range from around 5–50 g CO2-eq/kWh(excluding land-use change emissions—see Sect. 6) compared with fossil fuelthermal power generation ranging from 450 to 1,000 g CO2-eq/kWh (gas-firedbeing the lower range and coal-fired the higher). Future changes in climaticconditions could impact on GHG emission levels of RE technologies, but analysesare yet to be undertaken.

4 Costs

Several scenario studies have shown that if RE deployment is constrained,achieving targets for low GHG concentrations will be more difficult and themitigation costs will increase. By what amount it varies with the assumptionsmade in the analyses is uncertain.

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For most RE technologies, their levelised cost of energy (LCOE)5 largelydepends on the availability of local RE resources but often tends to be higher thanthe equivalent cost of conventional energy sources (electricity, natural gas, gas-oline, diesel, LPG, etc.). Energy prices vary widely between countries and states asdo RE prices, so only general comparisons can be made here.

Analysis is needed at the local level to assess whether or not RE options are costcompetitive. Certainly, there are many examples where RE is competitive withcurrent market energy prices (Fig. 6), usually in regions with favourable REresource conditions or where infrastructure is lacking for conventional energysystems to be supplied (such as national electricity grids not reaching rural areas).In most regions of the world, policy measures are still essential to ensure rapiddeployment of most RE systems. However, there are exceptions such as NewZealand where hydro, geothermal, bioenergy and wind produce about 75 % oftotal electricity generation with no policy supporting measures in place. Due to

Fig. 5 Estimates of life cycle GHG emissions for a range of electricity generation technologies,including biopower, natural gas-fired and coal-fired power generation plants linked with CCS.Notes Biopower and hydropower exclude land-use impacts. Negative GHG emissions frombiopower are due to avoided emissions from organic wastes and landfills, not from GHG removalfrom the atmosphere. Linking biopower with CCS can remove CO2 from the atmosphere—seeSect. 6

5 The LCOE represents the cost of an energy generation system over its assumed lifetime. It iscalculated as the price per unit at which energy from a specific source must be generated in orderto break-even over the project lifetime. It excludes the cost of delivery to the final customer, anycosts of integration, subsidies, tax credits or external environmental costs.

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very good natural resources, RE power-generation can compete in the free marketwith gas and coal-fired generation options, even though using national supplies ofnatural gas and coal.

Range of Oil and Gas Based Heating Cost

Range of Non-RenewableElectricity Cost

Range of Gasoline and Diesel Cost

[UScent 2005 /kWh]

0 10 20 30 40 50 60 70 80 90 100

[USD2005 /GJ]

Biofuels

Geothermal Heat

Solar Thermal Heat

Biomass Heat

Wind Electricity

Ocean Electricity

Hydropower

Geothermal Electricity

Solar Electricity

Biomass Electricity

27525022520017515012510075500 25

Non-Renewables

Heat

Transport Fuels

Electricity

Lower Bound

Upper Bound

Medium Values

Biofuels:1. Corn ethanol2. Soy biodiesel3. Wheat ethanol4. Sugarcane ethanol

5. Palm oil biodiesel

Biomass Heat:1. Municipal solid waste based PCH2. Anaerobic digestion based PCH3. Steam turbine CHP4. Domestic pellet heating system

Solar Thermal Heat:1. Domestic hot water systems in China2. Water and space heating

Geothermal Heat:1. Greenhouses2. Uncovered aquaculture ponds3. District heating4. Geothermal heat pumps5. Geothermal building heating

Biomass:1. Cofiring2. Small scale combined heat and power, CHP (Gasification internal combustion engine)3. Direct dedicated stoker& CHP4. Small scale CHP (steam turbine)5. Small scale CHP (organic Rankine cycle)

Solar Electricity:1. Concentrating solar power2. Utility-scale PV (1-axis and fixed tilt) 3. Commercial rooftop PV4. Residential rooftop PV

Geothermal Electricity:1. Condensing flash plant2. Binary cycle plant

Hydropower:1. All types

Ocean Electricity:1. Tidal barrage

Wind Electricity:1. Onshore2. Offshore

Transport FuelsHeatElectricity

Notes: Medium values are shown for the following subcategories, sorted in the order as they appear in the respective ranges (from left to right):

The lower range of the levelized cost of energy for each RE technology is based on a combination of the most favourable input- values, whereas the upper range is based on a combination of the least favourable input values. Reference ranges in the figure background for non-renewable electricity options are indicative of the levelized cost of centralized non-renewable electricity generation. Reference ranges for heat are indicative of recent costs for oil and gas based heat supply options. Reference ranges for transport fuels are based on recent crude oil spot prices of USD 40 to 130/barrel and corresponding diesel and gasoline costs, excluding taxes.

Fig. 6 Ranges of levelised costs of energy for selected RE technologies compared with typicalcosts of non-renewable electricity, heating using oil or natural gas, and gasoline and dieseltransport fuels. (The wide ranging cost bars result from including the full range of sub-technologies (e.g. both on- and off-shore wind) and also projects located where poorer RE sourcesexist (such as solar thermal water heating in high latitude regions where low solar radiation levelsexist). The lower cost ends of the ranges are based on the most favourable situations, whereas theupper ends of the ranges are based on a combination of least favourable inputs.) Note Range oftypical non-renewable electricity costs are based on the LCOE of centralised generation plants.Heating, gasoline and diesel costs are based on oil spot prices between US$ 40–130/barrel

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Possible technological advances may result in lower prices over the next decadeor two, for example from:

• enhanced geothermal systems (originally termed ‘‘hot dry rocks’’),• improved delivery logistics for biomass feedstocks,• increased energy crop yields,• advanced biofuels produced using new processes,• multi-product bio-refineries,• advanced solar PV manufacturing technologies,• CSP systems,• several emerging ocean energy technologies, and• off-shore wind deep-water foundations and turbines.

Hydropower technologies are relatively mature but opportunities exist toupgrade existing turbines with improved designs that have improved technicalperformance and to further develop low-head, mini-systems that can operate in awide range of locations.

The price of most RE technologies has declined over the last few decades(Fig. 7) and this trend is expected to continue as a result of greater projectexperience, lower labour input intensity, increased mass production, higher marketcompetition and improved performance from continuing RD&D. Periods of risingprices, partly due to demand increasing above supply (e.g. wind turbines) orshortages of materials (e.g. silicon for solar PV cells), have been experienced for afew technologies, but normally only over short periods.

In addition to technology costs, increased deployment of RE technologies oftenrequires investment in new infrastructure. Total investment in RE systems to meeta future low-carbon economy (targeting 450 ppm CO2 atmospheric stabilisation

Sugarcane

Ethanol Prod. Cost (excl. Feedstock)

Cumulative Sugarcane Production in Brazil [106 Tonnes of Sugarcane

1,000 2,000 4,000 8,000 16,000

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Cumulative Ethanol Production in Brazil [106 m3]

2004

1975 1985

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(b)

Onshore Wind Power Plants (Denmark)

Onshore Wind Power Plants (USA)

Produced Silicon PV Modules(Global)

1 Cumulative Global Capacity [MW]

1

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10 100 1,000 10,000 1,000,000 100,000

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(a)

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1981[2.6 USD/W]

1984[4.3 USD/W]

2009[1.4 USD/W]

2009 [1.9 USD/W]

Fig. 7 Selected experience curves showing: (a) price reductions (USD/W of installed capacity)as installed total capacity increases over three decades or so for silicon solar PV modules, and foronshore wind turbines in Denmark and USA; and (b) the production cost trends over threedecades for sugarcane (USD/t) and ethanol (USD/m3) in Brazil. (Reductions in the price (or cost)of a technology per unit of capacity tend to understate the reductions in the LCOE whenperformance improvements occur.)

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levels), as estimated from the four scenarios that were selected to cover the widerange, will need to reach up to around US $5,100 billion between 2011 and 2020,with an additional US $7,180 billion needed over the following decade. Theannual average of these investments equates to less than 1 % of the world’s grossdomestic product (GDP). Taking the electricity generation sector as an example,the current global annual investment will need to be increased five times onaverage during this 20-year period.

The externality costs of conventional energy systems should be monetized inorder to make RE systems more competitive and for energy supply comparisons tothen be based on what is often termed a 0level playing field0. Increased marketprices also lead to more competitive RE systems. The LCOE is not the onlydeterminant of the value of RE technologies. Their attractiveness also depends onbroad environmental and social aspects such as their contribution to meetingspecific energy services, helping meet peak electricity demands and any ancillarycosts imposed on the overall energy supply system, such as the additional costsrelating to maintaining system stability in order to integrate high shares of variableRE electricity generation systems (wind, solar PV, waves).

5 Integration

Various RE resources have already been successfully integrated into some energysupply systems and end-use sectors at relatively high shares (Fig. 8). IntegratingRE into most existing energy supply systems and end-use sectors is

Fig. 8 In order to contribute towards providing energy services to consumers, RE integration canbe either indirect into existing energy supply systems or direct when used on-site by the end-usesectors

Renewable Energy and Climate Change Mitigation 103

technologically feasible, even at a greatly accelerated rate above the present rate.At higher shares of RE, additional challenges will result, whether for includingintegration directly into the end-use sectors or indirectly into supply systems.Whether RE is used for electricity, heating, cooling, gaseous fuels or liquid fuels,the integration challenges are contextual, site specific and can include the need foradjustments to existing energy supply systems.

The characteristics of a specific RE resource can influence the degree of dif-ficulty for successful integration. Although most RE resources are widely dis-tributed geographically, others, such as large hydro or geothermal, can be morecentralized so that integration options are constrained by geographic location.Wind, wave and solar resources are variable with limited predictability. Biomassresources tend to have lower physical energy densities and their technical speci-fications differ from fossil fuels. These sorts of characteristics can constrain theease of integration of RE and result in additional costs of the system, particularlywhen reaching higher shares of RE. The costs associated with RE integration areoften difficult to determine. They may include costs for additional networkinfrastructure investment, system operation, and losses and other adjustments tothe existing energy supply systems as needed. Research on the costs of RE inte-gration has been sparse and accurate cost estimates are lacking.

The costs and challenges of integrating increasing shares of RE into an existingenergy supply system depend on the current share of RE, the availability andcharacteristics of RE resources, the system characteristics and how the systemmight evolve and develop in the future.

Electricity systems. RE can be integrated into all system types, ranging fromlarge, inter-connected continental-scale grids down to small, stand-alone autono-mous systems on individual buildings. System characteristics of relevance includethe generation mix and its flexibility, network infrastructure, energy marketdesigns and institutional rules, location of energy demand, demand profiles, andcontrol and communication capability. Wind, solar PV and CSP without storagecan be more difficult to integrate than hydropower, bioenergy or CSP with storageand geothermal energy that are deemed to be dispatchable.6

As the shares of variable RE sources increase, maintaining system reliabilitymay become more challenging for the electricity supply system operator and alsoinvolve additional supply costs. Means of reducing the risks and costs of variableRE integration include:

• having a portfolio of RE technologies;• developing more flexible operation of existing systems;• building complementary flexible generation;

6 Power generation plants, such as reservoir-hydro, geothermal or biopower that can bescheduled to generate electricity as and when required are classed as dispatchable. CSP plants areclassified as dispatchable only when some of the heat is stored for use at night or during periodsof low sunshine. Variable RE technologies such as wind, solar or wavepower are deemed aspartially dispatchable since generation can occur only when the RE resource is available.

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• improving short-term weather forecasting;• having better operation of the system using advanced planning tools;• identifying electricity demands that can respond to supply availability;• developing energy storage technologies (including pumped hydro and reservoir-

based hydropower);• and modifying institutional arrangements.

Strengthening and extending the electricity network transmission and/or dis-tribution infrastructure (including inter-connections between large systems) maybe necessary because of the fixed geographical distribution and remote locations ofmany RE resources.

District heating. Such systems can use low-temperature, RE heat inputs fromsolar thermal, geothermal and biomass combustion, including biomass sourceswith few competing uses such as refuse-derived fuels and municipal solid waste(MSW). The provision of thermal storage capability and flexible combined heatand power cogeneration can help to overcome the challenges of supply anddemand variability for heating systems as well as provide a demand responseservice for electricity systems.

District cooling. Not yet commonly deployed, this technology can make use ofany local, cold natural waterway. Where a district heating network exists, thissame network can be used to distribute the cold water.

Gas distribution grids. Biomethane (resulting from cleaning biogas or landfillgas) and, in the future, RE-derived hydrogen and synthetic natural gas, can beinjected into natural gas pipelines and then used for a range of applications.Successful integration requires that appropriate gas quality standards are met andpipelines upgraded where necessary.

Liquid fuel systems. Transport fuel distribution systems already successfullyintegrate biofuels for transport applications. Pure (100 %) biofuels, or more usu-ally, biofuels blended at lower proportions with petroleum-based fuels, usuallyneed to meet technical standards consistent with vehicle engine fuel specifications.Some liquid biofuels can also be used for cooking and heating applications, forexample, in the form of ethanol gels.

The ease of RE integration across end-use sectors depends on the region, thedesired RE characteristics specific to each sector and the technology. There aremultiple pathways for increasing the shares of RE in a sector.

Transport sector. Liquid and gaseous biofuels are already commonly integratedinto the fuel supply systems in a growing number of countries and this is expectedto continue. Other integration options for transport fuels include centralized pro-duction of RE hydrogen for fuel cell vehicles and RE electricity for rail andelectric vehicles. Future progress of these options will depend on the requiredinfrastructure and vehicle technology developments. Decentralized, on-site pro-duction of biofuels, hydrogen or electricity for local transport vehicle use may befeasible. Future uptake of electric vehicles could support the development offlexible, distributed, electricity generation systems by providing energy storageservices in the batteries.

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Building sector. RE technologies can be integrated into both new and existingbuilding structures to produce electricity, heating and cooling services for thebuilding users at both the commercial and domestic scales. Production of energysurplus to demand may be possible, particularly for energy efficient buildingdesigns, and the surplus can then be exported to the grid and sold to providerevenue. In developing countries, the integration of RE supply systems is feasiblefor even modest dwellings.

Industry sector. Agriculture, as well as food and fibre process industriesincluding wood processing, often use biomass to meet direct heat and powerdemands on-site. They can also be net exporters of surplus fuels, heat and elec-tricity to adjacent supply systems (FAO 2011). Increasing the integration of RE foruse by industries is an option in several sub-sectors, for example through electro-thermal technologies or, in the longer term, by using RE hydrogen.

Energy systems will need to evolve and be adapted in order to accommodatehigh RE shares. Long-term integration efforts could include investment in enablinginfrastructure; modification of institutional and governance frameworks; attentionto social aspects, markets and planning; and capacity building in anticipation ofRE growth. Integration of less mature technologies, including advanced biofuels,fuels generated from solar energy, solar cooling, ocean energy technologies, fuelcells and electric vehicles, will require continuing investments in RD&D as well ascapacity building and other supporting measures.

Electricity is expected to attain higher shares of RE earlier than either the heator transport fuel sectors at the global level. Parallel developments in electricvehicles, increased heating and cooling using electrical heat pumps, flexibledemand response services including the use of smart meters, energy storage andother technologies could become associated with this trend.

Overall, in spite of the complexities, in locations where suitable RE resourcesexist or can be supplied and infrastructure can be developed, there are few, if any,fundamental technological limitations to integrating a portfolio of RE technologiesinto an energy supply system to meet a majority share of total energy demand. Theactual rate of integration and the resulting shares of RE will be influenced byfuture costs, policies, environmental issues and social aspects.

6 Sustainable Development

Economic development has historically depended on fossil fuel consumptionleading to high GHG emissions. RE has the potential to reduce this dependenceand contribute to future sustainable development. For developing countries, thiswill help the achievement of the Millennium Development Goals (although RE isnot specifically mentioned).

In poor rural areas whose residents lack access to centralised energy systems,small RE systems can help provide heat and electricity cost-effectively. This canbe in the simple forms of:

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• domestic biogas plants using human, animal and crop wastes;• ethanol gels used as cooking fuels to displace fuelwood and dung;• windmills for water pumping or solar PV-powered water pumps;• solar hot water technologies;• solar crop-drying; and• solar PV and small wind home power generation systems.

At the larger scale, solar, wind, hydro or biogas can provide electricity forcommunity-scale mini-grids, and liquid biofuels can also be produced commer-cially at the small- to medium-scales for local use to enhance mobility. This couldhave positive impacts on job creation, improved access to markets and be astimulus for capacity building, skills development and education.

RE deployment can also help reduce expenditure on imported fuels, producegreater energy security by diversifying energy resources, and reduce vulnerabilityto supply disruptions. To ensure electricity supply reliability however, the vari-ability of wind and solar systems requires technical and institutional measuresappropriate to local conditions. In OECD countries, the expectations are thatelectricity will always be available at the flick of a switch and transport fuels willalways be available to purchase from a service station 24 h each and every day. Inmany non-OECD countries, especially in rural areas, such expectations do notexist and residents accept that energy services are supplied with a far lower degreeof reliability. Indeed, for the 1.4 billion without access to electricity, as well as theadditional 1.3 billion with some modern energy access but still dependent ontraditional biomass for heating and cooking, any means of improving their currentenergy access is welcomed.

Bioenergy deployment can lead to lowering GHG emissions resulting fromorganic waste disposal in landfills when the gas produced (mainly methane) iscollected and used, often in combined heat and power plants. Carbon dioxide isproduced during combustion of the methane gas, but this has a far lower green-house potential than the methane that would otherwise have been released into theatmosphere.

A combination of bioenergy projects combined with CCS technologies couldlead to reductions in atmospheric levels of CO2. Where energy crops are sus-tainably grown, harvested, combusted and linked with CCS, if the crops arereplanted after each harvest, then the crop plants continue to absorb CO2 duringthe photosynthetic process and therefore act as a ‘‘pump’’ to move carbon from theatmosphere to a permanent store (Fig. 9). In order to stabilise atmospheric levelsof GHG around 450 ppm, models show that annual global GHG emissions willneed to become negative by the end of this century. Therefore bioenergy/CCS willincrease in R&D priorities since the process is one of the few practical ways ofatmospheric CO2 removal, though the economics have yet to be determined.

The sustainability of biomass production is influenced by land use and man-agement practices. However, the GHG implications of land-use management andland-use changes in carbon stocks are not yet well understood. Changes in pro-ductive land and forest use or management can have direct or indirect effects on

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terrestrial carbon stocks that can be either negative or positive. Examples ofnegative impacts include the deforestation of peat lands to produce oil palm cropsand the increase of the land area under corn crops for biofuels resulting in othercrops such as soybean having to be grown elsewhere, at times necessitating furtherdeforestation. Where marginal land is utilised for energy crop production, orbiochar (IBI 2012) is incorporated into the crop production cycle, soil carboncontents can be increased and carbon, as part of the carbon cycle, is removed fromthe atmosphere. This concept could become a key mitigation option, althoughsince it is difficult to measure or model soil carbon uptake and retention over along term, a large degree of uncertainty remains.

Policies can be implemented for land use, zoning, choice of biomass productionsystems and minimising any adverse impacts that biomass production might makeon biodiversity. They can be designed to ensure that rural development,improvements to agricultural management and climate change mitigation can berealised, though their effectiveness in this regard has not been evaluated.

7 Co-Benefits, Barriers and Policies

In addition to climate change mitigation, RE technologies can provide other benefits.Maximising these benefits depends on the specific technology and site characteristicsfor each specific RE project. RE systems, in both OECD and non-OECD countries,can contribute to social and economic development, energy access, energy securityand a reduction of negative impacts on health and the natural environment, so long as

Fig. 9 Energy crops, if grown sustainably and replanted after every harvest, can continuallyabsorb CO2 from the atmosphere which can then be sequestered after conversion of the biomass touseful bioenergy carriers, thereby, over time, lowering the atmospheric CO2 concentration level

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their deployment is carefully implemented. For most countries, increasing thepresent share of RE in the total energy mix will require policies to stimulate changesin the conventional energy system and also to attract the necessary increases ininvestment for both technologies and the related infrastructure.

Other than higher costs, a variety of technology-specific challenges are barriersto the significant up-scaling of RE, thereby constraining its potential contributionto climate change mitigation. Some examples are given below.

• Sustainable production and use of biomass requires the proper design, imple-mentation and monitoring of frameworks to minimise the negative impacts. Thiscan also help to maximise the benefits relating to social, economic and envi-ronmental issues.

• Regulatory and institutional barriers can impede the deployment of solar PVsystems as can power supply system integration and electricity transmission anddistribution issues.

• Solar thermal systems for heating water can also be constrained by localplanning regulations governing building consents needed for any renovations.

• Geothermal systems, including enhanced systems, need careful design in somelocations to avoid land subsidence or even small earthquakes.

• Newly proposed large hydropower projects have been widely constrained inrecent years due to ecological and social impacts, cross boundary water supplyrestrictions as well as remoteness from load requiring costly transmission linesto be constructed. Power lines in themselves usually require planning consentsto be approved. These barriers tend to be site specific. They could possibly beovercome by sustainability assessment tools and by early collaboration betweenmultiple parties, such as all water-users along a waterway. Local developmentsof small, mini- and micro-projects may circumvent some of these barriers.

• Emerging ocean energy technologies require higher investments in R&D as wellas demonstrations than is presently the case, with dedicated policies and regu-lations needed to encourage early developments of these immature technologies.

• Wind energy projects often need to overcome technical and institutional solu-tions to transmission constraints and allay concerns about integration intoelectricity systems when high shares (around 10–20 % of total system genera-tion or above) are reached. Public acceptance has also proved to be an issue,especially as installed capacities increase in a locality.

8 Conclusions

There is strong agreement and much evidence that RE systems will have a greaterrole to play in meeting the ever-growing demands for energy services in the future.This will be in association with energy efficiency measures, as well as in parallelwith other low-carbon technology options such as nuclear power and fossil fuelslinked with CCS.

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The more recent Global Energy Assessment (Johansson et al. 2012) confirmedthe findings of the SRREN by stating that ‘renewable energies are abundant,widely available, and increasingly cost effective’. This report also concluded thatmost RE technologies are already commercially available and will be necessary inorder to meet a range of pathway objectives that aim to give the desired energytransition to support a sustainable future.

The many proven co-benefits of RE deployment will help to encourage a fasterdeployment than has been the case to date, even though growth of some tech-nologies has been high. This will be aided by on-going cost reductions for REtechnologies that are now more competitive with conventional energy systemsthan a decade ago. Both centralised scales of large electricity and heat generationplants and decentralised community and domestic scales with numerous smallgenerating plants, can be economically viable in locations where RE resources aregood.

The risk of the present RE resource availability declining in the future as aresult of climate change is worth considering when developing a specific project ina given location. However, based on the present knowledge of possible regionalclimate change impacts, overall global RE resources will be affected to a minimaldegree, if at all.

References

FAO (2011) Energy-smart food for people and climate, Issue paper, UN Food and AgriculturalOrganisation, Roma. http://www.fao.org/docrep/014/i2454e/i2454e00.pdf

IBI (2012) International biochar initiative. http://www.biochar-international.org/IEA (2010) World energy outlook 2010. International Energy Agency, OECD/IEA, Paris.

www.iea.orgIEA (2011) World energy outlook. International energy agency, OECD/IEA, Paris. www.iea.orgIEA (2012) Energy technology perspectives. International energy agency, OECD/IEA, Paris.

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fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), ISBN978 0521 88009-1 Hardback; 978 0521 70596-7 Paperback. https://www.ipcc-wg1.unibe.ch/publications/wg1-ar4/wg1-ar4.html

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