integrating renewable electricity on the grid integratingelec

7/31/2019 Integrating Renewable Electricity on the Grid Integratingelec

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A Report by the APS Panel on Public Affairs

Integrating Renewable Electricity on the Grid


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2 Integrating Renewable Electricity on the Grid

About APS & POPA

Founded in 1899 to advance and diuse the

knowledge o physics, the American Physical

Society is now the nations leading organization

o physicists with more than 48,000 members

in academia, national laboratories and industry.

APS has long played an active role in the ederal

government; its members serve in Congress

and have held positions such as Science Advisor

to the President o the United States, Director

o the CIA, Director o the National Science

Foundation and Secretary o Energy.

This report was overseen by the APS Panel on

Public Aairs (POPA). POPA routinely produces

reports on timely topics being debated in

government so as to inorm the debate with theperspectives o physicists working in the relevant

issue areas.

Report Committee

Co-Chairs

George Crabtree (Argonne National Laboratory)

Jim Misewich (Brookhaven National Laboratory)

Ron Ambrosio (IBM)

Kathryn Clay (Auto Alliance)

Paul DeMartini (Southern Caliornia Edison)

Revis James (Electric Power Research Institute)

Mark Lauby (North American Electric Reliability Corporation)

Vivek Mohta (Massachusetts Department o Energy Resources)

John Moura (North American Electric Reliability Corporation)

Peter Sauer (University o Illinois Urbana-Champaign)

Francis Slakey (American Physical Society)

Jodi Lieberman (American Physical Society)

Humayun Tai (McKinsey and Co.)

APS Staff

Kris Larsen

Jeanette Russo

Disclaimer

The content o this report refects the views o the members

o the Report Committee and not necessarily the views o

their employers.

American Physical Society | 529 14th Street, NW, Suite 1050 | Washington DC 20045 | 202-662-8700


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Contents

Executive Summary ....................................................................................................2

Introduction .................................................................................................................6

Technology Issues ......................................................................................................8

Forecasting .........................................................................................................10

Energy Storage ....................................................................................................14

Long-distance Transmission ..............................................................................21

The Business Case ...................................................................................................26

Conclusion ..................................................................................................................29

Case Study: New York State ...................................................................................30

Endnotes .....................................................................................................................33


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Integrating Renewable Electricity on the Grid 3

The variability o renewable energy is easily accommodated when demand and renew-able supply are matchedboth rising and alling together. However when demand andrenewable supply move in opposite directions, the cost o accommodation can rise

signifcantly. For example, i the wind blows strongly overnight when demand is low (asis oten the case), the renewable generation can be used only i conventional base-loadgeneration such as coal or nuclear is curtailed, an expensive and inefcient option thatmay cause signifcant reliability issues. Alternatively, on calm days when there is no windpower, the late-aternoon peak demand must be met entirely by conventional generation

resources, requiring reserves that eectively duplicate the renewable capacity. Reducingthe cost o dealing with these two cases is a major challenge acing renewable integration.

Recommendations:

The National Oceanic and Atmospheric Administration (NOAA), the National Weather

Service (NWS), the National Center or Atmospheric Research (NCAR) and private

vendors should:

Improve the accuracy o weather and wind orecasts, in spatial and temporal resolu-tion and on time scales rom hours to days. In addition to accuracy, the confdencelevel o the orecasts must be improved to allow system operators to reduce reserve

requirements and contingency measures to lower and more economical levels.

Forecast providers, wind plant operators, and regulatory agencies should:

Agree on and develop uniorm standards or preparing and delivering wind and power

generation orecasts.

Wind plant operators and regulatory agencies should:

Develop and codiy operating procedures to respond to power generation orecasts.

Develop, standardize and codiy the criteria or contingencies, the response to up- anddown-ramps in generation, and the response to large weather disturbances. Developresponse other than maintaining conventional reserve, including electricity storage

and transmission to distant load centers.

Energy Storage

As renewable generation grows it will ultimately overwhelm the ability o conventionalresources to compensate renewable variability, and require the capture o electricity

generated by wind, solar and other renewables or later use. Transmission level energystorage options include pumped hydroelectric, compressed air electric storage, and

ywheels. Distribution level options include: conventional batteries, electrochemicalow batteries, and superconducting magnetic energy storage (SMES). Batteries also

might be integrated with individual or small clusters o wind turbines and solar panelsin generation arms to mitigate uctuations and power quality issues. Although gridstorage requires high capacity and long lietimes, it oten allows a stationary location

and housing in a controlled environment, very dierent rom the conditions or portable

or automotive storage.


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Currently, energy storage or grid applications lacks sufcient regulatory history. Energy

storage on a utility-scale basis is very uncommon and, except or pumped hydroelectric

storage, is relegated to pilot projects or site-specifc projects. Some states such as NewYork categorize storage as generation, and hence orbid transmission utilities rom own-

ing it. In addition, utilities do not know how investment in energy storage technologieswill be treated, how costs will be recovered, or whether energy storage technologieswill be allowed in a particular regulatory environment.

Recommendations:

The Department o Energy (DOE) should:

Develop an overall strategy or energy storage in grid level applications that providesguidance to regulators to recognize the value that energy storage brings to both

transmission and generation services to the grid;

Conduct a review o the technological potential or a range o battery chemistries,

including those it supported during the 1980s and 1990s, with a view toward possibleapplications to grid energy storage; and

Increase its R&D in basic electrochemistry to identiy the materials and electrochemical

mechanisms that have the highest potential or use in grid level energy storage devices.

Long Distance Transmission

Renewable sources are typically distributed over large areas in the upper central andsouthwestern US, including the Dakotas, Iowa, Minnesota and Montana, and ar rom

demand centers east o the Mississippi and on the West Coast. New large area collectionstrategies and new long distance transmission capability are required to deliver large

amounts o power a thousand miles or more across the country. This long distance

transmission challenge is exacerbated by a historically low investment in transmissiongenerally: rom 19881998 demand grew by 30%, while transmission grew by only 15%;rom 19992009 demand grew by 20% and transmission by only 3%. In denser popula-tion areas there are community concerns around new right-o-way or above ground

transmission towers. The not in my backyard arguments are costly to overcome andcan delay or stop above-ground transmission construction.

While high voltage DC is the preerred transmission mode or long distances, the

drawbacks o single terminal origin and termination, costly AC-DC-AC conversion, and

the decade or more typically needed or approval or long lines create problems orrenewable electricity transmission. Superconductivity provides an new alternative to

conventional high voltage DC transmission. Superconducting DC lines operate at zeroresistance, eliminating electrical losses or any transmission length, and operate at lower

voltages, simpliying AC-DC conversion and enabling wide-area collection strategies.Superconducting DC transmission lines carrying 10 GW o power 1600 km can be

integrated into the Eastern and Western grids in the US while maintaining transient and

short-term voltage stability.


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Recommendations:

DOE should:

Extend the Ofce o Electricity program on High Temperature Superconductivity or

10 years, with ocus on DC superconducting cables or long distance transmission orenewable electricity rom source to market; and

Accelerate R&D on wide band gap power electronics or controlling power ow onthe grid, including alternating to direct current conversion options and development o

semiconductor-based circuit breakers operating at 200 kV and 50 kA with microsecond

response time.

Business Case

Utility renewable energy investments are typically assessed rom regulatory, projectfnance, and technical perspectives. The regulatory assessment ocuses on ensuring utility

compliance with renewable portolio standards (RPS) and that costs are kept within

prudent limits. The project fnance view looks at the merits o the investment within

discrete boundaries o the unding and cash ows exclusive to the project under review.

The technical assessment evaluates the engineering and operational risks o the project

and specifc technologies involved.

While these conventional views are important or investors, utilities, regulators and

ratepayers, they do not ully capture the set o benefts that a renewable energy invest-ment can deliver beyond the boundaries o a given project, such as the physical benefts

o transmission and storage and the organizational beneft o developing an integrated

picture o the grid. Inclusion o these additional benefts in an expanded business casewill enhance the profle o the renewables investment, and more importantly, begin torecognize the synergies inherent in the integration o renewables with the grid.

Recommendations:

The Federal Energy Regulatory Commission (FERC) and the North American ElectricReliability Corporation (NERC) should:

Develop an integrated business case that captures the ull value o renewable genera-

tion and electricity storage in the context o transmission and distribution; and

Adopt a uniorm integrated business case as their ofcial evaluation and regulatory

structure, in concert with the state Public Utility Commissions (PUCs).


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Technology Issues

The United States has ample renewable energy resources. Land based wind, the mostreadily available or development totals more than 8000 GW o potential capacity (seeFigure1).4 The capacity o concentrating solar power (solar thermal energy driving

conventional generators) is nearly 7,000 GW in seven southwestern states.5, 6 The genera-

tion potential o photovoltaics is limited only by the land area devoted to it, 100250GW/100 km2 in the United States.7,8By comparison, the United States generated electric

power at an average rate o approximately 450 GW in 2009, peaking to over 1000

GW during the summer months. By 2035, electricity demand is projected to rise 30%. 9

In 2009, wind accounted or about 1.8% and solar about 0.07% o the electricity gener-ated in the US. Wind and solar can easily supply a larger raction o the nations electricity

needs than the 20%30% RPS now under consideration.

However, developing renewable resources, presents a set o technological challenges not

previously aced by the grid: the location o renewable resources ar rom populationcenters, and the variability o renewable generation. The grid is an historical patchworko local or regional generation resources and loads, with electricity generation locatedas ar as 1000 miles rom population centers. The ownership and regulation o the gridis likewise divided along local or regional lines.10Transmitting wind electricity rom their

sources to distant population centers strains the physical, ownership and regulatory

structure o the grid. Thereore, at higher RPS levels, accommodating these renewable

resources requires new approaches to extending and operating the grid.11

Another issue is the variability o renewable resources due to the characteristics o

weather. This characteristic introduces uncertainty in generation output on time scaleso seconds, hours and days. These uncertainties, aecting up to 70% o daytime solar

capacity due to passing clouds, and 100% o wind capacity on calm days, are much

greater than the relatively predictable uncertainties o a ew per cent in demand thatsystem operators now deal with regularly. Variability becomes increasingly difcult to

manage as penetration levels increase. But technology can accommodate this variability

Figure 1.

Wind resources in the United States

(ater Black & Veatch 2007).


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by: augmenting generation by using ast-acting conventional reserves when renewableenergy resources are expected to decrease; by installing energy storage on the grid, orby better long distance transmission which enables access to larger pools o resourcesto balance regional and local excesses or defcits. Right now, renewable energy vari-ability is handled almost exclusively by ramping conventional reserves up or down onthe basis o orecasts. But, as renewable energy penetration grows, large-scale storage,ast-acting resources, and better long distance transmission will become more important

to accommodate high-levels o variability in generation.

Figure 2 illustrates the variability o renewable resources by depicting genera-

tion and load variation over a two-week period or the Xcel system in Minnesota,a system with 1,500 MW o wind capacity on a 10,000 MW peak-load system. 12

Wind variability is high, showing periods o maximum production or two days, and other

times o calm or nearly two days. New levels o accuracy and detail in orecasting todeal with these generation uncertainties will be required as RPS levels increase. This

includes: wind predictions on a much more requent basis (i.e. a sub-hourly, hourly anddaily basis) and the translation o those predictions to power generation orecasts orspecifc wind plants.13

Figure 2.

Wind generation and system load

over a two week period in the Xce

system in Minnesota. Wind provide

1500 MW capacity on a 10000

MW peak capacity system. (Ater

20% Wind Energy by 2030, Energy

Eciency and Renewable Energy,DOE/GO-102008-2567 (2008))

Figure 3.

The power output o a turbine

varies with wind speed, turning o a

high speed to protect rom damage

(ater H. Sharman, Proceedings

o ICE Civil Engineering 158, 161

(2005)).


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The magnitude and variability o wind power depends not only on the wind but also on

the turbines that convert wind to electric power. The power curve o a typical turbineis shown in Figure 3.14 The output o a turbine rises steadily with the wind speed andproduces maximum power over its designed operating range. At high wind speeds,

however, it turns o to protect itsel rom damage, and the output quickly drops to zero.

Turbine perormance is also aected by other local conditions, including topographicaleatures and the density o the air, which, in turn, depends on temperature and humidity.

The body o this report, on the ollowing pages, addresses the challenges o dealing withvariability and the remote location o renewable resources through orecasting, energystorage and long distance transmission.

Forecasting

It is important to distinguish between variability and uncertainty when discussing plan-ning and operations o the power grid. Variability describes the change o generation

output due to uctuations o wind or sun; uncertainty describes the inability to predictin advance the timing and magnitude o the changes in generation output. The purposeo orecasting is to reduce the uncertainty o renewable generation, so that its variabilitycan be more precisely accommodated.15

The variability o renewable resources70% or daytime solar due to passing clouds and

100% or wind due to calm daysis a major challenge to integrating renewable energyresources on the grid. When scaled by their RPS targets, the variability o renewable

energy is comparable to the variability o demand, which changes by 20%50% between

aternoon peaks and overnight valleys. The crucial dierence between the variability orenewable generation and the variability o demand is predictability. Demand can be

anticipated to within a ew percent based primarily on weather orecasts o temperature,humidity and precipitation, on demand history, and on anticipating major energy eventssuch as the broadcast o television programs which a large expected viewing audience.Renewable generation depends primarily on specifc weather characteristics such as wind

or wind generation and sunlight exposure or solar generation, which do not occur inregular patterns and are not correlated to diurnal patterns o demand. The ability to

quickly ramp dispatchable resourcessuch as natural gas turbines or hydroelectric power

to ollow the variability o renewable generationup or down is a major consideration

or eectively accommodating renewable resources. 16,17,18,19, 20, 21, 22, 23

System operators consider the reliability o the grid to be the most critical priority.

This sacred principle drives up the cost o renewable integration, because opera-

tors must hold large amounts o reserves to cover an unexpected loss o renew-able generation. Increases in orecast quality translate into decreases in reserve

requirements and costs. An analysis o wind plant experience to date shows that re-

serves have been increased up to 9% to accommodate wind penetration o 15%.24

Reducing the ratio o added reserves to added renewable capacity by better orecasting

is a critical objective or reducing the cost o integrating renewable energy resourcesonto the grid.


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Forecasts must improve to accommodate the two most serious challenges in generation

variability: up-ramps at times o low demand and down-ramps at times o high demand.In the ormer case conventional reserves may already be turned o, so that accom-

modating the up-ramp may require turning down base-load conventional generation orcurtailing renewable generation. Both options are inefcient and expensive and may cause

signifcant reliability issues. In the latter case, most conventional reserves may alreadybe turned on, leaving ew options or compensating the power lost in the renewable

down-ramp. In the ERCOT event o February 26, 2008, service to certain customers

was curtailed in a controlled manner due to an earlier-than-expected wind down-ramp.25

The accuracy o orecasts and timely operational responses or these two worst-casescenarios are critical to maintaining reliability and lowering cost as renewable penetra-tion grows.

Accuracy and Confdence Level

The level o confdence or operators in orecasts is as important as accuracy. Low

confdence levels require operators to maintain high levels o reserves even i the orecastitsel calls or steady output. Estimating the confdence level o orecasts is becoming

more common, but the techniques must become more sophisticated. Once this occurs,

operators can have a greater degree o confdence in orecasts which will reduce thecost o balancing supply with demand by as much as 39%.26

Figure 4 illustrates the present state o wind orecasting.15 During a 24 hour peri-

od predictions o wind power generation or the Alberta Electric System Operatorvaried by a actor o 20 among three orecasts at times and by a actor o 1.52

over most o the range. The actual wind generation level varied over the course

o our hours rom ollowing the lowest o three orecasts to ollowing the high-est. At times, the actual wind was a actor o 10 below the two highest orecasts

and at other times 50% larger than the lowest orecast. Discrepancies o this size

between predicted and actual wind generation are typical o other wind plants. 27

At the present immature stage o orecasting accuracy, consulting several orecasts romindependent providers is a critically important practice.

Figure 4.

Three orecasts or wind power

in the Alberta Electric System

Operator wind system. Only

one o the three predicted the

our-hour morning lull, and none

predicted the range o variability.(AterAccommodating High Levels o

Variable Generation: Summary Report

NERC (2009)).


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The accuracy and confdence level o orecasts can be improved by aggregation over awider area. For example, over a distance o approximately 1000 km, typical or a German

orecast, the orecasting error is reduced to 42% o that or a single turbine, as shownin Figure 5.28 Combining the our orecasting areas o Germany reduces the two-hourahead orecasting error by 25%.29

The benefts o larger areas apply to balancing generation and load as well as to orecast-

ing. Extending the balancing area over which generation and load are matched and elimi-nating transmission constraints within this area signifcantly reduce the cost o renewable

integration by compensating local up-ramps with distant down-ramps. Consolidating the

our balancing areas o Minnesota, or example, reduces ramping requirements by 14%.

Even longer distance balancing can be achieved with national coordination o orecastsand power ows. An excess o generation in the north central US, or example, mightbe balanced by a generation defcit in the northeast. This requires not only high capacitylong-distance transmission, but also accurate and correlated orecasts or distant regions

at the hours-ahead or day-ahead time scale. Such national coordination o orecasts isnot currently done. A coordinating body would be required to match orecast excesses

with defcits and oversee the required long-distance power transmission.

Forecasting renewable generation and balancing generation with load illustrate the

need or new approaches to coordinating the grid across local physical ownership andregulatory boundaries to accommodate renewable energy.

Power Generation Forecasts

To be useul to the system operator, weather orecasts must be converted to orecastso the power expected to be generated by wind plants. This is typically done with theassistance o a physical model, a statistical analysis process, an artifcial intelligence-based

learning system, or some combination o these techniques. All o these techniques relyon historical wind plant output data rom the site to perorm the analysis, correlations,and training o the system to produce an accurate orecast. Such orecasts depend on

Figure 5.

The reduction in the error o

orecasts aggregated over large

areas (ater Focken et al, Journal o

Wind Engineering and Industrial

Aerodynamics 90, 231 (2002)).


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Flywheels are being eectively used in Caliornia and New York or requency regulation,which will become more important with increased integration o variable power sources.

The international usion community uses ywheels to store. Superconducting magneticenergy storage (SMES) with a capacity o a ew MJ is used or regulating power quality.Much higher power and energy SMESthat can deliver 100 MW o power or secondsto minuteshas been developed or usion applications. The opportunities or lower cost

and higher energy storage capacity are related to the cost and maximum magnetic feldstrength o superconducting wire. Synergies between DC superconducting transmission

and SMES oer cost and technology savings opportunities.

Increased interest in this area has led ARPA-E to recently issue a broad call or proposals

or utility scale energy storage including each o the categories described here.34, 35

Use o energy storage or utility applications can be divided into three categories: (1)or base load bulk power management, (2) or grid support in the orm o distributedor load leveling storage, or (3) or power quality and peak power storage, including

uninterruptable power supply applications. Within each o these broad categories,

dierent timescales rom seconds to hours apply. The purpose o the storage and thetimescale o response determine which energy storage technologies are best suited or a

given application. Figure 7 depicts a number o energy storage options, including several

dierent battery chemistries.

Currently, the most pervasive use o large-scale chemical energy storage is or powerquality in the orm o uninterrupted power supplies (UPS). UPS is used to protect ex-

pensive electrical assets such as computer data centers and critical inrastructure. Suchsystems do not require high-energy content since most power outages are less than aminute in length. Lead acid and metal hydride batteries are the mainstays o this industry.

In addition to peak shaving, storage can also help manage the transmission capacity orwind energy resources. By adding energy storage, wind plants located in remote areascan store energy rom peak periods, allowing or lower cost. Because the generated

electricity can be stored rather than used in real time it lowers the need or transmission

Figure 6.

Compressed air energy storage

system. Compressed air mixed with

natural gas is stored in a geological

ormation, to be released and

ignited to drive a turbine to produce

electricity. Photo courtesy o CAES

Development Company.


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lines, and also allows retailers to maximize profts by selling power during peak usageperiods, which do not usually correspond with peak wind output periods. For these

applications to become economically avorable, more advanced battery materials mustfrst become widely available.

The Physical Scale o Grid Energy Storage

The availability o wind and solar energy sources can vary signifcantly, sometimes in

a matter o seconds and at other times over hours or even days. The dierent time

rames impose dierent energy storage requirements: (1) relatively low capacity but astresponse or changes that occur within seconds or over a period o a ew hours and (2)

high capacity but slower response or changes that extend over one or more days. Weterm the frst storage need a power application and the second an energy application.

Although storage requirements extend continuously across the time spectrum, and many

storage technologies span the two applications, the simpliying classifcation allows us to

provide a sense o the physical scale o the storage challenge.

In the accompanying table, we illustrate the power application storage need or a 70%reduction in solar photovoltaic (PV) electricity generation or 20% reduction in wind

generation, assuming each occurs over a one-hour period. We also illustrate the energy

application storage need or accommodating 12 hours o solar production and 24 hours

o wind production. The table shows the physical sizes o various kinds o storage units

required or a 100 megawatt solar installationthe generating capacity o typical largephotovoltaic and moderate concentrating solar power (CSP) plantsand or a 750

megawatt wind armthe capacity o typical large wind installations. Note that a moltensalt thermal storage unit is appropriate only or a CSP plant.

Figure 7.

Energy storage options (ater

Electric Power Research Institute

and B. Roberts, Capturing Grid Power,

IEEE Power and Energy Magazine,

32, July/August (2009)).


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Power Applications

Storage Technology100 MW Solar PV or CSP70 MWh Storage Capacity

750 MW Wind150 MWh Storage Capacity

Lead-acid battery 1170 m3 2500 m3

Lithium-ion battery 194 m3 417 m3

Sodium-sulur battery 269 m3 558 m3

Flow battery 2340 m3 5000 m3

Molten salt thermal 5300 m3 Not Applicable

Energy Applications

Storage Technology100 MW Solar PV or CSP

1200 MWh Storage Capacity750 MW Wind

18000 MWh Storage Capacity

Flow battery 40000 m3 600000 m3

CAES 385000 m3 5.77 x 106 m3

Pumped hydro 2.14 x106

m3

(500 m head) 32.1 x 106

m3

(500 m head)Molten salt thermal 90900 m3 Not Applicable

Battery Energy Storage TechnologiesInterest in electric drive vehicles is driving a great deal o investment in energy storageR&D or mobile applications. There is the potential that technological developmentsor the mobile application will yield benefts or stationary, grid-scale application as

well. However, the electric vehicle application is considerably more demanding than the

grid-energy storage application. The requirement to store large quantities o energy per

unit weight or power delivery per unit weight is less rigorous in stationary applicationsthan immobile applications. Moreover, vehicle applications require the technology to be

highly impervious to a wide range o temperature and humidity variations, as well as toextreme vibration environments. The utility application allows a much greater ability tocontrol the ambient environment, making the battery design challenges less demanding.

Because o this, battery technologies developed under the DOEs vehicle technology

program in past yearsbut later discontinued because o their unsuitability or vehicleapplicationsmay, once again, be easible alternatives or stationary applications associ-

ated with the grid. In the 1980s and early 1990s, the DOE maintained a diverse portolio

o battery chemistry technologies or research support under its vehicle technologiesprogram. During the Clinton administration as part o the Partnership or the New

Generation o Vehicles (PNGV) program DOE ocused on two battery chemistries:

nickel metal hydride and lithium ion. However, in light o the potential need or batterystorage with greater integration o renewable energy resources on the grid, it may beuseul to revisit the discontinued battery chemistries to assess whether or not any othem are suitable candidates or todays utility applications.

Reerence and Technical InormationBattery energy densities: Electricity Storage Association (www.electricitystorage.org/ESA/technologies/)CAES energy density: McIntosh, AL InstallationMathew Wald, New York Times Sept 29, 1991(query.nytimes.com/gst/ullpage.html?res=9D0CEEDE103DF93AA1575AC0A967958260&sec=&spon=&pagewanted=print);

Roy Daniel, Power Storage, Batteries and Beyond, 2009 CERA Week, (www.ihscera.com/aspx/cda/ledisplay/

ledisplay.ashx?PK=35893)

Pumped hydro energy density: Assumes 500 m elevation dierence between upper and lower reservoirsMolten salt thermal energy density: Andasol 1 Installation, Spain David Biello, How to Use Solar Energy at Night,Scientic American, February 2009 (www.scienticamerican.com/article.cm?id=how-to-use-solar-energy-at-night);

Solar Millennium (www.solarmillennium.de/Technologie/Reerenzprojekte/Andasol/Die_Andasol_Kratwerke_

entstehen_,lang2,109,155.html)


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Battery Materials or Energy Storage

Currently, lead acid and sodium sulur systems have the most extensive track record

or large-scale energy storage.

Lead Acid In the 1980s, lead acid batteries or utility peak shaving were tested, butthe economics at that time did not support urther deployment. However, continued

incremental improvements in lead acid technology and increased energy costs are

making use o lead acid more economical. Recent innovations in lead acid technologydemonstrated three to our times the energy density with improved lietimes over

conventional lead acid batteries. One promising technology is the combination o ultracapacitors and lead acid batteries into integrated energy storage devices sometimes

reerred to as ultra batteries.

Sodium Sulur Sodium sulur batteries use molten sodium and sulur separated by

a ceramic electrolyte. This battery chemistry requires an operating temperature o

about 300C to maintain the active materials in a molten state. These batteries have a

high energy density, a high efciency, and a projected long cycle lie. O emerging bat-tery technologies suitable or utility applications, sodium sulur batteries are the mosttechnologically mature, and are deployed on a limited scale in Japan and in the UnitedStates. A Japanese frm, NGK Insulators, is responsible or most o the development

and commercialization o sodium sulur or utility applications.

With additional research and demonstration, other battery technologies also could prove

useul or large-scale energy storage.

Figure 8.

The principle o the fow battery,where energy is stored in liquid

electrolytes and recovered as

electricity.


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Flow Batteries A ow battery is a rechargeable battery that converts chemical energy

to electricity by reaction o two electrolytes owing past a proton-exchange membrane,

illustrated in Figure 8. The principle is similar to a uel cell except that the reaction isreversible and the electrolytes are reused instead o being released to the atmosphere.Additional electrolyte is stored in external tanks and pumped through the cell to charge

or discharge the battery. The energy storage capacity is limited only by the size o thetanks, making scale-up relatively easy, with cost-per-unit o energy storage generally lower

than or non-ow batteries, which improves the attractiveness or larger sizes. Flow

batteries oer potentially higher efciencies and longer lie than lead acid batteries. Flow

batteries such as vanadium and zinc bromide (ZnBr) show great promise. Flow batterieshave good efciencies (over 75%) and long lietimes (over 10,000 charge discharge cycles)

and are scalable because battery size is determined by the electrolyte holding tank size.

Vanadium Redox Flow batteries are a relatively new technology. Energy is stored chemi-

cally in dierent ionic orms o vanadium in a dilute suluric acid electrolyte. The electro-

lyte is pumped rom separate storage tanks into ow cells. Vanadium ow batteries o800 kW to 1.5 MW are being successully demonstrated outside o the United States in

applications such as UPS or semiconductor manuacturing, island grid capacity frmingand grid peak shaving applications.

Zinc bromide ow batteries are regenerative uel cells based on a reaction between

zinc and bromide. An aqueous solution o zinc bromide is circulated through two com-partments within the cell rom separate reservoirs. While zinc bromide batteries use

electrodes as substrates or the electrochemical reaction, the electrodes themselves

do not take part in the reaction; thereore, there is no electrode degradation with

repeated cycling. Several zinc bromide systems in the 200 to 500 kW range have beendemonstrated or peak shaving and island grid applications.

Further development o liquid metal batteries, polysulfde bromide cells and metal air

batteries could also prove useul. Liquid metal batteries are another class o batteriesthat potentially could provide up to 10 times the current energy storage capacity ocurrent batteries. Like the sodium sulur battery, liquid mental batteries are a high

temperature stationary technology. Polysulfde bromide (PSB) cells are ow batteries,based on regenerative uel cell technology, that react two salt solution electrolytes,

sodium bromide and sodium polysulfde. Metal air batteries have the potential to deliver

high energy densities at low cost, but challenges with recharging have so ar precludedcommercialization o the technology.

Barriers and Recommendations

Energy storage or grid applications lacks a sufcient regulatory history. This is due to

the act that utility scale energy storage is very uncommon and, except or pumpedhydroelectric storage, is only being used in pilot projects or site-specifc projects. Utilities

are thereore uncertain how investment in energy storage technologies will be treated,how costs will be recovered, or whether energy storage technologies will be allowedin a particular regulatory environment.

Energy storage applications can provide unctions related to both generation and

transmission, urther conusing the question o regulatory treatment o investments ingrid level energy storage. For example, a utility can use bulk energy storage to store


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electricity generated during a low-cost period, such as late at night, to a time o high-cost

generation, such as during peak daytime use. From a regulators perspective, the energyprovided rom the batteries during the peak period may look like generation. At the

same time, however, this strategy could also reduce transmission congestion, provide

voltage support at a time o peak use, and provide other ancillary services that supporttransmission unctions.27 The ability o energy storage technology to fll multiple rolesin both transmission and generation has created conusion and uncertainty about howenergy storage should be regulated.

Moreover, the current system does not ully credit the value o storage across the

entire utility value chain. Generation, transmission, and distribution have been viewed

historically as independent components o the grid system. As a result, cost recovery

or grid-level energy storage investments is challenging. Without clear rules governingcost recovery, utilities tend to under-invest in energy storage. It is comparatively easieror utilities to invest in conventional approaches to grid instability, such as natural gasspinning reserves. These more conventional investments are more likely to be includedin the utilitys rate base.

Vehicle-to-Grid Considerations

I plug-in electric hybrid vehicles (PHEVs) succeed in achieving signifcant market growth in

the coming decades, the potential will exist to use the on-board energy storage o these

vehicles as distributed energy storage that would be available to the larger grid whilethe vehicles are plugged in, or recharging. PHEVs could bring the capability o discharging

back to the grid to improve grid utilization, level demand, and improve reliability.

However, one challenge to such an application will be determining how PHEV usage will

interact with high levels o renewable energy generation capacity, especially wind and

solar power. Both solar and wind power vary diurnally. I the PHEV charging load matches

peak renewable energy productionsuch as wind power generation in areas where thewind blows more consistently overnightthen the PHEV load and renewable sourcewill be well matched temporally. I the PHEV charging does not match daily renewableenergy generation cycles well, then the mismatch is problematic, and deployment oenergy storage technology will take on an even more important role in supporting theattainment o high renewable portolio standards. Smart grid technologies that enabletime-o-use pricing could encourage consumers to match their vehicle charging with

times o higher renewable generating capacity.

Recommendations:

The Department o Energy (DOE) should:

Develop an overall strategy or energy storage in grid level applications that providesguidance to regulators to recognize the value that energy storage brings to both

transmission and generation services to the grid;

Conduct a review o the technological potential or a range o battery chemistries,

including those it supported during the 1980s and 1990s, with a view toward possible

applications to grid energy storage; and


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Increase its R&D in basic electrochemistry to identiy the materials and electrochemical

mechanisms that have the highest potential or use in grid level energy storage devices.

Long-distance Transmission

The advent o solar and wind renewable energy generation brings new challenges or the

collection and long distance transmission o renewable energy, and or distribution orenewable electricity in power-congested urban areas. Renewable sources are typicallydistributed over large areas in the upper central and southwestern United States, ar

rom demand centers east o the Mississippi and on the West Coast (see Figure 9). Thismeans new large area collection strategies and new long distance transmission capability

are required to deliver large amounts o renewable power a thousand miles or moreacross the country. Like the US road system beore interstate highways, the power gridis designed to serve local and regional customers with local and regional generation

and delivery inrastructure. To adequately address our national energy needs in therenewable energy era, the grid must change its character, rom a locally-designed, builtand maintained system to one that is regionally and nationally-integrated. Delivery o

increased renewables-based power to urban areas also presents new challenges. Today,82% o the US population lives in urban or suburban settings36 where power use is

high and demand or increased energy is, and will continue to be, strongest. Renewableelectricity rom remote sources helps to meet this demand without increasing carbondioxide emissions. However, the additional power currently must be distributed over

inrastructure designed and installed to meet much smaller needs. Congestion on existing

lines inhibits growth, and as urban areas expand and merge, the area over which powerdistribution needs to be coordinated grows. The urban setting makes installation o

new lines to meet demand growth expensive and challenging because o the difculty in

securing new right o way permits. This delays the installation o new distribution linesup to 10 years and loads the existing lines well beyond their design limits.

Wind

Sun

Wind

Demand

Figure 9.

The large separation between

renewable sources and demand

centers requires new long distance

transmission lines.

Source: Map based on inormation rom NASA and the National Renewable Energy Laboratory.


24/40


Long Distance Transmission Options

Until recently, long distance delivery o electricity over several hundreds o miles re-

mained a specialized area o technology with a airly small demand and ootprint. Mostcities are served by nearby ossil coal or gas generation plants, requiring transmis-

sion over short distances. An exception is hydroelectric generation in Canada andthe northwest US, which produces large amounts o power ar rom demand cen-ters and justifes long distance transmission. For distances greater than a ew hun-

dred miles, direct current (DC) transmission is avored over alternating current (AC)or its lower electrical losses and lower cost. The challenge or DC transmission is

the conversion technology rom AC sources to DC transmission and back to AC

or use. The frst commercial high voltage DC transmission lines in 1954 used mer-

cury arc converters or AC-DC conversion, replaced by semiconductor thyristors 37

in 1972, and by insulated gate bipolar transistors (IGBTs) in the 1980s. Although technical

progress is reducing the cost o semiconductor power electronics, the cost and technical

challenge o AC-DC conversion is still a major barrier or increasing DC transmission.

The mandated growth o wind and solar generation through Renewable PortolioStandards (RPS) to 20% or 30% o electricity supply by 2020 or 2030 dramatically changes

the landscape o long distance transmission. Such large ractions o renewable power

oten are not ound within a 100 miles o urban load centers, and community concernabout visual esthetics creates barriers to installation o the large scale wind or solar

plants needed to supply such population centers. Rootop photovoltaics can alleviate

some o the need or long-distance transmission, but oten at a higher cost than wind or

concentrating solar power, and with smaller but signifcant esthetic concerns. Renewableportolio standards and the development o large-scale wind and solar resources require

a signifcant investment in raising the capacity and efciency o long-distance electricitytransmission. This long distance transmission challenge is exacerbated by the historically

low investment in transmission in the U.S. From 19881998 electricity demand grew by

30% while transmission increased by only 15%. From 19992009 demand grew by 20%and transmission by only 3%.38

Direct Current Transmission Options

The looming investments in long distance electricity transmission justiy a close look

at the technology choices available to meet the need. Electric power is proportional

to the product o current and voltage, while losses are proportional to the squareo current. Raising voltage and signifcantly lowering current reduces losses when

transmitting high power over long distances requires. For example, the largest high

voltage direct current transmission project, the Xiangjiaba line terminating in Shanghai,China, operates at 800 kV and delivers 6 GW o power over 2000 km.39Such high

voltages strain the capability o semiconductor power electronics to interconvertbetween AC and DC, driving up the cost and limiting the penetration o conventionalDC technology. The losses in such a long DC transmission line can be as high as 10%.40

While high voltage DC is the preerred transmission mode or long distances, there

are drawbacks to implementing it or renewable electricity transmission. It requires asingle point o origin and termination, precluding wide area DC collection and end user

distribution schemes. In addition, the high voltage requires expensive and technically

challenging conversion by semiconductor power electronics between AC and DC, and


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it requires unsightly towers and substantial right o way that can take a decade or moreto gain approval in all the relevantbut uncoordinatedregulation zones. Despite these

drawbacks, conventional high voltage DC transmission is a mature technology that can be

implemented to meet renewable electricity transmission needs over moderate distances.

Additional high voltage DC transmission within one- or two-state regions is needed tolink regional renewable electricity sources to population centers.

Underground superconducting DC transmission lines are an emerging option that

oers a potential route to a national renewable electricity transmission system.41, 42, 43, 44Superconducting DC lines operate at zero resistance, eliminating electrical losses or

any transmission length. Because they eliminate loss and produce no heat, superconduc-tors carry much more current and power than conventional conductors (see Figure

10). Without losses to minimize, there is no need to raise voltage and lower current

to extreme levels. Operation at 200 kV400 kV enables multi-terminal entrance andexit ramps that collect power rom several wind or solar plants and deliver it to

several cities as it makes its way east or west. Recent easibility studies by EPRI showthat superconducting DC transmission lines carrying 10 GW o power 1600 km can be

integrated into the grid, while maintaining transient and short term voltage stability.45

While superconducting DC cables have no electrical losses, they require rerigerationto maintain tham at superconducting temperatures, oten to the point o liquid nitrogen,

77 k. Technology development o rerigeration systems and dielectric or electricalinsulation that operate eectively at these temperatures are needed to lower the

cost o long-distance superconducting transmission. Superconducting DC transmis-sion couples naturally with superconducting magnetic energy storage (SMES), where

electrical energy is stored in superconducting magnets with low loss, deep discharge

capability and ast response time. The potential synergies o DC superconducting trans-

mission and SMES are promising and remain to be evaluated. Laboratory demonstration

o DC superconducting cable has been carried out at Chubu University in Japan. 46

A proposal or a DC superconducting electricity pipeline is shown in Figure 11.

Figure 10.

Superconducting cables made rom

tapes like those shown on the right

carry up to ve times the power o

conventional copper in the same

cross sectional area. (Courtesy o

American Superconductor)


26/40


Long distance transmission oers a partial solution to the variability challenge o renew-able energy. Balancing generation with load typically takes place within a local or regional

balancing area with sufcient dispatchable conventional resources to meet load uctua-

tions. Aggregating wind power over many wind plants substantially increases reliabilityand decreases uctuations, reducing the need or conventional reserves and loweringcost.47, 48, 49, 50

The complexity o balancing over large areas with many generation and load resourceseventually limits the size o the balancing area. Even in this case, however, long distancetransmission plays a role. Generation excesses and defcits across the country can beanticipated by orecasting and matched over long distances to balance the system. An

excess o wind power in the upper central US might be balanced by transmission toa power defcit in the East. Under these conditions specifc excesses and defcits are

identifed and balanced much like conventional generation is switched in or out to balance

load at present. With adequate orecasting, such specifc opportunities can be identifed

and arranged in advance and executed dynamically as the situation develops. 43, 44 This

distant generation balancing requires additional high-capacity long distance transmissionthat is operator controllable by power electronics, allowing excess generation in onearea to be directed to specifc targets o defcit ar away, instead o getting sidetrackedin the grid by local conditions

Figure 11.

The proposed DC superconductor

electricity pipeline or carrying large

amounts o renewable power long

distances. This network provides

an interstate highway system or

electricity. (Image courtesy o

American Superconductor.)


27/40


28/40


The Business Case

Utility renewables investments are typically assessed rom the regulatory, project fnance

and technical perspectives. The regulatory assessment ocuses on ensuring utility compli-

ance with renewable portolio standards (RPS), and that imprudent cost overruns areavoided. . The project fnance oversight looks at economic merits o the investment

within discrete unding and cash ow boundaries exclusive to the project under review.

The technical assessment evaluates projects engineering and operational risks and thespecifc technologies involved.

While these conventional views are important or the investors, utilities, regulators and

ratepayers, they do not ully capture the set o benefts that a renewables investmentcan deliver beyond the boundaries o a given project. Accounting or these additional

benefts in an expanded business case can enhance the profle o the renewables invest-

ment, but more importantly, such an evaluation will recognize the synergies inherent inthe integration o renewables with the grid.

Signifcant Value at Stake

Beore discussing the current structural challenges that prevent the ull accounting ovalue created rom the integration o renewable energy and the grid, it is important tooutline the benefts that are delivered and those typically overlooked.

Understanding o the benefts o combining centralized and distributed renewable energy

is in its early stages.

Through a number o recent studies to assess dierent value drivers associated with

grid integration, the Department o Energy (DOE), along with several national labs,

is beginning to understand the value o renewables on the grid. Because grid-based

large-scale storage is in its inancy, there is limited knowledge and a cautious approachremains when extrapolating potential benefts rom pilot, one-o projects, to larger scale

deployment on the grid.

However, as the deployments continue and grow in penetration, as technology improvessignifcantly or hardware and in power electronics, and as sotware and inormation

technology is created to derive urther value rom the integration o renewables into the

grid, there is growing confdence in the nature and size o benefts that can be generated.

There are a number o benefts at stake, which can be synthesized into several key areas:

Flexibility in generation that can lower overall system peak consumption

requirement

Distributed generation that goes beyond peak reduction to overall consumption

reduction

Addition o storage o renewables increases the capabilities in managing peak

and overall energy consumption

Additional grid stability with the capability to provide ramp-up/ramp-down o

power

Distributed generation that helps maintain local supply continuity


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A variety o secondary and tertiary benefts is also generated, but may be less certainat this point. These benefts will become clearer as deployments o both centralized and

distributed renewables generation increase.

Current Challenges

A number o challenges continue to drive a more narrow view o the value o renew-ables benefts. Some o these challenges are driven by the structure o the utilities andrenewables industry, while others reect the lack o knowledgegiven the early stageso the industrythat the industry has in technically integrating and seamlessly operatingrenewables into the grid. The key actors include:

Beyond the grid boundary:renewables projects are typically seen as generation

projects and, thereore, the value they bring to the grid is not seen as a primarybeneft

Uncertainty on what the benefts are: there are signifcant challenges in actually

estimating the benefts that an intelligent connection rom a renewable into thegrid delivers. This requires a complicated engineering and fnancial analysis involv-

ing power markets, storage potential, time shiting o usage, peak consumptionreductions and the consequences on prices paid. This enters a level o complexity

with many unknowns.

The mandatory game:The mandatory nature o RPS oten negates the need

to account or the ull benefts that a given project delivers. As long as projecteconomics work the project is justifed. The corollary to this is that utilities andrenewables developers oten perceive the actual integration as an exercise in

justiying the rate basing o enabling equipment (such as inverters, instrument

transormers, and back-up generation). In addition, many stakeholders (e.g.,

regional transmission operators) view system investments to enable integration

as critical to maintaining system stability; hence, investments are made based

on risk/consequence rather than with an understanding o the fnancial upside

Too theoretical: Given that technologies are still developing and industry experi-ence is still limited, skepticism is common and many view these benefts as

too theoretical. To date, the ocus has been on getting renewables to run welloperationally rather than on the ull benefts that the grid integration can deliver.

These challenges are preventing the inclusion o value that is generated by integratingrenewables with the grid.

The Importance o Uncaptured Benefts

Appropriately accounting or the ull benefts that renewables can deliver strengthensthe case or the renewables investments and their integration with the grid. Key actors

important to consider include:

Achieves a strengthened net present value: as additional sources o value beyond

the project boundaries are incorporated, the overall net present value o the

project is enhanced. The value o renewables to both the generation and the

transmission and distribution sides o renewables investments can be captured.


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Brings a broader set of stakeholders into alignment: pushing to assess and include the

benefts to both the grid and the generation side will also help push alignmentacross multiple stakeholders which include regulators, utilities, developers, cogen-

eration, commercial and industrial customers, and ratepayer groups. A number ostakeholder groups have conicting views on the costs o renewables and whoand how to pay or these investments. Defning the additional sources o valueshould help create additional ground or agreement across stakeholder groups.

Creates an important act-base:by bringing attention to the additional beneftsthat can be included into the broader renewables business case, an importantact-base is created which goes a long way to mitigate the skepticism around

both the sources and estimation o value rom renewables and grid integration

Develops an integrated picture: bringing the generation and the transmission anddistribution aspects into a single view unifes the operation o the grid with

distributed resources such as non-centralized wind-based renewables. This is akey issue given the signifcant discussion taking place on the utility o the uture,

and the role o distributed generation and renewables.

Documenting these benefts spans both hard beneftssuch as net present valueand

sot benefts such as developing an integrated picture. All these benefts are importantand are collectively required to enhance the capabilities o the grid.

Recommendations:

The Federal Energy Regulatory Commission (FERC) and the North American ElectricReliability Corporation (NERC) should:

Develop an integrated business case that captures the ull value o renewable genera-

tion and electricity storage in the context o transmission and distribution; and

Adopt a uniorm integrated business case as their ofcial evaluation and regulatorystructure, in concert with the state Public Utility Commissions (PUCs).


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Conclusion

The demand or carbon-ree electricity is driving a growing movement o adding renew-

able energy to the grid. Renewable Portolio Standards mandated by states and underconsideration by the ederal government envision a penetration o 20-30% renewableenergy in the grid by 2020 or 2030. The renewable energy potential o wind and solarar exceeds these targets, suggesting that renewable energy ultimately could grow wellbeyond these initial goals.

The grid aces two new and undamental technological challenges in accommodating re-newables: location and variability. Renewable resources are concentrated at mid-continent

ar rom population centers, requiring additional long distance, high-capacity transmission

to match supply with demand. The variability o renewables due to the characteristics oweather is high, up to 70% or daytime solar and 100% or wind, much larger than the ew

percent uncertainty in load that the grid now accommodates by dispatching conventional

resources in response to demand.

Solutions to the challenges o remote location and variability o generation are neededto meet the Renewable Portolio Standards now in place in 30 states and the District

o Columbia. The options or DC transmission lines, avored over AC lines or transmis-sion o more than a ew hundred miles, need to be examined. Conventional high voltage

DC transmission lines are a mature technology that can solve regional transmissionneeds covering one- or two-state areas. Conventional high voltage DC has drawbacks,however, o high loss, technically challenging and expensive conversion between AC and

DC, and the requirement o a single point o origin and termination. SuperconductingDC transmission lines lose little or no energy, produce no heat, and carry higher power

than conventional lines. They operate at moderate voltage, allowing many on-rampsand o-ramps in a single network and reduce the technical and cost challenges o ACto DC conversion. A network o superconducting DC cables overlaying the existingpatchwork o conventional transmission lines would create an interstate highway system

or electricity that moves large amounts o renewable electric power efciently over

long distances rom source to load. Research and development is needed to identiy thetechnical challenges associated with DC superconducting transmission and how it canbe most eectively deployed.


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The challenge o variability can be met by switching conventional generation capacity

in or out in response to sophisticated orecasts o weather and power generation.This can be done by large scale energy storage by heat; by pumped hydroelectric or

compressed air: by stationary batteries designed or the grid, or by national balancing o

regional generation defcits and excesses using long distance transmission. Each o these

solutions to variability has merit and each requires signifcant research and development

to understand its capacity, perormance, cost and eectiveness. Variability is likely to bemet by a combination o these three solutions, and the interactions among them andthe appropriate mix needs to be explored.

The long distances rom renewable sources to demand centers span many o the gridsphysical, ownership regulatory boundaries. This introduces a new eature to grid structure

nd operation: national and regional coordination. The grid is historically a patchwork olocal generation resources and load centers built, operated and regulated to meet localneeds. Although it is capable o sharing power across moderate distances, the arrange-ments or doing so are cumbersome and inefcient. The advent o renewable electricity

with its enormous potential and inherent regional and national character presents

an opportunity to examine the local structure o the grid and establish coordinatingprinciples that will not only enable eective renewable integration but also simpliy andcodiy the grids increasingly regional and national character.


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Case Study: New York State

New York State serves as a microcosm o the nations renewable energy challenges.

New York aces signifcant transmission challenges with its renewable resources largelyupstate and consumption largely downstate. There are substantial power congestionchallenges near dense population areas. By executive order, New York has mandated an80% reduction in greenhouse gas emissions by 2050, goals that are not atypical.New

Yorks Renewable Portolio Standard calls or an aggressive 30% renewable electricitypenetration by 2015. All paths toward meeting these goals require signifcant electrif-cation o the states energy portolio including light vehicle transportation.52 Replacingossil uels or transportation with electricity is an eective carbon mitigation strategyprovided the electricity is generated rom renewable sources.

In 2008, New Yorks electricity consumption was 166,547 GWh, corresponding to an

average power consumption o 19 GW and a summer peak consumption o 34 GW.53The

summer generating capability in New York in 2009 was 38 GW with approximately 70%

rom ossil uels.47 In March 2009 the installed wind nameplate capacity (the maximumdesigned output in strong winds) in New York was 1.275 GW,47 with a winter rating o30% o nameplate capacity and a summer rating o 10% o nameplate capacity.47 There

are approximately 4.5 GW o hydroelectric power in the state.54 The challenge is clear:to meet 10% o New Yorks electricity consumption with wind (hydropower, biomass and

solar can supply the remaining RPS) requires 1.9 GW o wind electricity or 9.5 GW onameplate capacity, about 7.5 times the current installed capacity. New Yorks aggressive

renewable energy goals are consistent with its leading position on energyin 2008 itwas the second most energy-efcient state on a per capita basis, accounting or 4.1% o

the nations energy ootprint despite having 6.4% o the nations population.55

New York is ahead o much o the nation in having signifcant energy storage capabilityincluding two pumped hydro acilities providing 1.3 GW47 and development o compressed

air energy storage (CAES) o about 150 MW is under way.56The spin-up times o energy

storage, about two to three minutes or pumped hydro and about 10 minutes or CAES,

allow quick response to renewable generation variability; ossil uel powered turbinestartup times are somewhat longer, 2030 minutes. However, pumped hydro and CAESare not broadly deployable. The scale o renewable generation envisioned will requiresignifcantly enhanced storage, possibly rom utility-scale conventional or ow batteryinstallations, and rom distributed systems such as community storage, home storage, and

plug in electric vehicles. The system management issues include orecasting renewablegeneration and balancing it with demand using reserves and storage.


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The geographical separation o renewable generation rom consumption is compounded

by transmission system congestion during times o peak load; both challenges requiresignifcant investment in transmission. Although it is not discussed in this report, NewYork has signifcant investments in smart grid inrastructure through the recent SmartGrid Investment Grants and Smart Grid Demonstration Projects that will promote

the integration o storage, orecasting, and transmission advances as they mature. These

investments are laying the groundwork or demand management, two-way communica-tion (which also enables distributed storage management), better demand prediction

and control, and the potential or enhanced monitoring o the distribution and transmis-

sion systems.

Like the nation, New York has ample renewable resources to meet its renewable portolio

standards. The challenge is not capacity, but implementation: developing technology toharvest the plentiul renewable resources, operating procedures to integrate them on the

grid, and regulatory structures to ensure that the grid is reliable and that value and costare shared appropriately among stakeholders. The remote location o renewable energy

resources and their high variability requires a new level o wide-area coordination across

traditional physical, ownership, and regulatory boundaries. Developing the necessarytechnological, operating and regulatory structures to address these integration challenges

is the major energy task or New York and the nation in the coming decades.


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Endnotes

1 Renewable Energy Portolio Standard (RPS): Background and Debate over a National

Requirement, CRS Report or Congress, Order Code RL34116, Updated December

5, 2007, Fred Sissine, CRS-1

2 Ibid, CRS-4

3 The Senate bill would allow Governors to petition or permission to allow up to 26.6%o their states RPS requirement to be met through energy eciency measures.

4 Black & Veatch, Twenty Percent Wind Energy Penetration in the United States: A Technical

Analysis o the Energy Resource, Walnut Creek, CA (2007).

5 M. Mehos and D. Kearney, Potential Carbon Emissions Reductions rom Concentrating

Solar Power by 2030, in Tackling Climate Change in the US, Charles F. Kutscher (Ed),

American Solar Energy Society (2007), ISBN-10: 0895533065

6 To convert the capacities o wind and concentrating solar power to electricity

generation potential, multiply by the capacity actor, which accounts or the variability

o wind and sun: 2040% or wind, 1020% or sun. The capacity actor is included in

the quoted photovoltaic electricity generation potential.

7 2008 Solar Technologies Market Report, DOE Energy Eciency and Renewable

Energy (2010), http://www.nrel.gov/analysis/re_market_data_solar.html, accessed June

8, 2010.

8 Darren M. Bagnall and Matt Boreland, Photovoltaic technologies, Energy Policy 36

43904396 (2008).

9Annual Energy Outlook 2010, Energy Inormation Agency, http://www.eia.doe.gov/oia/

aeo/index.html, accessed June 19, 2010.

10 Mason Willrich, Electricity Transmission Policy or America, Enabling a Smart Grid, End to

End, MIT-IPC-Energy Innovation Working Paper 09-003 (2009).

11 Manred Lenzen, Current State o Development o Electricity-Generating Technologies: A

Literature Review, Energies 3, 462-591 (2010).12 20% Wind Energy by 2030, Energy Eciency and Renewable Energy, DOE/GO-

102008-2567 (2008).

13 Plant is a term used to describe a collection o variable generators as they typically

occur in groups, or example multiple wind turbines constitute a wind plant.

14 H. Sharman, Proceedings o ICE Civil Engineering 158, 161 (2005).

15Accommodating High-Levels o Variable Generation: Summary Report, NERC (2009),

http://www.nerc.com/ > Integrating Renewables, accessed June 19, 2010.

16 Eastern Wind Integration and Transmission Study, EnerNex Corp., Knoxville TN, NREL/

SR-550-47078 (2010), http://www.nrel.gov/wind/systemsintegration/ewits.html,

accessed June 17, 2010.

17 Western Wind and Solar Integration Study, GE Energy, NREL/SR-550-47434 (2010),

http://www.nrel.gov/wind/systemsintegration/wwsis.html, accessed June 17, 2010.


36/40


18 Real-Time Forecasting or Renewable Energy Development, Hearing o the House

Science and Technology Committee, Subcommittee on Energy and Environment,

June 16, 2010, http://science.house.gov/publications/hearings_markups_details.

aspx?NewsID=2857, accessed June 17, 2010.

19

K. Porter and J. Rogers, Central Wind Power Forecasting Programs in North Americaby Regional Transmission Organizations and Electric Utilities, NREL/SR-550-46763,

December 2009.

20 Eastern Wind Integration and Transmission Study, EnerNex Corp., Knoxville TN, NREL/

SR-550-47078 (2010), http://www.nrel.gov/wind/systemsintegration/ewits.html,

accessed June 17, 2010.

21 Western Wind and Solar Integration Study, GE Energy, NREL/SR-550-47434 (2010),

http://www.nrel.gov/wind/systemsintegration/wwsis.html, accessed June 17, 2010.

22 Real-Time Forecasting or Renewable Energy Development, Hearing o the House

Science and Technology Committee, Subcommittee on Energy and Environment,

June 16, 2010, http://science.house.gov/publications/hearings_markups_details.

aspx?NewsID=2857, accessed June 17, 2010.23 K. Porter and J. Rogers, Central Wind Power Forecasting Programs in North America

by Regional Transmission Organizations and Electric Utilities, NREL/SR-550-46763,

December 2009.

24 H. Holtinen, Estimating the impacts o wind power on power systemssummary o IEA

Wind collaboration, Environ. Res. Lett. 3, 025001 (2008)

25 E. Ela and B. Kirby, ERCOT Event on February 26, 2008: Lessons Learned, NREL Technical

Report NREL/YP-500-43373 (2008), www.nrel.gov/docs/y08osti/43373.pd, accessed

May 15, 2010.

26 H. Madsen and H.A. Nielsen, The State-o-the-art o Wind Power Forecasting in Europe,

IAWIND Symposium, Ames, Iowa, April 2010, http://www.iawind.org/presentations/

madsen.pd, accessed July 25, 2010.27 Bonneville Power Administration, Balancing Act: BPA grid responds to huge inux o wind

power, DOE/BP-3966, November 2008.

28 Ulrich Focken, Matthias Lange, Kai Monnich, Hans-Peter Waldl, Hans Georg Beyer,

Armin Luig, Short-term prediction o the aggregated power output o wind armsa

statistical analysis o the reduction o the prediction error by spatial smoothing eects,

Journal o Wind Engineering and Industrial Aerodynamics 90, 231 (2002).

29 B. Kirby and M. Milligan, Facilitating Wind Development: The Importance o Electric

Industry Structure, NREL/TP 500-43251, May 2008.

30 Steven E. Koonin, Testimony beore the Senate Energy and Natural

Resources Committee, Dec 10, 2009, http://energy.senate.gov/public/index.

cm?FuseAction=Hearings.Hearing&Hearing_ID=d36b718-e767-4437-7703-

c8db3ea58cd, accessed August 29, 2010.


37/40


31 B. Roberts, Capturing Grid Power, IEEE Power and Energy Magazine, 32, July/August

(2009), www.electricitystorage.org/images/uploads/docs/captureGrid.pd, accessed

August 29, 2010.

32 Bottling Energy: Storage as a Strategic Tool or Managing Variability and Capacity Concerns

on the Modern Grid, Report to the Department o Energy by the Electricity AdvisoryCommittee, December 2008.

33 R. Gabbrielli and C. Zamparelli, Optimal Design o a Molten Salt Thermal Storage Tank

or Parabolic Trough Solar Power Plants,Journal o Solar Energy Engineering 131, 041001

(2009).

34 Grid-Scale Rampable Intermittent Dispatchable Storage (GRIDS), https://arpa-e-oa.

energy.gov/FoaDetailsView.aspx?oaId=85e239bb-8908-4d2c-ab10-dd02d85e7d78,

accessed July 25 2010.

35 Mark Johnson, David Danielson and Imre Gyuk, Grid Scale Energy Storage, ARPA-E Pre-

Summit Workshop, March 1, 2010, http://arpa-e.energy.gov/LinkClick.aspx?leticket=k-

81ITzv34%3D&tabid=259, accessed July 25, 2010.

36 CIA World Factbook, https://www.cia.gov/library/publications/the-world-actbook/elds/2212.html, accessed April 2010.

37 A thyristor is a our-layer semiconductor that is oten used or handling large amounts

o power.

38 Karl Stahlkop, Vice President, Power Delivery, EPRI, Presentation at University o

Wisconsin, October 20, 2000, http://www.pserc.wisc.edu/documents/general_

inormation/presentations/presentations_by_iab_members/Stahlkop_EPRI.ppt,

accessed July 25, 2010.

39 Sonal Patel, The Age o the 800 kV HVDC, Global Energy Network Institute, Feb, 2010,

http://www.geni.org/globalenergy/library/technical-articles/transmission/powermag.

com/the-age-o-the-800-kv-hvdc/index.shtml, accessed July 25, 2010.

40 Peter Hartley, Rice University, HVDC Transmission: part o the Energy Solution?, http://

cohesion.rice.edu/CentersAndInst/CNST/emplibrary/Hartley%2004May03%20

NanoTechCon.ppt, accessed July 25, 2010.

41 Workshop on Superconducting DC Electricity Transmission, January 21-22, 2010,

Houston, TX, http://events.energetics.com/DCCableWorkshop2010/, accessed May

19 2010.

42 Program on Technology Innovation: a Superconducting DC Cable, EPRI Final Report

1020458, S. Eckroad, Principal Investigator, December 2009

43 Program on Technology Innovation: Study on the Integration o High Temperature

Superconducting DC Cables within the Eastern and Western North American Power

Grids, EPRI Repor t 1020330, T. Overbye P. Ribeiro T. Baldwin, Principal Investigators,

November 2009.


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