Medium-term reliability: System Balancing

Debbie Lew

WIEB/WIRAB Tutorial

April 22, 2020

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Webinar Outline

• April 15 – Resource Adequacy – long-term reliability

• April 22 – System Balancing – medium-term reliability

• April 29 – System Stability part 1 – short-term reliability

• May 6 – System Stability part 2 – short-term reliability

• May 20 – 100% Clean Energy and Distributed Energy Resources

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3

Short-term Medium-term Long-term

System Stability System Balancing Resource Adequacy

• Seasonal mismatch of supply and

demand

• Multiple days in a row of low

wind/solar/hydro

• 1 day in 10 years Loss of Load

Expectation

• Wind and solar variability and

uncertainty

• Reducing curtailment

• Managing imbalance

• High penetrations of inverter-based

resources (IBR)

• Essential reliability services

• Frequency, transient, and small signal

stability issues

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Graphics from left to right: EU-MIGRATE 2016

CAISO, Fast Facts 2016

A. Bloom, Energy Systems Integration Group’s Planning WG Oct 2018

Timescales of grid reliability

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Short-term Medium-term Long-term

System Stability System Balancing Resource Adequacy

• Seasonal mismatch of supply and

demand

• Multiple days in a row of low

wind/solar/hydro

• 1 day in 10 years Loss of Load

Expectation

• Wind and solar variability and

uncertainty

• Reducing curtailment

• Managing imbalance

• High penetrations of inverter-based

resources (IBR)

• Essential reliability services

• Frequency, transient, and small signal

stability issues

0

500

1,000

1,500

2,000

2,500

3,000

3,500

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4,500

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rtai

led

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ergy

(MW

h)

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ad (

MW

h)

Hour of Year

Graphics from left to right: EU-MIGRATE 2016

CAISO, Fast Facts 2016

A. Bloom, Energy Systems Integration Group’s Planning WG Oct 2018

Timescales of grid reliability

These are all fundamentally about the generation and

load balance

Wind and solar are uncertain and variable

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Uncertainty

• Wind and solar generators are not always available when called upon

• Output is predicted by a forecast

• Actual power output differs from forecasts

Variability

• Wind and solar generation vary as the intensity of their energy sources

• Several timescales … minute (regulation), hour (ramping), daily, seasonal, inter-annual

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CSP Forecasted

A perfect forecast eliminates uncertainty but there is still variability

Overview of system operations with conventional generation

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• Forecast load

• Day-ahead – run security-constrained unit commitment and economic dispatch

• Determine hourly schedules for all generators

• Dispatch generators to set points at each interval (5-60 min)

• Regulation reserve adjusts generator output to manage variability within the interval

Graphic source: E. Ela, EPRI, ESIG Forecasting workshop, 2018

From coarse to fine control of generation/load balance

Security-constrained unit commitment and economic dispatch

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• Optimize operations for lowest production cost (fuel and variable O&M)

• Which units need to be on (unit commitment)?

• How much output from each unit (economic dispatch)?

• Generators have constraints – Pmin(minimum generation), minimum downtime, minimum runtime, ramp rates, startup times

• Hold headroom for operating reserves

• Power flows respect transmission limits. “Security-constrained” accounts for credible contingencies like a transmission outage and ensures resulting power flow will still respect limits

Graphic: Goggin, AWEA, 2017

Need to meet NERC standards

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• Area Control Error (ACE) is essentially the Balancing Authority’s (BA’s) power balance error

• Real Power Balancing Control Performance BAL-001-2• Control interconnection frequency within defined limits• Control Performance Standard 1 (CPS1) is a measure of ACE

variability. Want CPS1≥100%• BA ACE Limit (BAAL) limits ACE as a function of frequency• Regulation reserves provide this control. BA’s decide how much

reg to hold

• Disturbance Control Standard BAL-002-3/BAL-002-WECC-2a• Contingency reserve for recovery from an event to balance

resources and restore ACE• WECC BA’s hold the greater of 1) most severe single

contingency or 2) sum of 3% of load plus 3% of generation• Capable of full response within 10 minutes• Half must be spinning (online, responds to frequency)

Graphic: NERC 2013,

https://www.nerc.com/pa/StandProject2010141Phase1of

BalancingAuthorityRe/BAL-001-

2_Background_Document_Clean-20130301.pdf

https://www.nerc.com/pa/StandProject2010141Phase1ofBalancingAuthorityRe/BAL-001-2_Background_Document_Clean-20130301.pdf

Ancillary services provide fine control and respond to events

9Source: Ela, et al, NREL, 2011 https://www.nrel.gov/docs/fy11osti/51978.pdf

https://www.nrel.gov/docs/fy11osti/51978.pdf

Add wind, PV, DER, more variable load

• Forecast wind/PV!• Forecasts are more accurate when they

are closer to real-time: make decisions as close to real-time as possible.

• Forecasts should line up with decision points (such as whether to commit a new unit)

• The grid will need for more flexibility for:• Variability and uncertainty of wind/PV• More variable load• DER

Graphic: T. Miller, SPP, ESIG Forecasting Workshop, June 2018; Goggin, AWEA, 2017

Mea

n a

bso

lute

% e

rro

r10

Wind and solar impact the grid differently

Source: Ela, 2008.

http://www.nrel.gov/

docs/fy08osti/43373.

pdf

Source:

CAISO

Projected net

load: spring

2020

Solar

• Ramp management

• Diurnal mismatch

• Turn off or turn down other power plants midday

Wind

• Ramp prediction

• With geographic diversity, relatively smaller ramps

• Hold more reserves

• Wind ramp forecasts

http://www.nrel.gov/docs/fy08osti/43373.pdf

Finer control and look-ahead

• Visibility and fine control for balancing and congestion

• Faster dispatch

• Far look-ahead to position system for ramps

• Situational awareness

• DER can complicate this

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Finer control and look-ahead

Seconds (PrimaryFrequencyResponse)

Minutes (FrequencyRegulation)

Hourly (Dispatch) Day-ahead (Unitcommitment)

Traditional control for system balancing

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Finer control and look-ahead

Seconds (PrimaryFrequencyResponse)

Minutes (FrequencyRegulation)

Hourly (Dispatch) Day-ahead (Unitcommitment)

Traditional control for system balancing

Four-hour-ahead(Unit commitment)

5-minute (dispatch)Fast Frequency

Response

Flexibility/ ramping reserves

Dispatch look-ahead 1-2 hours

Unit commitment look-ahead

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New ancillary services

Graphic: C. Loutan, CAISO, “Operating Impacts of higher VG Penetrations – A Panel Discussion,” UVIG 2017 Fall Workshop, Oct 2017

• ERCOT recently revised ancillary services to include fast frequency response

• Ireland added seven system services including ramping products

• CAISO and MISO have ramping products

• Xcel/PSCO holds a 30-min flex reserve

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It can be difficult for CAISO to balance their

system in the late afternoon

Reserve requirements based on risk

• ERCOT - Islanded grid: 73.5 GW peak; 22 GW wind and 2 GW PV

• Non-spin reserve service (NSRS) manages load/wind/solar forecast errors.

• NSRS requires full output in 30 minutes.

• Previously procured fixed levels of NSRS, but now based on expected conditions and need.

• Cover 95% of uncertainty during high variability risk periods and 70% during low risk periods

Source: Lew, et al, Secrets of Successful Integration, IEEE PES Magazine, Nov/Dec 2019

Must ensure adequate reserves for these events

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No wind/solar

High wind

High solar

High wind case

25% wind

8% solar

High solar case

8% wind

25% solar

No wind/solar

case

System dispatch

Lew et al, “Western Wind and Solar Integration

Study,” NREL, 2013

The grid needs flexibilityBefore you spend money on new infrastructure, consider:

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• What do I need it to do? Can I do that with existing infrastructure?

• Can I recover my costs through revenue? Will it pay for itself?

• Is it the cheapest way to address my need?

• Storage competes with load flexibility from customer prices (eg, time-of-use rates) and demand response

• These options interact. The more constrained your system is, the more value one of these options will provide.

Source: US Dept of Energy Wind Program

There are many options for flexibility and a range of costs

Flexibility Options

1. Transmission, larger markets, big and fast trading

2. Forecasting

3. Extract flexibility from non-variable resources

4. Extract flexibility from wind and solar

5. Storage

6. Demand-side flexibility

Each tool can saturate – we need them all

Energy Strategies, “Western Flexibility Assessment,” WIEB, Dec 10, 201919

1) Geographic diversity provides flexibility

Left: Lew et al, Western Wind and Solar Integration Study Phase II, NREL, 2013; Right: GE, Western Wind and Solar Integration Study, NREL, 2010.

New Mexico (2006)

• Geographic diversity smooths load, wind and solar

• Geographic diversity also provides more dispatchable generators to help manage variability/uncertainty

• Transmission and markets enable diversity

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Bigger and faster tradingReal-time energy imbalance market being transitioned to day-ahead market

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EDAMEIM

Left: https://www.westerneim.com/Documents/ISO-EIMBenefitsReportQ2-2019.pdf;

right E. Ela, EPRI, ESIG Forecasting workshop, 2018

EIM allows trading partner to dispatch down in real-time, in order to buy lower cost generation from a neighbor

EDAM enables trading partner to not startup a generator, in order to buy

lower cost generation from a neighbor

https://www.westerneim.com/Documents/ISO-EIMBenefitsReportQ2-2019.pdf

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• Denmark has 6.1 GW of peak demand, 5.7 GW wind and 1 GW PV. Half of their load is served by wind/PV annually.

• Instantaneous wind penetration reached 149% of demand

• Interconnections (6 GW) are well-exploited – day-ahead market coupling has expanded to intra-day markets which mitigates intra-day forecast errors and variability.

• Denmark sources flexibility from all resources: thermal plants, wind plants, demand-side resources can all provide down-regulation

Energinet has used many sources of flexibility

Graphic: P. Jorgensen, Energinet, 2019

2) Forecasting saves money

23Left: GE Energy, Western Wind and Solar Integration Study, 2010 https://www.nrel.gov/grid/wwsis.html ; Right: Kari Hassler, PSCO,

ESIG Forecasting Workshop, June 2018

Forecasting saves up to

14% in annual operating

costs. If forecasts were

perfect, an additional 1-2%

could be saved.

Savings over time from

optimized operations with

continually improvements

of wind and PV forecasts

https://www.nrel.gov/grid/wwsis.html

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• SPP has 21.4 GW wind; 50.6 GW peak demand, 72% instantaneous

• Low pressure systems cause instabilities. Low-level jet movement significantly impacts wind output

• Largest wind down-ramp 16.1 GW in 21 hours – it was forecast. Largest one-hour ramp was 4 GW

• SPP has 5 GW that can start-up within 1 hour

• What if a forecast error occurred during:• In May 2018, all quick-starts were committed in day-

ahead market• The largest wind ramp had steep down-ramps during

morning and evening when load was increasing which exacerbated net load ramps.

• Uncertainty Response Team assesses risk in 1, 4 and 8 hour look-ahead horizons over next 7 days

Advanced forecasting in Southwest Power Pool (SPP)

Source: B. Rew, SPP, 2019; Lew, et al, Secrets of Successful Integration, IEEE PES Magazine, Nov/Dec 2019

7 GW wind forecast error

3) Flexibility of non-variable generatorsCalifornia Pumped Hydro Storage

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Left, adapted from: A. Park, Stanford University, “Data-

driven unit generating parameters,” WIEB, May 2019; Right:

ORNL, DOE 2017 Hydropower Market Report, April 2018

Pmin from operating data in WECC

Pm

in(%

)

Some WECC plant operators are already

achieving very low Pmin

Impacts of wind/PV on cycling costs and emissions

26Lew et al, “Western Wind and Solar Integration Study Phase 2,” NREL, 2013

$0.035 – $0.157 Billion

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4) Wind and PV can provide flexibility

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• Dispatch wind and PV (eg, MISO DIR)• Move away from ‘must-take’ resources and manual curtailment

• Use real-time forecast as maximum output

• Rooftop PV is not easily dispatched

• Regulation reserves (eg, Xcel)• Reduced curtailment and improved control

• Contingency reserves (eg, Xcel)

• Wind and PV can provide other essential reliability services (see next week’s webinar)

• If wind and PV provide essential reliability services, you may avoid reliability-must-run thermal generation, which has economic and emissions consequences

Think of curtailed wind/solar as a resource

The grid needs essential reliability services to operate stably

Graphic: Milligan, et al, “Alternatives No More,” IEEE PES Magazine, Nov/Dec 2015.

MW

ERCOT reduces regulation while increasing windDeclining regulation reserve requirements Improved CPS1 reliability metric

Source: Lew, et al, Secrets of Successful Integration, IEEE PES Magazine, Nov/Dec 2019

Reg-up

requirement

decreasing

Wind

increasing

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5) Storage

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• Energy storage is the most obvious answer to the duck curve.

• Difficult to make a case for stand-alone batteries based on price arbitrage alone. But battery storage is increasingly providing capacity to meet daily peak, and other services.

• A portfolio of storage resources will likely be in our future

• Electricity storage technologies: pumped hydro storage, compressed air energy storage, liquid air energy storage, flow batteries, hydrogen, vehicle-to-grid

• Thermal energy storage may provide low-cost solutions

Top: CAISO; bottom: Valmoro, Viking Cold Solutions, “Intelligent Thermal Energy Storage,” ESIG Spring 2020

• Hybrid plants proliferating, largely because of the 30% investment tax credit:• PV/battery

• Wind/battery

• PV/wind/battery

• Gas turbine/battery

• Hybridizing plants can improve their attributes• Diurnal mismatch between load and generation

• To firm variable renewables

• Meet ramp-down rates (eg Hawaii)

• Faster startup times

• Faster ramp times

• Reduce Pmin of conventional units to zero (eg SCE)

Hybrid plants increase flexibility of generators

Pictures: THEenergy, 2017; V. Kaushik, SCE, “Reality Check on Storage,” IEEE PES T&D 201830

Kauai manages high penetrations of PVRan at 100% renewables for 8 hours

31Source: Rockwell, KIUC, personal communication, 2020

• Operating reserves:• Ample quick-start diesel

reciprocating engines but can’t start-up fast enough (seconds not minutes) to meet cloud events

• Pioneered hybrid PV/battery plants. Battery storage provides spinning contingency reserves for those PV plants.

• Holds 50% of real-time PV output for those PV plants that are not backed by battery storage

Batteries enable 100% renewables in the Kauai island system

6) Dispatchable demand

We used to control a portfolio of

generators to balance a fixed demand

In the future, we’ll control both demand

and generation to balance the system

Demand

Instead of using generation to balance demand,

can we use demand to balance generation? 32

April 22, 2020 33

We know how to clean this part up

Electrification can help clean this part up

We need to integrate other energy sectors

We need to integrate other energy sectors

April 22, 2020 34

High renewables

penetrations in the

electricity sector will require

significant flexibility that

may be cost-effectively

sourced from the existing

fuel-based heating and

transportation sectors

Programs and pricing for demand-side flexibility

35Hines, Tierra Resource Consultants, PLMA, Apr 2020; Thompson, APS, “What if Your Neighboring Utility Goes to 100% Renewables,” CREPC April 2019;

Lew, GE, “DER Compensation: Colorado Springs Utilities Solar Program Design Study,” ESIG Oct 2017

APS sells cheap midday power

Rates and programs are critical enablers

of demand-side flexibility

DSM exacerbating duck curveOrchestrating TOU rates and DR programs

Conclusions

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• System operators already have a number of tools to balance the system. Additional tools may be needed to provide finer control and better look-ahead.

• There are various measures that can provide flexibility to integrate wind/PV. At some point, the effect of one mitigation option saturates so a suite of mitigation options is necessary.

• Wind and PV can provide essential reliability services and this can help reduce reserves and balance the system.

• Electrification is a key because other energy sectors may have natural flexibility in their demand, but it can help or hurt the grid depending on how it done. The ‘ultimate lever’ that we have to address system balancing is controllable and/or price-sensitive demand. Orchestrating demand with prices and programs will be critical.

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References

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• Integration studies: • Western Flexibility Assessment https://westernenergyboard.org/wp-content/uploads/2019/12/12-10-19-ES-WIEB-Western-

Flexibility-Assessment-Final-Report.pdf

• Western Wind and Solar Integration Study Phases 1&2 https://www.nrel.gov/grid/wwsis.html

• Electrification futures study https://www.nrel.gov/analysis/electrification-futures.html and https://www.nrel.gov/docs/fy18osti/71500.pdf

• Best practices https://www.esig.energy/wp-content/uploads/2020/01/MPE2930855-final-Lew.pdf

• Demand response https://brattlefiles.blob.core.windows.net/files/16639_national_potential_for_load_flexibility_-_final.pdf

• Essential reliability services from wind/PV https://www.caiso.com/Documents/UsingRenewablesToOperateLow-CarbonGrid.pdf

• Operating reserves https://www.nrel.gov/docs/fy11osti/51978.pdf

• NERC Standards full set 2020 https://www.nerc.com/pa/Stand/Reliability%20Standards%20Complete%20Set/RSCompleteSet.pdf

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https://westernenergyboard.org/wp-content/uploads/2019/12/12-10-19-ES-WIEB-Western-Flexibility-Assessment-Final-Report.pdfhttps://www.nrel.gov/grid/wwsis.htmlhttps://www.nrel.gov/analysis/electrification-futures.htmlhttps://www.nrel.gov/docs/fy18osti/71500.pdfhttps://www.esig.energy/wp-content/uploads/2020/01/MPE2930855-final-Lew.pdfhttps://brattlefiles.blob.core.windows.net/files/16639_national_potential_for_load_flexibility_-_final.pdfhttps://www.caiso.com/Documents/UsingRenewablesToOperateLow-CarbonGrid.pdfhttps://www.nrel.gov/docs/fy11osti/51978.pdfhttps://www.nerc.com/pa/Stand/Reliability%20Standards%20Complete%20Set/RSCompleteSet.pdf

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Debbie Lewdebbie@debbielew.com

(303) 819-3470

mailto:Debbie@debbielew.com