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Western Wind and Solar Integration Study

Dr. Debra Lew

Energy Seminar

Stanford University

Nov 3, 2010

NATIONAL RENEWABLE ENERGY LABORATORY

Welcome to Renewatopia

Presenter

Presentation Notes

Renewatopia is a balancing area – must balance supply and demand. That means generation and load must match up.


Welcome to Renewatopia


A systems perspective


Getting help from your neighbors


Today


2017


Quick background on US power system

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Three electrical interconnections in the U.S.

1 2

3Western Electricity Coordinating Council

Presenter

Presentation Notes

First, a little background – the US is made up of 3 interconnections or grids.


The West doesn’t have a lot of markets

NPPD is Joining SPP

Presenter

Presentation Notes

More background The east has a lot of big markets – they have lots of utilities in these markets and the markets help make the operation of these utilities more efficient by allowing the load to be met by the most economic energy source The west lacks these big markets. In the west, the utilities operate individually for the most part, and schedule interchanges with each other on an hourly basis. Generally speaking, each utility is a balancing area, meaning it has to balance its own supply and demand or face fines.


Time (hour of day)0 4 8 12 16 20 24

Syst

em L

oad

(MW

)

seconds to minutes

Regulation

tens of minutes to hours

LoadFollowing

day

Scheduling

A Chronological View

Hours to Day ahead: use load forecast to commit units10 minutes to few hours: manually adjust generator set pointsSeconds to minutes: AGC automatically adjusts generator output


Variability and Uncertainty

Variability: Wind and solar generator outputs vary as the intensity of their energy sources (wind and sun)– Several timescales: minute (regulation), hour (ramping), diurnal,

seasonalUncertainty: Wind and solar generation are similar to “load”

– Not dispatchable – output is predicted by a forecast– Actual power output is different that forecast output

A perfect forecast eliminates uncertainty, but there is still variabilityThe power system is designed to handle variability and uncertainty in

the load. Wind and solar add to this variability and uncertainty.

0

5000

10000

15000

20000

25000

0 6 12 18 24 30 36 42 48Hours

MW

Wind ActualForecasted Wind

0

500

1000

1500

2000

2500

0 6 12 18 24 30 36 42 48Hours

MW

CSP ActualCSP Forecasted


Western Wind and Solar Integration Study

19


Can we integrate 35% wind and solarin the West?

Goal - To assess the operating impacts and economics of wind and solar on the WestConnect grid.

• How do local resources compare to remote, higher quality resources via long distance transmission?

• Can balancing area cooperation help manage variability?

• Do we need more reserves?

• Do we need more storage?• How does geographic diversity help?

• What is the value of forecasting?


Scenario penetration levels

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Name WestConnect Rest of WECC

Wind Solar Wind Solar

10% 10% 1% 10% 1%

20% 20% 3% 10% 1%

20/20% 20% 3% 20% 3%

30% 30% 5% 20% 3%

Penetration levels are by energy (MWh), not capacity (MW). Solar is 70% concentrating solar power with thermal storage and 30% rooftop photovoltaics.

Highrenewables


Geographic Scenarios(high renewables case)

In-Area - each state meets target from sources within that state.

Mega Project - concentrated projects in best resource areas.

Local Priority - Balance of best resource and In-Area sites.


What do we model?

• Model the year 2017 three times• Use historical load and weather patterns from 2004,

2005, 2006 (need correlated load/wind/sun data!)• Statistical analysis of variability. Focus on extreme

events.• Power simulations of all of WECC on hourly basis and

down to 1 minute for extreme events.

• Need high resolution (in time and space) wind and solar data

23


Wind data

http://www.nrel.gov/wind/integrationdatasets

• 3TIER Group ran weather model to recreate weather for 2004, 2005, 2006

• 10 minute wind power output for 960 GW of wind sites in WECC.

• Power profiles were based on VestasV90 3MW turbine at 100m height.

• Hourly day-ahead power output forecasts.

http://www.nrel.gov/wind/integrationdatasets�


How does the system operate in the high renewables case?

25

Mid-July

The operator formerly managed to load but now has to manage the net load.

Load

Net Load = Load - Wind - Solar


How does the system operate in the high renewables case?

26

Mid-July Mid-April

Mid-April shows the challenges of operating the grid with 35% wind and solar.

This was the worst week of the 3 years studied.


Operations during mid-April

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No Wind/Solar High renewables case


What are the benefits of 35% wind and solar?

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High renewables case saves 40% in fuel and emissions costs

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40%, or $80 per MWh of wind/solar

Note: Assumes $30/ton CO2 tax.


High renewables case reduces CO2 by 25-45%

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At a $9.50/MBTU gas price, wind/solar displace gas, resulting in modest emissions reductions.

25%

5%

15% reduction



31


At a $3.50/MBTU gas price, coal is displaced, resulting in high emissions reductions.

45%

30% reduction

50%



32


At a $3.50/MBTU gas price, coal is displaced, resulting in high emissions reductions.

30% reduction

50%45%

That’s like taking 35 million cars off the road!


What do you need to make 35% wind and solar work?

33


You need Balancing Area Cooperation

34

Presenter

Presentation Notes

Tristate is parts of eastern WY 10 minute variability or 1 standard deviation of 10 minute deltas Ratio of 30% case to load alone LP case


You need Balancing Area Cooperation

35

Presenter

Presentation Notes

Tristate is parts of eastern WY 10 minute variability or 1 standard deviation of 10 minute deltas Ratio of 30% case to load alone LP case


Today


Today – Hourly schedules and interchanges


Sub-hourly scheduling


You need subhourly scheduling

39

Hourly scheduling puts more stress on the fast regulating reserves than the wind and solar variability does.


You need forecasting

40

Forecasting saves up to 14% in annual operating costs. If forecasts were perfect, an additional 1-2% could be saved.


You need demand response (or more expensive measures)

41

Forecast error distribution

Presenter

Presentation Notes

Forecast error is 12-16% on a state basis, 8% over the WestConnect footprint, and 7% in WECC.

NATIONAL RENEWABLE ENERGY LABORATORY 42

• Using existing rules for contingency reserves, there were occasional reserve shortfalls

• Increase spinning reserves for every hour of the year.• Add storage like pumped hydro storage.• We only have shortfalls for 89 hours of the year (1%), so

these options can be expensive.

• Demand response(paying loads to turn off) was found to be effective and was less expensive.

You need demand response (or more expensive measures)

Presenter

Presentation Notes

Forecast error is 12-16% on a state basis, 8% over the WestConnect footprint, and 7% in WECC.


You don’t necessarily need more variability reserves

43

Wind and solar double the variability reserve requirements (load following).

Because wind and solar cause some generators to be turned down, rather than off, the system actually has more up-reserves than it does in the no wind/solar case.

Additional reserves do not need to be committed to cover the increased variability reserve requirement.


You don’t need more storage

44

• We evaluated storage for price arbitrage only. We did not evaluate storage for ancillary services (reliability, regulation, etc).

• Wind and solar increased use of existing pumped hydro storage (PHS) slightly.

• We decreased pumping costs to increase use of PHS but overall production costs increased.

• We added a 100 MW PHS in Arizona and gave it perfect foresight of when to pump and generate. At high penetrations, value and use of storage increases, but not enough to justify costs.


You need to better utilize existing transmission

45

• Absolutely need some intra-state transmission to bring resources to load.

• Very little operational difference between the 3 geographic scenarios.

• Wind/solar displace other generation, freeing transmission capacity. If this new capacity can be used for wind/solar, then less new transmission is needed.

• Assuming better utilization of existing transmission, we could start integrating up to the medium renewables case before new interstate transmission is commissioned.


It is operationally feasible for WestConnect to accommodate 30% wind and 5% solar if:

46

• Substantially increase balancing area cooperation• Increase use of subhourly scheduling• Increase utilization of transmission.• Enable coordinated commitment and dispatch over wider regions.• Use forecasts in operations.• Increase flexibility of dispatchable generation.

Source: DOE

• Commit additional operating reserves as appropriate.

• Implement/expand demand response programs.

• Require wind to provide down reserves.


This is but one piece of the puzzle.

47

Integration StudyHourly production modelOperational FeasibilityVariable CostCapacity Value

Transmission PlanningN-1 contingencysecurity

Dynamic StudiesFrequency Response

AC AnalysisVoltageLine lossesReactive power


Thanks!

48

• Study Team - GE Energy, 3TIER Group, SUNY/CPR, Exeter Associates, Northern Arizona University, NREL

• Technical Review Committee• WestConnect• U.S. DOE• For full report or Executive Summary:

http://www.nrel.gov/wwsis

Photos and figures credit: Western Wind and Solar Integration Study: http://www.nrel.gov/wind/systemsintegration/pdfs/2010/wwsis_final_report.pdf and Western Wind and Solar Integration Study: Executive Summary: http://www.nrel.gov/wind/systemsintegration/pdfs/2010/wwsis_executive_summary.pdf.

Cover slide photos: PIX 25996, 08604, 10927, and 14898 (from left to right).

http://www.nrel.gov/wwsis�

http://www.nrel.gov/wind/systemsintegration/pdfs/2010/wwsis_final_report.pdf�

http://www.nrel.gov/wind/systemsintegration/pdfs/2010/wwsis_executive_summary.pdf�

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