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Tradeoffs and Synergies between CSP and PV at High Grid Penetration. * * NREL July 5, 2011. Bottom Line. As penetration of variable generation (solar, wind) increase, it is increasingly important to consider the interaction between these resources and the entire grid system

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slide1

Tradeoffs and Synergies between CSP and PV at High Grid Penetration

*

*

NREL

July 5, 2011

National Renewable Energy Laboratory Innovation for Our Energy Future

bottom line
Bottom Line

As penetration of variable generation (solar, wind) increase, it is increasingly important to consider the interaction between these resources and the entire grid system

Dispatchable energy (e.g. CSP w/storage) has a higher value than non-dispatchable energy.

At low penetration of solar and wind this difference is small

At higher penetration (15% on an energy basis) this difference may increase by as much as 4 cents/kWh

Overall penetration of solar energy can be increased by the use of CSP with storage which provides grid flexibility

Allows for higher levels of PV penetration by providing the ramping rate and range needed to accommodate the variable output of PV systems

2

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increase in energy value due to dispatchability of systems with thermal energy storage
Increase in Energy Value Due to Dispatchability of Systems with Thermal Energy Storage
  • Dispatchable solar energy sources:
  • Maintain high energy value
    • Always displaces the highest cost energy sources
  • Maintain high capacity value even at high solar penetration.
  • Lower curtailment than solar systems w/o storage
  • Lower integration/reserve costs

The actual difference in value is largely a function of penetration and overall grid system flexibility

3

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analytic methods
Analytic Methods

Detailed grid simulations of the Western Interconnect

Simulates the hourly dispatch of the power plant fleet

Ensures reliability by ensuring availability of operating reserves

Validates basic transmission operability using DC power flow

Enforces power plant constraints including ramp limits, operating limits

Calculates fuel burn and associated cost and emission

Assumed frictionless markets (best case scenario for PV)

Two scenarios

15% PV and 15% wind

10% PV, 5% CSP and 15% wind

Did not capture full range of integration costs due to uncertainty about reserve requirements of PV, short term variability and forecast errors – assumed perfect knowledge of solar resource

4

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1 difference in energy value
1) Difference in Energy Value

15% PV No CSP

Example WECC-wide dispatch during a 4-day period in spring

Dispatch of CSP results in less high cost gas and more low cost fuels

10% PV 5% CSP

Difference in gas burn

Storage enables a relative fuel savings benefit over PV of about 0.5 cents/kWh at $4.50/mmBTU gas

5

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2 difference in capacity value of pv
2) Difference in Capacity Value of PV

Normal peak at ~4-5 pm

At 10% PV, peak is shifted to 8-9 pm. PV provides no further peak capacity benefits

At this point PV cannot reduce the need for generation capacity

CSP capacity value remains close to ~100% by shifting energy production to evening (and morning during spring/winter months)

  • Capacity value adder depends on market conditions - typical values of $40-$70/kW/year
  • Depending on CSP system design and market conditions, adds a CSP value of 0.7-2.0 cents/kWh

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slide7

3) PV Curtailment Due to Ramping Requirements

Ramp rate of conventional generator requirements increases

Ramp range of conventional generator requirements increases

Curtailment results from two main constraints – ramping requirements and minimum generation constraints. Curtailment results when existing plants to not have the flexibility to ramp

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curtailment due to minimum generation constraints
Curtailment Due to Minimum Generation Constraints

15% PV No CSP

  • Marginal curtailment rate of PV moving from 10% to 15% of generation was 5%
  • At SunShot goals (~6 cents/kWh) this increases effective PV cost by about 0.3 cents/kWh due to underused capacity

10% PV 5 % CSP

Extensive coal and nuclear cycling unlikely to occur in current system

  • PV curtailment would be reduced if grid flexibility were increased
  • CSP/TES provides an option to replace “baseload” capacity with more flexible generation

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pv curtailment at higher penetration
PV Curtailment at Higher Penetration

Estimates marginal curtailment as a function of PV penetration (without additional grid flexibility)

Without storage or load shifting, marginal LCOE of PV increases rapidly

“Multiplier” to base LCOE

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4 integration and reserve requirements
4) Integration and Reserve Requirements
  • Variability and uncertainty of solar resource requires changes in operation, typically some re-dispatch of system resources to maintain reliability

Very large ramping of conventional generators is required. This potentially means more use of fast responding but lower efficiency generators

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reserve requirements
Reserve Requirements
  • We have not yet analyzed the increased need for frequency regulation or forecast uncertainty for either PV or CSP
    • One previous PV study estimated costs of re-dispatch at 0.4-0.7 cents/kWh, but used limited data sets and is not reproducible
    • Estimates from wind integration studies are in the range of 0.2-0.4 cents/kWh
  • Storage enables operation at part load and ability to hold back energy during periods of high uncertainty or large reserve requirements

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slide12

Summary: Impacts of Storage at 10-15% Solar

  • With gas prices in the range of $4.50-$9.00 mmBTU, the estimated value of CSP with storage is an additional 1.6-4.0 cents/kWh relative to PV due to:
  • Energy shifting value: ~0.5-1.0 cents/kWh
  • Capacity Value ~0.7-2.0 cents/kWh
  • Reduced curtailment: Depends on PV cost. At 6 cents/kWh, corresponds to ~0.3 cents/kWh
  • Reserve/integration costs 0.1-0.7 cents/kWh

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csp as a pv enabling technology
CSP as a PV Enabling Technology
  • The ability of a the grid to accommodate PV is inherently limited by the increased variability and uncertainty of net load
  • As PV penetration increases other generators will need:
    • Short start-up times
    • Large ramp rates
    • Large turn-down ratios
    • Good part load efficiency

CSP with storage can provide these requirements

Historical performance of U.S. small gas steam plants which are a good proxy for CSP – typical operating range of 78% with only a 7% heat rate penalty at 50% load.

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slide14

CSP as a PV (and Wind) Enabling Technology

Dispatch in a “conventional” system

Relying on thermal generators and ignoring flexibility benefits of CSP limits amount of demand that can be met with variable generation

Additional PV will largely be curtailed due to minimum generation constraints

CSP energy is shifted to morning and evening, increasing the contribution of solar technologies, but not providing a direct benefit to PV or wind.

Total RE contribution is 35% on an energy basis (solar provides 23%). About 5% is curtailed.

14

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slide15

CSP as a PV (and Wind) Enabling Technology

Dispatch in a “CSP-flexible” system

Adding the flexibility of CSP enables a greater fraction of the load to be served by variable generation

Minimum generation constraint reduced

CSP energy is still shifted, but also used to provide quick-start reserve capacity during periods of high PV output.

CSP provides additional ramping capacity in the evening and morning.

Total RE contribution is increased to 46% (solar contribution at 29%) with no increase in curtailment.

15

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summary
Summary

As penetration of variable generation (solar, wind) increase, it is increasingly important to consider the interaction between these resources and the entire grid system

Dispatchable energy (e.g. CSP w/storage) has a higher value than non-dispatchable energy.

At low penetration of solar and wind this difference is small

At higher penetration (15% on an energy basis) this difference may increase by as much as 4 cents/kWh

Overall penetration of solar energy can be increased by the use of CSP with storage which provides grid flexibility

Allows for higher levels of PV penetration by providing the ramping rate and range needed to accommodate the variable output of PV systems

16

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questions
Questions?

References (Note that several of the results in this presentation have not yet been published).

Madaeni, S., R. Sioshansi, and P. Denholm, "How Thermal Energy Storage Enhances the Economic Viability of Concentrating Solar Power" accepted in Proceedings of the IEEE.

Madaeni, S. H., Sioshansi, R., Denholm, P. (2011) “Capacity Value of Concentrating Solar Power Plants” NREL Report No. TP-6A20-51253.

Brinkman, G.L., P. Denholm, E. Drury, R. Margolis, and M. Mowers. (2011) “Toward a Solar-Powered Grid - Operational Impacts of Solar Electricity Generation” IEEE Power and Energy 9, 24-32.

Denholm, P., and M. Hand. (2011) “Grid Flexibility and Storage Required to Achieve Very High Penetration of Variable Renewable Electricity” Energy Policy 39 1817-1830.

Sioshansi, R. and P. Denholm. (2010) “The Value of Concentrating Solar Power and Thermal Energy Storage.” IEEE Transactions on Sustainable Energy. 1 (3) 173-183.

Denholm, P., E. Ela, B. Kirby, and M. Milligan. (2010) “The Role of Energy Storage with Renewable Electricity Generation” NREL/TP-6A2-47187.

Denholm, P., R. M. Margolis and J. Milford. (2009) “Quantifying Avoided Fuel Use and Emissions from Photovoltaic Generation in the Western United States” Environmental Science and Technology. 43, 226-232.

Denholm, P., and R. M. Margolis. (2007) “Evaluating the Limits of Solar Photovoltaics (PV) in Electric Power Systems Utilizing Energy Storage and Other Enabling Technologies” Energy Policy. 35, 4424-4433.

Denholm, P., and R. M. Margolis. (2007) “Evaluating the Limits of Solar Photovoltaics (PV) in Traditional Electric Power Systems” Energy Policy. 35, 2852-2861.

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