Achieving 50 percent renewable electricity in California:

The role of non-fossil flexibility in cleaning the electricity grid

Jimmy Nelson, Ph.D.Energy Modeler

jnelson@ucsusa.org

Avoid coincident gas generation and renewable

curtailment

2

The UCS “Duck Curve”

3Fact Sheet: Renewables and Reliability, Union of Concerned Scientists, March 2015.Available at: http://www.ucsusa.org/sites/default/files/attach/2015/03/california-renewables-and-reliability.pdf

Very difficult to meet long-term climate goals if gas is

online when renewables are available

Williams, J.H., et al., 2012. The technology path to deep greenhouse gas emissions cuts by 2050: the pivotal role of electricity.Science 335, 2012, 53-59. 4

Modeling

5

Acknowledgements

• Ryan Jones, Arne Olson, and Energy and Environmental Economics (E3)• Hourly renewable, reserve, outage,

and demand data• Production cost model framework• Discussions

• UCS for support, fellowship, and discussions

• NREL for discussions

• Energy Exemplar / PLEXOS for software support

• Report reviewers6

7

• RPS target: 33%, 40%, 50%

• Geographic scope: the CAISO footprint• ~80% of California

• Timeframe: 2024• Economy-wide decarbonization might necessitate very quick

renewable deployment• Results relevant to 2030 50% RPS policy discussion

• Modeling tool: PLEXOS production cost model• Focuses on electricity operations• NOT an investment model

Scope of analysis

A diverse portfolio of renewables is simulated

• Heavily weighted towards in-state renewables• Behind-the-meter photovoltaics (PV) don’t directly count

towards RPS 8

33% RPS 40% RPS 50% RPS0

20000

40000

60000

80000

100000

120000PV Behind-the-MeterPV Large Out-of-StatePV Large In-StateSolar ThermalWind Out-of-StateWind In-StateSmall HydroelectricBiogasBiomassGeothermalEl

ectr

icity

Pro

ducti

on (T

Wh/

Yr)

As the RPS is increased…[without additional operational flexibility]

GHG Emissions

9

33 40 500

10

20

30

40

50

60

RPS Target (%)

CO2 E

mis

sion

s (M

MTC

O2/

Yr)

Note: production costs do not include capital and maintenance costs,and are therefore only one important part of the total electricity cost

Production Costs

33 40 5001234567

RPS Target (%)

Prod

uctio

n Co

sts

($Bn

/Yr)

Renewable Curtailment

33 40 500

1

2

3

4

5

64.8

RPS Target (%)

% C

urta

ilmen

t

Reliability requirements cause renewable curtailment

10

0

1

2

3

4

5

64.8

1.51.0C

urt

ailm

en

t (%

)

50% RPS Base

Essential reliability services needed in grid operations[But some reliability requirements cause curtailment at a 50% RPS]

Load Followingand Regulation

DOWN

Increasing operational flexibilityat a 50% RPS:

What works and what doesn’t

12

13

Add non-generation flexibility:

StorageAdvanced Demand Response

Exports

Increase natural gas power plant fleet flexibility

Operate renewables more flexibly

14

Operating renewables flexibly is particularly effective

0123456

Hourly Curtailment

Sub-Hourly Curtailment

Curt

ailm

ent

(%)

Curtailment: nimble is much better than blocky

4.8

2.7

50% RPS Base

• More analysis needed on cost tradeoffs• Downward reserves from non-generation flexibility are valuable

Non-generation flexibility reducescurtailment and GHG emissions

Additional Non-Generation Flexibility (GW)= storage + advanced demand response + exports

15

0 3 6 90

1

2

3

4

5

6

0

10

20

30

40

5041.1 38.8 37.6 37.0

% C

urta

ilmen

t

CO2 E

mis

sion

s (M

MTC

O2/

Yr)

Gas power plant flexibility has important limits

16

Gas fleet changes in the Flexible Gas run:• Double ramp rate• Half minimum

power level• 1 hour start and

stop times• 2 hour minimum

uptime and downtime

• Providing some reliability services with gas requires electricity production, which “crowds out” renewables

Default Gas Flex-

ibility

Double Ramp Rate

Combined Cycle Half Minimum

Power Level

Flexible Gas

0

1

2

3

4

5

64.8 4.7

3.2 3.0

% C

urta

ilmen

t

• Duck Curve: “belly” is much more important than the “neck”

Non-Fossil Solutions:• Renewables can provide

reserves• 1 GW additional electricity

storage• 1 GW advanced demand

response• 1 GW net exports allowed

Operational flexibility:Non-fossil can go further than gas

17

Flexible Gas

50% RPS Non-Fossil Solutions

01020304050

39.0 41.1 37.4

CO2

Emis

sion

s (M

MTC

O2

/Yr)

Flexible Gas

50% RPS Non-Fossil Solutions

0123456

3.0

4.8

1.1

% C

urta

ilmen

t

50% RPS Base

50% RPS Base

18

33% RPS 50% RPS

Renewablecurtailment

Renewabledispatchability

• Increasing RPS from 33% to 50% reduces electricity GHG emissions by 22 - 27%

• Coincident gas generation and renewable curtailment should be avoided

• Reliability requirements cause renewable curtailment

• Operating renewables flexibly is particularly effective

• Non-generation flexibility can reduce GHG emissions

• Natural gas power plant flexibility has important limits

19

Key findings