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Modeling for System Integration Studies

Kirsten D. Orwig

Solar Resource and 

Forecasting Workshop

June 21, 2011

NREL/PR-5500-52110

Photo by Warren Gretz, 

NREL/PIX 00001

Photo from Courtesy Acciona

Energy Corp., NREL/PIX 15996 

Photo by Steve Wilcox, NRLE/PIX 15550 
National Renewable Energy Laboratory Innovation for Our Energy Future

Overview

• Renewable energy integration studies evaluate the 

operational impacts of variable generation.

• Transmission planning studies investigate where new 

transmission is needed to transfer energy from 

generation sources to load centers.

• Both use time-synchronized wind and solar energy 

production and load as inputs.

• Both examine high renewable energy penetration 

scenarios in the future. 
National Renewable Energy Laboratory Innovation for Our Energy Future

WWSIS

Western Wind and Solar 

Integration Study

What are the technical barriers to achieving 

20% wind energy penetration by 2030?

• Does geographic diversity of renewable 

energy resource help mitigate variability?

• How do local resources compare to out-ofstate resources?

• Can balancing area cooperation help 

mitigate variability?

• What is the role and value of energy 

storage?

• Should reserve requirements be modified?

• What is the benefit of forecasting?

• How can hydropower help with integration 

of renewables?

Wind and Solar Energy Penetrations

Case Name In Footprint Rest of WECC

Name Wind

+ Solar

Wind Solar Wind Solar

Pre-selected

case

3% 3% * 2% *

10% Case 11% 10% 1% 10% 1%

20% Case 23% 20% 3% 10% 1%

20/20% Case 23% 20% 3% 20% 3%

30% Case 35% 30% 5% 20% 3%

*Existing solar embedded in load
National Renewable Energy Laboratory Innovation for Our Energy Future

WWSIS Solar Inputs

• Satellite cloud cover model data (SUNY) used to represent 

irradiance over the US at a 10-km, hourly resolution;

• PV was modeled in 100-MW blocks as distributed 

generation on rooftops;

• CSP was modeled as 100-MW blocks of parabolic trough 

plants with six hours of thermal storage;

• 10 minute data derived from hourly production;

• Day-ahead hourly solar forecasts were also developed. 
National Renewable Energy Laboratory Innovation for Our Energy Future

WWSIS Phase 2

Penetration by 

Energy

High Wind Intermediate High Solar

11% WECC TEPPC 2020

8% wind

3% solar

22%

33% 25% wind

8% solar

16.5% wind

16.5% solar

8% wind

25% solar

• Solar consists of 40% CSP w/6-hour storage and 60% PV

• 40% of PV is rooftop for each scenario

*note that sensitivity analyses may include runs of various penetrations of solar with 

various PV/CSP ratios
National Renewable Energy Laboratory Innovation for Our Energy Future

High Solar ~(8% wind, 15% PV, 10% CSP)
National Renewable Energy Laboratory Innovation for Our Energy Future

Solar “Actuals” Dataset

• Utility-scale PV:

• Use existing WECC PV dataset which has 50-MW plants on 

10-km grid at 1-minute, 10-minute, and hourly resolution;

• Filter function under development to model PV plants up to 

500 MW.

• Distributed PV:

• Use rooftop PV data from WWSIS, Phase 1;

• Distribute generation identical to load in each load bubble.

• CSP:

• Rerun WECC CSP dataset using a variety of plant sizes up to 

200 MW;

• Revise sites as needed.
National Renewable Energy Laboratory Innovation for Our Energy Future

Topics

• Algorithm for downscaling hourly irradiance data;

• Modeling various time scales of interest;

• Using NWP for modeling PV production;

• Solar input data needed from an electrical 

perspective;

• PV forecast data requirements.