Electric System Flexibility and Storage
Options for Increasing Electric System Flexibility to Accommodate Higher Levels of Variable Renewable Electricity
Increased electric system flexibility, needed to enable electricity supply-demand balance with high levels of renewable generation, can come from a portfolio of supply- and demand-side options, including flexible conventional generation, grid storage, curtailment of some renewable generation, new transmission, and more responsive loads. NREL's electric system flexibility studies investigate the role of various electric system flexibility options on large-scale deployment of renewable energy.
NREL's electric system flexibility analyses show that:
- Key factors in improving grid flexibility include (1) increasing the ramp range and rate of all generation sources to follow the variation in net load and (2) the ability to better match the supply of renewable resources with demand via increased spatial diversity, shiftable load, or energy storage.
- Overall system flexibility largely depends on the mix of generation technologies in the system. A system dominated by gas or hydro units will likely have a higher level of flexibility than a system dominated by coal or nuclear generators.
- Even with a completely flexible system, achieving very high levels of variable generation requires enabling technologies to address the fundamental mismatch of supply and demand.
Highlights of Recent Studies
Grid Flexibility and Storage Required to Achieve Very High Penetration of Variable Renewable Electricity.
This study investigated the electric power system changes required to incorporate high penetration of variable wind and solar electricity generation—mixes of wind, solar photovoltaic and concentrating solar power meet up to 80% of the electric demand—in Texas, U.S. (ERCOT). Key findings from this study include:
- A highly flexible system — with must-run baseload generators virtually eliminated — allows for penetrations of up to about 50% variable generation with curtailment rates of less than 10%.
- For penetration levels up to 80% of the system's electricity demand, keeping curtailments to less than 10% requires a combination of load shifting and storage equal to about one day of average demand.
To find out more about this study, please download:
- Grid Flexibility and Storage Required to Achieve Very High Penetration of Variable Renewable Electricity (2011).
Find out more about NREL's Electric System Flexibility Analysis Approach (Tools, Models and Data):
- Regional Energy Deployment System (ReEDS) is a long-term capacity-expansion model for the deployment of electric power generation technologies and transmission infrastructure throughout the contiguous United States.
- The Renewable Energy Flexibility (REFlex) model is a reduced form dispatch model that compares VG supply with demand and calculates the fraction of load potentially met by VG considering flexibility constraints and curtailment. REFlex also can dispatch a variety of system flexibility options to determine the basic feasibility of matching RE supply with demand.
Find out more about other published electric system flexibility analyses:
- Renewable Electricity Futures Study. Volume 2: Renewable Electricity Generation and Storage Technologies. (Volume 2 of 4) (2012).
- Milligan, M.; Ela, E.; Hein, J.; Schneider, T.; Brinkman, G.; Denholm, P. (2012). Renewable Electricity Futures Study. Volume 4: Bulk Electric Power Systems: Operations and Transmission Planning. (Volume 4 of 4). Golden, CO: National Renewable Energy Laboratory 72 pp.; NREL Report No. TP-6A20-52409-4.
- Market and Policy Barriers to Deployment of Energy Storage (2012).
For questions, contact Paul Denholm.