Electric System Flexibility and Storage
NREL's electric system flexibility studies investigate the role of electric system flexibility options on the large-scale deployment of renewable energy.
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 renewable generation, new transmission, and more responsive loads. 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.
The Potential for Energy Storage to Provide Peaking Capacity in California under Increased Penetration of Solar Photovoltaics
The Potential for Energy Storage to Provide Peaking Capacity in California under Increased Penetration of Solar Photovoltaics investigated the potential for replacing conventional peaking capacity in California with energy storage, including analysis of the changing technical potential with increased storage deployment and the effect of deploying solar photovoltaics (PV). NREL examined nine years of historic load data, a range of storage durations (2–8 hours), and a range of PV penetration levels (0%–30%). Key findings from this study include:
- PV affects the technical potential of energy storage to meet peak demand in different ways, depending on how much PV is deployed.
- Under conservative assumptions, when PV penetration in California is lower than about 11%, the potential of 4-hour storage is lower than it would be with zero PV, because that amount of PV flattens the net demand shape.
- However, beyond about 11% PV penetration, PV creates a “peakier” shape that increases the potential of 4-hour storage.
The analysis provides timely information to California’s nation-leading energy storage and PV deployment efforts, while increasing the knowledge base available to system planners in all states and regions that might consider deploying substantial amounts of storage, PV, or both.
Grid Flexibility and Storage Required To Achieve Very High Penetration of Variable Renewable Electricity
Grid Flexibility and Storage Required To Achieve Very High Penetration of Variable Renewable Electricity investigated the electric power system changes required to incorporate high penetrations of variable wind and solar electricity generation—mixes of wind, solar photovoltaic, and concentrating solar power to meet up to 80% of the electric demand—in Texas. 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.
Data and Tools
- 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.
- Renewable Electricity Futures Study. Volume 2: Renewable Electricity Generation and Storage Technologies, NREL Technical Report (2012)
- Renewable Electricity Futures Study. Volume 4: Bulk Electric Power Systems: Operations and Transmission Planning, NREL Technical Report (2012)
- "Market and Policy Barriers to Deployment of Energy Storage," Economics of Energy and Environmental Policy (2012).