Why Increase Power System Flexibility?

Power system flexibility refers to a grid’s ability to balance supply and demand across all locations, over both short and long timeframes. Power systems have always needed flexibility, but it is increasingly important as more sources of variable generation, like wind and solar, are used.

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Main Points

• System operators use flexibility measures to keep supply and demand in near perfect balance at all times.
• More flexibility is essential as power systems integrate higher shares of renewables, but system operators have many flexibility options to choose from.
• Different flexibility options address variability at different timescales, from less than a second (frequency or voltage support) to decades (long-term planning of generators and transmission lines).
• Flexibility options vary in cost, institutional capacity and the time needed to implement.
• Increasing system flexibility can reduce overall system costs and improve the investment climate for new generation.

First, Read This

Power systems have always needed some flexibility, but increased flexibility is essential to achieve higher shares of variable renewable energy (VRE), like wind and solar.

Before solar and wind power became widely deployed worldwide, power systems were designed with flexibility attributes that would allow them to balance varying demand and deal with uncertainty related to unexpected losses of system elements. In conventional power systems (i. e., systems with low or no VRE shares) supply-side assets traditionally have been used as the main source of flexibility. Thermal generators with advanced cycling capabilities (e. g., open-cycle gas turbines), flexible renewables such as hydropower, and pumped hydro storage traditionally have been used to balance demand fluctuations and provide operational reserves.

Over the last five years the impact of solar and wind variability has begun to be felt in a number of power systems where aggressive VRE targets were in place. Even before this, studying the potential impacts of VRE integration on system operations had become a hot topic of research in institutions around the world. Multiple studies showed that additional sources of flexibility would be needed to effectively integrate high VRE shares.

Since then solutions of varying complexity, time scale, level of effectiveness and cost have been implemented successfully and have facilitated the integration of high shares of VRE in large interconnected systems (as in the case of Denmark), in gigawatt-scale isolated power systems (as in Ireland) and in small-island systems (such as King Island in Australia).

Text excerpt from pages 12-13 of IRENA: Power System Flexibility for the Energy Transition – Part 1

Now, See This Figure

There are many ways to increase power system flexibility by using existing assets and approaches, or by adopting new ones.

See: Figure 3 on page 12 of Power System Flexibility for the Energy Transition – Part 1 by IRENA.

And Read This

As power systems evolve to incorporate more renewable energy and responsive demand, regulators and system operators are recognizing that flexibility across all elements of power systems must be addressed by ensuring:

• Flexible generation: power plants that can ramp up and down quickly and efficiently and run at low output levels (i.e., deep turn-downs)
• Flexible transmission: transmission networks with limited bottlenecks and sufficient capacity to access a broad range of balancing resources, including sharing between neighboring power systems, and with smart network technologies that better optimize transmission usage
• Flexible demand-side resources: incorporation of smart grids to enable demand response, storage, responsive distributed generation, and other means for customers to respond to market signals or direct load control
• Flexible system operations: practices that help extract flexibility out of the existing physical system, such as making decisions closer to real time and more frequently, improved use of wind and solar forecasting and better collaboration with neighbors

Text excerpt from pages 2-3 of NREL: Flexibility in 21st Century Power Systems

Next, See This Figure

VRE has different impacts on different time scales, so different flexibility solutions are needed to address them.

See: Figure 8 on page 24 of Power System Flexibility for the Energy Transition by IRENA.

And This Figure

Some flexibility solutions are more relevant as shares of VRE increase. But in general, operational improvements are typically the least costly, followed by flexible generation and demand response. Every power system is unique, though, so comparing the costs of flexibility measures can be tricky.

See: Figure 9 on page 25 of Power System Flexibility for the Energy Transition by IRENA.

Finally, Read This

Without sufficient flexibility, system operators may need to frequently curtail (decrease the output of) wind and solar generation. Although low levels of curtailment (e.g., less than 3%) may be a cost-effective source of flexibility, significant amounts of curtailment can degrade project revenues and contract values, impact investor confidence in renewable energy revenues, and make it more difficult to meet emissions targets.

Increasing system flexibility reduces the need for curtailment of renewable resources, thereby reducing overall system costs and consumer prices, as well as improving the investment climate for new generation.

Text excerpt from pages 3-4 of 21CPP: Flexibility in 21st Century Power Systems

Suggested Actions & Next Steps

• Read the section on Flexibility in Power Systems from Power System Flexibility for the Energy Transition – Part 1, by IRENA.
• Think about how many of the flexibility measures mentioned in this section are in use in your grid today.