Ask the Expert: Your burning questions about frequency and inertia for renewables and Inverter-Based Resources

Meeting local and national CO2 emission goals and responding to social pressures related to global warming are primary factors driving decarbonization efforts in the energy industry across the world. At the same time, electricity demand is growing across the board. Together, decarbonization and increasing demand are creating a challenging environment for organizations tasked with ensuring grid resiliency.

Efficient and reliable grid management is becoming more complex as renewable and distributed energy resources are added to the power network. As the energy mix continues to shift, I’m often asked about inertia as it relates to renewables and Inverter-Based Resources (IBR). As you’re aware, solar and wind often use inverters to convert generated power into a form suitable for the grid. Given the growing interest in this topic, I thought I’d share the three most-asked questions I receive, and my responses.

 Q: Because wind turbines rotate, can they provide inertia or Fast Frequency Response (FFR)?

A: It is commonly understood that grid inertia is critical to maintaining grid stability. In traditional power systems, large rotating machines like turbines in coal or gas plants provide inertia, which helps stabilize the system against sudden changes in demand or supply. Wind turbine generators connect to the grid differently than traditional fossil power plants, but they can indeed be a part of system reliability. However, there are several considerations to keep in mind.

For instance, it is generally not possible to put “more fuel” through wind turbines to keep the speed constant during an event, as can be done with a steam turbine. Nonetheless, though not typically operating with synchronous generators, wind turbine generators do have a limited amount of kinetic energy stored in their large rotating blades. This, coupled with special logic, can often provide a fast response through their inverters to underfrequency conditions. Depending on the situation, this may be long enough to carry through the excursion event.

Q: What about PV/BESS inverters? How can they support the grid?

A: You’ll recall there are two types of inverters: “grid-following” and “grid-forming.” The key to inverter-based grid inertia in the future is through grid-forming inverters, as they are able to autonomously establish and maintain grid voltage and frequency. In some ways, grid-forming inverters are actually better than rotating inertia, as they provide faster response. However, the power must be available to allow grid-forming inverters to deliver the necessary response. This is easier with battery storage than with photovoltaic or wind, as those assets are likely already operating at maximum capacity.

Q: What are the latest standards for Inverter-Based Resources (IBRs)?

A; There is a lot of activity in the industry related to IBR reliability standards. Because IBRs are becoming more integral to our transmission system, it is critical that inverters offer excellent quality and functionality. Unfortunately, there have been issues related to inconsistent inverter design and poor reliability. In response, in October 2023, FERC directed NERC to draft standards that address performance gaps in IBRs, in turn promoting the more reliable integration of IBRs into the transmission system. This standard is IEEE Standard 2800.

The science behind maintaining a reliable grid is complex and being made more so by the new and differing resource types. However, it’s all achievable with planning. Ireland provides a good example of this. At an average of 45% wind power, there are days where wind supplies two-thirds of the island’s generation—at a stable frequency.

If I’ve piqued your interest, and you’re looking for additional resources on this topic, there are multiple sources online, including this guide to Inertia and the Power Grid from NREL and this Frequency Response Initiative Report from NERC.

Do you have a question that wasn’t addressed here? Reach out to me on LinkedIn!


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