Renewable energy is a solution the world needs. However, it is also creating challenges for the existing electrical grid due to its lack of rotational inertia. This can make the system less stable. In addition, the grid becomes more vulnerable if a major power plant suddenly goes offline. In such situations, understanding uninterruptible power supply hours becomes even more important for maintaining backup reliability. However, this dynamic can change with the use of grid-forming inverters. Here’s how.
Key Takeaways
- Renewable energy sources lack rotational inertia, making power grids unstable when a large plant goes offline.
- Grid-forming inverters are essential because they independently create and regulate voltage and frequency, enhancing grid reliability.
- In practical scenarios, such as on Kauai, grid-forming inverters successfully maintained power during outages, demonstrating their effectiveness.
- As renewable energy increases, traditional grid-tied inverters become liabilities, underscoring the need for grid-forming inverters in future power grids.
- High-frequency PCBs are crucial for building reliable grid-forming inverters in modern power grids.
Table of Contents
What Is Rotational Inertia?
Traditional power plants (hydro, coal, natural gas, diesel, or nuclear) rotate turbines or drive engines directly with energy from the fuel or via steam. This creates a rotational force with inertial energy that is synchronized in all power plants connected to the grid. The purpose is to maintain a stable 60 Hz frequency (in the Americas and parts of Asia). For the rest of the world, it is 50 Hz.
The rotational inertia in these turbines and engines helps maintain a stable frequency and provides a power-generation buffer to counter sudden changes in demand or supply. This is handy when issues occur at a power plant, causing it to go offline. If this happens, the grid’s frequency will start to drop. However, the rotational inertia keeps it somewhat stable. As a result, the grid gets time to react by rebalancing. This can be achieved through increasing generation from the online plants, load shedding, or activating reserves.
Current renewable energy sources, such as solar and wind, don’t have rotational inertia. You might think wind energy has it because the turbines rotate, but this isn’t true. Turbines rotate, that is true. But they aren’t connected directly to the grid because these turbines don’t rotate at the grid’s frequency. They can be faster or slower depending on the wind speed. So the AC output from these turbines is first converted to DC using rectifiers, then back to AC using inverters. This eliminates rotational inertia.
Some solutions to address the lack of rotational inertia include synchronous condensers (via mechanical rotation), BESS (Battery Energy Storage Systems), pumped hydro storage, and grid-forming inverters. Grid-forming inverters are perhaps the cheapest option. This makes them the most viable.
What Are Grid-Forming Inverters?
Grid-forming inverters are DC-to-AC converters that create and regulate their own voltage and frequency, either independently or in coordination with other sources. This effectively makes them virtual synchronous generators. Wind and solar have traditionally used grid-tied/grid-following inverters. These inverters rely on the grid’s frequency, voltage, and phase to inject power into it.
You can already see the problem here. If a power plant goes offline and there’s no neighboring grid to import power from, the frequency will drop, and grid-tied inverters will follow this. Since there’s no rotational inertia, the drop occurs instantaneously. This triggers a cascading shutdown of the connected power plants to prevent damage. Furthermore, grid-following inverters don’t create and regulate their own frequency and voltage, so they also cannot be used to restart the grid (black start). As a result, this creates a significant problem when trying to restore power.
How Grid-Forming Inverters Make Grids Powered By Renewable Energy More Reliable
The biggest advantage of grid-forming inverters is that they generate and regulate voltage and frequency, either independently or in coordination with other sources. So if a power plant goes offline, these inverters can help maintain the required frequency. This happens before the grid imports power or sheds some load to maintain supply-demand balance. This is better than the entire grid going down. That means better resilience.
Such an installation came in handy on the Hawaiian island of Kauai on 2nd April 2023, which relied on 70% renewable energy per year from solar. But on that date, solar output had dropped, and the sole 26MW oil-fired turbine was running near peak capacity to compensate for the lack of sunshine. At that time, this generator was providing 60% of the island’s power requirements. The rest came from small-scale generators and utility-scale solar and battery-storage systems. This generator went offline, but something interesting happened. The lights remained on.
On that date, Kauai had a battery storage system with over 150 megawatt-hours of capacity. This would’ve been worthless if this energy had been converted to AC using grid-tied inverters. But the island’s power operator, Kauai Island Utility Cooperative, had invested in grid-forming inverters. These inverters tapped into the stored battery power to power, control, and stabilize the grid. This gave the utility company time to fix the turbine or shed load where the power requirement wasn’t critical.
Why Grid-Forming Inverters Are Necessary
As the proportion of renewable energy in the grid (particularly wind and solar) increases to over 60%/70%, grid-tied inverters become more liabilities than assets. As the world races to achieve net-zero carbon emissions by 2050, grid-forming inverters are critical to delivering stable AC power across the globe.
Conclusion
As you can see, grid-forming inverters are critical in modern power grids, and they should be reliably made using high-frequency PCBs to ensure reliability. So, whether you want to explore this field or are already in it, it is important to work with a reputable PCB manufacturer and assembler to handle hardware production for you.
WellPCB has been fabricating PCBs for close to two decades and has amassed the expertise, equipment, and experience to handle complex electronics projects. The company assembles such critical infrastructure using IPC Class 3 standards to ensure maximum reliability and performance. Besides that, they keep costs as reasonable as possible. Reach out to them to learn more about how you can partner in developing the electrical grid for the future.
