On the Road to Increased Transmission: Flexible Alternating Current Transmission Systems
How Flexible Alternating Current Transmission Systems Can Reduce Transmission Line Traffic Jams
The current U.S. transmission system will need to be upgraded and expanded to make it possible to carry larger amounts of clean energy across longer distances. In a short video, NREL explains four options that can help do just that. This four-part series of articles dives deeper into each of those possibilities. This article discusses flexible alternating current transmission systems, or FACTS.
A Navigation App for Electric Highways
Just like busy roads, the U.S. transmission system can experience congestion, leading to inefficient travel of electricity.
"Imagine some small transmission lines run between two cities and are always congested, like a small road with a never-ending traffic jam," said Paul Denholm, a senior research fellow at the National Renewable Energy Laboratory (NREL).
In this case, reducing the congestion may require more than just increasing the transmission capacity of the existing lines. It could involve adding additional, larger "highways" of electricity between the two cities.
But even if a larger set of transmission lines is added, the electricity will not automatically take the new, less-congested route. In scenarios like this, the inefficiency in transmission is not caused by individual transmission lines but rather the physics of the transmission network as a whole.
"One of the peculiarities of our current transmission system is we can't actually control the flow of electricity across the various transmission lines," Denholm said. "Because of the physics behind conventional alternating current transmission, which is what the power grid primarily operates on, electricity will not naturally flow to more efficient routes, even if they are readily available. And that's where FACTS devices come in."
FACTS devices provide a way to steer electricity to less-congested transmission lines, like a navigation app on your phone. But unlike navigation apps, FACTS technology is not just a software—it requires physically changing the electrical characteristics of a transmission line by using new components. The new electrical characteristics resulting from FACTS devices make it harder for power to accidentally navigate to small roads with "traffic jams" and easier for power to navigate to fast-moving "highways."
"We can essentially use the laws of physics to our advantage by changing the way electricity flows on the system, steering electricity onto underutilized lines," Denholm said. "This can be a very cost-effective way to increase the capacity of our current transmission system."
Pinpointing Where To Deploy FACTS
FACTS, which is well-proven technology, can be applied to both existing and new transmission systems. But one key challenge is understanding what locations are most suitable for it.
"There are likely many, many places where FACTS could really help increase the capacity of the system, but that's not the case everywhere," Denholm said.
More studies are needed to understand what parts of the U.S. power grid will benefit most from installing FACTS devices, which can ultimately help utilities manage their power grids more effectively by reducing energy losses and improving system reliability.
The next article of this four-part series will discuss increasing the voltage of high-voltage alternating current lines. In the meantime, be sure to watch NREL's short video summarizing four ways to increase transmission and subscribe to NREL's energy analysis emails to receive updates.