More Than Just Storage: Long Duration Technology for the Modern Grid

The main conversation about the future of the world’s power grids focuses on the basics of supply and demand. It’s understandable: as variable renewable sources account for a growing portion of energy generation and as demand skyrockets and becomes increasingly dynamic, this once predictable balancing act has morphed into a major challenge for grid operators.

But there’s more to the grid than energy generation and consumption. To keep the power running smoothly as more renewable generation comes online, we need other stabilizing and support services like rotational mass and the ability to restart quickly after a disruption.

As the energy transition continues, it’s vital to keep these ancillary functions in the picture. We can see the need for these ancillary functions even more clearly in the aftermath of the recent power outage in Spain and Portugal, when the Iberian power system lost around 15 GW of generation in just five seconds. The good news is that some of the most promising long duration energy storage systems—including Hydrostor’s solution—do just that.

So let’s get technical.

1. Inertia & frequency control

How it works:

Over the last century, societies around the world have built their grids following a few foundational principles of physics like inertia and frequency control to ensure everyone can consistently access stable and reliable electricity on demand. Maintaining a stable AC grid frequency is a fundamental part of how utility-scale power systems remain reliable. As we add new energy resources to our grids like solar and wind, we need to continue to meet these same technical standards to ensure that we maintain the ability to control and maintain grid frequency.

One of the core rules is that our grids operate at a given frequency range which is tied to the rotational speed of large synchronous generators in power plants. Whether it’s gas power plants, coal-fired power plants, or nuclear reactors, we’ve historically generated our electricity through spinning masses, like heavy spinning turbines and generators, to maintain a stable grid frequency. In North America, the rate at which these electricity-generating masses spin has been stable and aligned with the grid’s frequency of 60 Hertz, and in Europe aligned at 50 Hertz.

Why it matters:

Grids have momentum and as different generators and loads push and pull power from a grid, the frequency will fluctuate and become slightly off 60 Hertz. As loads increase and exceed supply, generators slow down slightly and frequency drops; as generation increases and exceeds demand, generators speed up slightly and frequency rises. To remedy these fluctuations, our grids need stabilizing forces to keep their frequencies consistent.

To understand why our grids need inertia and frequency control services, it’s important to understand in real world terms what would happen without them. If a grid deviates too far off its operating frequency, there can be major consequences. If grid frequency drops too much, motors and other loads may underperform or stall. If grid frequency increases too much, sensitive equipment and electronics risk damage and failure. In either case, too much grid instability can cause synchronous machines to fall out of sync, protective relays will trip equipment offline, and there is potential for cascading failures leading to widespread blackouts.

But the importance and urgency of frequency control and inertia go beyond broken electronics and black outs. As the energy transition takes place, grids around the world continue to move away from traditional forms of power generation like thermal power plants (and their spinning masses) to solar, wind, and other intermittent sources, most of which do not provide frequency regulation to grids. In early reports, it seems like this was likely a key cause of the recent failure of the Iberian power system.

Emergent Long Duration Energy Storage technologies like Hydrostor’s Advanced Compressed Air Energy Storage (A-CAES) can provide this needed stabilizing force. In fact, Hydrostor’s A-CAES technology uses a spinning mass that generates power similar to a gas or steam turbine, providing frequency control and inertia services to the grid during discharge operations.

A-CAES can also provide these same stabilizing services to grids during standby operations if they’re designed into the system. Grids use a piece of technology called a synchronous condenser as a spinning mass to provide inertia and frequency control services. Hydrostor can install a clutch in between its turbine and generator, operating like a synchronous condenser and providing the same benefits to any grid, even when its stored energy isn’t needed.

Other forms of energy storage like batteries do not offer the foundational benefits of inertia and frequency control, which become all the more urgent as we transition to more renewable sources.

2. Voltage support

How it works:

Similar to inertia and frequency control, grids operate at a fixed voltage. A grid’s energy sources impact what that fixed voltage is. This also appears to be a contributing factor to Spain and Portugal’s recent outage – excessive voltage causing a reactive power collapse, amplifying the blackout.

Why it’s important:

Some types of Long Duration Energy Storage can provide voltage support, and Hydrostor’s A-CAES technology can provide voltage support during synchronous condenser operations. Without voltage support, grids don’t work and chaos ensues, as we saw recently in Spain and Portugal and even parts of the south of France, when millions of people lost power.

3. Black start

How it works:

As major power outages become more frequent with extreme weather, grid operators need assets in place that are stable relative to the grid and load size in order to quickly and safely restart power. This process is known as black start. Similar to inertia and frequency control, certain emergent LDES technologies can provide this additional technical benefit. For example, Hydrostor’s A-CAES technology can be designed to provide black start capabilities to grids of a certain size, and A-CAES may have helped to re-start power more quickly after the recent outage on the Iberian peninsula.

Why it’s important:

Consider Hydrostor’s Silver City A-CAES project in Broken Hill, New South Wales. At 200 MW, Silver City will be able to provide eight hours of energy storage on a full charge. While Silver City is embracing renewable energy sources, it is in a remote location at the end of a transmission line and faces the same cost prohibitions of adding new transmission lines.

The Silver City Energy Storage Centre will provide a significant amount of energy generation to the grid, and it can also deliver a black start for the grid should it ever face an outage. Other communities with few transmission lines but plenty of renewable power can add black start capabilities to their grids with LDES technologies like A-CAES in addition to their much-needed energy storage benefits.

This is only the beginning for how Long Duration Energy Storage technologies provide grid benefits beyond energy storage. Check out our Part 2 post that delves into the other vital grid benefits of Long Duration Energy Storage, including spinning and non-spinning reserve, regulation up and regulation down, and transmission deferral.

Click HERE to read Part Two of our “More Than Just Storage” Blog Series