How to tackle the power storage problem

Posted: October 4, 2024

One of Britain’s biggest batteries sits deep inside a mountain on the northern shore of Loch Awe, a scenic lake in western Scotland and one of the wettest areas in Europe. That suits this particular battery just fine: Cruachan, known as ‘The Hollow Mountain’, is a pumped hydropower plant.

Although they’re not always built underground, these power stations all work the same way. Two reservoirs, holding billions of gallons of water, sit at different elevations and are connected by a tunnel. When power is scarce, and prices for it are consequently high, water is released at the top and passes through a turbine that generates electricity. When power supply outstrips demand and prices drop, electricity is used to pump the water back into the pool at the top.

Why hydropower is still making waves

Pumped hydro stations were first built in the 1890s in Italy and Switzerland. Today, they provide more than 90% of the world’s long-duration energy storage. Although their growth has slowed in some parts of the world, including the US, they still find favor with utilities. Drax, the power company that owns Cruachan, wants to more than double the plant’s capacity by carving a new cavern into the mountain. It would require excavating two million tonnes of rock and soil and, once finished, could fit Big Ben lying on its side.

Globally, pumped hydropower capacity grew by 6.5 gigawatts to 179 gigawatts last year, according to the International Hydropower Association, and there are more than 100 projects planned or in development. China just completed the world’s largest pumped storage station after an 11-year construction period. Spanish utility Iberdrola is spending more than €1.5 billion to build three giant dams in northern Portugal that will raise the country’s pumped storage capacity by 30%.

So why is this century-old technology still so popular?

Because other renewable energy sources are inherently intermittent, batteries are a crucial element of the energy transition. To keep networks in balance and avoid blackouts, grid operators are constantly required to match supply and demand on a second-by-second basis. The more temperamental wind and solar you add to the equation, the harder this balancing act becomes.

Pumped hydro stations are a tried-and-tested solution to this problem, absorbing excess power when supply outstrips demand and jumping in when the sun doesn’t shine and the wind doesn’t blow. They also provide other crucial grid services, such as black start—when the power system needs to be brought back online after a blackout—since they can get going quickly and don’t require  external energy. In the U.S., for example, hydropower plants account for 40% of the units maintained and tested for black start despite only making up 10% of generation.

“Pumped hydroelectric power stations [are] the Swiss Army knives of the energy industry,” says Peter Apel, who manages hydropower plants for Swedish utility Vattenfall.

Read about how Vattenfall uses industrial software to help prevent catestrophic failuers with real-time condition-based maintenance

Of course, hydropower isn’t the only solution. In recent years, utilities have been installing scores of shipping containers filled with large lithium-ion batteries—similar to those used in electric cars—from southern Texas to the shores of Saudi Arabia’s Red Sea. These batteries can quickly store and dispatch energy to balance the grid and even help shave off peaks in electricity use, for example during periods of high demand from industrial plants.

More than 200 grid-scale battery projects started operating in the first quarter of this year alone, and there are now at least 5,000 installations across the world. Billions of dollars in investment are flowing into batteries each year.

Molten salt and liquid air energy storage

In recent years, companies have started to look at entirely different ways to tackle storage, too—specifically, by considering heat. After all, electricity is not the only form of energy. In fact, heating is the world’s largest energy end use and industrial processes consume more than half of it.

Enter Kyoto Group, a Norwegian company that has developed a process to use excess power to heat tanks of molten salt to up to 500 degrees Celsius, with the energy later released via a steam generator. The start-up has drawn investment from Iberdrola and deliberately markets its product to industries from paper and pulp to petrochemicals, food and steel production. Salt tanks like these have a few advantages over electric batteries: for one, they can be re-charged thousands of times and last for up to 40 years—much longer than many other storage options.

“With all the excitement about battery technology for electric vehicles, people have forgotten about the massive demand for heat for industries that can’t be produced from electrical batteries,” Kyoto’s chief technology officer, Bjarke Buchbjerg, told the Guardian. “Industrial heat is a big deal—we can’t afford to ignore it.”

Others have tackled the same issue: EnergyNest, another Norwegian company, offers industrial customers an on-site solution that funnels high-pressure steam into a hive of carbon steel pipes. They contain the company’s specially formulated thermal concrete, which it says can store heat for several hours with minimal loss.

Then there’s liquid air energy storage, which does exactly what it says: liquifying air by compressing and cooling it. UK-based Highview Power, one of the companies exploring liquified air, first tested the technology for two years at a landfill near Manchester. It now wants to work with the world’s largest offshore wind developer, Ørsted, to use it to reduce curtailment at the company’s power plants.

There may be a place for all of these technologies: they provide storage for varying lengths of time, and often target different applications.

The future of energy storage: Stacking LEGOs

When it comes to innovation in storage, EnergyVault, another start-up based in Switzerland, has one eye firmly on the past. It was the country’s oldest energy storage facilities, its pumped hydro plants, that inspired co-founder Bill Gross to pursue his own particular vision for solving the power storage puzzle.

“I always wanted to figure out a way to make what I was thinking was an artificial dam. How can we take the properties of a dam, which are so great, but build it wherever we want?” he told Wired in 2021.

Back then, the company had just built its first commercial demonstration unit: a 75-meter tall construction crane with three arms to lift and deposit 35-tonne concrete blocks, like a spider stacking LEGO bricks. The principle borrowed heavily from pumped hydro: like the pump sending water uphill, the crane would kick into action and lift blocks when electricity was plenty. As each block dropped, the motor would start spinning in reverse and generate electricity.

The idea, then and now, was to cut out the worst parts of hydropower: the long construction time, the need for highly specific natural environments, the impact on ecosystems. It was cheap, too, solving another problem hounding many other energy storage solutions.

Fast forward three years and the company now has a whole suite of gravity-based storage solutions. Its first commercial plant went online earlier this year outside Shanghai. The concept has evolved somewhat: it now features several cranes stacking weights into a sprawling concrete scaffold.

As it turns out, the future of energy storage might just look like a half-finished parking garage.