Over just seven years, the United Kingdom has quadrupled its production of solar, wind and other renewable energy sources to account for nearly 30 percent of all electricity generated in Britain. This is an impressive feat, but with it comes with another challenge: balancing the grid’s newly diversified supply of electricity with consumers’ demand.
The grid works like a delicately balanced machine in which energy supply has to be equal to demand. While wind towers and solar panels undoubtedly produce massive amounts of energy, they depend on fickle weather patterns — wind doesn’t always blow; nor does the sun predictably shine, particularly in England. Syncing the whims of Mother Nature with our daily patterns is nearly impossible, and power cranked out by a wind tower in the middle of the night doesn’t do sleeping customers any good. But what if power companies could store intermittent renewable energy for when it is needed?
Engineers at the energy storage company Highview Power have spent the last few years trying to solve the riddle, and this spring they unveiled an innovative solution. In early June, Highview Power launched the world’s first grid-scale liquid air energy storage system, known to the industry as LAES, at its Pilsworth plant. Funded partly with £8 million from the U.K. government, the plant serves as a demo model to prove how air, our planet’s most accessible resource, can help keep the lights on.
When chilled down to minus 320 degrees F, air transforms from gas into liquid. Highview Power has found a way to perform this neat chemistry experiment on a large scale and use it to store energy. For instance, late on a blustery night, the LAES system would funnel unused power from a wind farm into a charging device that triggers an industrial refrigerator to turn air into liquid. It would then store this latent energy in the enormous insulated low-pressure steel tanks.
The next morning, the system would pump the liquid air, evaporate it and send it into a machine called a turboexpander generator, manufactured by Baker Hughes, a GE company (BHGE). This machine, the size of a hotel room, comprises a maze of wheels that converts the energy of liquid into usable power. As the air expands, the same way it does in a hot-air balloon, it flows through a turbine and spins it to generate electricity for an awakening city ready to ramp up for a new day.
Because BHGE’s turboexpander can work with any gas, oil and gas companies have used the same technology for other purposes, including oil recovery, refinery and power generation. “It’s all the same concept,” explains Luca Maria Rossi, vice president of Industrial and Product Management Turbomachinery and Process Solutions at BHGE. “Air is a gas, and we have technology and engineering to unlock its power. Our unique experience in the oil and gas applications can perfectly support new technologies that facilitate the transition to a more sustainable energy mix.”
To warm the air, the Pilsworth plant uses waste heat from a neighboring landfill gas power plant to which it is connected. Similarly, Highview Power plans to operate future LAES units off excess heat produced by “peaker” plants. These power plants typically use natural gas turbines and spring into action when demand spikes.
The main purpose of Pilsworth is to demonstrate the technology for potential customers. Currently, that 5-megawatt plant can supply 15 megawatt-hours of electricity, enough to power around 5,000 homes for about three hours. Highview Power has far grander plans for the system, however. With the ability to handle capacity as high as 300 megawatts, LAES plants could help cities with populations as large as 100,000 diversify their energy mix and use more renewable power.
Engineers have hatched other types of successful storage systems. One in Germany produces roughly the same amount of power by compressing air, storing it in an underground cavern and then releasing it to generate electricity. Pumped hydro storage systems perform the same trick with a two-level reservoir. The system stores the energy, in the form of water, on a higher plane and then spins the turbines by releasing the water downhill. But unlike LAES these systems are reliant on specific geography and cannot always be located at the point of demand.
LAES plants can eventually coexist with grid-scale energy storage systems like the GE Reservoir, a 1.25-megawatt, 4-megawatt-hour lithium-ion modular system that stacks batteries like Legos. The GE Reservoir is equipped with sensors that gather information about the state of charge, temperature, voltage, current and other factors — all of which enables the battery system to react rapidly to tiny shifts in the electrical grid. Combining the GE Reservoir’s sixth sense with LAES’s massive storage capacity gets engineers one step closer to making renewable energy reliable. Now that’s cool.