Lithium ion batteries are great. They power much of the world around us and in our pockets, but trying to scale the technology up for the grid and storing massive amounts of renewable energy is challenging. Limited battery cell supply and manufacturing, difficulty supplying enough rare earth metals and minerals to make the lithium ion cells, and questions around longevity. What if there was another way? A method that used air to store energy? This … could change everything.

I’ve spent a lot of time on the channel diving into energy storage technologies and different kinds of batteries, like lithium ion and flow batteries. They’re absolutely essential to make renewable energy work as our primary energy source. Without energy storage, we’re wasting vast amounts of energy potential. When we can’t use all of the energy solar and wind are generating at the time they’re making it, we actually have to turn those systems off. It’s called curtailment. When you see wind farms with turbines not turning, that’s why.

But before we get to how air might be able to solve this energy storage problem … I can hear you already … but what about lithium ion batteries? Well, we are seeing lithium ion battery installations starting to pop up all over. One of the more notable examples is Tesla’s Hornsdale Power Reserve, which was recently expanded by 50MW. It’s helped to improve the electrical systems resilience and reduced the cost of frequency control ancillary services by about $116M in 2019 alone.1 2

But so far these battery systems are designed for 2-4 hours of energy storage. Solar and wind are some of the cheapest methods of generating electricity today at around $40 and $29 per MWh respectively.3 When you layer in lithium ion battery storage and calculate the cost per MWh, it stands around $150 for four hours of energy discharge.4 5 6 The price doesn’t scale well the larger you make the system … and that’s where the power of air comes in.

Liquid air energy storage, or cryogenic energy storage, is using a process that’s been around for a long time. The basic principle is simple. Use energy to compress air down into a small space. When you need energy, you release that air, letting it expand and turn a turbine to generate electricity on the way back out. It’s not that different from pumped hydro storage. The big difference is that you aren’t limited by geography … you can build these anywhere. And there’s far less impact on the environment since you’re not redirecting water and building out massive facilities. I had a chance to chat with the CEO of Highview Power, a company specializing in cryogenic energy storage … sometimes called a liquid air battery.

“I hope not to be a party pooper here when I say that this is extremely simple technology. There is nobody, no crazy nutty professor who is taking a rabbit out of a hat. What Highview Power has been doing during the first 15 years of life, the company is close to 16 years old, has been to develop a technology that is integrating processes that are pretty well known like liquefaction of gas. What we are doing is liquefying air, taking the air that we are breathing and storing the energy by the means of fluid. It’s a cryogenic fluid that this air that is in liquid state. For the normal person in the city, on the countryside, it sounds very strange, liquid air, but we’re doing that since middle of last century to produce nitrogen, to produce oxygen. We’re cooling down the air separating the different components to produce oxygen for hospitals, oxygen for industries, nitrogen for industrial applications. We are using that engineering to store energy.” -Javier Cavada

The process takes in the air around us, cleans and dries it, and then cools it down to -196°C, which shrinks the volume by a factor of 700 times. That means you’re taking 700 liters of ambient air and freezing it down to 1 liter of liquid air. This liquefaction process has been around for over 100 years and is known as the Claude Cycle, for the French inventor Georges Claude. Fun fact … he also invented neon lights by using neon that was a byproduct of his air liquefaction business.7 Anyway, when you freeze air into a liquid, you aren’t storing high pressure air … because it’s frozen, so you’re storing frozen air in insulated, low pressure vessels. Warming the air back up and releasing it through a turbine generates the electricity. The energy efficiency of this process on its own, the energy in vs. energy out, isn’t that great. According to the Institute of Mechanical Engineers, this process can be as low as 25% efficient. A far cry from a lithium ion battery that’s between 80-90% efficient, but that’s not the whole story with these systems. When you layer in capturing waste heat and cold that’s generated by the liquefaction process, you can drive that efficiency up to 60-70% … or even higher.

“Theoretically as you know, this is about the cooling down, extracting the heat, storing the heat or reusing that heat again when you gasify. You can isolate the whole system. Isolating means investing in isolation to the point that you can have … You never have 100% efficiency, but you can have as large as you want. What Highview has been doing is standardizing the system, making it modular so that having a standard product, a standard solution that has 60%, six, zero, 60%. You can invest more and get it bigger, and you can invest less and get it lower. I like to highlight that the pumped hydro and the hydro plants are in that 50 to 60 to 70% efficiency of the whole system.” -Javier Cavada

To break down how this works for Highview Power’s facility, they capture the waste cold that comes out of the thawing process when releasing the air. This cold is then reused during the next cycle’s freezing process with new air. And in the same vein, they’re capturing the waste heat from the freezing stage to reuse during the thawing stage. When re-purposing waste heat and cold like this you can pretty much design and scale the efficiency to fit your needs. But as Javier pointed out to me in our conversation, that’s not the thing to necessarily focus on.

“Again, you can really invest in the efficiency, but normally what you are going to look in, because at the end it’s do you look at the efficiency or do you look at dollars per megawatt-hour. I can tell you that I don’t know one single person that will look will prefer more efficiency at a higher dollar per megawatt-hour. At the end, the efficiency is in the formula calculating the dollar per megawatt-hour. How many megawatt-hour do I get, at what cost? You are including the efficiency insight. You will invest more in adding more tanks or having a bigger charge station or a bigger discharge station. You can really make your charging station bigger or smaller modularly. You can have 50 megawatts, but tomorrow you’re going to have 100. You just add another module and get benefits [inaudible 00:14:50] scale, the same with the discharge, but especially with the storage asset.” -Javier Cavada

Systems like these can be scaled up very quickly by just adding more storage tanks, which can be purchased from the existing natural gas supply chain. All of the major components of a liquid air energy storage are built off of components that are readily available. And the larger the system gets, the lower the per MWh price. Something that can’t be said of lithium ion. Lithium ion batteries are great at responding to energy needs within milliseconds. They’re excellent for rapid response and fluctuations in energy use, which, like in the case of the Hornsdale Power Reserve, can save huge amounts of money. Cryogenic energy storage hits its sweet spot at large scale. When you need 4, 6, 12, or even 24 hours of energy storage, then cryogenic air brings in the value.

If you look at where the sweet spot is for the major energy storage systems available today, you’ll find lithium ion in the 10-100 MW range with between 2-4 hours of storage. Right above that you have flow batteries, which I’ve done a separate video on if you’re interested. I’ll include a link in the description. Flow batteries have a lower specific energy than lithium ion, but are more scalable since you can easily increase the size of the fluid storage tanks. While the power capability is slightly smaller, they’re more capable of handling between 4-12 hours of energy storage. Pumped hydro is the big kid on the block being able to easily store 1GW of power and offering a full day of energy storage. The BathCounty Pumped Storage Station in Virginia is a 3GW facility with 24GWh of capacity.8 It’s massive. But like I said earlier, that’s highly dependent on geography for a storage system that size. With liquid air you can build a facility anywhere on a relatively small plot of land and have a system that can scale up to pumped hydro’s energy capabilities.9 10

Given its versatility, you’d think that this is the ideal solution across the board, but it’s not. You’re not going to have a liquid air powered smart phone. The system really requires scale and it isn’t as nimble in energy responsiveness as lithium ion batteries. In fact, Highview Power doesn’t see this as a choice between lithium ion and cryogenic air storage.

“I would say that brothers and sisters, we are like the big brother [inaudible 00:16:30] and the other ones are the very first ones, the quick ones and make a lot of really smaller businesses, but very needed in many other places. For us, the competition is, allow me to say is continue doing the same policy, burning gas, combustion, open cycle gas turbines, gas engines, gas turbines, combined cycles, burning the stuff to provide power, that’s the competition of this.” -Javier Cavada

It’s all about picking the right tool for the job and figuring out what the right mix is for a given areas needs. But when you’re talking about grid scale needs over 4 hours, liquid air batteries make a very persuasive argument for themselves.

Which leads me to my last point about availability. When are we going to see these out in the world. Well, they’re actually already here and coming fast … like within the next few years fast.

“We have another two projects that are entering into execution early next year in another part, in Scotland. We have several projects in the US. We have something like 40 projects in the pipeline, seven very advanced, one entered in execution end of the year.” -Javier Cavada

One of the facilities that’s underway is not too far from me, in Vermont. They’ve partnered with Vermont-based Encore Renewable Energy to build out a 40MW / 400 MWh (about 8 hours) storage system, which will help with curtailment issues in the area.11 12

When it comes to modernizing our grid and transitioning off of fossil fuels, the key always comes back to energy storage. Without being able to store energy generated by renewables from the time it’s generated to when we actually need it, it won’t matter how cheap solar and wind power get. There’s a mix of technologies needed to solve this problem and the deceivingly simple liquid air battery is lining itself up to be a major part of that solution. The more I learned about it, the more I kept thinking … why haven’t we done this sooner? It’s such a clever idea built from some tried and true technologies that have been around for a long time. There’s no cutting edge chemistry we need to wait for to make this viable … it’s taking advantage of what’s right in front of us … well, more like all around us.

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