This article is part of Troubleshooting Earth: a multi-part series that explores the bold, innovative, and potentially world-changing efforts to wield technology as a weapon against climate change.
Imagine if the entire world switched to 100 percent renewable energy production overnight.
Obviously this would never happen, but for the sake of illustration, let’s say that instead of making the transition to 100 percent renewables over the course of the next few decades, we somehow did it in the blink of an eye. Suddenly every coal plant, natural gas plant, and nuclear power facility on the planet was transformed into a solar, wind, or tidal energy plant.
Sounds awesome, right? Well, unfortunately, if this scenario magically came to pass, we’d be in trouble.
The problem, of course, is that renewable power is intermittent. Solar panels only generate power when the sun is shining, and wind turbines only do so when the wind is blowing — and neither of those things happen all the time. Furthermore, unlike coal or natural gas, we can’t just ramp up the sunshine or wind speed when we need more electricity. So if human civilization ran on 100 percent renewable energy, the amount of electricity we have at any given moment would be entirely decided by the whims of mother nature.
In other words, if we want our world to run on green energy, we need to figure out a way to store incredibly large quantities of that energy — and unfortunately, the methods we currently use aren’t going to cut it.
Energy storage: Pick your poison
Right now, the world relies predominantly on two different grid energy storage techniques: pumped/dammed hydroelectricity, and batteries. Other methods do exist, but batteries and “pumped hydro,” as they call it, are by far the most common.
Surprisingly, batteries only account for a tiny fraction of the world’s stored grid energy capacity.
Surprisingly, despite the fact that batteries tend to get the most attention, they currently account for only a tiny fraction of the world’s stored grid energy capacity. Dammed and pumped hydroelectric facilities account for the vast majority of it — a whopping 95 percent.
Dams are pretty straightforward. We block rivers, allow water to accumulate behind the dam, and then release the water through turbines to generate electricity whenever we need it. Pumped hydro is very similar. Think of it as a dam with a water reservoir that we fill up manually. During off-peak hours when electricity is cheap, we’ll pump water from low elevations and store it in a reservoir positioned higher up. Then, when demand for electricity is higher, we release the water and let gravity run it through turbines to generate electricity. Pretty clever, right?
Pumped hydro isn’t without its downsides, though. Arguably the biggest problem is that it requires very specific set of geographical criteria. A good site will have both height and naturally available water, which means that suitable locations are typically in mountainous areas that aren’t ideal for development. It also means sites aren’t always near the towns and cities which they serve, so miles and miles of transmission lines need to be installed in order to connect these facilities to the grid. As such, most of of the best pumped hydro sites are already used up.
Luckily, batteries don’t suffer from these same drawbacks. They can be installed practically anywhere, don’t require specific geographical features, and can store energy with a high degree of efficiency. But there’s a reason — many reasons, in fact — why batteries aren’t widely deployed as a grid storage medium. In addition to their comparatively high cost, they also have fairly short lifespans compared to pumped hydro facilities. Worst of all, batteries have a massive (but often overlooked) environmental footprint, as their creation requires the mining of specific elements like lithium, cobalt, nickel, and more.
Worst of all, batteries have a massive environmental footprint.
This puts us in a bit of a predicament. We need to scale up the planet’s electrical storage capacity so we can transition to a more renewable-heavy energy system, but our go-to methods are either poorly suited for scaling up, or so environmentally damaging that they would negate many of the benefits of switching to renewable energy in the first place.
Compressed air: The bagpipe solution
Nine years ago, a small Canadian company called Hydrostor spotted these problems and set out to solve them. “We figured there had to be something else like pumped hydro that could provide the synchronous inertia that the grid needs and batteries can’t provide,” CEO Curtis VanWalleghem explained to Digital Trends. “We also need something that can go where the grid needs it and break the site restrictions that pumped hydro suffers from.”
After some research, VanWalleghem and his partners landed on a well-established but somewhat uncommon storage technique known as compressed air energy storage (CAES). CAES has existed in various forms for decades — but it wasn’t until recently that it became advanced enough to be a viable alternative to batteries and pumped hydroelectricity.
To get an idea of how CAES works, think of playing a bagpipe. You start by blowing air into a chamber and storing it for later. Then, when you run out of breath while you’re playing your tune, you can just squeeze the bag and release some of the stored air to maintain a continuous, even sound. That’s essentially what compressed air storage facilities do — they just deliver electricity instead of music (and also happen to be thousands of times larger than the average bagpipe).
A turbine transforms the potential energy of the pressurized air into electrical energy that can be sent through the grid to your home.
Of course, the real thing is quite a bit more complicated. In the real world, CAES systems use electricity to pump air deep into naturally-occurring underground caverns, pressurizing it heavily in the process. Then, when that energy is needed, the pressurized air is released and used to spin a turbine, which transforms the potential energy of the pressurized air into electrical energy that can be sent to the grid for use.
There are caveats, though. For starters, when you compress air (especially at super high pressures), it gets hot. That’s just how physics works, and if you don’t capture that heat somehow, the compressed air loses some of its energy. This happens because if the air cools too much, it condenses and loses volume, so it therefore needs to be reheated/expanded in order to have as much turbine spinning potential as possible. For this reason, many CAES facilities burn natural gas to heat up the air before running it through a turbine — an effective but inefficient technique.
Another caveat is that if you store the compressed air in a fixed-volume chamber (like an underground salt cavern, which is where most CAES facilities are built), the air pressure decreases as the chamber gets emptier — much like a scuba tank. This leads to inconsistent power output, which isn’t ideal if you’re trying to deliver a steady amount of power to the grid.
The Hydrostor solution
“When we looked at the compressed air technology class, we found that it had two real limitations,” said VanWalleghem. “The first was that it does burn some fossil fuels, and second, it was only being built where there were salt caverns. So what we did is we spent years on the R&D side of things solving those two issues.”
The lack of natural gas burning not only makes Hydrostor’s CAES system more efficient, but also more eco-friendly.
The fruit of that labor is what Hydrostor calls advanced compressed air energy storage (A-CAES), and there are a few things that differentiate it from conventional CAES.
First and foremost, it’s designed to capture all that heat created during the air compression stage and make use of it. “We use an adiabatic system, which means we strip that heat out, store it in what’s effectively hot water, and then reintroduce it when we’re expanding the air, eliminating the need to burn any fossil fuel,” VanWalleghem explained.
This lack of natural gas combustion not only makes Hydrostor’s CAES system more efficient, but also more eco-friendly. As an added bonus, this means the company also doesn’t have to worry about carbon taxes, and can therefore operate anywhere in the world without being penalized financially.
The other big innovation is Hydrostor’s mining technique, which allows it to build its A-CAES sites practically anywhere — not just above naturally-occurring salt caverns. Instead, the company digs a 400 meter deep shaft and effectively creates its own underground cavern.
“We’ve adopted a rock mining technique so that we can build anywhere there’s reasonably competent rock.” said VanWalleghem. “So we’ve gone from 5-10 percent of potential sites to 80 percent of potential sites. And so now we have something that looks and feels like pumped hydro. In fact we have a little bit smaller footprint and better costs, and it now can be built virtually anywhere.”
The lack of site restrictions isn’t the only upside, either. Thanks to this DIY, dig-your-own-cavern approach, Hydrostor can engineer its subterranean air chambers so that they don’t have a fixed volume. Instead of being static and unchanging, the company’s man-made chambers are “hydrostatically compensated,” which essentially means they’re filled with thousands of liters of water, so when the cavern fills up with air, the pressurized air displaces the water and forces it up to a reservoir on the surface.
“It just pushes water out the backside up into a small little pond that we have sitting beside our plant,” said VanWalleghem, “And once you’ve filled your air cavity with cold pressurized air, it’s lifted the water up to the surface. So now you’re sitting with a charged system. Whenever the grid wants power, a valve opens and the weight of that water that we lifted to the surface pushes down, forcing the air back up.” This way, the air pressure remains constant for the duration of the release period, thereby providing a steady and predictable level of electricity.
All things considered, it’s certainly not a perfect process (VanWalleghem says it’s only about 65 percent efficient), but Hydrostor’s system has alleviated many of the pain points that have historically plagued CAES.
Under pressure
So is this the solution to our storage problems? Can we rest easy knowing that humanity now has an eco-friendly energy storage system to match its eco-friendly energy production systems?
Not quite. Just because Hydrostor has seemingly cracked the code to compressed air doesn’t mean we’re out of the woods yet. Regardless of how innovative the company’s technology might be, it will likely be decades before it’s widely deployed.
That said, this is most definitely a milestone that’s worth celebrating. In the very near future, the cost of wind and solar power is expected to drop below the cost of coal and natural gas, incentivizing its adoption even further and likely causing an uptick in the adoption of renewable energy. When this happens, demand for grid energy storage will rise along with it — and thankfully, we now have an effective and environmentally friendly storage method that can help us meet that demand.
“We know we’re still in the early days,” said VanWalleghem. “But we also know climate change is real. It’s scary and it’s happening quickly and we need solutions that can scale. So we’re building big scale projects that we can build rapidly — and as many as possible. We think that’s the key.”
To check out the rest of Troubleshooting Earth, head over to the series homepage.
