Professor Yulong Ding has had a long and distinguished career across several fields of engineering, going back some thirty years. Now he has turned his attention to finding new ways to store energy…
The way energy is generated is changing; moving away from fossil fuels to something less polluting and more sustainable. The catch is that, as with many solutions, it creates its own problem – renewable energy sources are not always available when they’re needed. What to do?
The issue is complex, difficult, and not as straightforward as we might like, with each silver lining bringing its own set of clouds.
The absence of heat
It was a cold day when we met on teams to discuss energy storage, Professor Yulong Ding, (founding Chamberlain Chair of Chemical Engineering at the University of Birmingham and founder of Birmingham Centre for Energy Storage) had himself well wrapped up in a jacket and scarf. He has spent much of his career on trying to solve our energy issues.
Gone before you know it
He begun by explaining the difficulty with batteries, “Today, lithium-ion batteries are very popular, and they are mainly being used in electric vehicles, but they are also used in electrical grids and power grids. But those batteries are mainly for addressing quick response, a relatively small amount.
If you look at installed batteries, the power they can store is measured in megawatts, tens of megawatts or sometimes hundreds of megawatts, but mostly used for storing electricity for a couple of hours, because it is too expensive to store a large amount of electricity for a long time. There are also concerns such as safety, the use of critical materials, and recycling challenges. Of course, people are working towards solving these problems, particularly long lifespan batteries, but they are not there yet.
Think about the renewable energy supply – sometimes you have weeks, sometimes months, where you have little or no wind, or don’t have much solar. Which would mean we’d have to store lots of energy for a lot longer, even cross-season. Batteries are not the best solution for this type of application, and there are other storage technologies that can better address that.”
What happens when the sun is momentarily hidden by cloud, or the wind slows down…and the power dips?
Geography and fast response times
“Pumped-hydro, compressed air, and liquid air energy storage technologies are mainly for large scale applications. They have a response time around two to ten minutes, too slow for some applications, such as frequency regulation of power grids, which need to be brought in within seconds or even milliseconds.”
“Net zero 2050 needs lots of energy storage to address the intermittent and fluctuating nature of renewables. This ranges from fast response, e.g. batteries, flywheels and supercapacitors, with short storage duration; to medium duration storage, e.g. pumped hydro, compressed air, liquid air, and thermal energy storage; to long duration storage, e.g. hydrogen and thermochemical energy storage. We are talking about some 50, even 80 terawatt hours. It's huge. And today we probably have 1%, even less than 1% of that storage capacity. So, there's a long way to go for us to achieve the net zero 2050 ambition.”
Lightning in a liquid
Within the medium duration energy storage, liquid air stands out for flexibility with no geographical constrains.
Professor Ding explained, “liquid air energy storage technology stores energy in two forms. One is in thermal form, essentially through temperature difference; the other in pressure form, through a slight high pressure, at, for example around 10 bars or even 20 bars. The way liquid air energy storage works is that where you have excess electricity e.g. from renewables or other low carbon generations, you use this energy to liquefy air.
Air is sustainable, it is free, it is clean. The liquefaction of air is done through compression and expansion of the air, so its temperature of the air can drop to around -190°C degrees, very cold, so that it becomes liquid with energy stored in such liquid.”
This (liquefaction process) would reduce some 800m3 of gaseous air to about 1m3 of liquified air. Its density would increase from 1kg per cubic metre to 800kg per cubic metre. Shrinking that amount of air through decreasing the temperature would allow for the storage of a lot of energy.
Professor Ding continued, “when you need energy, what you do is you evaporate the liquid air, because it is very cold. You could use the ambient temperature to evaporate it, and compression heat from the liquefaction process to increase the air temperature. To increase the gaseous air temperature further, you can use other sources of heat, for example from industrial waste heat or from solar or whatever you have. You can further superheat that air to produce high pressure air, which could then drive a turbine to produce electricity.
Gee, it’s cold in here
In a typical liquid air storage system, we will capture the compression heat and it for use in the expansion or power recovery step. And hence you can produce more power. That's one. Second, because liquid air has a temperature around -190°C or -196°C, when you evaporate such cold liquid air, you have lots of cold energy - very high value cold energy.
What we do is to capture and store that cold, we re-use that cold when you liquify air to reduce energy consumption. So essentially, there are three stores in the system. One is storing liquid air, one is storing compression heat, and one is storing high grade cold energy. In such a way, the system can have a good efficiency, by ‘good,’ I mean it can be 60%. Can that be higher if there are no external free energy sources? It's difficult to get it much higher. So, 60% efficiency is good, it's good enough.”
The good thing about liquid air energy storage is that it has no geographical constraints. The method with the greatest geographical impediment is pumped hydro, which requires a hill or mountain, with a lake at the top and at its foot. Clearly, this limits where the technology can be used.
Compressed air storage has its own geological requirement, this time a large underground space, such as a salt cavern. This is not the obstacle it might first seem - if that cannot be found, a space can be built below ground on campus or at an industrial park, or even in high pressure steel vessels though that is for small scale and likely to be expensive.
On the surface, finding new ways to power our societies without fossil fuels can seem daunting and full of setbacks. But Professor Ding and his colleagues surely give cause for optimism that seemingly intractable problems can ultimately be solved, there is always a solution.
What energy storage solutions do you find exciting and how long do you think it will take before we can say, ‘we’ve cracked the problem of storing energy’? Leave your thoughts in the comments below.