How Mature are Renewable Energy Technologies?

Technology Readiness Levels Explained

Rosemary Barnes
Jan 21 · 8 min read
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Airbus’ hydrogen aircraft concept — looks ready but how long should we expect to wait?

This is something that annoys me about the way that energy technology is covered in the media:

A scientific or technical advance is reported, the reporter tells us all about the problems with existing alternative technologies and the amazing potential of the new technology.

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I feel like I see a lot of this.

And we rarely hear about how much risk there is that it won’t work as expected, or how long it might take until it becomes available to use. The reporter might mention that “development is needed” or “it needs to be scaled”, or even describe the technology as “mature”, but the details of technology maturity are omitted. The reader has no way to determine how likely the new technology is to succeed or how long it might take to get there.

The reason this annoys me is that I feel bombarded with stories of new energy technologies that purport to be the solution to all of the challenges of the green energy transition. And if this new and perfect solution is coming up, why would we bother persevering with today’s non-perfect solutions? When we don’t specifically focus on technology maturity, it can cause people to feel less favourable towards current technologies, and divert resources away from their implementation. And this is important because we don’t have time to wait for the future’s perfect technologies, we need action on climate change now.

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A few energy technology headlines (composite by the author)

So what we need is a shared understanding of technology maturity and risk. A common language we can speak to communicate unambiguously what stage of maturity a technology is at now, and how much development work is left before commercial availability of the technology.

In fact, such a framework does exist. It’s called Technology Readiness Level, TRL. But I have never seen it mentioned outside of professionals who are intimately involved in technology development projects. I want to introduce the concept to a broader audience, in the hope that we can start to develop more realistic expectations about new technologies as they are reported.

I am an engineer with 15 years of experience developing renewable energy technologies. In this article, I want to tell you a bit about how the new technology development process works, and the Technology Readiness Levels framework we use to describe technology maturity. I’m going to explain the origin of the scale, how it’s used, and give some examples of green energy technologies and how they fit into the framework. And then I am going to discuss some of the limitations and problems associated with the TRL framework.

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Technology Readiness Levels with some example clean energy technologies (composite image by the author)

So: what is a “mature” technology? It’s a word that I often hear used to describe energy technologies. It gives a kind of reassuring feeling, don’t you think? And what about the opposite? What is an “immature technology?” Does this mean it doesn’t work, can’t be manufactured, is prohibitively expensive?

One reason this is a tricky thing to discuss is that this concept of a “mature” technology is kind of rubbery. A technology that one person calls mature, another person might see there’s a lot of development work still to be done. And this kind of mismatch isn’t limited to conversations between technology experts and the general public. It is also a common cause of problems within teams working on new technology development projects, especially when it comes time to hand over a technology from one group to another. So for example, when a new technology goes from a research and development team to the sales team: how do you know when it’s ready, and if you’re likely to experience problems with the integration of the new technology?

I have faced this challenge in probably every single job I’ve had in my career as a new technology development engineer. It was also apparently a problem for NASA back in the 1970s. (it is always nice to feel like you have something in common with a NASA engineer!)

There was concern at NASA about “the differing perceptions of the researchers and the mission planners between the intended and the actual proof of readiness.” And they invented Technology Readiness Levels to bridge these differences. Originally it was a 7-point scale with 1 being basically an idea someone had in the shower and 7 being a totally finished technology that had been to space.

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The original NASA TRL scale (From Sadin et al)

Now, TRL has spread way beyond just NASA and into other industries, like defence, infrastructure, oil and gas, and my own industry: renewable energy technologies. Companies use it to guide technology development projects, to make sure technologies are developed enough before they go to market. TRL assessments can also aid planning technology roadmaps, which companies use to make sure they’ve got a good stream of new technologies to launch over the coming years. Governments can also use it for technology roadmaps, like this Australian one below or as a criterion for eligibility to grants or procurement programs. So you might say, this grant is open to technologies TRL 7 and above for example, in an attempt to ensure you’re comparing like to like technologies and not funding an idea-in-the-shower level idea when you meant to buy a technology that would be commercially ready soon.

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TRL assessment of low emissions technologies by the Australian Government

The scale that is used now is most commonly a 9-point scale, and I’ll run through it quickly now.

TRL 1–3: Basic Technology Research

TRL 1 is just an idea, and TRL 2 is thinking of a potential application for that idea. TRL 3 provides some proof of feasibility of the critical function, which could be either some analysis or a lab scale proof of concept.

We can use the example of graphene to illustrate. Graphene is a material whose potential to revolutionise energy technologies amongst other applications has had technology reporters excited for decades. So TRL 1 for graphene was when someone had the idea that a single atom-thick layer of carbon might have some interesting properties. TRL 2 was when they came up with some specific applications it could be used for — in transistors or solar cells for example. And TRL 3 was when a graphene solar cell was actually made in the lab.

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Composite by the Author (images Canva and Mengyao Zhong et al, 2016)

Many of the most exciting new energy technologies that are reported are in the range of TRL 1–3. Examples include nuclear fusion and spaced-based solar power. And some of these technologies, like fusion, have been at TRL 3 for decades. It is an annoyingly common technology joke that nuclear fusion is always 30 years away, and this highlights the fact that these early level technologies may never progress to maturity. If you or your company or your country want to invent a really innovative technology starting from an idea, then you’re going to want a large number of them in development at once to be sure that something works out. Because most of them won’t.

TRL 4–5: Beginning Technology Development

So next we get to TRL 4, which is component testing or some basic integration of functions in a lab environment, and then TRL 5 where components or maybe a small-scale or simplified prototype is tested in a realistic environment.

It’s at this point that we have gone from an idea that *might* have a practical application, to an actual technology. This is the level that I usually start to work with a technology, and at this point, you pretty much know that with enough time and budget you could get it to work. But there is no guarantee of how long it might take, or whether the end product will be cheap or reliable enough to make it commercially viable.

It might sound like TRL5, with a prototype tested in a realistic environment is pretty much a mature technology. However, any engineer who, like me, works on technologies from this level on can tell you that there are still *so* many things that can go wrong, and do go wrong every single time. Examples of TRL 4 to 5 energy technologies include electric or hydrogen aircraft, electrified steel manufacturing and small modular nuclear.

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Airbus hydrogen aircraft concept and small modular nuclear reactor

TRL 6–9: System Development

After this, we are starting to get to technologies in a form that closely resembles what you will see when they are fully commercialised. These next few levels are about more realistic testing and more performance data.

TRL 6 is a functional prototype in a representative environment, and TRL 7 is a demonstration of a prototype in the actual environment. An example of a technology moving from TRL5 to 7 is a wave energy converter moving from a scale model tested in a wave pool (TRL 5) to a full-scale prototype tested in the actual ocean (TRL 7).

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Colombia Power Technologies 33rd scale tank test and ocean test (NREL 24535, 19381)

TRL 8 is more rigorous testing of a prototype in its actual environment. So for our wave energy converter, this means a longer duration of testing at several sites. This is to help understand how the technology will behave in the full range of possible ocean conditions.

Smart charging, ultra-high voltage transmission, and carbon capture and storage of direct industrial emissions are other clean tech examples that currently fit in this range of TRL 6–8.

The final level on the scale is TRL 9, which is a commercially mature technology with verified performance data. This includes battery electric vehicles, heat pumps, wind and solar, pumped hydro — all technologies that are commercially available and have a large amount of verified performance in different conditions.

Beyond TRL 9: early adoption vs. mature technologies

There are also sometimes extensions to the TRL scale. Some systems use a 9+ to distinguish between recently commercialised technologies “early adoption” and ones that have a long history of use. Some systems prefer to swap to a “commercial readiness level” after TRL 9, to describe much the same thing.

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Examples of different TRL scales used in industry and government

What did you think about where I placed different technologies within the scale? Did you disagree on some? I would be surprised if you didn’t actually, because even though the TRL scale tries really hard to be an objective measure, there is inevitably judgement involved.

And if you are interested, I also covered this topic in a video on my YouTube channel. Check it out here along with my other videos on renewable energy technologies.

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Rosemary Barnes

Written by

PhD in engineering. Passionate about renewable energy, new technology and engineering communication. Engineering with Rosie on YouTube: https://bit.ly/3hVkrLb

Digital Diplomacy

Technology, digital, and innovation, at the intersection with government and foreign policy

Rosemary Barnes

Written by

PhD in engineering. Passionate about renewable energy, new technology and engineering communication. Engineering with Rosie on YouTube: https://bit.ly/3hVkrLb

Digital Diplomacy

Technology, digital, and innovation, at the intersection with government and foreign policy

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