Auke Hoekstra, director of NEONresearch, email@example.com, @aukehoekstra
Many scientific publications assert copper scarcity is a roadblock on the way to renewable energy, but almost none take substitution into account. Although copper demand could increase about 30% because the transition to renewable energy, substitution with aluminum is possible for almost all applications. Therefore, it is implausible that copper scarcity will hamper the transition to renewable energy.
The increasing demand for copper
Many authors have noted that the transition to renewables leads to greater demands for copper. A 2022 Nature article by Daehn et al. notes: “Demand for copper, crucial for electrification, may be 30% higher with the necessary energy transition compared with similar estimates using current energy carriers.”1
Many of those papers (I stopped counting at 30 papers) noted that this will lead to copper scarcity that might or will hamper the transition to renewable energy. Goldman Sachs called it “the New Oil”. (A lot of stuff is called the New Oil nowadays.) Bloomberg warns of a ‘Huge Crisis’ before asserting “The transition to clean energy depends on copper” and speaking of “the metal’s troubled future”.
But something curious is going on. The Bloomberg paper is 2500 words long but zero words are used to talk about substitution. And that’s true for almost all articles about copper scarcity.
For the Bloomberg journalist I can understand that: you don’t want to make your article less important by pointing out there are solutions. But for the scientific papers I was expecting more. Although as a researcher I understand the temptation: it’s much easier to stay within the confines of your academic discipline, so if you are an expert on mining or geology you don’t want to expose yourself by saying something about how copper is used and could be substituted.
But would a shortage of copper indeed be a significant roadblock in the transition to renewable energy? Or are there alternatives that we can use to substitute copper with?
Substitution of copper with aluminum
Copper is mostly used to conduct electricity, but that is a function that aluminium can do too, and aluminum is 1200 times more abundant than copper. It’s even more abundant than iron in the earths crust.
In 2021 the Journal of Cleaner production published a letter to the editor titled: “Copper substitutability might be about 60% or more of current copper use”.2 I would argue that this is very conservative indeed.
The letter by Reijnders is partly a rebuttal to an article by Heckens and Worrell that claims only 10% substitution is possible. Almost all Heckens and Worrel’s claims are based on an 2002 book by Ayres et. al.3 from which Heckens and Worrell distill claims like: “Because overhead transmission lines are considered ugly … high voltage transmission may happen more through underground copper lines [than] overhead aluminum lines … for interior wiring, copper is preferred to aluminum, because aluminum has led to problems of overheating and fires [and] in some applications copper seems virtually irreplaceable such as for local distribution of electric power.”
And this leaves me wondering: how can somebody spend months writing an article about the availability of copper and nickel for future generations, without any inkling of how you can replace it? Are they afraid they will not understand articles on electricity? Don’t they want to know because it will make their article about scarcity less relevant?
If you want to replace copper with aluminum there’s only a few things you need to know:
- aluminum has 60% of the conductivity of copper, so
- you need a 25% thicker wire for the same results. However,
- the aluminum in this equivalent wire will cost and weight about half as much.
So aluminum in power lines? Of course! Also underground! In transformers and coils, e.g. in motors? Good idea!
Electric vehicles are often mentioned as one of the biggest problems. The IEA claims we will need about 50kg per car (roughly double that of a conventional car). So if we were to replace all 1.7 billion cars by EVs, we would need an additional 42 Mton of copper: 5% of reserves and 0.8% or resources. Assuming that happens over a 42 year period that’s 1 Mton per year or an additional 5% of yearly copper production.
That might seem doable but it’s not the end of the story. Aluminum is researched a lot because almost all copper in an electric vehicle could be replaced by aluminum. The motor is where most of the copper is found. Can we replace that by aluminum? Yes we can4–6 although efficiency might drop by 1% or so6,7 (but this does give you a lighter motor). Next is the wire harness: you guessed it.8 All in all the replacement is in full swing, although the scarcity of copper to give it urgency is so far missing.
Of course we all know by now that wind turbines are the number one copper problem. Wood Mackenzie9 pegs it at 7 ton per MW and the IEA10 at 8 ton. But wait, isn’t that for their motors and for the power lines to shore that could be replaced by aluminium? And that is indeed the case. Aluminum instead of copper in wind turbine windings is a mature option and we already discussed power lines. But for subsea cables aluminum doesn’t work right? Wrong, and it’s market share is increasing.
Aluminum in houses did get a bad rep because the wrong type was installed the wrong way (especially in the US in the 70s when copper was deemed too expensive). And yes, you need to take care at the points of termination since aluminum has more thermal expansion that can wriggle loose connections and since aluminum oxide insulates (potentially causing fires through bad connections), so although the material is cheaper, you have to do it properly and it can be a bit more work, esp. if you are not used to working with aluminum. But substitution is already a mature option for everyone who wants to use it.
Copper is also used for heatsinks and here the story is basically the same: aluminum has 60% of the conductivity so your aluminum replacement is slightly larger but the aluminum is half as heavy and expensive.
So it’s really hard to find large scale applications where you couldn’t replace copper with aluminum if you wanted to. I would estimate that about 90% of copper can be replaced by aluminum using mature and available options. In their 2022 article “Copper and Aluminum as Economically Imperfect Substitutes”, Bartos et al11 look at what it would take for most of copper to be replaced with aluminum. Their conclusion: “Research has confirmed that copper and aluminium may be imperfect substitutes in some respect, but they can generally be considered complementary. Copper mining has stabilised in recent years, but aluminium production has increased significantly in the last decade, and it can be expected to grow in the near future.”
Aluminum is better for the environment than copper
Of course aluminum (or aluminium), even though it’s abundant, requires mining too. And although these mines tend to have less averse direct environmental impacts, it takes roughly three times more energy to produce new aluminum, currently leading to about 50% more emissions per kilo. However, as electricity production becomes low carbon, aluminum actually emits less CO2, while it doesn’t contaminate marine environments as much, has less adverse effects on human health, and has less harmful heavy metals as by-product.12 So if copper scarcity forces us to substitute aluminum this is actually a good thing for the environment.
I think journalists and scientists talking about copper scarcity without talking about substitution should be ignored, and preferably nudged into changing their irresponsible behavior. All these signals that we can’t switch to low carbon energy for made up reasons are not helping in the fight against climate change.
- Reijnders, L. Copper substitutability might be about 60% or more of current copper use. Journal of Cleaner Production 284, 124774 (2021).
- Daehn, K. et al. Innovations to decarbonize materials industries. Nat Rev Mater 7, 275–294 (2022).
- Ayres, R. U., Ayres, L. W. & Råde, I. The Life Cycle of Copper, Its Co-Products and Byproducts. vol. 13 (Springer Netherlands, 2003).
- Acquaviva, A., Diana, M., Raghuraman, B., Petersson, L. & Nategh, S. Sustainability Aspects of Electrical Machines For E-Mobility Applications Part II: Aluminium Hairpin vs. Copper Hairpin. in IECON 2021 – 47th Annual Conference of the IEEE Industrial Electronics Society 1–6 (2021). doi:10.1109/IECON48115.2021.9589649.
- Petrelli, G. et al. Comparison of Aluminium and Copper Conductors in Hairpin Winding Design for High Power Density Traction Motors. in 2022 International Conference on Electrical Machines (ICEM) 1635–1641 (2022). doi:10.1109/ICEM51905.2022.9910796.
- Dhulipati, H. et al. Investigation of Aluminium and Copper Wound PMSM for Direct–drive Electric Vehicle Application. IOP Conf. Ser.: Mater. Sci. Eng. 654, 012002 (2019).
- Viego, P., Santos, V., Gómez Sarduy, J., Yanes, J. & Quispe, E. Induction motors with copper rotor: a new opportunity for increasing motor efficiency. International Journal of Electrical and Computer Engineering 13, 2409–2418 (2023).
- Li, C., Shen, T., Zhou, Y. & Dai, M. EMPC of aluminium wire and copper terminal for electric vehicles. Materials and Manufacturing Processes 38, 306–313 (2023).
- Mackenzie, W. Global wind turbine fleet to consume over 5.5Mt of copper by 2028. https://www.woodmac.com/press-releases/global-wind-turbine-fleet-to-consume-over-5.5mt-of-copper-by-2028/ (2019).
- The Role of Critical Minerals in Clean Energy Transitions. 287 (2021).
- Bartoš, V., Vochozka, M. & Šanderová, V. Copper and Aluminium as Economically Imperfect Substitutes, Production and Price Development. Acta Montanistica Slovaca 27, 462–478 (2022).
- Burger Mansilha, M., Brondani, M., Farret, F. A., Cantorski da Rosa, L. & Hoffmann, R. Life Cycle Assessment of Electrical Distribution Transformers: Comparative Study Between Aluminum and Copper Coils. Environmental Engineering Science 36, 114–135 (2019).
I bought my current house in 1990 (it was built in 1981). I have lived in it most of the time. I cannot recall the wires coming into it ever being replaced. Recently I had the power lines dropped to take down some trees. I noticed when the lines were restored that they were aluminium. That surprised me as I thought the place was too long established to have aluminium cables.
There’s a little more complexity to substituting aluminum for copper than just 40% lower volumetric conductivity. There are two other main issues relevant to wiring:
1. Aluminum’s coefficient of thermal expansion is about 35% greater for typical aluminum alloys than for copper. This means that electrical connections can get loose over repeated thermal cycling, which can result in poor electrical contact, heat generation, and potentially fires. This can be largely addressed by using lugs and electrical contacts made from materials with carefully chosen and compatible thermal expansion coefficients, and by using fasteners with some sort of spring mechanism to maintain pressure despite expansion (e.g. bolts with split washers).
2. Aluminum is susceptible to surface oxidization, and the surface oxide layer is a strong electrical insulator, which can result in poor electrical contact, heat generation, and potentially fires. This can be largely addressed by applying an antioxidant compound to all aluminum connections.
These issues were poorly understood in the 1960s and 1970s, when the Vietnam War caused a copper shortage and a boom in aluminum wiring in housing construction, and that resulted in a lot of poor aluminum wiring installations and many fires. With modern practice, these problems can be avoided, though at the cost of a bit more labor.
These issues don’t negate your thesis, but you do a disservice to your readers by glossing over them entirely.
I agree Jonathan and in the article I said: “And yes, you need to take care at the points of termination since aluminum oxide insulates, so although the material is cheaper, it can be a bit more work, esp. if you are not used to working with aluminum.” I’ve added a few words about the thermal expansion”. It is also described in the link I provided by the way, so it’s not my intention to gloss over these issues. Just to be brief and to the point.
Thank you for your comment!
This is an old mistake which has been repeated for over a century. Back in the early 1900s, some engineers and commentators hadn’t even considered substitution with aluminum when it came to overhead power cables (they used to be made of copper). Many people assumed that the electrical grid would be a short-lived phenomenon as we ran out of copper for overhead wires:
“[T]he age of electricity and of copper will be short. At the intense rate of production that must come, the copper supply of the world will last hardly a score of years. […] Our civilization based on electrical power will dwindle and die.” –Ira Joraleman, 1924