In the first part of this look into the impact of critical resources on the transition to renewable energy, I identified which resources are critical. I showed that, for the foreseeable future, there is no shortage of suitable sites for wind and solar power generation. In fact, one study has shown that just the onshore wind sites in Europe could power the entire world. One potential issue, however, is that these intermittent sources of energy require storage to ensure we have access to electricity when it is needed. Although conventional pumped-storage hydroelectricity (PSH) provides efficient and economical long-term energy storage, there is a shortage of sites with suitable geology and water supply close to major population centers.
Despite promising new methods of PSH, such as using concrete spheres submerged in the sea or pumped seawater close to high cliffs in areas such as Scandinavia, it seems likely that battery storage will be a vital part of the energy system. Batteries will be needed for electric vehicles to use renewable power, as well as potentially for grid-level storage. Metals required for current battery chemistries, such as lithium and cobalt, are currently in short supply. This may present a significant challenge for rapid decarbonization.
Other areas where shortages of critical metals may become bottlenecks are the rare earth magnets used to produce efficient generators in wind turbines and electric motors in vehicles, and the supply of silver, tellurium, selenium and gallium required for solar panels.
This article focuses on the two areas where critical metals affect both renewable energy supply and electrification of transport—rare earth magnets and metals required for battery production. A future article will cover the resources for photovoltaic cell production.
Batteries consist of an anode, a cathode and the electrolyte. In current lithium-ion batteries, the electrolyte is a lithium-containing a salt compound dissolved in an organic solvent, the anode is graphite and the cathode can be various compositions, all involving relatively rare metals. Battery electric vehicles (BEVs) currently use lithium-ion batteries with nickel-manganese-cobalt (NMC) cathodes, typically containing equal parts of each metal. This cathode composition is known as NMC 111 and results in batteries containing approximately 0.4kg of each metal per kWh. There is considerable hope that NMC 811 production may soon scale to automotive production, requiring just 0.094kg of cobalt and 0.088kg of manganese but 0.75kg of nickel per kWh. The compositions for current lithium-ion battery technologies and those expected to enter production within the next five years are given below.
The table below shows that if the current rates of automotive production are maintained and state-of-the-art NMC 811 batteries are used with average capacities of 50kWh, very significant increases in supply would be required just to achieve 30 percent electrification. For 100 percent electrification, approximately 22 times the world’s current supply of manganese, seven times the supply of lithium and three times the supply of cobalt would be required. This is especially challenging considering that almost all of the current production capacity for these critical metals is already required for other uses.
Many land-based reserves are not easily extracted, and the required level of scaling in mining operations is likely to take decades. All of these critical metals are also present in large quantities within the world’s oceans, and there is some hope these may prove easier to extract at scale.
A number of as-yet untapped mineral resources exist within the oceans, which may soon provide economical sources for the critical metals required for BEV production. These include manganese nodules, cobalt crusts and seafloor massive sulfides. There is particular commercial interest in mining ocean nodules within initial experimental extraction already completed. However, there are significant concerns over the ecological impacts and resultant climate effects. Supporting a fully electrified global automotive industry could require mining about 5,000km2 of the ocean floor annually. This would directly impact local ecosystems and produce plumes of sediment-laden water covering a much larger area. The deep ocean habitat is over 95 percent of the volume of Earth inhabited by animal life. Although much about these deep-water environments remains unknown, it is understood that canyons and other slope environments sequester large quantities of carbon and methane. It is, therefore, likely that damaging this massive habitat will negatively impact the oceans’ ability to buffer against climate change.
There is also plentiful cobalt and lithium within sea water itself. Experiments suggest that critical metals could be extracted from water flowing past floating structures, such as disused oil rigs and floating wind turbines. In time, this may provide a rich supply but, like deep-ocean nodule mining, it is unlikely to be available at the scale and rate required to meet urgent climate objectives.
Similar shortages exist for the rare earth elements praseodymium, neodymium and dysprosium. These are required to produce high-efficiency permanent magnets for motors in electric vehicles and generators in wind turbines. In this case, greater substitution is possible. Motors and generators can be constructed using conventional steel and copper windings, but they are less efficient. Superconducting motors offer even higher energy efficiency and power density and are well-suited to wind turbines because the powerful magnetic fields allow very high torques at slow speeds. A superconducting wind turbine has already completed operational testing in Denmark.
Recycling critical metals will be vital to ensure a long-term supply. This will require both sufficient quantities already circulating in the economy and methods of extracting them from alloys. For many critical metals, such as praseodymium, neodymium and dysprosium, the recycling rates are currently less than 1 percent.
Extracting the required quantities of critical metals will involve technical and commercial challenges, as well as potential ecological damage. In the long term, scarcity should not be a barrier to the plentiful supply of zero emissions energy. However, in the immediate future, technologies that use these critical resources as efficiently and sparingly as possible should be given precedence.