Opinion
The energy transition, the World Bank says, will require more aluminum than any other metal. In order to keep temperatures below a two-degree increase, clean energy technologies will need almost six million tons of the metal each year by 2050. By comparison, the combined total of lithium, cobalt and nickel, the mineral poster children of the energy transition for their use in batteries, is not expected to pass four million tons. These estimates rely heavily on myriad assumptions, but they underline the importance that metals have along the path to zero-emission energy.
Almost all this aluminum for clean energy will be used in solar module frames. Its resistance to corrosion and light weight make it an optimal choice for exposure to the elements and ensuring modules structural stability.
Aluminumโs energy challenge
Aluminum may be needed for the climate, but the industryโs main environmental challenge is its own climate impact, according to engineering professor Guรฐrรบn Sรฆvarsdรณttir at the University of Reykjavik. Production is reaching ever higher volumes, but so are the industryโs carbon emissions.
โThere has been a large increase in the production volume of aluminum [over the past two decades], it has more than doubled since the year 2000,โ says Sรฆvarsdรณttir. โAnd a lot of that development has been based on coal power, unfortunately.โ
New Chinese aluminum smelters have driven the spike in production, and they now produce more than half the worldโs new aluminum. While the country relies on coal for 70% of its power, the power mix of aluminum smelters is more than 90% coal, according to Sรฆvarsdรณttirโs research.
Mining, refining and smelting new aluminum produces nearly 2% of the worldโs total carbon emissions. Every ton of aluminum produces on average roughly 15 tons of CO2ย equivalents. Thatโs almost four tons higher than 20 years ago. By some measures the jump in aluminum production may mean 400 million more tons of CO2ย equivalents each year by 2040.
A number of aluminum companies are developing new smelting processes and building new types of plants to reduce the industryโs footprint on the planet, but scientists have said more development is needed to align its GHG emissions with its renewable energy product.
โWeโre at a critical juncture at the moment,โ says Cameron Jones, director of assurance with the Aluminum Stewardship Initiative. The ASI, a nonprofit industry certification group, is conducting โhealthy and rigorousโ discussions to update its standard that encourages companies to target 8 tons of C02 equivalents by 2030. It plans to create a more โinclusive and challengingโ target, but there are technological and policy barriers to overcome.
The process problem
New aluminum typically begins as bauxite ore, which is sent to refineries that extract alumina, or aluminum oxide. Separating aluminum from alumina requires temperatures approaching 1000ยบC, and the sending of a powerful electric current through the molten mineral.
The process is not only energy intensive, but the mineralโs oxygen combines with carbon anodes to emit CO2. The direct carbon emissions make up roughly 10% of the processโs total emissions, and electricity consumption contributes 71%, according to Sรฆvarsdรณttirโs work.
โWeโre not going to get rid of these emissions unless something is done about the process,โ says Sรฆvarsdรณttir.
Recycling dramatically reduces the energy required to feed the metal into circulation, and aluminum is in theory infinitely recyclable. The Aluminum Association, an industry representative body, estimates that 75% of all aluminum ever produced is still in circulation. Mining companies are inching toward investing in recycling plants, such as Rio Tintoโs Canadian plant announced in September.
In the World Bankโs two-degree scenario, the proportion of recycled aluminum will grow, but it will still only cover 61% of demand. The ASI expects to release proposed standards to address climate impacts in the next several months for consultation, but establishing a path for carbon reduction may take much longer.
โItโs such a complex, diverse supply chain that we canโt do a one-size-fits-all,โ says Jones. โItโs very difficult to come up with a single pathway or methodology thatโs going to work across the whole sector. So, this is the real issue at the moment.โ
Search for solutions
Firms in aluminum production have chosen several routes to reduce their carbon footprint. Aluminum smelters that use renewable energy have mostly connected to hydro power, such as in Norway and Iceland, but hydro capacity is limited and depends heavily on geography. The proportion of smelters that use hydropower has decreased from 46% in 2000 to 26% in 2018, while coal now powers 61% of aluminum production.
Smelting often requires an order of magnitude more energy than other steps. To ensure they are supplied by renewable energy, some smelters in China are discussing whether to transport entire operations to areas where the grid relies on renewables, Jones says, but none have moved yet.
Smelters are designed for constant power, but German firm Trimet has transformed some of its furnaces in an aluminum smelter to adapt to variable power. While smelters need to keep materials in a molten state, engineers add flexibility that allows the smelter to work with 25% less or 25% more power than typically used. When there is excess electricity available on local grids, sometimes a result of surplus solar and wind generation, process controls ensure that electrolysis chambers only freeze on the edges, allowing smelting to continue, albeit at lower capacity. In a sense, such a smelter acts as a form of battery on the grid.
โIt can really be a significant contribution to stabilizing the grid, so we should not ignore that opportunity,โ says Sรฆvarsdรณttir.
Reducing emissions
In the last few years, two ventures have claimed to replace a smelterโs direct carbon emissions with oxygen. Arctus Metals in Iceland has begun trialingsmelting processes which use inert anodes that will not react with the oxygen in alumina to produce carbon dioxide. Sรฆvarsdรณttir, who is involved in the project, is also researching the possibility of using carbon capture for direct emissions.
Rio Tinto and Alcoa have partnered to create a carbon-free smelting process โ via joint venture subsidiary Elysis โ founded in 2018. Consumer product companies like Apple have made deals to buy from Elysis to reduce its carbon footprint. The company, based in Canada, declined to comment for this piece and has spoken to few reporters since its launch.
Alumina refiners are accustomed to frequent technical problems and interruptions in supply, which may make them more adaptable to dependence on intermittent solar or wind energy, says Jones. Alcoa announced in September a brand of alumina produced with half the carbon emissions as the industry average.
In Australiaโs Northern Territory, indigenous-owned bauxite miner Gulkula relies on a combination of solar PV and battery storage for its operations. A Rio Tinto mine in Queensland relies partially on solar power, a move that is a part of a larger resource-industry trend towards the adoption of on-site PV.
โThe industry is moving the right way, but there havenโt been any โoh wowโ moments at this stage,โ says Jones.
This past summer, Sรฆvarsdรณttir presented her research on aluminumโs carbon emissions problem to new engineering students. Her goal was to entice new recruits into solving industryโs biggest greenhouse gas problems, like the direct emissions from aluminum smelting. While electricity is responsible for a quarter of the worldโs emissions, industry is close behind at 21%, according the IPCC.
โSomeone needs to work on the 21%. Everyone wants to work on renewable energy, but someone needs to work on this, otherwise we will not reach carbon neutralityโฆ I think this is the biggest opportunity to help the climate.โ
Author: Ian Morse
This article was originally published inย pv magazineย and is republished with permission
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