Renewable energy from aluminium – it’s possible!

    When thinking about aluminium, most people would connect it with consumer electronics, plane or car parts, construction material or the ubiquitous aluminium can or foil. And for good reason, as these are among the most widespread uses of this recyclable and versatile metal. But what if someone told you that primary aluminium could be used to produce renewable energy and heat?

    However, primary aluminium production is very energy intensive, as roughly 17,000 kWh of electricity are required to produce one ton of this non-noble metal. 

    The so-called Hall-Heroult process dominates worldwide aluminium production at the moment. In this process, aluminium oxide is dissolved in molten cryolite and then electrolyzed in a molten salt bath. The process results in around 99.5 – 99.8 % pure aluminium. 

    But what if the primary aluminium could then be used to produce energy and heat? Wouldn’t that mean that the input electricity could be harvested again and used in other areas? 

    The SFP Institute for Solar Technology at the University of Eastern Switzerland has been awarded an innovation prize for developing a technology that uses aluminium as a power source for electricity and heat production. Researchers described their project as follows: “Aluminium is used as an energy carrier in the building technology required for buildings not connected to a heat or natural gas network, which can be completely heated and supplied with electricity with locally produced energy”.

    A large part of the input electricity used for primary aluminium production is converted into chemical energy and stored within the aluminium itself. Essentially, this energy can be rereleased when the aluminium is oxidized to heat buildings or generate electricity. In other words, aluminium could be part of the answer for how we solve the intermittency issues related to electricity production from renewables by serving as a clean storage device for green energy. 

    For the production of primary aluminium, bauxite ore (the primary source of aluminium) needs to run through two chemical processes; one to produce alumina (aluminium oxide) and another through an electrolysis process to produce pure aluminium metal. Even though, aluminium is earths most commonly found metal, it is too reactive to be found naturally. The ore is acquired through strip mining operations that can have quite an impact on the environment if not done responsibly. 

    Contrarily, aluminium can be indefinitely recycled without losing any of its properties. Therefore, around 75 percent of worldwide aluminium ever produced is still in use today. This makes the metal quite unique; so is the idea of the swiss project. The oxidized aluminium is recycled and treated again to serve another household, or two, in the future. Some challenges with this reprocessing technology are still to overcome, but we have faith in the many smart minds on this planet to also solve these challenges. 

    According to lab results, 1kg of aluminium can generate as much as 8.7 kWh of energy. A standard household uses on average not more than 40 kWh per day. This means that a 4-5-kilogram aluminium block could power a single home. The Swiss researchers put it differently, saying that a cube with an edge length of 1 meter could heat two households for an entire year and also supply electricity. With the help of an aluminium converter and a fuel cell, electricity is generated and ready to use. 

    What is even better is that heat produced using aluminium produces hydrogen. Reacting aluminium with water produces energy in different forms which are all usable: (i) heat, (ii) hydrogen gas, and (iii) water vapour. The gravimetric hydrogen capacity obtained from an aluminium-water reaction to form aluminium hydroxide and hydrogen is 3.7 weight percent (wt. %) (which is an important measure for storing large amounts of hydrogen) and the volumetric hydrogen capacity is 46 g H2/L, which is almost three times that of gasoline. The biggest challenge, however, is the costs of this method of hydrogen production. Estimates are around US$20 per kg of hydrogen, which is in no way feasible at a big scale. Nevertheless, if the hydrogen is produced while heat and electricity are sourced from the blocks of aluminium at the same time, then the costs of hydrogen production would not matter so much, as these are set-off with the generation of heat and electricity. 

    A successful energy transition faces challenges related to baseload energy and the intermittency gap of renewable energy resources such as solar or wind, are known not to be suitable for delivering baseload energy. Hydropower or geothermal, on the other hand, is. 

    What’s more, producing heat from aluminium could serve as a bridge that can safely, cost-efficiently, and relatively simply be achieved. A prerequisite for reducing GHG emissions is that primary aluminium be produced from renewables entirely, as can be seen in Canada or Iceland. Chinese or Russian aluminium is currently unsuitable for a green solution, as fossil fuels serve as an input energy source. Another advantage of using an aluminium block to heat and power your house is that no connection to the gas or heating network is needed. 

    After having read this, we hope that you now look at aluminium a little differently, and not just as a drinks can you throw away. 

    Co-Authored by Norbert Bürger

    Norbert Bürger is an industrial/mechanical engineer and a senior executive within the aluminium industry. His love to nature drives the urge for sustainability and innovation, which combined with his technical background set the basis for his economic activities.

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