Every six months, the Green500 list ranks supercomputers by their energy efficiency. Their latest list, published on the 14th of June 2025 in Hamburg, shows Luxembourg-based supercomputer MeluXina in 80th position. So, what lessons can we learn from a supercomputer that manages to stay green without compromising computing power?
What is a supercomputer?
How does a supercomputer differ from the laptop on which you’re probably reading this article? A supercomputer uses more than one Central Processing Unit (CPU) to execute several tasks at once. They are used for everything from weather forecasting to safeguarding nuclear weapons to predicting patients’ health. We also use supercomputers to train AI models.
MeluXina runs on renewables and reuses waste heat
Located 30 kilometres from Luxembourg’s city centre, MeluXina is completely run on renewable energy. The majority of this energy comes from hydroelectric power plants in Norway. MeluXina’s computing power is equivalent to tens of thousands of computers combined, so, unsurprisingly, the servers have high cooling requirements.
Data centres that boast low energy use often make this possible by using water-based cooling systems. They therefore negate their energy savings by putting pressure on local water supplies, impacting local land systems and communities, particularly in drought-stricken areas. MeluXina has taken a different approach. The same water has remained in its cooling system for many years; this closed-circuit method means that no new water is required. While this ensures water and energy consumption are as low as possible, costs are higher, as water must be purified and re-cooled.
Another way MeluXina reduces its consumption is by heating its building with waste heat from its operations. They also power their cooling systems with a biomass power plant that burns waste wood. As well as environmental concerns, they also prioritise data protection. MeluXina is one of a few supercomputers in Europe with the ISO 27001 certification, demonstrating that it adheres to strict information security.
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We must consider how MeluXina is used
We asked Dr Ralph Hintemann, a researcher from the Borderstep Institute focusing on the sustainable design of data centres, for his opinion on MeluXina’s environmental credentials. He told us that MeluXina’s position on the Green500 list “is definitely a sign that [the developers attached] great importance to energy efficiency”. He continues, “The utilisation of waste heat is also a good thing [as] no additional energy has to be used.” But, “we don’t know how much waste heat is utilised in this specific case,” he points out.
The fact that MeluXina uses climate-friendly electricity is another positive for Hintemann. But MeluXina’s electricity supply travels all the way from Norway to power the computer. This is standard practice for Luxembourg, which imported 77 percent of its electricity in 2024. “[But regional electricity] would be even better,” says Hintemann.
So, can MeluXina be considered truly sustainable? “Despite everything, it requires large amounts of energy and raw materials for the production of devices and systems,” Hintemann says. He also brings up how MeluXina’s supercomputing power is being used. “If it’s used to discover new oil deposits, it’s certainly not a sustainable system.”
It’s unclear whether developers are selective about what MeluXina is used for. But they do plan to expand to create a so-called AI factory where AI start-ups can train their models. AI is a double-edged sword for the planet, often offering energy-saving solutions but requiring energy to bring them to life. So if MeluXina can train these AI systems while running on green electricity and reusing waste heat, we could reap the benefits of AI while shrinking its environmental impact.
