Solid-State Air Conditioners: A Cool Future, But Scientists Remain Cautious

As the world grapples with a relentless succession of record-breaking heatwaves, the reliance on air conditioning is set to intensify. The International Energy Agency projects a tripling of AC units by 2050, a trend that, while crucial for public health – preventing nearly 200,000 premature deaths in 2019 alone – poses a significant threat to the planet. Traditional air conditioning already consumes 7% of global electricity and contributes 3% of greenhouse gas emissions. Furthermore, improper disposal can release refrigerants with global-warming potential thousands of times higher than carbon dioxide. In response to this escalating crisis, scientists and startups are exploring solid-state cooling technologies, currently limited to niche applications like mini-fridges, EV batteries, and high-end gaming computers. Unlike conventional ACs that use compressors and refrigerants to transfer heat, solid-state systems move heat through conductive materials such as gadolinium and bismuth telluride. This approach theoretically promises to cool spaces and surfaces with fewer environmental side effects, offering a cleaner and potentially more durable alternative due to fewer moving parts. The primary hurdle for solid-state cooling remains its efficiency. Pramod Reddy, a professor at the University of Michigan specializing in heat transfer, highlights the critical question: "Why are the solid-state coolers not as efficient as typical thermodynamic cycles?" Experts, particularly in thermoelectrics, express skepticism about their ability to match the coefficient of performance (COP) of modern HVAC systems, which typically stands at 3 – meaning they move three units of heat for every unit of energy consumed. Thermoelectrics, for instance, tend to perform poorly at high temperature differentials, limiting their utility to specific, smaller-scale applications. Despite these challenges, various research and pilot programs are actively underway. Brooklyn-based Mimic Systems is trialing a room-scale thermoelectric climate control system in a Vancouver apartment. Germany’s Magnotherm is testing a magnetocaloric system in supermarkets, which transfers heat by magnetizing and demagnetizing materials. A Hong Kong team has developed an elastocaloric device that can achieve sub-zero temperatures by expanding and contracting its material, while the UK’s Barocal is developing barocaloric systems that respond to pressure changes. However, proponents argue that efficiency isn't the sole metric. Lindsay Rasmussen, a manager at the Rocky Mountain Institute’s climate tech accelerator Third Derivative, points out that many existing ACs use refrigerants like R410A, with a global-warming potential over 2,000 times that of CO2. Solid-state models, with their mechanical simplicity, also promise greater durability. Rasmussen emphasizes the need for long-term energy consumption comparisons against conventional models, rather than just COP, to truly assess their viability. Mimic, for example, claims its room-scale model can match a typical AC unit's annual energy draw. While a complete replacement of compressor-based ACs by solid-state technology seems unlikely in the near future, its potential impact remains significant. As countries like India prepare to install tens of millions of new AC units in the coming decade, even a modest market penetration – perhaps just 5% – could lead to a substantial reduction in environmental harm. The ongoing innovation in elastocaloric and barocaloric systems also holds promise, with room-scale prototypes anticipated within two to three years, signaling a gradual but meaningful shift towards a more sustainable cooling future.