Solid-state ACs promise eco-friendly cooling, but efficiency lags behind

After three years of record-breaking heat, air-conditioning demand is soaring—the IEA projects the number of AC units will triple by 2050. Yet traditional ACs contribute 7% of global electricity use and leak potent refrigerants like R410A, which has over 2,000 times the global-warming potential of CO2. To address this, scientists and startups are advancing solid-state cooling technologies that use materials like gadolinium and bismuth telluride to transfer heat without compressors or harmful refrigerants.

Companies like Brooklyn-based Mimic Systems (thermoelectric cooling) and Germany's Magnotherm (magnetocaloric) are piloting room-scale systems. A Hong Kong team's elastocaloric device can dip below 0°C, and UK's Barocal uses barocaloric pressure changes. However, University of Michigan professor Pramod Reddy questions why solid-state coolers aren't as efficient as thermodynamic cycles. Traditional ACs achieve a coefficient of performance (COP) of 3, while thermoelectrics struggle at high temperature changes. Still, supporters like Lindsay Rasmussen of RMI argue that even a 5% market share could have a large climate impact, as long-term energy consumption comparisons are needed.