In the European Union (EU), the energy households use for cooling has doubled over six years. According to Eurostat, it rose from 40.5 thousand terajoules (TJ) in 2018 to 80.4 thousand TJ in 2024. Europe is the fastest-warming continent in the world, and heat is spreading even to regions that previously had little need for cooling. At the same time, the EU is working to phase fluorinated refrigerants—used in air conditioners and heat pumps—out of the market. The timing of rising demand has collided with the deadline for switching refrigerants.
This is drawing attention to "solid-state cooling," which transfers heat through temperature changes in metals or crystals rather than using gaseous refrigerants. In Europe, a residential air-conditioning project backed by about €3.98 million is underway. Still, it's too early to call this a revolution. While Europe's project is designing a 500-watt (W) class experimental unit, a research team in China and Hong Kong has recorded 1,284W. The competition has shifted from discovering materials to competing on overall device performance and mass-producibility.
What 80.4 Thousand TJ Reveals About Rising Cooling Demand
In 2024, EU household cooling energy use rose 15.3% from the previous year. By country, usage was 26.3 thousand TJ in Italy, 14.3 thousand TJ in Spain, and 11.9 thousand TJ in Greece—these three countries alone account for roughly two-thirds of the EU total. The share of cooling in household energy consumption reached 16.0% in Cyprus and 15.0% in Malta.
Looking at the EU average alone, cooling accounts for just 0.8% of final household energy consumption—a stark contrast to heating's 61.5%. But what troubles the power grid isn't the annual total but the concentration of demand on heatwave afternoons. When the hours requiring cooling overlap across a region, even a use case that looks small on average can erode the margin of power generation and transmission capacity. The European Environment Agency (EEA) warns that the simultaneous rise in cooling demand and decrease in cooling water available for thermal power plants could heighten the risk of blackouts.
Moreover, this growth in demand isn't confined to southern Europe. Observations from the Copernicus Climate Change Service show that European temperatures have risen by about 0.53 degrees per decade since the mid-1990s—more than double the global average of about 0.26 degrees. Switzerland, the UK, and Norway are cited as countries where the relative increase in cooling demand will be especially large as global average temperature rise progresses from 1.5 to 2 degrees.
The UK's Climate Change Committee estimates that by 2050, 92% of existing homes will be at risk of overheating. Buildings that have prioritized winter insulation struggle to release heat in summer. This forecast signals that the low prevalence of cooling can no longer be explained by cultural differences alone.
Fluorinated Refrigerant Options Narrow Starting in 2027
Current air conditioners compress refrigerant and cycle it between liquid and gas states to carry indoor heat outdoors. The technology is mature, but if the refrigerant leaks, it accelerates global warming. The EU's F-Gas Regulation progressively expands sales bans according to equipment type and capacity, and the refrigerant's Global Warming Potential (GWP).
For self-contained air conditioners and heat pumps with a rated capacity of 12 kilowatts (kW) or less, products using fluorinated gases with a GWP of 150 or higher will, in principle, no longer be able to enter the market starting in 2027. By 2032, fluorinated gases in general will be covered in the same category. For split air-to-air systems, units of 12kW or less with a GWP of 150 or higher will, in principle, be banned starting in 2029, with fluorinated gases in general banned from 2035. Because exceptions exist—for cases where installation-site safety requirements can't be met, for instance—this doesn't mean "air conditioners will stop being sold in the EU a few years from now."
Switching to low-GWP refrigerants can address the regulations. But propane is flammable, and it requires changes to equipment design and installation conditions. The reason solid-state cooling holds promise is that, rather than swapping refrigerant candidates, it can remove the leaking gas itself from the thermal cycle entirely. It's an approach that reframes compliance with refrigerant regulations—from a matter of chemical selection to one of materials and mechanical design.
Of course, going solid-state doesn't mean electricity becomes unnecessary. You still need drive mechanisms that apply force or magnetic fields to materials, and heat exchangers that transfer heat absorbed from indoors to the outdoors. What must be evaluated isn't the temperature change of the material alone, but how many watts of heat the device can move while maintaining a practical temperature difference, and how many watts of electricity it consumes to do so.
Europe's SMACool: Targeting 500W at 15K
Europe's "SMACool" project uses nickel-titanium (NiTi) shape-memory alloy as a solid refrigerant. When the alloy is compressed, its crystal structure changes and it generates heat; when the force is released, it returns to its original state while absorbing heat from its surroundings. By repeating this cycle and using a heat-transfer fluid, indoor heat is moved outside. This mechanism is called elastocaloric cooling.
The project began in October 2024 and runs through September 2027. The EU contribution is about €3,977,000, with three universities in Germany, Italy, and Slovenia, plus Ireland's Exergyn, participating. To build a functional residential prototype, the team is improving the materials and compression mechanism, and setting up numerical models and measurement environments.
The first-year progress report, published in June 2026, offers a fairly concrete picture of where things stand. The device's design targets are a cooling capacity of 500W or more, a temperature difference of 15 Kelvin (K) representing indoor/outdoor conditions, and as high a coefficient of performance (COP) as possible. NiTi material production has been scaled up to ingots exceeding 100 grams. Two climate chambers have also been prepared to reproduce seasonal outdoor temperatures and indoor heat loads, for measuring seasonal COP including power consumption.
Meanwhile, current results are centered on design and simulation. SMACool aims for efficiency 2 to 3 times higher than existing HVAC systems, but the device configuration chosen through calculation still awaits experimental verification. A design is needed that rapidly transfers heat through thin NiTi structures while preventing buckling during compression. Two candidate drive mechanisms for converting rotary motion into linear compression are also under consideration. The 500W figure isn't the finished value for a product that cools an entire home—it's the entry point toward an integrated prototype.
China Surpasses the Kilowatt Mark; Europe's Challenge Shifts to Implementation
In the race for solid-state cooling output, Europe isn't the sole frontrunner. In 2025, a research team including Hong Kong University of Science and Technology reported in Nature a structure that divides thin-walled NiTi tubes into 10 cells, arranging force transmission in series and heat-exchange fluid flow in parallel. Operating at 3.5 hertz, the device achieved 12.3W per gram of NiTi and a total cooling capacity of 1,284W for the whole unit. Previous devices had been capped below 300W, so this marks the first time the kilowatt barrier has been crossed.
However, this 1,284W figure was measured under conditions with no temperature difference between inlet and outlet. A real air conditioner must lower room temperature while pushing heat out into the hot outdoors. As the temperature difference increases, cooling capacity and COP decrease. Confirming performance over an initial 500,000 cycles is also progress, but the lifespan and maintenance costs for a residential appliance used every summer need to be verified separately. Noise and mass-production material costs will also determine commercial viability.
The International Energy Agency (IEA), in its 2026 technology innovation report, cited this Chinese kilowatt-class demonstration as a milestone for 2025. Europe has research institutions, startups, and an early market created by F-gas regulation. But the record for high-output devices has already moved to Asia. What will determine Europe's advantage isn't the number of inventions, but whether it can demonstrate seasonal efficiency exceeding existing units at a temperature difference of around 15K, and connect that device to companies and supply chains capable of mass production.
Even so, building countermeasures can't be delayed while waiting for solid-state cooling to become practical. External blinds and trees can block solar radiation, while nighttime ventilation and insulation retrofits can reduce the heat entering homes. UK estimates suggest that prioritizing retrofits for the 30% of urban households most vulnerable to overheating could avoid 57% of heat-related mortality risk in the 2050s. Cooling should handle the remaining heat load, and should be delivered first to hospitals, schools, care facilities, and residents vulnerable to heat.
If there is to be a cooling revolution in Europe, it won't take the form of a single new air conditioner overturning the market overnight. Whether solid-state cooling can move from a research topic to household equipment will be decided once the refrigerant regulations starting in 2027, the SMACool demonstration running through September 2027, and kilowatt-class device performance measured with a real temperature difference, all fall into place in sequence.