Solar thermal is best known for heating, but the same collectors that provide hot water and space heating can also drive cooling systems. Cooling demand is one of the fastest-growing sources of energy use in buildings worldwide, and solar thermal offers a way to meet it without adding to the electricity peaks and fossil fuel use that conventional air conditioning relies on. Air conditioning already accounts for close to a fifth of building electricity demand globally, and without intervention that could nearly triple by 2050 — reaching around 30% of all building electricity use. Solar thermal cooling can help absorb that growth sustainably.
Heat that produces cold
It sounds counterintuitive, but the physics work in solar’s favour. A solar thermal cooling system looks much like a standard solar thermal installation on the supply side: collectors, a storage tank, a control unit and pipework. The difference lies in what the heat is used for, instead of warming water directly, it drives a thermally driven sorption chiller, which uses heat rather than electricity to produce a cooling effect.
The most common approach is the absorption cycle, in which heat is used to separate a refrigerant from an absorbent (commonly a water/lithium bromide or ammonia/water pair). As the refrigerant expands and evaporates, it produces cooling, which is then distributed as chilled water. A closely related technology, adsorption cycle, uses a solid material such as silica gel or zeolite in place of a liquid absorbent. In both cases, an effective heat rejection system (usually a cooling tower or dry cooler) is essential, since the process still needs somewhere to dissipate the heat it draws off.
There is also a second, distinct family of systems — desiccant (or open-cycle) cooling — which conditions air directly rather than producing chilled water. These use a desiccant material to dehumidify air, combined with evaporative cooling, and are typically integrated into a building’s ventilation system rather than its water-based cooling loop.
Where it's used
Solar thermal cooling scales from small systems to large commercial and industrial installations, with current R&D and demonstration projects spanning a range from around 2 kW up to 5,000 kW.
- Residential — single-family and multi-family housing, particularly where cooling and heating (including heated pools) are both needed.
- Tertiary buildings — offices, hotels, shopping centres, schools, hospitals and other institutional buildings, where cooling loads are often substantial and predictable.
- Industry — low-temperature process cooling needs such as washing, dyeing or pasteurisation.
Applications that need both heating and cooling, such as schools and hotels, are typical examples particularly well suited, since a single solar thermal system can serve both loads across the year.
The technology performs best in sunny, dry climates, but it isn’t limited to them. Of the world’s small and medium-scale solar cooling systems (below 350 kW), around 70% are installed in Europe.
Why the timing works in solar's favour
One of the most compelling features of solar thermal cooling is that supply and demand are naturally aligned: cooling needs peak when solar irradiation is highest, so the system delivers most when it’s needed most. This is different from solar heating, where demand often peaks in winter when solar resource is lowest.
Because a typical solar thermal system can provide space heating and hot water alongside cooling, the same installation can be useful across the whole year rather than sitting idle outside the cooling season, improving the overall economics of the investment.
Benefits
- Environmental — lower CO₂ emissions from reduced use of carbon-based electricity, and avoidance of the high-GWP refrigerants used in many conventional air conditioning systems.
- Economic — reduced energy costs, and local jobs in manufacturing, installation and maintenance.
- Energy security — lower electricity demand at exactly the moment (hot summer days) when grids are often under the most strain, reducing dependence on energy imports.
A growing technology
Solar thermal cooling remains a relatively small segment of the broader solar thermal market, but it is growing steadily and maturing technically. Worldwide installations reached close to 2,000 in 2023, up from around 1,200 a decade earlier, and international research collaboration continues through the IEA’s Solar Heating and Cooling Programme, most recently through a four-year project (2020–2024) focused on adapting and de-risking solar cooling for fast-growing, high-cooling-demand regions.
Solar Heat Europe also joined the EU LIFE project Cooling Down, between 2022 and 2025, addressing the contribution of renewable cooling technologies, such as solar thermal and geothermal, in climate change adaptation, with a specific focus on the mitigation of the urban heat island effect.
Proven in practice
Solar thermal cooling isn’t a theoretical technology, it’s already operating in a range of real buildings across different climates and scales, from university campuses to schools to retail buildings. You can find out more about some of these installations in our case studies.