What Is Solar Cooling?

Solar cooling is the use of solar energy, either as heat or electricity, to drive refrigeration and air conditioning systems. Rather than relying entirely on grid electricity, solar cooling systems convert incident solar radiation into useful cooling effect, reducing dependence on fossil-fueled generation and lowering peak electrical demand during the hottest hours of the day. The field draws on thermodynamics, solar thermal engineering, and refrigeration cycle theory, and encompasses a range of physical principles including thermal sorption, vapor compression, and desiccant dehumidification.

Solar cooling is particularly significant in tropical and subtropical regions, where cooling demand peaks precisely when solar irradiance is highest, creating a natural alignment between supply and load. The IEA Solar Heating and Cooling Programme's Task 65 design guidelines specifically address this opportunity for sunbelt regions, documenting system configurations, performance data, and economic benchmarks for a range of climates and building types.

Absorption and Adsorption Cooling

Thermally driven absorption chillers are the most established solar cooling technology. In an absorption cycle, a refrigerant-absorbent working pair, most commonly water and lithium bromide (LiBr) or ammonia and water, is driven by heat rather than mechanical work. Solar thermal collectors, particularly evacuated tube collectors with efficiencies exceeding 70%, supply heat to a generator that drives the refrigerant out of the absorbent solution; the refrigerant then cycles through a condenser, expansion valve, and evaporator to produce cooling. Single-effect absorption systems require heat sources in the 80-100 degrees Celsius range, while double-effect configurations push COP above 1.0 but need temperatures above 140 degrees Celsius, typically requiring concentrating solar collectors. Adsorption chillers use solid sorbents such as silica gel or zeolite in a cyclic sorption process and can operate at lower driving temperatures, around 60-90 degrees Celsius, making them compatible with flat-plate solar collectors.

Solar Desiccant Cooling

Desiccant cooling systems use hygroscopic materials to dehumidify air before it is cooled, reducing or eliminating the need for vapor compression refrigeration in humid climates. Solar heat regenerates the desiccant by driving off the absorbed moisture, closing the cycle. Open-cycle liquid desiccant systems circulate a concentrated salt solution such as lithium chloride or calcium chloride through a contactor where it absorbs moisture from supply air; the diluted solution is then regenerated in a solar-heated column. Solid-wheel desiccant systems rotate a desiccant-impregnated rotor between the air stream and a regeneration stream heated by solar collectors. NREL evaluations of hybrid desiccant and vapor compression configurations demonstrated reductions in primary energy consumption relative to conventional air conditioning in a range of U.S. climate zones.

Photovoltaic-Driven Cooling

Photovoltaic (PV) systems convert sunlight directly to electricity that can power conventional vapor-compression chillers or refrigerators. This approach benefits from the maturity and falling cost of both PV modules and standard compressor-based refrigeration equipment, and requires no high-temperature heat source. PV-driven systems are highly modular and scalable, from small off-grid vaccine refrigerators to rooftop solar systems powering commercial building chillers. An overview of PV and PV-thermal technologies for refrigeration applications surveys system configurations, control strategies, and performance metrics across different deployment contexts, including ice production, food preservation, and space cooling.

Applications

Solar cooling has applications across a wide range of fields, including:

• Building air conditioning in commercial, institutional, and residential settings
• Off-grid vaccine and pharmaceutical cold chain in regions without reliable electricity
• Food preservation and cold storage for agricultural produce in developing regions
• Industrial process cooling where waste heat or rooftop solar resources are available
• District cooling networks in high-irradiance urban environments