Passive daytime radiative cooling (PDRC) can lower temperatures with zero energy consumption or pollution by radiating heat into outer space. Widespread application has been proposed as a solution to global warming.[1]
Passive daytime radiative cooling (PDRC) can lower temperatures with zero energy consumption or pollution by radiating heat into outer space. Widespread application has been proposed as a solution to global warming.[1]

Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero energy consumption or pollution.[1][2][3][4] Because all materials in nature absorb more heat during the day than at night, PDRC surfaces are designed to be high in solar reflectance (to minimize heat gain) and strong in longwave infrared (LWIR) thermal radiation heat transfer through the atmosphere's infrared window (8–13 µm) to cool temperatures during the daytime.[5][6][7] It is also referred to as passive radiative cooling (PRC), daytime passive radiative cooling (DPRC), radiative sky cooling (RSC), photonic radiative cooling, and terrestrial radiative cooling.[6][7][8][9] PDRC differs from solar radiation management because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation.[10]

Some estimates propose that if 1–2% of the Earth's surface area were dedicated to PDRC that warming would cease and temperature increases would be rebalanced to survivable levels.[11][12] Regional variations provide different cooling potentials with desert and temperate climates benefiting more from application than tropical climates, attributed to the effects of humidity and cloud cover on reducing the effectiveness of PDRCs.[13][14][15] Low-cost scalable PDRC materials feasible for mass production have been developed, such as coatings, thin films, metafabrics, aerogels, and biodegradable surfaces, to reduce air conditioning, lower urban heat island effect, cool human body temperatures in extreme heat, and move toward carbon neutrality as a zero-energy cooling method.[16][17][18][19][20]

Application of PDRCs may also increase the efficiency of solar energy systems, dew collection techniques, and thermoelectric generation.[21][22] PDRCs can be modified to be self-adaptive if necessary, 'switching' from passive cooling to heating to mitigate any potential "overcooling" effects in urban environments.[17][23] They have also been developed in colors other than white, although there is generally a tradeoff in cooling potential, since darker color surfaces are less reflective.[24][25] Research, development, and interest in PDRCs has grown rapidly since the 2010s, which has been attributed to a scientific breakthrough in the use of photonic metamaterials to achieve daytime cooling in 2014,[26][27] along with growing concerns over energy use and global warming.[28][29]

Classification

Passive daytime radiative cooling is not a carbon dioxide removal (CDR) or Solar Radiation Management (SRM) method, but rather enhances longwave infrared thermal radiation heat transfer on the Earth's surface through the infrared window with the coldness of outer space to achieve daytime cooling.[30][31] Solar radiation is reflected by the PDRC surface to minimize heat gain and to maximize thermal emittance.[6] PDRC differs from SRM because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation.[10] PDRC has been referred to as an alternative or "third approach" to geoengineering.[30][31][32] PDRC has also been classified as a sustainable[33][34] and renewable cooling technology.[35][36][37]

Global implementation

PDRCs can slow and reverse rising temperature trends associated with climate change.[1][10]
PDRCs can slow and reverse rising temperature trends associated with climate change.[1][10]

When applied globally, PDRC can lower rising temperatures to slow and reverse global warming.[1] Aili et al. concludes that "widescale adoption of radiative cooling could reduce air temperature near the surface, if not the whole atmosphere."[9] To address global warming, PDRCs must be designed "to ensure that the emission is through the atmospheric transparency window and out to space, rather than just to the atmosphere, which would allow for local but not global cooling."[10]

PDRC is not proposed as a standalone solution to global warming, but to be coupled with a global reduction in CO2 emissions and transition off of fossil fuel energy. Otherwise, "the radiative balance will not last long, and the potential financial benefits of mitigation will not fully be realized because of continued ocean acidification, air pollution, and redistribution of biomass" from high remaining levels of atmospheric CO2, as per Munday,[10] who summarized the global implementation of PDRC as follows:

Currently the Earth is absorbing ∼1 W/m2 more than it is emitting, which leads to an overall warming of the climate. By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth (...) If only 1%–2% of the Earth’s surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease.[10]

The estimated total surface area coverage is 5×1012 m2 or about half the size of the Sahara Desert.[10] Global implementation may be more predictable if distributed in a decentralized manner, rather than in a few heavily centralized locations on the Earth's surface.[12] Mandal et al. refers to this as a "distributed geoengineering" strategy that can mitigate "weather disruptions that may arise from large-scale, centralized geoengineering."[38] Desert climates have the highest radiative cooling potential due to low year-round humidity and cloud cover while tropical climates have a lower cooling potential due to the presence of humidity and cloud cover.[9][39]

Total costs for global implementation have been estimated at around $1.25 to $2.5 trillion or about 3% of global GDP, with probable reductions in price at scale.[10] This has been described as "a small investment compared to the estimated $20 trillion global benefits predicted by limiting global warming to 1.5°C rather than 2°C," as per Munday.[10] Low-cost scalable materials have been developed for widescale implementation, although some challenges toward commercialization remain.[18][40]

Some studies have recommended efforts to focus on maximizing the solar reflectance or albedo of surfaces from very low values to high values, so long as a thermal emittance of at least 90% can be achieved. For example, while the albedo of an urban rooftop may be 0.2, increasing reflectivity to 0.9 is far more impactful than increasing an already reflective surface to be more reflective, such as from 0.9 to 0.97.[41]

Benefits

Studies have noted the following benefits of widescale implementation of passive daytime radiative cooling:

Advantages to solar radiation management

Passive daytime radiative cooling is referred to as more stable, adaptable, and reversible when compared to stratospheric aerosal injection, which proposes injecting particles into the atmosphere to increase radiative forcing to reduce temperatures. Studies have warned against stratospheric aerosol injection's potential to contribute to further ozone loss and heat the Earth's lower stratosphere further, stating that the injection of sulfate particles "would reflect more of the incoming solar radiation back into space, but it would also capture more of the outgoing thermal radiation back to the Earth" and therefore accelerate warming.[46]

Wang et al. states that stratospheric aerosol injection "might cause potentially dangerous threats to the Earth’s basic climate operations" that may not be reversible, and thus put forth a preference for passive radiative cooling.[47] Munday noted that although "unexpected effects will likely occur" with the global implementation of PDRC, that "these structures can be removed immediately if needed, unlike methods that involve dispersing particulate matter into the atmosphere, which can last for decades."[10]

When compared to the reflective surfaces approach of increasing the reflectivity or albedo of surfaces, such as through painting roofs white, or the space mirror proposals of "deploying giant reflective surfaces in space," Munday states that "the increased reflectivity likely falls short of what is needed and comes at a high financial cost."[10] PDRC differs from the reflective surfaces approach by "increasing the radiative heat emission from the Earth rather than merely decreasing its solar absorption."[10]

Function

PDRCs maximize outgoing infrared radiation (shown in orange) and minimize the absorption of Solar Radiation (shown in yellow).
PDRCs maximize outgoing infrared radiation (shown in orange) and minimize the absorption of Solar Radiation (shown in yellow).

The basic function of PDRCs is to be high in both solar reflectivity (in 0.4–2.5 µm) and in heat emissivity (in 8–13 µm),[6] to maximize "net emission of longwave thermal radiation" and minimize "absorption of downward shortwave radiation."[9] PDRCs use the infrared window (8–13 µm) for heat transfer with the coldness of outer space (~2.7 K) to radiate heat and subsequently lower ambient temperatures with zero energy input.[9]

PDRCs mimic the natural process of radiative cooling, in which the Earth cools itself by releasing heat to outer space (Earth's energy budget), although during the daytime, lowering ambient temperatures under direct solar intensity.[9] On a clear day, solar irradiance can reach 1000 W/m2 with a diffuse component between 50–100 W/m2. The average PDRC has an estimated cooling power of ~100–150 W/m2.[17] The cooling power of PDRCs is proportional to the exposed surface area of the installation.[48]

Measuring effectiveness

To measure a PDRC surface's cooling power, the absorbed powers of atmospheric and solar radiations must be quantified.[17] PDRC should not be measured when the surface is in a balanced or controlled state, but rather in a real-world setting.[49] Standardized devices to measure PDRC effectiveness have been proposed.[49]

Evaluating atmospheric downward longwave radiation based on "the use of ambient weather conditions such as the surface air temperature and humidity instead of the altitude-dependent atmospheric profiles," may be problematic since "downward longwave radiation comes from various altitudes of the atmosphere with different temperatures, pressures, and water vapor contents" and "does not have uniform density, composition, and temperature across its thickness."[9]

Broadband emitters (BE) vs. selective emitters (SE)

Broadband PDRC emitters emit in both the solar spectrum and the infrared window (8 and 14 μm), while selective PDRC emitters only emit in the infrared window.[17]
Broadband PDRC emitters emit in both the solar spectrum and the infrared window (8 and 14 μm), while selective PDRC emitters only emit in the infrared window.[17]

PDRCs can be broadband in their thermal emittance capacity, meaning they possess high emittance in both the solar spectrum and atmospheric LWIR window (8 to 14 μm), or selective emitters, meaning they narrowband emit longwave infrared radiation only in the infrared window.[17]

In theory, selective thermal emitters can achieve higher cooling power.[17] However, selective emitters also face additional challenges in real-world applications that can weaken their performance, such as from dropwise condensation, which is common even in semi-arid environments, that can accumulate on the PDRC surface even when it has been made hydrophobic and alter the narrowband emission.[50] Broadband emitters also outperform selective materials when "the material is warmer than the ambient air, or when its sub-ambient surface temperature is within the range of several degrees."[19]

Both emitters can be advantageous for different types of applications. Broadband emitters may be less problematic for horizontal applications, such as on roofs, whereas selective emitters may be more useful if implemented on vertical surfaces like building facades, where dropwise condensation is inconsequential and their stronger cooling power can be actualized.[50]

Broadband emitters can be made angle-dependent to potentially enhance their cooling performance.[17] Polydimethylsiloxane (PDMS) is a common broadband emitter used for PDRC.[50] Most PDRC materials are broadband primarily credited to their lower cost and higher performance at above-ambient temperatures.[33]

Hybrid systems

Combining PDRCs with other systems may increase their cooling power. When included in a combined thermal insulation, evaporative cooling, and radiative cooling system consisting of "a solar reflector, a water-rich and IR-emitting evaporative layer, and a vapor-permeable, IR-transparent, and solar-reflecting insulation layer," 300% higher ambient cooling power was demonstrated. This could extend the shelf life of food by 40% in humid climates and 200% in dry climates without refrigeration. The system however requires water "re-charges" to maintain its cooling power, with more frequent re-charges in hot climates than cooler climates.[51]

A dual-mode asymmetric photonic mirror (APM) consisting of silicon-based diffractive gratings could achieve all-season cooling, even under cloudy and humid conditions, as well as heating. The cooling power of APM could perform 80% more when compared to standalone radiative coolers. Under cloudy sky, it could achieve 8 °C more cooling and, for heating, 5.7 °C higher.[34]

Climatic variations

The global cooling potential of various areas around the world varies primarily based on climate zones and the presence of weather patterns and events. Dry and hot regions generally have a higher radiative cooling power (estimated up to 120 W/m2), while colder regions or those with high humidity or cloud cover generally have lower global cooling potentials.[39] The cooling potential of various regions can also change from winter to summer due to shifts in humidity and cloud cover.[9] Studies mapping the daytime radiative cooling potential have been done for China[52] and India,[53] the United States,[54] and on a continental scale across Europe.[55]

Regional cooling potential

Desert climates

Desert climates have the highest radiative cooling potential due to low humidity and cloud cover.[9]
Desert climates have the highest radiative cooling potential due to low humidity and cloud cover.[9]

Dry regions such as western Asia, north Africa, Australia and the southwestern United States are ideal for PDRC application due to the relative lack of humidity and cloud cover in both winter and summer. The cooling potential for desert regions has been estimated at "in the higher range of 80–110 W/m2," as per Aili et al.[9] and 120 W/m2 as per Yin et al.[39] The Sahara Desert and western Asia is the largest area on Earth with a high cooling potential in both winter and summer.[9]

The cooling potential of desert regions risks being relatively unfulfilled due to very low population densities, which may lower interest in applying PDRCs for local cooling. However, in the event of global implementation, lowly populated or unpopulated desert climates may be an important "land surface contribution to the planetary albedo" which could "reduce air temperature near the surface, if not the whole atmosphere."[9]

Temperate climates have a moderate to high radiative cooling potential.[9]
Temperate climates have a moderate to high radiative cooling potential.[9]

Temperate climates

Temperate climates have a high radiative cooling potential and higher average population densities when compared to desert climates, which may increase willingness to apply PDRCs in these zones. This is because these climatic zones tend to be "transitional" zones between dry and humid climates.[9] High population areas in temperate climatic zones may be susceptible to an "overcooling" effect from PDRCs (see: overcooling section below) due to temperature shifts from hot summers to mild winters, which can be overcome with the modification of PDRCs to adjust for temperature shifts.[17]

Tropical climates

Tropical climates have a lower radiative cooling potential due to high humidity and cloud cover.[9]
Tropical climates have a lower radiative cooling potential due to high humidity and cloud cover.[9]

While passive radiative cooling technologies have proven successful in mid-latitude regions of Earth, to reach the same level of performance has faced more difficulties in tropical climates. This has primarily been attributed to the higher solar irradiance and atmospheric radiation of these zones, particularly humidity and cloud cover.[13] The average cooling potential of hot and humid climates varies between 10–40 W/m2, which is significantly lower than hot and dry climates.[9]

For example, the cooling potential of most of southeast Asia and the Indian subcontinent is significantly diminished in the summer due to a dramatic increase in humidity, dropping as low as 10–30 W/m2. Other similar zones, such as tropical savannah areas in Africa, see a more modest decline during summer, dropping to 20–40 W/m2. However, tropical regions generally have a higher albedo or radiative forcing due to sustained cloud cover and thus their land surface contributes less to planetary albedo.[9]

A study by Han et al. determined criteria for a PDRC surface in tropical climates to have a solar reflectance of at least 97% and an infrared emittance of at least 80% to achieve sub-ambient temperatures in tropical climates. The researchers used a BK coating with a "solar reflectance and infrared emittance (8–13 μm) of 98.4% and 95% respectively" in the tropical climate of Singapore and achieved a "sustained daytime sub-ambient temperature of 2°C" under direct solar intensity of 1000 W/m2.[13]

Variables

Humidity and cloud coverage

Global map of cloud cover. Data taken from 2002 to 2015. The darker the color, the clearer the sky.
Global map of cloud cover. Data taken from 2002 to 2015. The darker the color, the clearer the sky.

Humidity and cloud coverage significantly weaken PDRC effectiveness.[16] A study by Huang et al. noted that "vertical variations of both vapor concentration and temperature in the atmosphere" can have a considerable impact on radiative coolers. The authors put forth that aerosol and cloud coverage can also weaken the effectiveness of radiators and thus concluded that adaptable "design strategies of radiative coolers" are needed to maximize effectiveness under these climatic conditions.[14] Regions with high humidity and cloud cover have less global cooling potential than areas with low humidity and cloud cover.[9]

Dropwise condensation

The formation of dropwise condensation on PDRC surfaces can alter the infrared emittance of the surface of selective PDRC emitters, which can weaken their performance. Even in semi-arid environments, dew formation on PDRC surfaces can occur. Thus, the cooling power of selective emitters "may broaden the narrowband emittances of the selective emitter and reduce their sub-ambient cooling power and their supposed cooling benefits over broadband emitters," as per Simsek et al., who discuss the implications on the performance of selective emitters:[50]

In showing that dropwise condensation on horizontal emitters leads to broadband emittance regardless of the emitter, our work shows that the assumed benefits of selective emitters are even smaller when it comes to the largest application of radiative cooling – cooling roofs of buildings. However, recently, it has been shown that for vertical building facades experiencing broadband summertime terrestrial heat gains and wintertime losses, selective emitters can achieve seasonal thermoregulation and energy savings. Since dew formation appears less likely on vertical surfaces even in exceptionally humid environments, the thermoregulatory benefits of selective emitters will likely persist in both humid and dry operating conditions.[50]

Rain

Global map of average annual precipitation. The darker the color, the higher the precipitation.
Global map of average annual precipitation. The darker the color, the higher the precipitation.

Rain can generally help clean PDRC surfaces that have been covered with dust, dirt, or other debris and improve their reflectivity. However, in humid areas, consistent rain can result in heavy water accumulation on PDRC surfaces which can hinder performance. In response, porous PDRCs have been developed.[56] Another response is to make hydrophobic PDRCs which are "self-cleaning." Scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed that repel rainwater and other liquids.[57]

Wind

Wind may have some effect on altering the efficiency of passive radiative cooling surfaces and technologies. Liu et al. proposes using a "tilt strategy and wind cover strategy" to mitigate effects of wind. The researchers found regional differences in regard to the impacts of wind cover in China, noting that "85% of China's areas can achieve radiative cooling performance with wind cover" whereas in northwestern China wind cover effects would be more substantial.[15] Bijarniya et al. similarly proposes the use of a wind shield in areas susceptible to high winds.[14]

Materials and production

Solar reflective and heat emissive surfaces can be of various material compositions. However, for widespread application to be feasible, PDRC materials must be low cost, available for mass production, and applicable in many contexts. Most research has focused on PDRC coatings and thin films, which tend to be more available for mass production, lower cost, and more applicable in a wider range of contexts, although other materials may provide potential for diverse applications.[18][40][58][59]

Some PDRC research has also developed more eco-friendly or sustainable materials, even if not fully biodegradable.[28][60][61][62][63] Zhong et al. state "most PDRC materials now are non-renewable polymers, artificial photonic or synthetic chemicals, which will cause excessive CO2 emissions by consuming fossil fuels and go against the global carbon neutrality goal. Environmentally friendly bio-based renewable materials should be an ideal material to devise PDRC systems."[64]

Multilayer and complex structures

Advanced photonic materials and structures, such as multilayer thin films, micro/nanoparticles, photonic crystals, metamaterials, metasurfaces, have been tested to significantly facilitate radiative cooling.[65] However, while multilayer and complex nano-photonic structures have proven successful in experimental scenarios and simulations, widespread application "is severely restricted because of the complex and expensive processes of preparation," as per Cui et al.[40] Similarly, Zhang et al. noted that "scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging."[66] This has advanced research of simpler structures for PDRC materials that are more suited for mass production.[65]

Coatings

A scalable colored PDRC coating using Bismuth oxide (pictured) was developed by Zhai et al.[24]
A scalable colored PDRC coating using Bismuth oxide (pictured) was developed by Zhai et al.[24]

PDRC coatings or paints tend to be advantageous for their direct application to surfaces, simplifying preparation processes and reducing costs,[40] although not all PDRC coatings are inexpensive.[38] Coatings generally offer "strong operability, convenient processing, and low cost, which have the prospect of large-scale utilization," as per Dong et al.[18] PDRC coatings have been developed in colors other than white while still demonstrating high solar reflectance and heat emissivity.[24]

Coatings must be durable and resistant to soiling, which can be achieved with porous PDRCs[67] or hydrophobic topcoats that can withstand cleaning, although hydrophic coatings use polytetrafluoroethylene or other similar compounds to be water-resistant.[38] Negative environmental impacts can be mitigated by limiting use of other toxic solvents common in paints, such as acetone. Non-toxic or water-based paints have been developed. More research and development is needed.[38][61]

The cost of PDRC coatings was significantly lowered with a 2018 study by Atiganyanun et al. which demonstrated how "photonic media, when properly randomized to minimize the photon transport mean free path, can be used to coat a black substrate and reduce its temperature by radiative cooling." This coating could "outperform commercially available solar-reflective white paint for daytime cooling" without using expensive manufacturing steps or materials.[68]

PDRC coatings that are described as scalable and low-cost include:

Films

A photonic radiator film based on the longicorn beetle neocerambyx gigas exhibited 95% solar irradiance and 96% emissivity.[66]
A photonic radiator film based on the longicorn beetle neocerambyx gigas exhibited 95% solar irradiance and 96% emissivity.[66]

Many PDRC thin films have been developed which have demonstrated very high solar reflectance and heat emittance. However, films with precise patterns or structures are not scalable "due to the cost and technical difficulties inherent in large-scale precise lithography," as per Khan et al.,[19] or "due to complex nanoscale lithography/synthesis and rigidity," as per Zhou et al.[71] Some researchers have attempted to overcome this with various methods:

Metafabrics

PDRCs can also come in the form of metafabrics, which can be worn as clothing to shield and regulate body temperatures in times of extreme heat. Most metafabrics are made of petrol-based fibers, although research and development of sustainable or regenerative materials is ongoing.[73] For instance, Zhong et al. states that "new flexible cellulose fibrous films with wood-like hierarchical microstructures need to be developed for wearable PDRC applications."[64]

Aerogels

Aerogels may be used as a potential low-cost PDRC material scalable for mass production. Some aerogels can also be considered a more environmentally friendly alternative to other materials, with degradable potential and the absence of toxic chemicals.[75][62] Aerogels can also be useful as a thermal insulation material to reduce solar absorption and parasitic heat gain to improve the cooling performance of PDRCs.[76]

Biodegradable surfaces

With the proliferation of PDRC development, many proposed radiative cooling materials are not biodegradable. As per Park et al., "sustainable materials for radiative cooling have not been sufficiently investigated."[28]

Applications

Passive daytime radiative cooling has "the potential to simultaneously alleviate the two major problems of energy crisis and global warming"[1] while being an "environmental protection refrigeration technology."[18] PDRCs thereby have an array of potential applications, but are now most often applied to various aspects of the built environment, such as building envelopes, cool pavements, and other surfaces to decrease energy demand, costs, and CO2 emissions.[78] PDRC has been tested and applied for indoor space cooling, outdoor urban cooling, solar cell efficiency, power plant condenser cooling, among other applications.[16][27] For outdoor applications, the lifetime of PDRCs should be adequately estimated, both for high humidity and heat as well as for UV stability.[33]

Indoor space cooling

Single-family detached homes in the US suburbs are estimated to lower energy costs by 26% to 46% with PDRC implementation.[79]
Single-family detached homes in the US suburbs are estimated to lower energy costs by 26% to 46% with PDRC implementation.[79]

The most common application of passive daytime radiative cooling currently is on building envelopes, including PDRC cool roofs, which can significantly lower indoor space temperatures within buildings. A PDRC roof application can double the energy savings of a white roof.[80] This makes PDRCs a sustainable and low-cost alternative or supplement to air conditioning by decreasing energy demand, alleviating energy grids in peak periods, and reducing CO2 emissions caused by air conditioning's release of hydrofluorocarbons into the atmosphere which can be thousands of times more potent that CO2.[16][48][40][81]

Air conditioning alone accounts for 12%-15% of global energy usage,[16][73] while CO2 emissions from air conditioning account for "13.7% of energy-related CO2 emissions, approximately 52.3 EJ yearly"[18] or 10% of emissions total.[73] Air conditioning applications are expected to rise, despite their negative impacts on energy sectors, costs, and global warming, which has been described as a "vicious cycle."[24] However, this can be significantly reduced with the mass production of low-cost PDRCs for indoor space cooling.[16][81][82] A multilayer PDRC surface covering 10% of a building's roof can replace 35% of air conditioning used during the hottest hours of daytime.[16]

In suburban single-family residential areas, PDRCs can lower energy costs by 26% to 46% in the United States[79] and lower temperatures on average by 5.1ᵒC. With the addition of "cold storage to utilize the excess cooling energy of water generated during off-peak hours, the cooling effects for indoor air during the peak-cooling-load times can be significantly enhanced" and air temperatures may be reduced by 6.6–12.7 °C.[83]

In cities, PDRCs can result in significant energy and cost savings. In a study on US cities, Zhou et al. found that "cities in hot and arid regions can achieve high annual electricity consumption savings of >2200 kWh, while <400 kWh is attainable in colder and more humid cities," being ranked from highest to lowest by electricity consumption savings as follows: Phoenix (∼2500 kWh), Las Vegas (∼2250 kWh), Austin (∼2100 kWh), Honolulu (∼2050 kWh), Atlanta (∼1500 kWh), Indianapolis (∼1200 kWh), Chicago (∼1150 kWh), New York City (∼900 kWh), Minneapolis (∼850 kWh), Boston (∼750 kWh), Seattle (∼350 kWh).[83] In a study projecting energy savings for Indian cities in 2030, Mumbai and Kolkata had a lower energy savings potential, Jaisalmer, Varansai, and Delhi had a higher potential, although with significant variations from April to August dependent on humidity and wind cover.[53]

The growing interest and rise in PDRC application to buildings has been attributed to cost savings related to "the sheer magnitude of the global building surface area, with a market size of ∼$27 billion in 2025," as estimated in a 2020 study.[78]

Outdoor urban space cooling

See also: Urban heat island

A PDRC installed on a roof in Kolkata exhibited a nearly 4.9ᵒC decrease in surface ground temperatures (with an average reduction of 2.2ᵒC).[19]
A PDRC installed on a roof in Kolkata exhibited a nearly 4.9ᵒC decrease in surface ground temperatures (with an average reduction of 2.2ᵒC).[19]

Passive daytime radiative cooling surfaces can mitigate extreme heat from the Urban Heat Island Effect which occurs in over 450 cities worldwide, where it can be as much as 10–12ᵒC hotter in Urban areas in comparison to surrounding rural areas.[19][41] On an average hot summer day, the roofs of buildings can be 27–50ᵒC hotter than the surrounding air, warming air temperatures further through convection. Well-insulated dark rooftops are significantly hotter than all other urban surfaces, including asphalt pavements,[41] further expanding air conditioning demand (which further accelerates global warming and urban heat island through the release of waste heat into the ambient air) and increasing risks of heat-related disease and fatal health effects.[19][44][45]

PDRCs can be applied to building roofs and urban shelters to significantly lower surface temperatures with zero energy consumption by reflecting heat out of the urban environment and into outer space.[19][41] The primary obstacle of PDRC implementation in urban areas is the glare that may be caused through the reflectance of visible light onto surrounding buildings. Colored PDRC surfaces may mitigate glare issues,[38] such as Zhai et al.[24] "Super-white paints with commercial high-index (n∼1.9) retroreflective spheres," as per Mandal et al.,[38] or the use of retroreflective materials (RRM) may also mitigate glare, although further research and development is needed.[41] Surrounding buildings without PDRC application may weaken the cooling power of PDRCs.[79]

Even when installed on roofs in highly dense urban areas, broadband radiative cooling panels have been shown to lower surface temperatures at the sidewalk level.[84] A study by Khan et al. published in 2022 assessed the effects of PDRC surfaces in winter, including for both non-modulated and modulated PDRCs, in the Kolkata metropolitan area. A non-modulated PDRC with a reflectance of 0.95 and emissivity of 0.93 decreased ground surface temperatures by nearly 4.9ᵒC and with an average daytime reduction of 2.2ᵒC.[19]

While in summer the cooling effects of broadband non-modulated PDRCs may be desirable, they could present an uncomfortable "overcooling" effect for city populations in winter and thus increase energy use for heating. This can be mitigated by broadband modulated PDRCs, which they found could increase daily ambient urban temperatures by 0.4–1.4ᵒC in winter. While in the tropical metropolitan area of Kolkata, for instance, "overcooling" is unlikely, elsewhere it could impact the willingness to apply PDRCs in urban spaces. Therefore, modulated PDRCs may be preferred in cities with warm summers and cold winters for controlled cooling, while non-modulated PDRCs may be more beneficial for cities with hot summers and moderate winters. The authors expected "low-cost optically modulated passive systems" to be commercially available soon.[19]

In a study on urban bus shelters, it was found that most shelters fail at providing thermal comfort for commuters, noting that, on average, a tree could provide 0.5ᵒC more cooling.[79] Other methods to cool shelters often resort to air conditioning or other energy intensive measures that can crowd commuters in an enclosed space for cooling. Urban shelters with PDRC roofing can significantly reduce temperatures with zero added costs or energy input, while adding "a non-reciprocal mid-infrared cover" can increase benefits by reducing incoming atmospheric radiation as well as reflecting radiation from surrounding buildings, as per Mokharti et al.[79]

For outdoor urban space cooling, it is recommended that PDRC implementation in urban areas primarily focus on increasing albedo so long as heat emissivity can be maintained at the standard of 90%, as per Anand et al. This can rapidly and significantly lower temperatures while reducing energy demand and costs for cooling in urban environments.[41]

Solar energy efficiency

Solar cell efficiency can be improved with PDRC application to reduce overheating and degradation of cells.[8]
Solar cell efficiency can be improved with PDRC application to reduce overheating and degradation of cells.[8]

Passive daytime radiative cooling surfaces can be integrated with solar energy plants, referred to as solar energy–radiative cooling (SE–RC), to improve functionality and performance by preventing solar cells from 'overheating' and thus degrading. Since solar cells have a maximum efficiency of 33.7% (with the average commercial PV panel having a conversion rate around 20%), the majority of absorbed power produces excess heat and increases the operating temperature of the system.[8][85] Solar cell efficiency declines 0.4-0.5% for every 1ᵒC increase in temperature.[8]

Passive daytime radiative cooling can extend the life of solar cells by lowering the operating temperature of the system.[85] Integrating PDRCs into solar energy systems is also relatively simple, given that "most solar energy harvesting systems have a sky-facing flat plate structural design, which is similar to radiative cooling systems." Integration has been shown to "produce a higher energy gain per unit area" while also increasing the "total useful working time." Integrated systems can mitigate issues of "limited working time and low energy gain" and are "a current research hotspot," as per Ahmed et al.[22]

Methods have been proposed to potentially enhance cooling performance. Lu et al. proposes using a "full-spectrum synergetic management (FSSM) strategy to cool solar cells, which combines radiative cooling and spectral splitting to enhance radiative heat dissipation and reduce the waste heat generated by the absorption of sub-BG photons."[86]

Outdoor tests using various PDRC materials, some more scalable than others, have demonstrated various degrees of cooling power:

Personal thermal management

The usage of passive daytime radiative cooling in fabrics to regulate body temperatures during extreme heat is in research and development. While other fabrics are useful for heat accumulation, they "may lead to heat stroke in hot weather."[90] Zeng et al. states that "incorporating passive radiative cooling structures into personal thermal management technologies could effectively defend humans against intensifying global climate change."[91]

Wearable PDRCs can come in different forms and be particularly useful for outdoor workers. Readily available wearable PDRCs are not yet available, although prototypes have been developed. This field of research is referred to as personal thermal management (PTM).[74][92] Although most textiles developed are in white, colored wearable materials have also been developed, although only in select colors that are relatively successful for solar reflectance to minimize heat gain.[21]

Power plant condenser cooling

Passive daytime radiative cooling can be used in various power plant condensers, including thermoelectric power plants and concentrated solar plants (CSP) to cool water for effective use within the heat exchanger. A generalized study of "a covered pond with radiative cooler revealed that 150 W/m2 flux could be achieved without loss of water."[16] PDRC application for power plant condensers can reduce high water use and thermal pollution caused by water cooling.[9]

For a thermoelectric power plant condenser, one study found that supplementing the air-cooled condenser for radiative cooling panels "get a 4096 kWhth/day cooling effect with a pump energy consumption of 11 kWh/day."[16] For a concentrated solar plant (CSP) "on the CO2 supercritical cycle at 550ᵒC can be improved in 5% net output over an air-cooled system by integration with 14 m2 /kWe capacity radiative cooler."[16]

Thermal regulation of buildings

In addition to cooling, passive daytime radiative cooling surfaces can be modified to be self-adaptive for temperature-dependent 'switching' from cooling to heating or, in other words, for full-scale thermal regulation.[19] This can be achieved through switching the thermal emittance of the surface from a high to low value.[93] Applications are limited to testing and commercially available self-switching PDRCs are in research and development.[19][93]

Thermoelectric generation

When combined with a thermoelectric generator, a passive daytime radiative cooling surface can be used to generate electricity during the daytime and nighttime, although the power generated in tests has been relatively low. Research and development is preliminary.[93]

Automobile and greenhouse cooling

Thermally enclosed spaces, including automobiles and greenhouses, are particularly susceptible to harmful temperature increases, especially during extreme weather. This is because of the heavy presence of windows, which are transparent to incoming solar radiation yet act as opaque to outgoing long-wave thermal radiation, which causes them to heat rapidly. The temperature of an automobile in direct sunlight can rise to 60–82ᵒC when ambient temperatures is only 21ᵒC.This accumulation of heat "can cause heat stroke and hyperthermia in the occupants, especially children," which can be alleviated with passive radiative cooling.[93]

Water harvesting

Dew harvesting yields may be improved with passive daytime radiative cooling application. Selective PDRC emitters that have a high emissivity only at the atmospheric window (8–13 μm) and broadband emitters may produce varying results. In one study using a broadband PDRC, the research condensed "∼8.5 mL day of water for 800 W m2 of peak solar intensity."[93] Whereas selective emitters may be less advantageous in other contexts, they may be more advantageous for dew harvesting applications.[50] PDRCs could improve atmospheric water harvesting by being combined with solar vapor generation systems to improve water collection rates.[33]

Water and ice cooling

Passive daytime radiative cooling surfaces can be installed over the surface of a body of water for cooling. In a controlled study, a body of water was cooled 10.6ᵒC below the ambient temperature with the usage of a photonic radiator.[16]

PDRC surfaces have been developed to cool ice and prevent ice from melting under sunlight. It has been proposed as a sustainable method for ice protection. This can be applied to protect iced or refrigerated food from spoiling.[94]

Unwanted side effects

Jeremy Munday writes that although "unexpected effects will likely occur" with global PDRC implementation, that "these structures can be removed immediately if needed, unlike methods that involve dispersing particulate matter into the atmosphere, which can last for decades."[95] Wang et al. state that stratospheric aerosol injection "might cause potentially dangerous threats to the Earth’s basic climate operations" that may not be reversible, preferring PDRC.[96] Zevenhoven et al. state that "instead of stratospheric aerosol injection (SAI), cloud brightening or a large number of mirrors in the sky (“sunshade geoengineering”) to block out or reflect incoming (short-wave, SW) solar irradiation, long-wavelength (LW) thermal radiation can be selectively emitted and transferred through the atmosphere into space".[97]

"Overcooling" and PDRC modulation

Modifying PDRCs with vanadium dioxide (pictured) can achieve temperature-based 'switching' from cooling to heating to mitigate the "overcooling" effect.[17]
Modifying PDRCs with vanadium dioxide (pictured) can achieve temperature-based 'switching' from cooling to heating to mitigate the "overcooling" effect.[17]

"Overcooling" is cited as a side effect of PDRCs that may be problematic, especially when PDRCs are applied in high-population areas with hot summers and cool winters, characteristic of temperate zones.[17] While PDRC application in these areas can be useful in summer, in winter it can result in an increase in energy consumption for heating and thus may reduce the benefits of PDRCs on energy savings and emissions.[19][23] As per Chen et al., "to overcome this issue, dynamically switchable coatings have been developed to prevent overcooling in winter or cold environments."[17]

The detriments of overcooling can be reduced by modulation of PDRCs, harnessing their passive cooling abilities during summer, while modifying them to passively heat during winter. Modulation can involve "switching the emissivity or reflectance to low values during the winter and high values during the warm period."[19] In 2022, Khan et al. concluded that "low-cost optically modulated" PDRCs are "under development" and "are expected to be commercially available on the market soon with high future potential to reduce urban heat in cities without leading to an overcooling penalty during cold periods."[19]

There are various methods of making PDRCs 'switchable' to mitigate overcooling.[17] Most research has used vanadium dioxide (VO2), an inorganic compound, to achieve temperature-based 'switchable' cooling and heating effects.[17][23] While, as per Khan et al., developing VO2 is difficult, their review found that "recent research has focused on simplifying and improving the expansion of techniques for different types of applications."[19] Chen et al. found that "much effort has been devoted to VO2 coatings in the switching of the mid-infrared spectrum, and only a few studies have reported the switchable ability of temperature-dependent coatings in the solar spectrum."[17] Temperature-dependent switching requires no extra energy input to achieve both cooling and heating.[17]

Other methods of PDRC 'switching' require extra energy input to achieve desired effects. One such method involves changing the dielectric environment. This can be done through "reversible wetting" and drying of the PDRC surface with common liquids such as water and alcohol. However, for this to be implemented on a mass scale, "the recycling, and utilization of working liquids and the tightness of the circulation loop should be considered in realistic applications."[17]

Another method involves 'switching' through mechanical force, which may be useful and has been "widely investigated in [PDRC] polymer coatings owing to their stretchability." For this method, "to achieve a switchable coating in εLWIR, mechanical stress/strain can be applied in a thin PDMS film, consisting of a PDMS grating and embedded nanoparticles." One study estimated, with the use of this method, that "19.2% of the energy used for heating and cooling can be saved in the US, which is 1.7 times higher than the only cooling mode and 2.2 times higher than the only heating mode," which may inspire additional research and development.[17]

Glare and visual appearance

Glare caused from surfaces with high solar reflectance may present visibility concerns that can limit PDRC application, particularly within urban environments at the ground level.[24] PDRCs that use a "scattering system" to generate reflection in a more diffused manner have been developed and are "more favorable in real applications," as per Lin et al.[98]

Low-cost PDRC colored paint coatings, which reduce glare and increase the color diversity of PDRC surfaces, have also been developed. While some of the surface's solar reflectance is lost in the visible light spectrum, colored PDRCs can still exhibit significant cooling power, such as a coating by Zhai et al., which used a α-Bi2O3 coating (resembling the color of the compound) to develop a non-toxic paint that demonstrated a solar reflectance of 99% and heat emissivity of 97%.[24]

Generally it is noted that there is a tradeoff between cooling potential and darker colored surfaces. Less reflective colored PDRCs can also be applied to walls while more reflective white PDRCs can be applied to roofs to increase visual diversity of vertical surfaces, yet still contribute to cooling.[25]

Commercialization

The commercialization of passive daytime radiative cooling technologies is in an early stage of development.[40]

SkyCool Systems, founded by Aaswath P. Raman, who authored the scientific breakthrough study demonstrating the use of photonic metamaterials in making PDRC possible,[26] is a startup that is commercializing radiative cooling technologies.[38] SkyCool panels have been applied to some buildings in California, reducing energy costs. The company has received a grant from the California Energy Commission for further application opportunities.[99]

3M, an American multinational corporation, has developed a selectively emissive passive radiative cooling film. The film has been applied through pilot programs that are open for expansion.[5] The film was tested on bus shelters in Tempe, Arizona.[100] 3M's film achieved "10–20% energy savings when deployed on SkyCool Systems panels and integrated with a building's HVAC or refrigeration system."[101]

History

The Saharan silver ant's ability to cool its body temperature in extreme heat inspired early PDRC research.[102]
The Saharan silver ant's ability to cool its body temperature in extreme heat inspired early PDRC research.[102]

Nocturnal passive radiative cooling has been recognized for thousands of years, with records showing awareness by the ancient Iranians, demonstrated through the construction of Yakhchāls, since 400 B.C.E.[103]

Passive daytime radiative cooling was hypothesized by Félix Trombe in 1967. The first experimental setup was created in 1975, but was only successful for nighttime cooling. Further developments to achieve daytime cooling using different material compositions were not successful.[16]

In the 1980s, Lushiku and Granqvist identified the infrared window as a potential way to access the ultracold outer space as a way to achieve passive daytime cooling.[7]

Early attempts at developing passive radiative daytime cooling materials took inspiration from nature, particularly the Saharan silver ant and white beetles, noting how they cooled themselves in extreme heat.[27]

Research and development in passive daytime radiative cooling evolved rapidly in the 2010s with the discovery of the ability to suppress solar heating using photonic metamaterials, which widely expanded research and development in the field.[27][104] This is largely credited to the landmark study by Aaswath P. Raman, Marc Abou Anoma, Linxiao Zhu, Eden Raphaeli, and Shanhui Fan published in 2014.[26]

See also

References

  1. ^ a b c d e f g Chen, Meijie; Pang, Dan; Chen, Xingyu; Yan, Hongjie; Yang, Yuan (2022). "Passive daytime radiative cooling: Fundamentals, material designs, and applications". EcoMat. 4. doi:10.1002/eom2.12153. S2CID 240331557 – via Wiley. Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming.
  2. ^ Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Archived from the original on 22 February 2022. Retrieved 27 September 2022 – via ScienceDirect. By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth.
  3. ^ Yin, Xiaobo; Yang, Ronggui; Tan, Gang; Fan, Shanhui (November 2020). "Terrestrial radiative cooling: Using the cold universe as a renewable and sustainable energy source". Science. 370 (6518): 786–791. Bibcode:2020Sci...370..786Y. doi:10.1126/science.abb0971. PMID 33184205. S2CID 226308213. ...terrestrial radiative cooling has emerged as a promising solution for mitigating urban heat islands and for potentially fighting against global warming if it can be implemented at a large scale.
  4. ^ Bijarniya, Jay Prakash; Sarkar, Jahar; Maiti, Pralay (November 2020). "Review on passive daytime radiative cooling: Fundamentals, recent researches, challenges and opportunities". Renewable and Sustainable Energy Reviews. 133: 110263. doi:10.1016/j.rser.2020.110263. S2CID 224874019 – via Elsevier Science Direct. Passive radiative cooling can be considered as a renewable energy source, which can pump heat to cold space and make the devices more efficient than ejecting heat at earth atmospheric temperature.
  5. ^ a b "What is 3M Passive Radiative Cooling?". 3M. Archived from the original on 22 September 2021. Retrieved 27 September 2022. Passive Radiative Cooling is a natural phenomenon that only occurs at night in nature because all nature materials absorb more solar energy during the day than they are able to radiate to the sky.
  6. ^ a b c d Wang, Tong; Wu, Yi; Shi, Lan; Hu, Xinhua; Chen, Min; Wu, Limin (2021). "A structural polymer for highly efficient all-day passive radiative cooling". Nature Communications. 12 (365): 365. doi:10.1038/s41467-020-20646-7. PMC 7809060. PMID 33446648. Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.
  7. ^ a b c Zevenhovena, Ron; Fält, Martin (June 2018). "Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach". Energy. 152 – via Elsevier Science Direct.
  8. ^ a b c d Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  9. ^ a b c d e f g h i j k l m n o p q r s t u v w x y Aili, Ablimit; Yin, Xiaobo; Yang, Ronggui (October 2021). "Global Radiative Sky Cooling Potential Adjusted for Population Density and Cooling Demand". Atmosphere. 12 (11): 1379. doi:10.3390/atmos12111379.
  10. ^ a b c d e f g h i j k l m n Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Archived from the original on 22 February 2022. Retrieved 27 September 2022 – via ScienceDirect.
  11. ^ Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Archived from the original on 22 February 2022. Retrieved 27 September 2022 – via ScienceDirect. If only 1%–2% of the Earth's surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease.
  12. ^ a b Zevenhovena, Ron; Fält, Martin (June 2018). "Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach". Energy. 152 – via Elsevier Science Direct. With 100 W/m2 as a demonstrated passive cooling effect, a surface coverage of 0.3% would then be needed, or 1% of Earth's land mass surface. If half of it would be installed in urban, built areas which cover roughly 3% of the Earth's land mass, a 17% coverage would be needed there, with the remainder being installed in rural areas.
  13. ^ a b c Han, Di; Fei, Jipeng; Li, Hong; Ng, Bing Feng (August 2022). "The criteria to achieving sub-ambient radiative cooling and its limits in tropical daytime". Building and Environment. 221 (1): 109281. doi:10.1016/j.buildenv.2022.109281 – via Elsevier Science Direct.
  14. ^ a b c Huang, Jingyuan; Lin, Chongjia; Li, Yang; Huang, Baoling (May 2022). "Effects of humidity, aerosol, and cloud on subambient radiative cooling". International Journal of Heat and Mass Transfer. 186: 122438. doi:10.1016/j.ijheatmasstransfer.2021.122438. S2CID 245805048 – via Elsevier Science Direct.
  15. ^ a b Liu, Junwei; Zhang, Ji; Zhang, Debao; Jiao, Shifei; Xing, Jingcheng; Tang, Huajie; Zhang, Ying; Li, Shuai; Zhou, Zhihua; Zuo, Jian (September 2020). "Sub-ambient radiative cooling with wind cover". Renewable and Sustainable Energy Reviews. 130: 109935. doi:10.1016/j.rser.2020.109935. S2CID 219911962 – via Elsevier Science Direct.
  16. ^ a b c d e f g h i j k l Bijarniya, Jay Prakash; Sarkar, Jahar; Maiti, Pralay (November 2020). "Review on passive daytime radiative cooling: Fundamentals, recent researches, challenges and opportunities". Renewable and Sustainable Energy Reviews. 133: 110263. doi:10.1016/j.rser.2020.110263. S2CID 224874019 – via Elsevier Science Direct.
  17. ^ a b c d e f g h i j k l m n o p q r Chen, Meijie; Pang, Dan; Chen, Xingyu; Yan, Hongjie; Yang, Yuan (2022). "Passive daytime radiative cooling: Fundamentals, material designs, and applications". EcoMat. 4. doi:10.1002/eom2.12153. S2CID 240331557 – via Wiley.
  18. ^ a b c d e f g h Dong, Yan; Han, Han; Wang, Fuqiang; Zhang, Yingjie; Cheng, Ziming; Shi, Xuhang; Yan, Yujing (June 2022). "A low-cost sustainable coating: Improving passive daytime radiative cooling performance using the spectral band complementarity method". Renewable Energy. 192: 606–616. doi:10.1016/j.renene.2022.04.093 – via Elsevier Science Direct.
  19. ^ a b c d e f g h i j k l m n o Khan, Ansar; Carlosena, Laura; Feng, Jie; Khorat, Samiran; Khatun, Rupali; Doan, Quang-Van; Santamouris, Mattheos (January 2022). "Optically Modulated Passive Broadband Daytime Radiative Cooling Materials Can Cool Cities in Summer and Heat Cities in Winter". Sustainability. 14 – via MDPI.
  20. ^ a b c d e f g Liang, Jun; Wu, Jiawei; Guo, Jun; Li, Huagen; Zhou, Xianjun; Liang, Sheng; Qiu, Cheng-Wei; Tao, Guangming (September 2022). "Radiative cooling for passive thermal management towards sustainable carbon neutrality". National Science Review. doi:10.1093/nsr/nwac208 – via Oxford Academic.
  21. ^ a b Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  22. ^ a b c Ahmed, Salman; Li, Zhenpeng; Javed, Muhammad Shahzad; Ma, Tao (September 2021). "A review on the integration of radiative cooling and solar energy harvesting". Materials Today: Energy. 21: 100776. doi:10.1016/j.mtener.2021.100776 – via Elsevier Science Direct.
  23. ^ a b c Wang, Zhaochen; Kim, Sun-Kyung; Hu, Run (March 2022). "Self-switchable radiative cooling". Matter. 5 (3): 780–782. doi:10.1016/j.matt.2022.01.018. S2CID 247329090 – via Elsevier Science Direct.
  24. ^ a b c d e f g h Zhai, Huatian; Fan, Desong; Li, Qiang (September 2022). "Scalable and paint-format colored coatings for passive radiative cooling". Solar Energy Materials and Solar Cells. 245: 111853. doi:10.1016/j.solmat.2022.111853. S2CID 249877164 – via Elsevier Science Direct.
  25. ^ a b Dang, Saichao; Xiang, Jingbo; Yao, Hongxin; Yang, Fan; Ye, Hong (March 2022). "Color-preserving daytime passive radiative cooling based on Fe3+-doped Y2Ce2O7". Energy and Buildings. 259: 111861. doi:10.1016/j.enbuild.2022.111861. S2CID 246105880 – via Elsevier Science Direct.
  26. ^ a b c Raman, Aaswath P.; Anoma, Marc Abou; Zhu, Linxiao; Raphaeli, Eden; Fan, Shanhui (2014). "Passive Radiative Cooling Below Ambient air Temperature under Direct Sunlight". Nature. 515 (7528): 540–544. Bibcode:2014Natur.515..540R. doi:10.1038/nature13883. PMID 25428501. S2CID 4382732 – via nature.com.
  27. ^ a b c d e f g Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  28. ^ a b c d Park, Chanil; Park, Choyeon; Nie, Xiao; Lee, Jaeho; Kim, Yong Seok; Yoo, Youngjae (2022). "Fully Organic and Flexible Biodegradable Emitter for Global Energy-Free Cooling Applications". ACS Sustainable Chem. Eng. 10 (21): 7091–7099. doi:10.1021/acssuschemeng.2c01182 – via ACS Publications.
  29. ^ Miranda, Nicole D.; Renaldi, Renaldi; Khosla, Radhika; McCulloch, Malcolm D. (October 2021). "Bibliometric analysis and landscape of actors in passive cooling research". Renewable and Sustainable Energy Reviews. 149: 111406. doi:10.1016/j.rser.2021.111406 – via Elsevier Science Direct. In the last three years, however, publications on radiative cooling and solar control have been the most numerous and hence are promising technologies in the field.
  30. ^ a b Zevenhovena, Ron; Fält, Martin (June 2018). "Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach". Energy. 152 – via Elsevier Science Direct. An alternative, third geoengineering approach would be enhanced cooling by thermal radiation from the Earth's surface into space.
  31. ^ a b Wang, Tong; Wu, Yi; Shi, Lan; Hu, Xinhua; Chen, Min; Wu, Limin (2021). "A structural polymer for highly efficient all-day passive radiative cooling". Nature Communications. 12 (365): 365. doi:10.1038/s41467-020-20646-7. PMC 7809060. PMID 33446648. One possibly alternative approach is passive radiative cooling—a sky-facing surface on the Earth spontaneously cools by radiating heat to the ultracold outer space through the atmosphere's longwave infrared (LWIR) transparency window (λ ~ 8–13 μm).
  32. ^ Cao, Di; Li, Xiaoming; Gu, Yu (June 2022). "Highly optically selective polyethylene porous films as versatile optical shields for daytime radiative cooling applications". Solar Energy Materials and Solar Cells. 240: 111727. doi:10.1016/j.solmat.2022.111727. S2CID 247963303 – via Elsevier Science Direct. Radiative cooling technology holds great promise in reducing energy consumptions for cooling and is perceived as a geoengineering approach to fight climate change as well.
  33. ^ a b c d Zhou, Lyu; Rada, Jacob; Tian, Yanpei; Han, Yu; Lai, Zhiping; McCabe, Matthew F.; Gan, Qiaoqiang (September 2022). "Radiative cooling for energy sustainability: Materials, systems, and applications". Physical Review Materials. 6 (9): 090201. Bibcode:2022PhRvM...6i0201Z. doi:10.1103/PhysRevMaterials.6.090201. S2CID 252416825 – via APS Physics.
  34. ^ a b Ly, Kally Chein Sheng; Liu, Xianghui; Song, Xiaokun; Xiao, Chengyu; Wang, Pan; Zhou, Han; Fan, Tongxiang (May 2022). "A Dual-Mode Infrared Asymmetric Photonic Structure for All-Season Passive Radiative Cooling and Heating". Advanced Functional Materials. 32 (31). doi:10.1002/adfm.202203789. S2CID 248804080 – via Wiley.
  35. ^ Hu, Mingke; Zhao, Bin; Suhendri, Suhendri; Cao, Jingyu; Wang, Qiliang; Riffat, Saffa; Su, Yuehong; Pei, Gang (November 2022). "Quantitative characterization of the effect of inclination angle on flat-plate radiative cooling performance in buildings". Building Engineering. 59. Radiative sky cooling is a renewable technology that has attracted increasing attention in the research community
  36. ^ Yu, Xinxian; Yao, Fengju; Huang, Wenjie; Xu, Dongyan; Chen, Chun (July 2022). "Renewable Energy". Renewable Energy. 194 – via Elsevier Science Direct. Radiative cooling is a renewable technology that is promising to meet this goal. It is a passive cooling strategy that dissipates heat through the atmosphere to the universe. Radiative cooling does not consume external energy but rather harvests coldness from outer space as a new renewable energy source.
  37. ^ Vall, Sergi; Johannes, Kévyn; David, Damien; Castell, Albert (July 2022). "A new flat-plate radiative cooling and solar collector numerical model: Evaluation and metamodeling". Energy. 202 – via Elsevier Science Direct. Radiative cooling is a renewable technology that can complement or partially replace current cooling technologies.
  38. ^ a b c d e f g Mandal, Jyotirmoy; Yang, Yuan; Yu, Nanfung; Raman, Aaswath P. (July 2020). "Paints as a Scalable and Effective Radiative Cooling Technology for Buildings". Joule. 4 (7): 1350–1356. doi:10.1016/j.joule.2020.04.010. S2CID 219749984 – via Elsevier Science Direct.
  39. ^ a b c Yin, Xiaobo; Yang, Ronggui; Tan, Gang; Fan, Shanhui (November 2020). "Terrestrial radiative cooling: Using the cold universe as a renewable and sustainable energy source". Science. 370 (6518): 786–791. Bibcode:2020Sci...370..786Y. doi:10.1126/science.abb0971. PMID 33184205. S2CID 226308213.
  40. ^ a b c d e f Cui, Yan; Luo, Xianyu; Zhang, Fenghua; Sun, Le; Jin, Nuo; Yang, Weiman (August 2022). "Progress of passive daytime radiative cooling technologies towards commercial applications". Particuology. 67: 57–67. doi:10.1016/j.partic.2021.10.004. S2CID 243468810 – via Elsevier Science Direct.
  41. ^ a b c d e f g Anand, Jyothis; Sailor, David J.; Baniassadi, Amir (February 2021). "The relative role of solar reflectance and thermal emittance for passive daytime radiative cooling technologies applied to rooftops". Sustainable Cities and Society. 65: 102612. doi:10.1016/j.scs.2020.102612. S2CID 229476136 – via Elsevier Science Direct.
  42. ^ Lv, Jinpeng; Chen, Zhuo; Li, Xingji (April 2022). "Calcium Phosphate Paints for Full-Daytime Subambient Radiative Cooling". ACS Applied Energy Materials. 5 (4): 4117–4124. doi:10.1021/acsaem.1c03457. S2CID 247986320 – via ACS Publications. Passive radiative cooling is of great significance for energy-saving and global carbon neutrality because of its zero energy consumption, no pollution, and low cost.
  43. ^ Chen, Guoliang; Wang, Yaming; Qiu, Jun; Cao, Jianyun; Zou, Yongchun; Wang, Shuqi; Jia, Dechang; Zhou, Yu (August 2021). "A facile bioinspired strategy for accelerating water collection enabled by passive radiative cooling and wettability engineering". Materials & Design. 206: 109829. doi:10.1016/j.matdes.2021.109829. S2CID 236255835 – via Elsevier Science Direct.
  44. ^ a b Chen, Meijie; Pang, Dan; Yan, Hongjie (November 2022). "Colored passive daytime radiative cooling coatings based on dielectric and plasmonic spheres". Applied Thermal Engineering. 216: 119125. doi:10.1016/j.applthermaleng.2022.119125. S2CID 251420566 – via Elsevier Science Direct. One such promising alternative is radiative cooling, which is a ubiquitous process of losing surface heat through thermal radiation. Instead of releasing waste heat into ambient air as conventional cooling systems, radiative cooling passively discharges it into outer space.
  45. ^ a b Kovats, Sari; Brisley, Rachel (2021). Betts, R.A.; Howard, A.B.; Pearson, K.V. (eds.). "Health, Communities and the Built Environment" (PDF). The Third UK Climate Change Risk Assessment Technical Report. Prepared for the Climate Change Committee, London: 38. Although uptake may increase autonomously in the future, relying on air conditioning to deal with the risk is a potentially maladaptive solution, and it expels waste heat into the environment – thereby enhancing the urban heat island effect.
  46. ^ Chen, Shau-Liang; Chang, Sih-Wei; Chen, Yen-Jen; Chen, Hsuen-Li (2021). "Possible warming effect of fine particulate matter in the atmosphere". Communications Earth & Environment. 2 (1): 208. Bibcode:2021ComEE...2..208C. doi:10.1038/s43247-021-00278-5. S2CID 238234137 – via nature.com.
  47. ^ Wang, Tong; Wu, Yi; Shi, Lan; Hu, Xinhua; Chen, Min; Wu, Limin (2021). "A structural polymer for highly efficient all-day passive radiative cooling". Nature Communications. 12 (365): 365. doi:10.1038/s41467-020-20646-7. PMC 7809060. PMID 33446648.
  48. ^ a b Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  49. ^ a b Yoon, Siwon; Chae, Dongwoo; Seo, Junyong; Choi, Minwoo; Lim, Hangyu; Lee, Heon; Lee, Bong Jae (August 2022). "Development of a device for characterizing radiative cooling performance". Applied Thermal Engineering. 213: 118744. doi:10.1016/j.applthermaleng.2022.118744. S2CID 249330437 – via Elsevier Science Direct.
  50. ^ a b c d e f Simsek, Eylul; Mandal, Jyotirmoy; Raman, Aaswath P.; Pilon, Laurent (December 2022). "Dropwise condensation reduces selectivity of sky-facing radiative cooling surfaces". International Journal of Heat and Mass Transfer. 198: 123399. doi:10.1016/j.ijheatmasstransfer.2022.123399. S2CID 252242911 – via Elsevier Science Direct.
  51. ^ Lu, Zhengmao; Leroy, Arny; Zhang, Lenan; Patel, Jatin J.; Wang, Evelyn N.; Grossman, Jeffrey C. (September 2022). "Significantly enhanced sub-ambient passive cooling enabled by evaporation, radiation, and insulation". Cell Reports Physical Science. 3 (10): 101068. doi:10.1016/j.xcrp.2022.101068. S2CID 252411940 – via Elsevier Science Direct.
  52. ^ Chang, Kai, and Qingyuan Zhang. "Modeling of downward longwave radiation and radiative cooling potential in China." Journal of Renewable and Sustainable Energy 11, no. 6 (2019): 066501.
  53. ^ a b Sarkar, Jahar; Bijarniya, Jay Prakash (December 2020). "Climate change effect on the cooling performance and assessment of passive daytime photonic radiative cooler in India". Renewable and Sustainable Energy Reviews. 134 – via Elsevier Science Direct.
  54. ^ Li, Mengying, Hannah B. Peterson, and Carlos FM Coimbra. "Radiative cooling resource maps for the contiguous United States." Journal of Renewable and Sustainable Energy 11, no. 3 (2019): 036501.
  55. ^ Vilà, Roger; Medrano, Marc; Castell, Albert (2021). "Mapping Nighttime and All-Day Radiative Cooling Potential in Europe and the Influence of Solar Reflectivity". Atmosphere. 12 (9): 1119. Bibcode:2021Atmos..12.1119V. doi:10.3390/atmos12091119. ISSN 2073-4433.
  56. ^ Weng, Yangziwan; Zhang, Weifeng; Jiang, Yi; Zhao, Weiyun; Deng, Yuan (September 2021). "Effective daytime radiative cooling via a template method based PDMS sponge emitter with synergistic thermo-optical activity". Solar Energy Materials and Solar Cells. 230: 111205. doi:10.1016/j.solmat.2021.111205 – via Elsevier Science Direct.
  57. ^ Chen, Meijie; Pang, Dan; Yan, Hongjie (April 2022). "Sustainable and self-cleaning bilayer coatings for high-efficiency daytime radiative cooling". Journal of Materials Chemistry. 10 (2).
  58. ^ Carlosena, Laura; Andueza, Ángel; Torres, Luis; Irulegi, Olatz; Hernández-Minguillón, Rufino J.; Sevilla, Joaquín; Santamouris, Mattheos (2021). "Experimental development and testing of low-cost scalable radiative cooling materials for building applications". Solar Energy Materials and Solar Cells. 230: 111209. doi:10.1016/j.solmat.2021.111209 – via Elsevier Science Direct.
  59. ^ Huang, Xin; Mandal, Aaswath; Raman, Huang (November 2021). "Do-it-yourself radiative cooler as a radiative cooling standard and cooling component for device design". Photonics Energy. 12 (1). doi:10.1117/1.JPE.12.012112. S2CID 244383874 – via SPIE Digital Library.
  60. ^ a b Nie, Shijin; Tan, Xinyu; Li, Xinyi; Wei, Ke; Xiao, Ting; Jiang, Lihua; Geng, Jialing; Liu, Yuan; Hu, Weiwei; Chen, Xiaobo (November 2022). "Facile and environmentally-friendly fabrication of robust composite film with superhydrophobicity and radiative cooling property". Composites Science and Technology. 230 (1): 109750. doi:10.1016/j.compscitech.2022.109750. S2CID 252425283 – via Elsevier Science Direct.
  61. ^ a b c Wang, Tong; Zhang, Yinan; Chen, Min; Gu, Min; Wu, Limin (March 2022). "Scalable and waterborne titanium-dioxide-free thermochromic coatings for self-adaptive passive radiative cooling and heating". Cell Reports Physical Science. 3 (3): 100782. Bibcode:2022CRPS....300782W. doi:10.1016/j.xcrp.2022.100782. S2CID 247038918 – via Elsevier Science Direct.
  62. ^ a b c Liu, Xianhu; Zhang, Mingtao; Hou, Yangzhe; Pan, Yamin; Liu, Chuntai; Shen, Changyu (September 2022). "Hierarchically Superhydrophobic Stereo-Complex Poly (Lactic Acid) Aerogel for Daytime Radiative Cooling". Advanced Functional Materials. 32 (46). doi:10.1002/adfm.202207414. S2CID 252076428 – via Wiley.
  63. ^ a b Fan, Ting-Ting; Xue, Chao-Hua; Guo, Xiao-Jing; Wang, Hui-Di; Huang, Meng-Chen; Zhang, Dong-Mei; Deng, Fu-Quan (May 2022). "Eco-friendly preparation of durable superhydrophobic porous film for daytime radiative cooling". Journal of Materials Science. 57 (22): 10425–10443. Bibcode:2022JMatS..5710425F. doi:10.1007/s10853-022-07292-8. S2CID 249020815 – via Springer.
  64. ^ a b c Zhong, Shenjie; Zhang, Jiawen; Yuan, Shuaixia; Xu, Tianqi; Zhang, Xun; Xu, Lang; Zuo, Tian; Cai, Ying; Yi, Lingmin (January 2023). "Self-assembling hierarchical flexible cellulose films assisted by electrostatic field for passive daytime radiative cooling". Chemical Engineering Journal. 451 (1): 138558. doi:10.1016/j.cej.2022.138558. S2CID 251488725 – via Elsevier Science Direct.
  65. ^ a b Yinan Zhang, Xi Chen, Boyuan Cai, Haitao Luan, Qiming Zhang, Min Gu, Photonics Empowered Passive Radiative Cooling, Advanced Photonics Research,2,2000106, 2021
  66. ^ a b c Zhang, Haiwen; Ly, Kally C. S.; Liu, Xianghui; Chen, Zhihan; Yan, Max; Wu, Zilong; Wang, Xin; Zheng, Yuebeng; Zhou, Han; Fan, Tongxiang (2020). "Biologically inspired flexible photonic films for efficient passive radiative cooling". Applied Physical Sciences. 117 (26): 14657–14666. Bibcode:2020PNAS..11714657Z. doi:10.1073/pnas.2001802117. PMC 7334532. PMID 32541048.
  67. ^ a b Weng, Yangziwan; Zhang, Weifeng; Jiang, Yi; Zhao, Weiyun; Deng, Yuan (September 2021). "Effective daytime radiative cooling via a template method based PDMS sponge emitter with synergistic thermo-optical activity". Solar Energy Materials and Solar Cells. 230: 111205. doi:10.1016/j.solmat.2021.111205 – via Elsevier Science Direct.
  68. ^ Atiganyanun, Sarun; Plumley, John B.; Han, Seok Jun; Hsu, Kevin; Cytrynbaum, Jacob; Peng, Thomas L.; Han, Sang M.; Han, Sang Eon (February 2018). "Effective Radiative Cooling by Paint-Format Microsphere-Based Photonic Random Media". ACS Photonics. 5 (4): 1181–1187. doi:10.1021/acsphotonics.7b01492 – via ACS Publications.
  69. ^ a b Li, Na; Wang, Junfeng; Liu, Defang; Huang, Xia; Xu, Zhikui; Zhang, Chenyang; Zhang, Zhijie; Zhong, Mingfeng (June 2019). "Selective spectral optical properties and structure of aluminum phosphate for daytime passive radiative cooling application". Solar Energy Materials and Solar Cells. 194: 103–110. doi:10.1016/j.solmat.2019.01.036. S2CID 104321878 – via Elsevier Science Direct.
  70. ^ Li, Xiangyu; Peoples, Joseph; Yao, Peiyan; Ruan, Xiulin (April 2021). "Ultrawhite BaSO4 Paints and Films for Remarkable Daytime Subambient Radiative Cooling". ACS Applied Materials & Interfaces. 13 (18): 21733–21739. doi:10.1021/acsami.1c02368. PMID 33856776. S2CID 233259255 – via ACS Publications.
  71. ^ Zhou, Lei; Zhao, Jintao; Huang, Haoyun; Nan, Feng; Zhou, Guanghong; Qu, Qingdong (2021). "Flexible Polymer Photonic Films with Embedded Microvoids for High-Performance Passive Daytime Radiative Cooling". ACS Photonics. 8 (11): 3301–3307. doi:10.1021/acsphotonics.1c01149 – via ACS Publications.
  72. ^ Zhang, Shuai; Jing, Weilong; Chen, Zhang; Zhang, Canying; Wu, Daxiong; Gao, Yanfeng; Zhu, Haitao (July 2022). "Full daytime sub-ambient radiative cooling film with high efficiency and low cost". Renewable Energy. 194: 850–857. doi:10.1016/j.renene.2022.05.151. S2CID 249423146 – via Elsevier Science Direct.
  73. ^ a b c d Liu, Yanran; Zhang, Hanfang; Zhang, Yihe; Liang, Ce; An, Qi (July 2022). "Rendering passive radiative cooling capability to cotton textile by an alginate/CaCO3 coating via synergistic light manipulation and high water permeation". Composites Part B: Engineering. 240: 109988. doi:10.1016/j.compositesb.2022.109988. S2CID 249109763 – via Elsevier Science Direct.
  74. ^ a b Li, Yiping; An, Zhimin; Liu, Xinchao; Zhang, Rubing (October 2022). "A radiative cooling paper based on ceramic fiber for thermal management of human head". Solar Energy Materials and Solar Cells. 246: 111918. doi:10.1016/j.solmat.2022.111918. S2CID 251335644 – via Elsevier Science Direct.
  75. ^ a b Li, Tao; Sun, Haoyang; Yang, Meng; Zhang, Chentao; Lv, Sha; Li, Bin; Chen, Longhao; Sun, Dazhi (2023). "All-Ceramic, Compressible and Scalable Nanofibrous Aerogels for Subambient Daytime Radiative Cooling". Chemical Engineering Journal. 452: 139518. doi:10.1016/j.cej.2022.139518. S2CID 252678873 – via Elsevier Science Direct.
  76. ^ Leroy, A.; Bhatia, B.; Kelsall, C.C.; Castillejo-Cuberos, A.M.; Capua H., Di; Zhang, L.; Guzman, A.M.; Wang, E.N. (October 2019). "High-performance subambient radiative cooling enabled by optically selective and thermally insulating polyethylene aerogel". Materials Science. 5 (10): eaat9480. Bibcode:2019SciA....5.9480L. doi:10.1126/sciadv.aat9480. PMC 6821464. PMID 31692957. S2CID 207896571.
  77. ^ Yue, Xuejie; Wu, Hai; Zhang, Tao; Yang, Dongya; Que, Fengxian (April 2022). "Superhydrophobic waste paper-based aerogel as a thermal insulating cooler for building". Energy. 245: 123287. doi:10.1016/j.energy.2022.123287. S2CID 246409163 – via Elsevier Science Direct.
  78. ^ a b Yang, Yuan; Zhang, Yifan (2020). "Passive daytime radiative cooling: Principle, application, and economic analysis". MRS Energy & Sustainability. 7 (18). doi:10.1557/mre.2020.18. S2CID 220008145. Archived from the original on 27 September 2022. Retrieved 27 September 2022.
  79. ^ a b c d e Mokharti, Reza; Ulpani, Giulia; Ghasempour, Roghayeh (July 2022). "The Cooling Station: Combining hydronic radiant cooling and daytime radiative cooling for urban shelters". Applied Thermal Engineering. 211 – via Elsevier Science Direct.
  80. ^ Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  81. ^ a b Benmoussa, Youssef; Ezziani, Maria; Djire, All-Fousseni; Amine, Zaynab; Khaldoun, Asmae; Limami, Houssame (September 2022). "Simulation of an energy-efficient cool roof with cellulose-based daytime radiative cooling material". Materials Today: Proceedings. doi:10.1016/j.matpr.2022.08.411. S2CID 252136357 – via Elsevier Science Direct.
  82. ^ Feng, Chunzao; Yang, Peihua; Liu, Huidong; Mao, Mingran; Liu, Yipu; Xue, Tong; Fu, Jia; Cheng, Ting; Hu, Xuejiao; Fan, Hong Jin; Liu, Kang (July 2021). "Bilayer porous polymer for efficient passive building cooling". Nano Technology. 85 – via Elsevier Science Direct.
  83. ^ a b Zhou, Kai; Miljkovic, Nenad; Cai, Lili (March 2021). "Performance analysis on system-level integration and operation of daytime radiative cooling technology for air-conditioning in buildings". Energy and Buildings. 235: 110749. doi:10.1016/j.enbuild.2021.110749. S2CID 234180182 – via Elsevier Science Direct.
  84. ^ Younes, Jaafar; Ghali, Kamel; Ghaddar, Nesreen (August 2022). "Diurnal Selective Radiative Cooling Impact in Mitigating Urban Heat Island Effect". Sustainable Cities and Society. 83: 103932. doi:10.1016/j.scs.2022.103932. S2CID 248588547 – via Elsevier Science Direct.
  85. ^ a b c Wang, Ke; Luo, Guoling; Guo, Xiaowei; Li, Shaorong; Liu, Zhijun; Yang, Cheng (September 2021). "Radiative cooling of commercial silicon solar cells using a pyramid-textured PDMS film". Solar Energy. 225: 245. Bibcode:2021SoEn..225..245W. doi:10.1016/j.solener.2021.07.025 – via Elsevier Science Direct.
  86. ^ Lu, Kegui; Zhao, Bin; Xu, Chengfeng; Li, Xiasheng; Pei, Gang (September 2022). "A full-spectrum synergetic management strategy for passive cooling of solar cells". Solar Energy Materials and Solar Cells. 245: 111860. doi:10.1016/j.solmat.2022.111860. S2CID 250159405 – via Elsevier Science Direct.
  87. ^ Lee, Kang Won; Lim, Woojong; Jeon, Min Soo; Jang, Hanmin; Hwang, Jehwan; Lee, Chi Hwan; Kim, Dong Rip (2022). "Visibly Clear Radiative Cooling Metamaterials for Enhanced Thermal Management in Solar Cells and Windows". Advanced Functional Materials. 32 (1). doi:10.1002/adfm.202105882. S2CID 242578536 – via Wiley Online Library.
  88. ^ Tang, Huajie; Zhou, Zhihua; Jiao, Shifei; Zhang, Yunfei; Li, Shuai; Zhang, Debao; Zhang, Ji; Liu, Junwei; Zhao, Dongliang (January 2022). "Radiative cooling of solar cells with scalable and high-performance nanoporous anodic aluminum oxide". Solar Energy Materials and Solar Cells. 235: 111498. doi:10.1016/j.solmat.2021.111498. S2CID 244299138 – via Elsevier Science Direct.
  89. ^ Zhao, Bin; Lu, Kegui; Hu, Mingke; Lu, Jie; Wu, Lijun; Xu, Chengfeng; Xuan, Qingdong; Pei, Gang (May 2022). "Radiative cooling of solar cells with micro-grating photonic cooler". Renewable Energy. 191: 662–668. doi:10.1016/j.renene.2022.04.063. S2CID 248142250 – via Elsevier Science Direct.
  90. ^ Fang, Yunsheng; Chen, Guorui; Bick, Michael; Chen, Jun (July 2021). "Smart textiles for personalized thermoregulation". Chem. Soc. Rev. 50 (17): 9357–9374. doi:10.1039/D1CS00003A. PMID 34296235. S2CID 236198429 – via Royal Society of Chemistry.
  91. ^ Zeng, Shaoning (July 2021). "Hierarchical-morphology metafabric for scalable passive daytime radiative cooling". Science. 373 (6555): 692–696. Bibcode:2021Sci...373..692Z. doi:10.1126/science.abi5484. PMID 34353954. S2CID 236929292.
  92. ^ Cui, Chaofan; Lu, Jun; Zhang, Siqi; Su, Juanjuan; Han, Jian (October 2022). "Hierarchical-porous coating coupled with textile for passive daytime radiative cooling and self-cleaning". Solar Energy Materials and Solar Cells. 247: 111954. doi:10.1016/j.solmat.2022.111954. S2CID 252097903 – via Elsevier Science Direct.
  93. ^ a b c d e Heo, Se-Yeon; Ju Lee, Gil; Song, Young Min (June 2022). "Heat-shedding with photonic structures: radiative cooling and its potential". Journal of Materials Chemistry C. 10 (27): 9915–9937. doi:10.1039/D2TC00318J. S2CID 249695930 – via Royal Society of Chemistry.
  94. ^ Li, Jinlei; Liang, Yuan; Li, Wei; Xu, Ning; Zhu, Bin; Wu, Zhen; Wang, Xueyang; Fan, Shanhui; Wang, Minghuai; Zhu, Jia (February 2022). "Protecting ice from melting under sunlight via radiative cooling". Science Advances. 8 (6): eabj9756. Bibcode:2022SciA....8.9756L. doi:10.1126/sciadv.abj9756. PMC 8836806. PMID 35148187.
  95. ^ Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Archived from the original on 22 February 2022. Retrieved 27 September 2022 – via ScienceDirect.
  96. ^ Wang, Tong; Wu, Yi; Shi, Lan; Hu, Xinhua; Chen, Min; Wu, Limin (2021). "A structural polymer for highly efficient all-day passive radiative cooling". Nature Communications. 12 (365): 365. doi:10.1038/s41467-020-20646-7. PMC 7809060. PMID 33446648. Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.
  97. ^ Zevenhovena, Ron; Fält, Martin (June 2018). "Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach". Energy. 152 – via Elsevier Science Direct. An alternative, third geoengineering approach would be enhanced cooling by thermal radiation from the Earth's surface into space.
  98. ^ Lin, Kaixin; Du, Yuwei; Chen, Siru; Chao, Luke; Lee, Hau Him; Ho, Tsz Chung; Zhu, Yihao; Zeng, Yijun; Pan, Aiqiang; Tso, Chi Yan (December 2022). "Nanoparticle-polymer hybrid dual-layer coating with broadband solar reflection for high-performance daytime passive radiative cooling". Energy and Buildings. 276: 112507. doi:10.1016/j.enbuild.2022.112507. S2CID 252510605 – via Elsevier Science Direct.
  99. ^ Kaplan, Sarah (7 October 2020). "Bringing the chill of the cosmos to a warming planet". Washington Post.
  100. ^ "ASU testing new material to make Tempe bus stops cooler". ABC 15. 4 August 2021.
  101. ^ "3M advances decarbonization technologies, showcases power of science to address climate change during Climate Week NYC". PR News Wire. 20 September 2022.
  102. ^ Wu, Wanchun; Lin, Shenghua; Wei, Mingming; Huang, Jinhua; Xu, Hua; Lu, Yuehui; Song, Weijie (June 2020). "Flexible passive radiative cooling inspired by Saharan silver ants". Solar Energy Materials and Solar Cells. 210: 110512. doi:10.1016/j.solmat.2020.110512. S2CID 216200857 – via Elsevier Science Direct.
  103. ^ Kazemi, A.G.; Shirvani, A.H. (2011). "An Overview of Some Vernacular Techniques in Iranian Sustainable Architecture in Reference to Cisterns and Ice Houses". Journal of Sustainable Development. 4 (1). doi:10.5539/jsd.v4n1p264.
  104. ^ Banik, Udayan; Agrawal, Ashutosh; Meddeb, Hosni; Sergeev, Oleg; Reininghaus, Nies; Götz-Köhler, Maximilian; Gehrke, Kai; Stührenberg, Jonas; Vehse, Martin; Sznajder, Maciej; Agert, Carsten (2021). "Efficient Thin Polymer Coating as a Selective Thermal Emitter for Passive Daytime Radiative Cooling". ACS Applied Materials & Interfaces. 13 (20): 24130–24137. doi:10.1021/acsami.1c04056. PMID 33974398. S2CID 234471290 – via ACS Publications.