Review of Polygeneration Schemes with Solar Cooling Technologies and Potential Industrial Applications

: The trend to reduce CO 2 emissions in cooling processes has made it possible to increase the alternatives for integrating solar energy with thermal equipment whose viability depends on its adaptation to polygeneration schemes. Despite the enormous potential offered by the industry for cooling and heating processes, solar cooling technologies (SCT) have been explored in a limited way in the industrial sector. This work discusses the potential applications of industrial SCTs and classiﬁes hybrid polygeneration schemes based on supplying cold, heat, electricity, and desalination of water; summarizes the leading SCTs, and details the main indicators of polygeneration conﬁgurations in terms of reductions on primary energy consumption and payback times. To achieve an energy transition in refrigeration processes, the scenarios with the most signiﬁcant potential are: the food manufacturing industry (water immersion and crystallization processes), the beverage industry (fermentation and storage processes), and the mining industry (underground air conditioning).


Introduction
The main world organizations have focused on reducing the CO 2 emissions associated with electricity generation through the implementation of policies and incentives that promote renewable energies (RE) [1]. The International Energy Agency (IEA) projected that with current policies, it is possible to increase the share of renewable energies from 36% to 52% by 2050. However, it proposes reaching 84% as a response to the climate crisis [2]. Another strategy is to reduce the electricity demand from key high-consumption processes by implementing energy-saving, passive, or more efficient solutions. According to the IEA, one of these high-consumption processes is cooling processes (RP), which consumed 2075 TWh of electricity in 2018, accounting for 10% of the world's energy consumption. If the current trend of refrigeration energy consumption continues, in 2040, demand could triple the current level [2][3][4]. Consequently, such continuous growth will hinder the decarbonization goals in the electricity sector [2, 5,6]. Part of the strategies for reducing the electricity consumption in RPs considers policies along three lines: energy-efficient buildings, optimization of conventional refrigeration equipment (CRS) and investigation of alternative cooling equipment [7,8].
For this reason, research has been directed towards driving RPs by RE to reduce the dependence on the electricity grid. Solar energy has advantages over wind, geothermal or nuclear power due to its adaptability in installation, reduced costs, and availability of resources even in remote areas. The most recurrent renewable sources for alternative cooling equipment are solar photovoltaic (PV) and solar thermal (ST) [9]. In particular, PVs tend to be used primarily for the advantage of adapting to previously installed electrical cooling equipment. Furthermore, PVs are attractive in the residential sector due to the increased efficiency and the current trend in cost reduction. However, the overall efficiency of a PV system in heat processes tends to decrease due to the conversion efficiency for heat processes. For this reason, electricity supply strategies with PVs are oriented towards conventional cooling equipment and supplying electricity to equipment connected to the grid. From the point of view of heat processes, the use of solar collectors (SC) makes it possible to increase the solar fraction by improving the techno-economic relationship of the system. Previous reviews regarding solar thermal cooling technologies have focused on the operating principles, working temperatures and equations of state of the adsorption [10][11][12][13], absorption [14][15][16], and thermomechanical [17,18] machines. In addition, the technical limits of the operational aspects and the conversion efficiency were detailed [11,[19][20][21]. For reducing heat losses or improving the operating strategies of cooling equipment, the hybridization of sorption equipment and its design strategies were also evaluated [22][23][24][25]. Although several novel prototypes for solar cooling technologies have been developed in recent years, the focus has been in increasing the coefficient of performance (COP) with little consideration for the economic aspects of its construction. which can raise costs substantially, having a potentially significant effect in technological selection. However, several other studies have evaluated the technical and economic performance of solar cooling technologies to analyze how well they can perform when compared to conventional cooling systems [22,26]. These evaluations have been mainly done on residential cases of study, which have focused on air-conditioning processes highlighting design optimization methods, supply strategies, and the architectural integration of solar energy in buildings for cooling [27][28][29]. This fact, along with the previous argument, have resulted in a limited vision of the potential of solar cooling technologies applied to other commercial or industrial settings, where the potential to significantly impact CO 2 reduction is considerable. In particular, solar thermal cooling has economic disadvantages when compared to conventional systems. Thermal cooling equipment driven by SC is expensive due to low conversion efficiency requiring high CO 2 tax for its economic feasibility with respect to conventional equipment. Therefore, one could argue that it is necessary to integrate solar cooling with heating processes to improve the joint techno-economic performance [30].
The feasibility of the application of the systems depends on the ability to maximize the use of the solar field. In this perspective, the trend in the design and evaluation of polygeneration plants has increased in recent years, but has focused so far on the residential sector [9]. The reviews conducted on polygeneration have focused on evaluating in the residential sector the simultaneous supply of cooling, electricity and heating with combined PV-SC schemes and the integration of photovoltaic thermal systems (PVT). In addition, the possibility of its adaptation to the market based on primary energy savings and CO 2 reduction compared to a conventional system has grown [9,[31][32][33]. However, studies focusing on residential sector are significantly different in terms of the thermal loads observed for the industrial sector. This is because the industry requires temperature control in processes that vary between <0 • C to >30 • C. Industrial processes like deodorization, pasteurization, crystallization, refrigeration, etc. can work simultaneously. In addition, due to quality standards, temperatures must be kept constant despite external and internal changes due to climatic seasons or variations in the volume of the product.
In this sense, the most widely used alternative equipment are reversible heat pumps and absorption cooling equipment. Consequently, solar cooling systems have been evaluated in the residential sector to supply cold with sorption equipment with a nominal capacity greater than 1000 kW, comparable to cooling equipment used in the mid-scale food industry [34].
In addition to the above, except for the agro-industry and food industry, solar refrigeration applied in the industrial sector has hardly been investigated despite the strict requirements of constant temperature control and the high energy demand in refrigeration processes [35][36][37]. In the current context of a reduction of the environmental impact of productive activities, the possibility of optimizing RE integration in RP by the adoption of polygeneration schemes as well as the huge potential that industries offer in terms of the magnitude and the multiplicity of their energy demands make it interesting to review the main solar cooling technologies adapted to polygeneration schemes and to discuss their potential integration in the industrial sector.
This work, after providing a technical and historical overview of development of the refrigeration equipment and the ways in which they can use solar energy as a primary energy source, includes a comprehensive analysis of the scientific literature on how solar cooling systems can be integrated into hybrid schemes for cooling, heating, electricity, and desalinated water. In addition, aiming to serve as a reference for project implementation this work also analyses the published figures of the key techno-economical indexes for these systems as well as the realizations and case studies implemented all over the world.

Historical Evolution of Cooling Equipment and Main Solar Cooling Technologies
Studies of cooling processes for their integration with solar energy have grown consistently during the last 40 years due to the benefits of harnessing solar radiation as a source of direct renewable energy [30,[38][39][40]. The operating principles and first patents began to be developed in the 19th century. Regarding solar energy, absorption equipment (ABS) was the first to be integrated with solar collectors (SC) [10,26,41]. However, the low costs of coal added to the technological limitations of SC and the temperature control system relegated ABS to rural applications during the first half of the 20th century [42,43]. Furthermore, in the same period, commercial alternatives to adsorption equipment (ADS) emerged that were economically more attractive on a small scale than ABS [42,44]. On the other hand, vapor compression cycle (VCC) cooling equipment has remained the leading technology since the beginning of the 20th century due to the adaptation of VCC to electric currents [43,45,46]. Research on solar energy for cooling processes was resumed due to the oil crisis in 1973 and the restrictions on chlorofluorocarbon refrigerants (CFCs) with the Montreal Protocol [26,27,43]. The first evaluations of photovoltaic refrigeration (PVR) configurations emerged in the 1970s and have been evaluated in vaccine storage, air conditioning in residential buildings, and vehicles [47][48][49][50]. PVRs can achieve primary energy savings of between 20% and 70% due to the supply of electricity to other equipment when the CRS is not in operation [51,52]. In recent years, studies have focused on reversible heat pump systems and the removal of the battery set for direct drives, reducing the investment cost of the system by up to 84% [53][54][55].
In the 1970s, new proposals for solar-powered equipment, such as Stirling refrigeration equipment (SCE), emerged. Although ECSs were marketed during the first half of the 20th century with an electric drive, prototypes were also developed for their drive with thermal energies using the reversible liquid piston cycle [18,[56][57][58][59][60]. Research has focused on improving performance by modifying the geometry of the evaporator and condenser, increasing performance up to 32% [61]. Furthermore, working fluids, such as hydrogen, have been tested to reach a COP of 0.53, similar to commercial ADS machines [62]. However, the integration with solar heat remains at the stage of evaluating the performance of the equipment using solar collectors. and Fresnel lenses [22,58,63].
Another device developed was thermoelectric devices (TE) in the 1940s for electricity generation and, later modified for refrigeration (TEC) in the military industry [64,65]. The devices have the advantage of working with direct current, which facilitates their integration with PV panels [66][67][68][69]. However, due to the low efficiency of TEC, studies have focused on developing materials that enable improving ZT efficiency, which is an indicator relating the material to thermal conductivity, electrical conductivity, and Seebeck coefficient as a function of device temperature [70]. In recent years, TECs have been integrated into photovoltaic modules with Fresnel lenses to dissipate heat in PV plants [71][72][73]. In addition, TECs were combined with PV panels for applications of refrigeration, freezing and radiant walls in buildings [22,29,33,64,74,75]. The prototypes integrated into the façade of buildings are called building-integrated photovoltaic thermoelectric (BIPVT) [76][77][78]. BIPVTs in clear sky conditions in summer reach peaks in electricity consumption savings of up to 100% compared to a CRS [79][80][81]. Furthermore, devices have been designed that replace the condenser-evaporator assembly with the TEC and are integrated with a TES for heating in a CRS. The configuration manages to reduce electricity consumption by up to 8.5% compared to the CRS [82,83]. Despite the technical advantages due to the small size, the possibility of reaching freezing temperatures, and the lack of moving parts, the TEC lacks an analysis of the economic sensitivity with respect to other solar cooling technologies.
Ejector cooling systems (EJC) have been evaluated since the 1970s but became more relevant during the 1990s [26,[84][85][86]. The EJCs are sensitive to meteorological variations and the size of the solar field, being of interest to improve the global COP of the system (SC-TES) -EJC [17,[87][88][89][90][91]. In this sense, the use of cold storage with phase change material (PCM) and a variable geometry ejector nozzle is proposed [92][93][94][95][96]. However, increased components and a more robust control system can negatively affect equipment costs [97,98]. In addition, EJC systems integrated into reversible heat pumps and the heat supply for sanitary water have been developed [99][100][101]. In addition, the EJCs have been evaluated by substituting the R141b refrigerant for isobutane, reducing the EJC of the generator temperature to ranges below 80 • C, achieving competitive performance against adsorption cycles [102,103].
At the beginning of the 2000s, desiccant refrigeration equipment (DES) was developed, operation of which is based on sorption and desorption processes [104]. DES has been tested for low-irradiation tropical environments, but DES efficiency is highly sensitive to relative humidity [21,105]. On the other hand, ADS equipment can be classified like adsorption by phisisorption (ADS-PH) and adsorption by chemisorption (ADS-CH). ADS equipment has been commercialized for small-scale domestic refrigeration and ice-making applications [26,42,44]. In addition, at the end of the 20th century and the beginning of the 21st, applications of solar ADS for food preservation and air conditioning for bus and train locomotives have deepened [20,22,40,106]. Similarly, ABS equipment since the late 1970s is being evaluated for HVAC applications, vaccine storage, and food preservation. ABS equipment can be classified like ABS of half effect (ABS-HE), ABS of simple effect (ABS-SE), ABS of double effect (ABS-DE) and generation absorption heat exchange (ABS-GAX) [10,38].
Despite the potential of alternative cooling equipment, heat-driven solar cooling systems have not achieved significant market penetration. According to general review articles focused on the design and operation of solar cooling, systems are significantly affected in the short and long term due to the natural variability of the solar resource [25,28,31,105]. Therefore, to overcome climate variability, systems require thermal storage (TES) and large solar fields that increase the initial investment cost. Consequently, at the end of the 2010s, solar heat cooling was considered unfeasible for the urban sector and PV-VCC systems were positioned as the best option for the residential sector [51,107,108].
However, with the declining costs of solar technology in recent years, research on optimizing energy delivery and demand has been highlighted to improve the viability of sorption systems [11,102,109]. New prototypes have also been developed, and the working fluids have been evaluated to decrease the generation temperature or increase the COP, as shown in Table 1. In addition, the trend to hybridize refrigeration equipment such as ADS-ABS, ABS-VCC, ABS-VCC, EJC-ABS, EJC-ADS, EJC-VCC to improve system performance and decrease generator temperature open alternatives to maximize solar field energy [12,23,24,31,110]. The performance of a chiller prototype for cooling and heating applications that integrates ADS equipment with vacuum tubes and phase change material is evaluated. A compact ABS (NH 3 ) equipment was designed with mass exchangers and monolithic microscale exchange for space conditioning.
The generator was redesigned by changing the heat exchanger for a column of a bundle of tubes that allows a distributed heat transfer to improve waste and low-quality heat utilization.
[ The hybridization allows increasing the COP from 0.79 to 1.09 with inlet temperatures lower than 155 • C. Figure 1 shows a timeline that marks significant advances in the development of solar cooling equipment. In the last decade, research has intensified to improve the viability of solar cooling processes for urban applications with polygeneration plants. The intention is to maximize the continuous use of the energy generated by the solar field, which is characteristic of residential applications that supply process heat, refrigeration, and electricity production [9,133]. Energies 2021, 14,6450 For this reason, the systems combine various energy sources such as PV panels, SC, biomass boilers, and geothermal energy that must be optimized to maximize primary energy savings [32,134,135]. However, to optimize the systems, it is necessary to select the cooling equipment by relating the nominal chiller power (Q Ch ) with the COP, generator temperature (T Gen ) and evaporator temperature (T Evap ). According to the literature of the present review, Figures 2 and 3 detail the operating ranges of prototypes and the main commercial heat-driven cooling chillers. ADS by physisorption (ADS-Ph) equipment has a COP between 0.13-0.62 and requires a T Gen between 50-130 • C [14,[136][137][138][139][140][141][142]. The most widely used adsorbate-adsorbent is silica gel/water and reaches T Evap of up to 5 • C [15,[143][144][145].  Systems with activated carbon/methanol have also been evaluated, but the COP and the T Gen increase with respect to silica gel/water [16,[146][147][148][149]. In comparison, ABS equipment has a COP between 0.7-1.8 and a T Gen between 80-220 • C [13,109,150,151]. Before crystallization, using LiBr/H 2 O as working fluid, the evaporator temperature is 5 • C, while using NH 3 /H 2 O as working fluid, the system can reach temperatures as low as −5 • C [152][153][154][155][156][157][158]. The difference in the performance of the ABS equipment of medium effect (ABS-HE), single effect (ABS-SE), double effect (DE-ABS) can be evaluated based on increasing the COP to optimize the heat received by the generator, reduce the risk of crystallization of the equipment due to low evaporator temperatures, or increase the cooling capacity [19,[159][160][161][162].

Polygeneration Schemes Integrated with Solar Cooling Technologies
According to the literature, the feasibility of the success of heat-driven refrigeration equipment is directly related to the use of the energy supply from the solar field. In this sense, thermomechanical generators (TMG) have been evaluated for joint operation with VCC and reversible heat pumps (RHP) [163]. The systems are composed of an organic Rankine cycle generator (ORC) and concentration manifolds to deliver temperatures above 100 • C [164,165]. However, TMGs are also subjected to polygeneration systems to achieve their economic viability. This section describes the main solar cooling studies integrated into the polygeneration scheme for cooling, heating, electricity, and desalinated water.

Cooling Heat/Electricity Generation (CH/E)
The generation of cold and heat or electricity (CH/E) combines two or more renewable energy sources such as SC, PV, or external sources such as biomass. Figure 4 shows the integration schemes for refrigeration-heat (CH) or refrigeration-electricity (CE). On the other hand, Table 2 summarizes the main configuration schemes. Table 2, like Figure 4, is divided according to solar technology (SEH), auxiliary electric heating equipment (EH), fuel for the auxiliary boiler (F), integration of auxiliary heat (I1), integration of heat generated by renewable sources (I2), unconventional refrigeration equipment (UR), electrical generation unit (GPU), conventional air-conditioning equipment (HVAC), energy consumption lines produced (I3), type of energy generated (generation), process (P), supply (S) and electricity generation (E). BIPVT applications have also been adapted for electricity supply and cooling; the excess electricity produced by the PV panel is used to power the electrical grid. Evaluations for residential applications show a 70% potential to reduce heat from a typical wall [166]. Reversing the polarity of TEC also makes it possible to supply heat in winter, obtaining a COP of 0.45 with thermal efficiencies of 12.06% and electrical efficiencies of 10.27% [167]. On the other hand, in an ORC electricity generation plant, replacing the VCC with ABS or ADS equipment allows cold generation by cogeneration [168]. In this sense, the results show a higher exergetic efficiency for the ORC-ADS equipment because the residual heat from the ORC feeds the ADS equipment [169]. Evaluation of the ORC-ABS configuration for cooling agricultural soil with a capacity of 3.5 kW and 7 kW allowed a payback of 9.4 years with the highest capacity [170].
ABS systems can be combined with a power generation unit (PGU) that recovers heat (HR) for domestic hot water (DHW). The electricity generated is supplied to a reversible heat pump (RHP) to produce CH. The configuration could reduce the annual demand of a building by approximately 87% in heating, DHW, and cooling processes [171,172]. However, the configuration can increase investment costs because the profitability of the cogeneration system depends on the cost of heat generation fuel and local electricity.   The evaluations of Calise F. et al. [173] suggest eliminating the auxiliary boiler and designing the ABS to cover 20% of the demand with constant operation that, together with an electric heat pump (EHP), supplies cold to a storage tank (TC). The proposed approach saves 64.7% of primary energy with a solar fraction of 46.2% in winter and 27.7% during summer [173]. However, a multi-objective optimization considering an auxiliary heater's application shows greater energy efficiency by preheating the fluid before entering the ABS. Despite the encouraging results in energy saving, it is concluded that public financing is necessary for its profitability [108]. In this sense, Shirazi A. et al. [109] propose to include the penalty costs for CO 2 production in the economic analysis. Under this approach, the optimized system achieves an annual cost balance equal to zero with savings of between 44.5 and 53.8 tons of CO 2 [109]. On the other hand, by incorporating a fuel boiler with a solar field of ETC of 230 m 2 for heat generation, a simple payback (SPB) of 20.3 years is achieved and a solar fraction (SF) of 0.275 [108]. In comparison, a CPC with a 500 m 2 solar field and a hot water boiler (HWB) integrated with a diesel generator engine minimize the SPB to five years [174]. However, there was an increase in pollutants derived from diesel combustion. In this sense, the combining of a biomass boiler (BM) with SC-TES has the peculiarity that the burning of BM is considered carbon neutral. Therefore, incorporating 800 m 2 of CPC makes it possible to achieve an FS of 81.8% and an SPB of 9.33 years [107]. The BM-SC-TES-ABS system was also evaluated for restaurants in China with four possible configurations that reached solar fractions between 17% and 32% [175]. Furthermore, preheating the fluid before entering the ABS allows energy savings of 30% in summer and 60% in winter, minimizing the use of BM [175,176]. The reason is that BM provides heat during climate variability without oversizing SC-TES systems, which is attractive when considering penalties for CO 2 production from the electricity grid [174]. However, the main limitation of biomass is that it requires drying before combustion to reduce the humidity of the granules. Otherwise, it increases pollutants such as sulfur dioxide, nitrogen dioxide, and other particulate matter.

Cooling, Heat and Electricity Generation (CHG)
Trigeneration configurations combine electrical and mechanical drive technologies to produce cold, heat, and power generation (CHG). These systems tend to increase the solar field area because they are designed to meet the higher energy demands around electricity generation. Figure 5 shows the CHG schemes and can be interpreted from reading Table 3. ElHelw M. et al. [179] adapted conventional cooling equipment with hot and cold coils, an enthalpy wheel and a radiant wall TEC powered by PV and SC. The study shows savings in cities such as Cairo of up to 60% of primary energy consumption compared to conventional equipment [179]. On the other hand, Buonomano A. et al. [180] evaluated the performance of a system to generate electricity, cold and heat by comparing the performance between hybrid solar collectors CPVT and PVT coupled to an ABS-SE cooler and two ADS coolers.  PVT PV G HT HR S1-S2-S3 ABS ORC a-f (DHW-HE-SC-PW-SP) • • [188] The heat generated also allows for pool water heating (HEP). The results show that the best combination of CPVT-PVT is the ABS equipment for high radiation conditions, reaching 84% of SF with an SPB of fewer than 13 years [180]. In addition, the generation of electricity with PV panels opens up the possibility of using HP as an auxiliary equipment for heat generation. However, HP systems tend to be suitable on a small scale, with the use of photovoltaic panels coupled to an RHP being even more beneficial to produce HEP, DHW, HE and SC. On the other hand, Lu, Zu. [181] developed a prototype that combines ABS and ORC equipment. The system can operate with a hot water heat source between 80-95 • C and industrial waste heat between 100-140 • C [181]. On the other hand, a PGU integrated to a gas HP as auxiliary heat was compared, achieving 38% energy savings compared to conventional equipment. However, the configuration with a Stirling engine (STR) with ABS equipment, powered by solar thermal and photovoltaic panels, shows favorable results for the residential sector [182]. In that sense, simulations in the United States of PV-SC-ORC-ABS schemes reduced annual costs by up to 48% compared to conventional equipment [177]. The configuration SC-PVT-ABS-PUG was evaluated for harnessing the residual heat of ORC and supply heat to ABS equipment, space heating, DHW and HEP [183][184][185]. On the other hand, the inclusion of geothermal energy (GT) and the ability to take advantage of its annual power allows obtaining an SPB between 7.6 years and 2.5 years considering the worst and best-operating conditions, respectively [186]. On the other hand, a biomass gasifier was included replacing the solar collector system with solar dish collectors (DC). The gas drives an internal combustion generator, and the waste heat is used for heating, cooling and DHW [187].
The integration of technologies requires a technical and economic analysis to determine the optimal configuration of the system. For this reason, Sameti M. et al. [188] developed an optimization with the mixed-integer linear programming method (MILP). The objective was to determine the minimum cost of the system based on investment costs, operation, electricity and carbon emissions [188]. Furthermore, the SHC-TASK-53 project makes it possible to compare integration schemes for the residential sector in Mediterranean climatic conditions [184]. However, residential applications tend to have design differences compared to the demand for industrial applications.

Cooling, Heat, Electricity Generation and Desalinization (CHGD)
Although CHG systems have a high potential to be integrated into residential and industrial processes due to the generation of medium and high-temperature process heat, CHGD systems are often designed as high-capacity thermal power plants. Figure 6 and Table 4 show diagrams in which the use of ABS equipment predominates and there is the desalination of water in the condenser of ADS equipment. Multi-effect desalination plants (MED) integrated with ORC-ABS-SC-TES are attractive for desert climates, high irradiation, and lack of water. Depending on the need to be supplied, the MED polygeneration plant can be configured to produce heat and cold that contribute to the electricity generation process, the MED desalination process. Therefore, the proposed configurations can simultaneously contribute heat, refrigeration, electricity, and desalinated water (CHGD) [189]. In this sense, the schemes have been evaluated by integrating Kalina cycle absorption refrigeration and freeze desalination (CPCD) technologies. The results show that even though high evaporator temperatures produce more refrigerant, the energy and exergy efficiencies of CPCD are better under low-temperature conditions [190].   [193,194] In order to identify the techno-economic and exergetic advantages of the system, thermo-economic evaluations were recommended due to the precision to consider the exergetic destruction of the solar thermal circuit and the power block [191]. Furthermore, according to integration evaluations, the configurations with the most significant potential in high solar irradiation conditions were the plants that replace the power cycle condenser with the MED plant, and the refrigeration plant and the process heat plant were coupled to the turbine [192]. On the other hand, the production of heat, cooling, and desalination is possible from an ADS-SC-TES configuration that includes two adsorption beds. In this system, the water evaporates by the suction effect of the adsorbent. Later, the water vapor from the adsorber bed is sent to the condenser and, as the temperature drops, the desalinated water is collected in a collection tank [193,194]. The advantage of adsorption desalination systems is that the system has few moving parts. However, its viability in relation to size is limited by the low efficiency of the adsorption cycle. In contrast to MED-ORC configurations, the ADS-DES system does not produce electricity. Therefore, when considering annual assessments, ADS-DES could be affected by annualized costs for large-scale applications. In this sense, there is no integration analysis that evaluates the best selection criteria for industrial applications and their life cycle in terms of primary energy saving and investment. On the other hand, integration configurations are limited to heat recovery to power the MED plant and the air-conditioning equipment, minimizing the power loss of the PGU.

Discussion of Potential Applications of Solar Cooling Technologies
Solar systems require an analysis of parameters such as the levelized cost of energy (LCOE), simple pay back (SPB), and primary energy savings (PES). In addition, it is crucial to evaluate the cooling loads based on the target cooling process. This section is divided into the costs of polygeneration integrated cooling systems and the potential applications of cooling systems in the industry.

Costs of Polygeneration Integrated Cooling Systems
Solar cooling systems have shown that their viability is possible with schemes that supply heat and electricity simultaneously. Even the integration of polygeneration systems has shown better exergetic performance than conventional equipment, the main limitation being the efficiency and cost of the solar system. In that sense, solar systems must be evaluated based on their useful life cycle since the initial investment tends to be high due to the solar field and the cost of alternative cooling equipment. In addition, the viability of solar cooling systems varies depending on the application site and the economic factors given by local policies. An example is an ABS system in Dubai, which despite increasing the initial investment to almost 93%, the SPB is 2.49 years. This is possible because the system reduces 303.68 tCO 2 /yr being highly beneficial due to the CO 2 taxes [174]. Whereas ABS-SC configurations in Sidney reduced emissions by 166 tCO 2 /yr, but the SPB is 63 years [109]. Table 5 summarizes the costs, and key indicators of some case studies of cooling systems with energy polygeneration.   On the other hand, PV, SC, and conventional renewable energy prices are described widely in the literature. However, even though solar collectors have lowered costs in the last two decades, thermal cooling systems have made modest progress in reducing costs. Cooling systems reduce the cost per kW as a function of increasing the nominal capacity (NC) of the equipment. Table 6 shows the main functions (F) considered in the literature to estimate the specific cost of refrigeration equipment according to NC. F1 was obtained from Broad Air Conditioning Ltd. Suppliers, while F2 was performed under a polynomial relationship developed by Waier P. in 2008 [157]. The values determined by Shirazi A. et al. [109] for F3, F4 and F5 were estimated from supplier data obtained between 2012 and 2014. On the other hand, F6, F7, and F8 were based on estimates referring to 2016 [180]. While F8, F9, and F10 are approximation functions obtained from the Task-53 project, based on 2012 data from Central Europe [184]. Thermal cooling equipment costs change depending on the manufacturer, year of production, equipment type, capacity, COP, transportation, taxes, etc. Regarding the technical aspects, it is expected that ABS equipment increases as a function of COP. However, the functions detailed in Table 6 are estimates based on the capacity and type of equipment, leaving out several technical and economic parameters that directly influence the final costs.
In this sense, Figure 7 shows the reported nominal capacity versus the specific prices per kW of cooling, and Figure 8 shows the relationship between specific cost, COP and equipment capacity. The values reported are studies described in this document and compared with the estimated values described by Hang Y. et al. [157] and Neyer D. et al. [184] for ABS-SE ABS-DE equipment transforming into Euros using the exchange closing rate as of 31 December 2020, for USD, AUD, AED, and MYR. The figures show a clear difference between the cost functions assumed and the costs reported by other authors. Consequently, using the reported functions to determine costs without adapting to the local market could limit the precision of a techno-economic analysis.

Potential Applications of Cooling Systems in the Industry
The adaptations of PV panels with HR or VCC equipment for air-conditioning and CH/E schemes are most commonly found in the residential sector. The challenges of residential air conditioning are based on reaching the comfort temperature, which is standardized according to the ASHRAE standards and adapted according to each country's local legislation. District refrigeration systems have also been evaluated to supply heat and cold, requiring them to cover cooling loads of 12 MW [160]. However, evaluations for industrial applications have hardly been evaluated, limiting themselves to the agricultural sector for soil cooling for alstroemeria cultivar with temperature control in greenhouses [170]. The temperature control requirements for the above processes require T set > 3 • C. The cold storage of fruit, pre-cooling, and cooling pork meat after cutting has been evaluated [151,152]. Based on the review developed in this document, Figure 9 shows location maps of solar cooling plants in which residential sector applications predominate. Solar cooling systems have potential because the industry requires controlling the temperature for manufacturing processes, and the economic viability of solar thermal systems tends to be improved in polygeneration schemes. In this sense, the fruit and vegetable industry require reducing the temperature from 23 • C to −1 • C. Cooling time is essential to avoid deformations in vegetables such as cabbage and spinach. On the other hand, the storage of meat derivatives requires set temperatures of the evaporator equipment that can reach up to −35 • C, being unfeasible for sorption equipment. In this sense, studies suggest evaluating processes derived from canned foods. The process requires cooling from 70 • C to 4 • C but must occur between 565 and 855 min to prevent microorganism growth [196].   [196] Forced-air cooling Cabbage, spinach 23 −1 1. 13 188 [196] High flow hydrocooling Cabbage, spinach 23 −1 0.67 64 [196] Low flow hydrocooling Cabbage, spinach 23 −1 0.78 84 [196] Air blast cooling Cooked pork 70 4 -565 [196] Water immersion cooling Cooked pork 70 4 -855 [197] Cooling on crystallization Shortening production 60 12 -100 [197] Cooling on crystallization Shortening production 60 12 -100 In addition, chemical processes such as crystallization are required in the food industry, which is part of the reduction of production [197]. The cooling on crystallization is also present in other manufacturing processes in the chemical industry. Table 7 summarizes the food industry processes with the potential to be evaluated with solar cooling systems.
Supermarket applications require cooling demands of more than 100 kW, comparable to medium-scale winemaking processes. However, the advantage in winemaking processes is the possibility to take advantage of the heat of the solar field, even when the sorption chiller is not in operation [176]. Solar systems have only been evaluated on a small scale for fermentation processes and storage in white wine warehouses.
On the other hand, mining applications require strict control of the cooling temperature to guarantee the thermal comfort of the workers. The temperature should be kept below 28 • C, but activities stop if it exceeds 32 • C [198]. Refrigeration loads will vary depending on the location, depth, number of workers, machinery, etc. A mine's cooling system can be centralized on the surface or underground.
Therefore, mine cooling systems can be classified as icy refrigeration, cooled air stream, ventilation cooled air stream, etc. In that sense, to obtain an optimal result, it is important to consider the disposition of the equipment in the mine. According to some authors, coal mines require equipment between 4 MW and 16.3 MW and gold mines between 0.8 MW and 39 MW, as shown in Table 8. Although absorption systems have been evaluated with cooling equipment of 12 MW, the systems have not been evaluated for mining applications.

Conclusions
Achieving the decarbonization of electricity in 2050 requires reducing electricity consumption growth, and cooling processes are responsible for 10% of such consumption. The investigations have been oriented to using renewable energies with alternative equipment integrated with thermal or PV panels. However, there is a marked imbalance in the number of studies in the residential sector, despite the potential benefits of reducing electricity and CO 2 with renewable energies This present work details polygeneration schemes focusing on solar refrigeration and the potential application in the industry. In this sense, the review presented the unconventional refrigeration equipment, polygeneration schemes, and scope of applicability in industry.

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Alternative solar cooling technologies have energy limitations due to their low COP and limiting their overall efficiency. However, the hybridization of cooling devices to reduce heat transfer losses allows the COP to be maximized. In this sense, STR and TEC devices combined with conventional refrigeration equipment and facades must be evaluated to determine their viability. • PV-VCC or PV-HPR configurations outperform typical SC-TES systems and thermal cooling equipment schemes due to the economic viability and SPB of fewer than 10 years. The reason is that conventional refrigeration equipment is preserved, and excess electricity production is used by other equipment connected to the electrical network. However, the economic viability of photovoltaic systems must be evaluated considering simultaneous heat and cold thermal loads to determine the sizing limits of PVR systems in industrial applications. • The literature presented confirms that the viability of alternative equipment depends on its adaptation to polygeneration schemes that allow CE and CH to be supplied. The schemes evaluated for simultaneous production of electricity and cold have managed to reduce up to 64.7% of primary energy. However, the operating and investment costs of the system remain high. Therefore, they require CO 2 taxes to achieve a financial balance with an SPB of fewer than 20 years. • The CHG polygeneration schemes designed to meet the demand of the ORC generator and the absorption chiller allow reaching solar fractions of up to 84% with an SPB of fewer than 13 years. The reason is that DHW and heating are obtained from the residual heat of the ORC subsystem. • The CHGD schemes have been evaluated based on their exergetic performance but, the systems must be studied and adapted to meet energy demand conditions in the industrial and residential sectors. In this sense, district refrigeration systems can be convenient scenarios to assess the viability of the system. On the other hand, the mining industry sector is conditioned to reduce its environmental footprint in extraction processes. In the same way methods for evaluating the economic benefits of reducing CO 2 have been extensively detailed; assessing the positive ecological impact of CHGD systems in the mining industry is pertinent. • In Industries with processes that have different demand levels for cooling, a consensus has not been established regarding heat integration schemes that improve the technical and economic performance of cooling systems powered by thermal energy. In this sense, solar cooling has been partially evaluated for industrial applications, obtaining favorable results in small-scale agriculture and for the wine sector. However, it is necessary to deepen the technological limits and cooling times required by the precooling and crystallization processes in the food industry. • The solar system made up of collector fields and thermal storage is responsible for the largest share of the investment expenses, which can be as high as 70%. Meanwhile, alternative refrigeration equipment can reach up to 30% of the initial investment cost. The costs of solar thermal and photovoltaic technologies tend to be updated based on IEA publications, while storage costs are estimated using different methodologies. However, the potential for using thermal refrigeration equipment reported in the literature is based on local prices that, in some cases, are more than eight years old. In this sense, to obtain results with less economic uncertainty, a cost update of thermal cooling equipment is necessary. • Finally, the economic viability of the systems is subject to balance in the size of the solar field with the savings of primary energy. In this sense, optimization studies focus on the system's sizing based on the TMY. However, the industrial trend is in a transition towards a dynamic diagnosis of refrigeration systems. In other words, operation of the system is based on the dynamic prediction of thermal loads to automate energy dispatch strategies and detect cooling system faults. In this sense, it is reasonable to propose forecasting methods that will allow the adaption of alternative refrigeration equipment powered by solar energy.
In summary, future work focused on solar cooling is the integration of Stirling cooling equipment in polygeneration systems and, in turn, determining the viability of hybridization with sorption equipment. Regarding the relationship of the solar resource and the presented polygeneration schemes, it is pertinent to develop selection methods that allow the systems to be adapted to medium and low solar radiation conditions depending on the characteristics of industrial demand. On the other hand, the industries with the most significant potential for integration with CHG schemes are the beverage and food-processing industries due to multiple heat and cold processes. In contrast, underground mines close to the sea have a high potential for implementing CHGD systems. In this regard, it is necessary to develop an optimization method that integrates the benefits of saving water and CO 2 without affecting the techno-economic viability of the CHGD systems.