Design of Solar-Powered Cooling Systems Using Concentrating Photovoltaic/Thermal Systems for Residential Applications

Abstract

This paper addresses the potential of integrating a concentrating photovoltaic thermal (CPV/T) system with an absorption chiller for the purpose of space cooling in residential buildings in the United Arab Emirates (UAE). The proposed system consists of a low concentrating photovoltaic thermal (CPV/T) collector that utilizes mono-crystalline silicon photovoltaic (PV) cells integrated with a single-effect absorption chiller. The integrated system was modeled using the Transient System Simulation (TRNSYS v17) software. The obtained model was implemented in a case study represented by a villa situated in Abu Dhabi having a peak cooling load of 366 kW. The hybrid system was proposed to have a contribution of 60% renewable energy and 40% conventional nonrenewable energy. A feasibility study was carried out that demonstrated that the system could save approximately 670,700 kWh annually and reduce carbon dioxide emissions by 461 tons per year. The reduction in carbon dioxide emissions is equivalent of removing approximately 98 cars off the road. The payback period for the system was estimated to be 3.12 years.

1. Introduction

According to the US Energy Information Administration (EIA), an increase of more than 50% of world energy consumption is predicted by 2050 [1]. This enormous increase is a result of urbanization, population growth and economic growth, especially in developing countries. The increase in energy demand is often associated with the higher cooling loads in hot countries due to the desert climates. In 2014, the UAE’s energy consumption peaked to a record-breaking 11,088 kWh [2], consequently having the largest ecological footprint across the globe along with carbon emissions per capita being twice as high than developed countries. With the energy demand being exceptionally high, the UAE greatly depends on the use of fossil fuels to provide an excellent lifestyle, which has a great impact on the environment due to carbon emissions. The residential sector of the UAE is the leading energy consumer with an astounding 47% need for space cooling, while exceeding 60% during summer peak hours [3]. In 2017, the government of the UAE announced its 2050 energy strategy, which constituted a clean energy mix of 50% accompanied with a 40% reduction in energy demand, whilst reducing carbon emissions by 70% [4,5,6]. As the need for increased space cooling arises, larger conventional chillers tend to have a significantly higher contribution to carbon emissions; hence, any measure to reduce the cooling loads would have a positive impact on the environment. Peak cooling loads are often associated with summertime due to the high ambient temperatures, leading to an extensive use of air conditioners. However, the UAE experiences an outstanding solar profile during this time, peaking up to an average global solar irradiance of 6 kWh/m²/day [7]. This indicates a high potential toward using the abundant solar radiation for cooling, through thermally driven refrigeration cycles such as absorption, adsorption and desiccant cooling [8,9]. While each of these processes follow the same principles of using heat to drive a cooling process, their applications are much unlike each other. Out of the available technologies, absorption cooling is the most widely used and commercialized technology, which works on the same principle as a conventional vapor compression system, except the compressor is replaced by a thermally driven generator. Absorption chillers can be integrated with systems that are designed for the purpose of polygeneration, where waste heat from a process is used for cooling [10]. These chillers consist of a refrigerant/absorbent mixture at the generator, which undergoes the processes of absorption and desorption to provide the cooling effect at the evaporator [11]. Single-effect chillers are the most common and simple types of absorption chillers being used, while double-effect and triple-effect chillers are used when higher temperatures can be received from the heat source. Kaushik et al. [12] conducted a study where the performances of single-effect and double-effect absorption systems were compared. The authors concluded that the coefficient of performance (COP) of double-effect chillers was much higher than that of single-effect; however, they require generator temperatures of around 150–180 °C compared to a minimum temperature requirement of 91 °C for single-effect chillers to achieve the optimum COP. This makes single-effect chillers a viable option when significantly high generator temperatures cannot be achieved. In the last decade, researchers have focused on different technologies for solar cooling that incorporate the use of FPC, ETC, PVT, CPV/T and CPC [13,14,15,16,17,18,19,20,21]. From these studies, it can be concluded that parabolic trough collectors and compound parabolic collectors are well suited for high temperatures at the generator (up to 280 °C), enabling the operation of double- and triple-effect absorption chillers, while other types are more suitable for relatively lower generator temperatures. However, there seems to be limited research on the use of CPV/T systems for cooling, especially in the MENA region. Ghaith and Abusitta [22] investigated the potential of using solar heating cooling (SHC) systems for residential buildings in the UAE using FPC and ETC collectors coupled with single-effect absorption chillers. The proposed system was found capable of reducing the annual electricity consumption by approximately 176 MWh and cut off carbon dioxide (CO₂) emissions equivalent to removing around 31 cars from the road. Ghaith and Haseeb also carried out a study on using a parabolic trough collector to operate a double-effect absorption chiller, concluding with promising results [23]. The proposed system was capable of achieving around 519 MWh savings in annual electricity consumption with a payback period of 2.49 years. Al-Alili et al. [7] assessed the feasibility of a solar powered absorption cycle for its application in Abu Dhabi, UAE. They proposed that a 60 m² area of evacuated tube collectors (ETCs) tilted at 12° from horizontal is sufficient to power an absorption cycle while achieving 60% annual electricity savings when compared to a conventional vapor compression cycle (VCC) system. The system performance was modeled using the Transient System Simulation (TRNSYS) program to assess the proposed system annually with varying factors such as irradiation, ambient temperature and wind velocities. However, this was carried out for a small-scale application because the capacity of the chiller was only 10 kW. In 2012, Al-Alili et al. [24] assessed the performance of another solar-driven process using concentrating photovoltaic/thermal technology (CPV/T). The authors used CPV/T to drive a hybrid cooling system that used dry desiccant wheel cooling along with the conventional VCC. The thermal energy obtained during the day was used to power the desiccant wheel cooling cycle, whereas the electrical power attained during the daytime was used to power the VCC. The model, however, showed an average cooling COP of 0.68 with the hybrid configuration, which is due to the low COP of desiccant cooling techniques. Villarruel-Jaramillo et al. [25] evaluated the energy advantages of hybridizing solar thermal collector fields with PV modules to meet heating and cooling demands. The proposed system reached a solar fraction of 0.85 and reduced the area of the solar field by 27%. Shohdy et al. addressed the enhancement of the performance of a low concentrator PV system using radially microchannel heat sinks. The proposed enhancement achieved a minimum cell temperature of 83.6 °C and showed environmental benefits by reducing CO₂ emissions by 131.1 tons/m²/year [26]. A solar-powered combined cooling, heating and power (CCHP) plant integrated with a water electrolysis unit was investigated by Aieneh et al. [27]. In this study, a comprehensive parametric study and optimization was conducted to evaluate the key performance parameters of the system for efficiency and economic factors. Whilst this study represented a comprehensive design of the polygeneration cycle, however, the obtained results still need to be validated by relevant experimental analysis.

Up to this point, it is evident that existing relevant literature has not fully addressed the technical and commercial feasibility of employing a CPV/T system for residential space cooling. Furthermore, it is noted that the research in this area is still in the experimental phase and has not been commercialized. The primary objective of this paper was to evaluate and assess the thermal and electrical performance of a proposed CPV/T collector for solar cooling using an absorption chiller. The system’s performance was assessed by using a case study in the UAE, while the reductions in annual energy consumption and CO₂ emissions were evaluated. Additionally, a cost analysis of the designed system was performed to comprehend the feasibility of the model.

2. Problem Statement and Operating Principle

The UAE often experiences ambient temperatures surpassing 45 °C in summer with an average of 11 sunshine hours a day. It is of no surprise that a significant high proportion of electricity consumption is due to air conditioning [23]. Energy statistics showed that the cooling loads in buildings alone are found to have over a 47% contribution to the total electricity consumption in the UAE [3]. These figures revealed an ample potential of energy savings by proposing a design of a CPV/T system that can harvest solar energy and convert it in the form of electrical energy and thermal energy. The cooling loads can significantly be reduced with the use of commercially available absorption chillers. These chillers are driven by thermal energy, and the working principle is quite similar to that of the conventional vapor compression cycles (VCCs), except that the mechanical compressor is replaced by a thermally driven generator for the same purpose. Figure 1 represents the schematic of the proposed integrated CPV/T system. The proposed system consists of a low concentrating photovoltaic thermal (CPV/T) collector that utilizes mono-crystalline silicon photovoltaic (PV) cells integrated with a single-effect absorption chiller. The chiller mainly consists of a generator, regenerator, condenser, evaporator and the absorber, as shown in Figure 2.

The absorbent/refrigerant of lithium bromide and water (LiBr/H₂O) was used in this study because it represents the most mature and commercially developed pair. The thermal energy is generated from the solar collector and the hot water is supplied to the generator where the concentrated solution of LiBr and H₂O is present. In the generator, the solution is heated and H₂O is passed on toward the condenser at a high pressure and temperature, whereas the LiBr is returned to the generator through a rectifier. At the condenser, the heat is rejected and the refrigerant is passed on to the evaporator through an expansion valve at a low pressure and temperature. The evaporator is responsible for producing the cooling effect where chilled water is produced and used for air conditioning. The refrigerant is then returned to the absorber and mixed with the solution where it flows to the generator through a regenerator, completing the cycle. The concentrated photovoltaic thermal system was utilized for the cogeneration of electricity and thermal energy. The thermal energy is used to operate the absorption chiller while the electrical energy is used to provide electricity for the auxiliary heater as well as other residential electrical appliances.

3. System Description and Methodology

The system was divided into two main subsystems: the CPV/T solar system and the absorption cooling system. The solar subsystem consists of the solar collector, stratified thermal storage, the inverter and the battery storage. Thermal stratification refers to the formation of horizontal layers within a fluid, where each layer has a different temperature. In this phenomenon, warmer fluid layers are positioned above the cooler ones. A typical CPV/T collector is shown in Figure 3.

Referring to Figure 3, a cooling circuit was considered to prevent PV cells from overheating and to improve the electrical efficiency. The cooling circuit consists of a heat exchanger to exchange the heat from the heat transfer fluid circulated in the cooling channels and the water fed to the storage tank. The pumping power of water in water cooling systems is directly proportional to the channel height and the average water flow rate.

The thermal storage was modeled as a stratified storage tank with six temperature nodes. An auxiliary electric heater has been integrated in the solar cooling loop to ensure that the minimum inlet temperature to the absorption chiller is always supplied. The auxiliary heater is required mainly at nighttime and occasionally during cloudy weather with low solar radiation. To evaluate the performance of the system, a case study has been selected. The case study is a four-floor residential building located in Abu Dhabi with a total available roof area of 400 m². The building materials, number of occupants, heat gains and other relevant information about the building are listed in

Table 1. Residential building heat gains and material properties [22].

Roof Area of Building = 400 m2
Component	Material	Thickness (mm)	Density (kg/m2)	Thermal Conductivity (W/mK)	Specific Heat Capacity (kJ/kgK)
Exterior Walls	Plaster (light weight)	0.02	2699	0.16	0.9
	Light weight, dry, 750 kg/m3	0.07	30	0.83	1.12
	Extruded Polystyrene	0.06	25	0.03	1.2
	Light weight, dry, 750 kg/m3	0.07	30	0.83	1.12
	Plaster (light weight)	0.02	2699	0.16	0.9
Floor	Concrete Slab	150	2500	1.95	0.9
	Sand cement screed	50	2080	1	0.84
	Tiles	20	2284	1.104	0.8
Roof	Tiles	0.028		1.1	0.8
	Cement mortar	0.01		0.72	0.4
	Alluvial Clay, 40% sands	0.058		1.21	6
	Polyisocyanate	0.05		0.021	0.8
	Fiber board, wet felted	0.004		0.051	1.12
	Foamed, 700 kg/m3	0.05		0.15	1.507
	Dense, reinforced	0.27		1.9	1.1
	Plaster (light weight)	0.02		0.16	0.9
Internal Heat Gains and Zone Infiltration		Flat Type		Office Type
Number of People		8		6
Lighting (W/m2)		26		26
Electrical Equipment (W/m2)		100		150
Zone Infiltration (ACH)		1		0.5

. Considering the building information, the cooling load requirement was calculated using IES-VE 2021 software. IES-VE stands for Integrated Environmental Solutions-Virtual Environment. This software allows virtual replicas of buildings to be modeled. Parameters such as the occupancy, ventilation rate, air supply systems, building fabric and even drainage systems were used to produce an estimate of how the building will perform annually. The software helps in estimating the carbon emissions and can also predict the cooling and heating loads throughout the year. The properties of the building materials were assigned to the model created in IES along with the load profiles, which includes the occupancy and internal heat gain profiles. Accordingly, the cooling load of the building was estimated by taking into account the geographical location, building orientation and internal load profiles. The weather data used for the simulation were taken from the built-in weather file for the location of Abu Dhabi International Airport. A net cooling load requirement of 366 kW was estimated that is associated with the material properties and corresponding heat gains. A hybrid system is potentially looked upon in order to meet the cooling requirement, which is then evaluated against the conventional system. The proposed integrated CPV/T system was modeled using the Transient Response System (TRNSYS v17) software. TRNSYS constitutes of a library with several mathematically modeled subroutines called ‘TYPEs’. These TYPEs or components are linked together with other components with their respected parameters to model the desired system. It is therefore recommended to create a system information flow diagram representing the system prior to modeling the system on TRNSYS.

The flow diagram illustrated by Figure 4 shows the components that are required to model the system in TRNSYS. These components represent mathematically modeled subroutines and make up the entire library of TRNSYS. Figure 4 depicts the linkage between the system components and the TYPE number being used. CPV/T was modeled using TYPE50 in the TRNSYS standard library. The concentration ratio of TYPE 50 is defined by the ratio of the aperture area to the area of PV for the CPV/T. The electrical performance of TYPE 50 is a function of the operating cell temperatures and the ambient wind velocities. A low concentration design was adopted because higher concentrations would result in higher operating cell temperatures, leading to a significant drop in the cell efficiency. For the weather conditions, a Typical Meteorological Year 2 (TMY2) data file was used to obtain the annual weather conditions for Abu Dhabi, which includes the ambient temperatures, wind velocities, solar radiation, site elevation and more parameters.

Upon constructing the information flow diagram, the input design parameters were specified, which included the area of the solar collector, mass flow rate and power of the pumps, storage size of the tank, rated power of the auxiliary heater, capacity of the absorption chiller and battery storage specification. The input parameters to the components have been listed in

Table 2. System parameters.

CPV/T Model
Aperture Area	$300{ \mathrm{m}}^2$
Concentrating Ratio	40
Heat Transfer Coefficient	$13.1 \mathrm{W}/{\mathrm{m}}^2\mathrm{K}$
Type of PV	Monocrystalline Silicon
Single-Effect Absorption Chiller
Hot Water Inlet Temperature	110 °C
Hot Water Outlet Temperature	90 °C
Hot Water Flow Rate	$22.8{ \mathrm{m}}^3/\mathrm{h}$
Cooling Water Inlet Temperature	35 °C
Cooling Water Outlet Temperature	40.5 °C
Cooling Water Flow Rate	138 ${\mathrm{m}}^3/\mathrm{h}$
Chilled Water Inlet Temperature	12.2 °C
Chilled Water Outlet Temperature	6.7 °C
Chilled Water Flow Rate	57.2 ${\mathrm{m}}^3/\mathrm{h}$
Coefficient of Performance (COP)	0.72
Auxiliary Heater
Efficiency	95.4%
Rated Power	4.5 kW

. The annual energy consumption (AEC) for the proposed system was estimated. The AEC of the proposed system was compared to that of a conventional chiller, hence evaluating the annual energy savings. The capital cost for the proposed system and the payback period were evaluated.

4. Theory

This section describes the set of equations used to derive the mathematical model of the system. The equations were used as subroutines that were executed with respect to the inputs defined by the user. The assumptions underlaying the model formulation are:

• The flow rate is at steady-state conditions.
• Negligible heat losses through the pumps.
• Negligible heat loss from the solar collector to the storage tank, since the pipes are well insulated.
• Negligible heat loss from the storage tank to the absorption chiller, since the temperature drop would be small and can be neglected.
• The pumping rate is constant in the absorption chiller loop.

4.1. Concentrating Photovoltaic Thermal (CPV/T) Collector

The CPV/T collector has been modeled using TRNSYS. The thermal output of the collector has been modeled by modifying the ‘Hottel–Whillier–Bliss’ equation, which is commonly used for solar thermal flat plate collectors, and can be expressed as

$$Q_{{Coll}_{out}}=A_a{F}_R\left[G\left(\tau \alpha \right)-{\displaystyle \frac{U_L}{C}}(T_{F.i}-T_{amb})\right]$$

(1)

The useful thermal energy produced by the collector is calculated by

$$Q_u=m{c}_p(T_{c,o}-T_{c,i})$$

(2)

The thermal efficiency of the system can be found such that

$$\eta ={\displaystyle \frac{Q_u}{G_B\times A_a}}={\displaystyle \frac{m\times c_p(T_{c,o}-T_{c,i})}{G_B\times A_a}}$$

(3)

The electrical side of the CPV/T collector was modeled taking into consideration the temperature coefficients of the photovoltaic side as well as the reference temperature of the cell at specific reference conditions, and can be expressed as

$$P_{{coll}_{out}}=P_r\left[1+\beta \left(T_c+T_r\right)\right]$$

(4)

4.2. Storage Tank

The stratified thermal storage system was modeled using the energy balance in the tank and can be expressed as

$$m_i{\displaystyle \frac{dTi}{dt}}={\left({\displaystyle \frac{UA}{Cp}}\right)}_i\left(T_{amb}-T_i\right)+F_i^s{m}_s\left(T_s-T_i\right)+F_i^L{m}_L\left(T_L-T_i\right)$$

(5)

4.3. Auxiliary Heater

The heater is required mainly at nighttime and partially at low solar radiation levels during the day. The power associated with the heater can be expressed as

$$Q_{ht}=m_{ht}{c}_p(T_{h,i}-T_{h,o})$$

(6)

4.4. Absorption Chiller

The coefficient of performance (COP) of the single-effect absorption chiller is given by

$$\mathrm{C}\mathrm{O}\mathrm{P}={\displaystyle \frac{Q_{evap}}{Q_{gen}}}$$

(7)

The required power at the generator is given by

$$Q_{gen}=m_g{c}_p(T_{g,i}-T_{g,o})$$

(8)

5. Results and Discussion

According to the analysis carried out on IES-VE, the maximum requirement of the cooling load was found on the 26th of July. Therefore, the system was analyzed using TRNSYS for that particular day with a peak cooling load of 366 kW.

5.1. Transient Analysis Solar Radiation

Figure 5 depicts the solar radiation analysis for a typical hot summer day (i.e., 26 July) and a typical winter day (i.e., 15 January) in Abu Dhabi. It was observed that the solar radiation profile is rich in the summer with 15 sunshine hours, and a peak solar radiation of around 975 W/m². This indicates the high potential of using the proposed CPV/T to generate a good amount of both electrical and thermal energy. Also, it was observed that the solar profile in winter is relatively decent and still holds potential for both electrical and thermal performance, keeping in mind that the cooling demand is minimal in winter. When the cooling load is being met in winter by the hybrid system, the thermal output from the collector can be used for the purpose of domestic hot water supply. Since the focus of this work is to address the potential of meeting the high cooling demand required in summer using the proposed CPV/T system, the subsequent analyses were carried out in summer climatic conditions.

5.2. Transient Analysis of Collector Outlet Temperature

The collector outlet temperature versus time throughout the day is shown in Figure 6. It was observed that after 7 A.M., a steady rise in the collector outlet temperature occurred and it reached a maximum of 136 °C at 12:30 P.M. Considering that the inlet temperature of the absorption chiller is 110 °C, it is clear that the collector is able to provide the sufficient thermal energy for over 8 h during the daytime without the need for the auxiliary heater. Since the collector was able to generate thermal energy higher than required, the excess energy can be used for domestic hot water purposes by bleeding a fraction of the stored thermal energy.

5.3. Chiller Inlet Temperatures and Auxiliary Heater Requirement

The generator’s inlet temperature of the absorption chiller versus time throughout the entire day (i.e., daytime and nighttime) is shown in Figure 7a. It is apparent that the auxiliary heater is required to operate when the generator’s inlet temperature is less than 110 °C. Figure 7b shows the working hours of the auxiliary heater throughout the day and the corresponding power requirements. It was found that without using the auxiliary heater, the chiller can still operate for a period of 10 h (i.e., from 9:30 A.M. to 7:30 P.M.) with the aid of the stratified thermal storage. This clearly indicates that the proposed system is capable of meeting the cooling demand most needed in the day. A peak power consumption of 1.6 kW was observed by the auxiliary heater at nighttime. Considering the auxiliary heater operating hours during the nighttime as well as in the early morning when the level of solar radiation is not sufficient to power the absorption chiller, which is estimated to be about 14 h, the total electricity consumption was found to be 22 kWh. It is important to note that the auxiliary heater power requirements are met by the power generated from the PV system as explained in Section 5.4.

5.4. Analysis of CPV/T Power Generation

Figure 8 shows the power generated by the CPV/T versus time throughout the day. The system was found sufficient to generate electrical power right after sunrise (i.e., 5 A.M.) up until sunset (i.e., 8 P.M.) in the prolonged sunlight hours. It was found that a maximum of 4.25 kW of power was produced at 1:00 P.M., with a cumulative electricity generation of around 35 kWh during the day. The accumulated power generated was stored in the form of chemical energy in batteries, which was utilized to power the auxiliary heater and the pumps at times of little-to-no solar radiation. Quantitively, the generated electricity from the system can power the auxiliary heater for about 21 h, which is much more than the required electricity by the auxiliary heater.

5.5. Model Validation

For the validation purposes, the developed CPV/T model in this study was compared to the study reported by Al-Alili et al. [24]. Common TRNSYS components were used (CPV/T, TYPE 50) while the system input parameters of this study were modified to accurately map the input parameters used by Al-Alili et al. [24]. Accordingly, the model was evaluated at the following conditions:

• The area of the collector is 60 m².
• The storage tank size is 1 m³.
• The mass flow rate is varied from 200 kg/h to 1500 kg/h.

Figure 9 represents the mass flow rate versus the useful output energy for both studies. It showed a good agreement between the results obtained in this study and the corresponding results reported by Al-Alili et al. [24] with a maximum deviation of 1.9%.

6. Feasibility and Cost Analysis

A cost analysis was conducted to evaluate the feasibility of the proposed system. Initial capital costs of major equipment—including the absorption chiller, solar collector, storage tank, pumps, auxiliary heater and conventional vapor compression chiller (VCC)—were considered, as detailed in

Table 3. Cost of components used in the feasibility study.

Components	Price (AED)	Reference
Collector	887,477	[31]
Pump	57,558	[7]
Abs. Chiller	385,000	[28]
Battery	130,634	[32]
Storage Tank	16,250	[29]
AUX Heater	16,000	[32]
Conv. Chiller	222,975	[31]

. Costs were determined based on relevant literature and direct supplier quotations [28,29]. The operating costs were estimated using the current tariff rate from the Dubai Electricity and Water Authority (DEWA) of 0.38 AED/kWh [30].

Table 4. Comparison between the renewable and conventional cooling systems.

Parameters	Description and Values
System Type	Single-Effect Hybrid System		Fully Conventional
Solar: Conventional Energy Share Percentage	Renewable	Conventional	100%
	60%	40%
Type of Chiller	Absorption	Air Cooled	Air Cooled
Load Consumption (kW)	219.6	164.4	366 kW
Initial Costs (AED)	1,715,900	557,400	620,274.4
Installation Costs (15%) (AED)	257,400	83,600	93,041.2
Total (Initial+ Installation) (AED)	1,973,300	641,000	713,315.6
Total Renewable and Conventional (AED)	2,614,300		713,315.6
Operating Costs (AED)	87,200		410,284.6
Operating Cost Savings (AED)	323,100		-
Payback Period (Years)	3.12		-
Annual Energy Consumption (kWh)	63,323	166,245	892,071.5
AEC Savings (kWh)	670,718		-
Annual CO2 Emissions (kg)	69,655	182,869	713,657.2
Annual CO2 Emissions Saving (kg)	460,474		-
CO2 Savings (ton/year)	460.47		-
Equivalent to X Cars Not Used	97.97		-

shows the comparison between the proposed system and the conventional cooling system. Table 4 outlines the operating costs associated with the proposed system and the consequent energy savings and the subsequent reduction in CO₂ emissions. The installation costs of the solar system and the conventional chillers were also included in this analysis. The annual energy savings have been calculated using the power consumption and the operating hours for each system (i.e., renewable versus conventional). Referring to Table 4, it was found that the system was capable of contributing 670,718 kWh of annual energy savings compared to the fully conventional cooling system. Also, it was found that the proposed system has a short payback period of 3.12 years. On the environmental aspect, the implementation of this system reduced the carbon dioxide emissions by 461 tons per year, which is equivalent to removing approximately 98 cars off the road.

Figure 10 shows a comparison of costs and electricity consumption between the proposed hybrid system and the conventional system. It was found that despite the initial costs for the hybrid system being 3.6 times that of the conventional system, the high annual energy savings (i.e., 670,718 kWh) and the significant reduction in operating costs outweigh the initial costs, resulting in an attractive payback period of just over 3 years. A comparison of CO₂ emissions between the proposed hybrid and conventional systems is portrayed in Figure 11. The conventional system contributed 713 tons of CO₂ emissions every year, whilst the hybrid system emitted only 253 tons of CO₂ per year, which represents a deduction of around 65% in carbon emissions.

7. Conclusions

This paper investigated the thermal and environmental performance of a concentrating photovoltaic thermal system integrated with a single-effect absorption chiller. The proposed system was simulated using TRNSYS for a selected case study based in the UAE with a maximum cooling load of 366 kW. A cost analysis was performed to assess the feasibility of the proposed model. The proposed model was designed in a hybrid manner where 60% of the cooling load would be met using the solar cooling technique, whereas the remaining 40% of the cooling load would be fulfilled by the conventional cooling method. The model was validated with the existing literature and proved to be accurate in terms of the gained useful energy. Based on the conducted analysis, the system was able to attain 670,718 kWh of annual energy savings with a payback period of 3.12 years. Implementation of the proposed model would also lead to a reduction in carbon dioxide emissions by 461 tons per year, which is equivalent to removing approximately 98 cars from the road.