Bhowmik et al. (2021) presented an experimental investigation of a solar-assisted thermal liquid desiccant dehumidification system (See Figure 4) that employs a structured packed bed dehumidifier and regenerator using a novel mixed desiccant solution (LiBr + CaCl₂ at an 85:15 mass ratio). The system is thermally driven by evacuated tube solar collectors (ETCs) and operates in a closed loop to ensure continuous dehumidification and regeneration cycles. Key technological innovations include the use of a counter-flow configuration to enhance heat and mass transfer, and a comprehensive instrumentation setup to evaluate performance metrics. The system’s dehumidification performance is characterised by a maximum latent heat ratio (LHR) of 0.92 and a thermal coefficient of performance (TCOP) of 1.1. In addition, an Adaptive Neuro-Fuzzy Inference System (ANFIS) was developed to predict performance parameters such as condensation rate, evaporation rate, and effectiveness indices (latent, enthalpy, and sensible), achieving high prediction accuracy with MAPE values of 2.7% and 2.3%. The results highlight that a higher solution-to-airflow (S/A) ratio favours dehumidification, while a lower S/A ratio enhances regeneration. The system demonstrates effective integration of solar energy for sustainable HVAC applications in hot and humid climates.

Zhang et al. (2025) presented an optimised PV/T-assisted desiccant evaporative cooling system (PV/T-DCS) designed for hot and humid urban environments (See Figure 5). By integrating a PV/T system with a liquid desiccant dehumidification and evaporative cooling unit, the system enhances energy efficiency while reducing emissions. The desiccant, lithium chloride, is regenerated using solar thermal energy, reducing the need for conventional power sources. A multi-objective optimisation approach using NSGA-III and Response Surface Methodology (RSM) was applied to balance energy savings, cooling capacity, economic feasibility, and environmental impact. Numerical simulations and performance modelling helped identify the best operational parameters, including air velocity, solution concentration, and recirculation ratio. The results show a 58.1% reduction in energy consumption and a 61% decrease in CO₂ emissions compared to conventional cooling systems, with an effective cooling capacity of 22.9 kW. Under peak conditions, the system achieved a 62.3% energy savings rate and a 64.66% CO₂ reduction. Despite these benefits, the system faces limitations due to its complexity and dependence on solar radiation. Variations in weather conditions impact its effectiveness, and the study does not consider energy storage solutions. Future research could explore ways to simplify the design, improve adaptability across different climates, and integrate energy storage for better reliability.

Ali et al. (2022) presented presents an experimental investigation of a hybrid solar-assisted air-conditioning system that integrates a solid desiccant dehumidification unit with an NH₃–H₂O (ammonia–water) absorption chiller (See Figure 6). The system is designed to improve energy efficiency by thermally coupling the desiccant wheel and the absorption chiller: the waste heat from the absorber and condenser of the absorption cycle is recovered to regenerate the solid desiccant. The cooling system operates in two parallel streams—one primarily focused on latent load removal via the desiccant wheel, and the other handling the sensible cooling via the absorption chiller. Solar thermal collectors are employed to drive the generator of the absorption chiller, reducing dependency on fossil fuels. Experimental results indicate that the integrated system can achieve a cooling COP of approximately 0.72, while significantly improving the overall energy utilisation due to heat recovery. The desiccant wheel effectively reduces the latent load on the absorption chiller, allowing the system to perform efficiently even under high humidity conditions. However, the system presents certain limitations: its performance is sensitive to solar irradiance fluctuations, and precise thermal management is required to coordinate heat recovery between the subsystems. The study also notes operational challenges related to desiccant regeneration temperature stability and system control complexity. The authors suggest that optimal integration and advanced control strategies are essential for maximising system efficiency under variable climatic conditions.

Riffat et al. (2022) presented an innovative passive-active hybrid absorption cooling system that integrates Phase change materials (PCMs) with a chilled ceiling panel and a transparent infrared membrane, powered by a solar PV driven variable speed DC compressor refrigeration system (See Figure 7). The core technology involves using hydrated salt-based PCM with a melting point of 13°C embedded in a ceiling-mounted radiant cooling panel. The panel is covered with an infrared-transparent membrane to allow radiative cooling while suppressing convective heat transfer, thus preventing surface condensation in humid environments. The system stores excess cooling energy generated during the day in the PCM, which is then used to maintain comfort conditions at night. PV-driven DC compressor system is employed to match variable solar input, eliminating the need for batteries or inverters, which often add cost and inefficiencies. The results showed that the PCM-integrated system maintained 2–2.5°C lower temperatures compared to the non-PCM case for up to 4.5 hours. The transparent membrane effectively prevented condensation but slightly reduced cooling capacity due to the limited convection. Comparisons between chilled beam and chilled ceiling configurations indicated that the chilled ceiling panel with membrane covering provides superior thermal stability in the post-cooling period, due to better PCM utilisation. However, the system’s reliance on radiant cooling and lack of active humidity control may restrict its applicability in extremely humid climates without additional dehumidification strategies. Future work is needed to optimise system configurations, scale up for field testing.

Jarimi et al. (2024) proposed an absorption system integrates a solar PV-powered DC vapour compression cooling unit with a low-cost ice gel thermal battery as a PCM-based thermal energy storage to mitigate the intermittency of solar power and reduce reliance on expensive batteries or grid extension (See Figure 8). The study introduces four operation modes combining solar PV, grid, battery, and ice gel storage, but identifies Mode B, which is a configuration where the PV system operates the DC vapour compression unit at full power for three hours with the support of ice gel thermal storage and limited battery use as the most optimal. This configuration showed superior COP, particularly COPₚᵥ of 4.04 and COPₛᵧₛₜₑₘ of 5.05, and the highest SFPVVC (9.10) among the four modes. Moreover, the levelised cost of cooling (LCOC) for Mode B was only 0.0979 USD/kWh, significantly lower than the grid-based or conventional PV systems without thermal storage, making it an economically viable and sustainable alternative for off-grid cooling. Besides, the system employs a DC-powered variable refrigerant flow (VRF) compressor that directly utilises solar energy during the day. Excess cooling is stored in the ice gel thermal battery, a PCM composed of water, glycerine, and alcohol with a freezing point of ~1.9°C and latent heat capacity of 361.86 J/g. The thermal storage enables stable indoor temperatures (22–26°C) even during periods of low or no solar irradiance, enhancing thermal comfort and operational reliability in remote settings. To validate system performance, the study also combines artificial neural networks (ANN) for predicting evaporator and inlet temperatures with TRNSYS for building and system simulation. Experimental validation shows great agreement with simulations. The system was field evaluated for a rural healthcare facility in Malaysia, demonstrating it can reliably meet a monthly cooling demand of 631 kWh, with sufficient storage and cooling performance maintained during cloudy conditions. While the system demonstrates significant promise, the authors highlight limitations, including reliance on a proof-of-concept prototype, need for real-world long-term testing, and potential optimisation of control strategies for improved thermal management. Nevertheless, the approach offers a compelling low-cost, sustainable cooling alternative for underserved rural areas.

Suhendri et al. (2022) presented a hybrid passive ventilation strategy integrating a solar chimney (SC) and a radiative cooling (RC) cavity (see Figure 9). This dual-system approach is proposed to address the limitations of conventional SC systems by extending ventilation effectiveness into nighttime hours, leveraging the distinct thermodynamic mechanisms of solar-induced buoyancy and nocturnal radiative cooling. The authors developed a two-dimensional transient computational fluid dynamics (CFD) model using ANSYS Fluent to investigate the dynamic performance of the SC-RC system under a range of design and environmental conditions. The simulations were validated against experimental data and applied to a prototypical building model situated in multiple global climate zones. The results indicate that the SC-RC system outperforms conventional SC ventilation in terms of both thermal and ventilation performance, particularly in arid and semi-arid climates. The system achieved a maximum indoor temperature reduction of 2 °C and an average of 0.56 °C below ambient, with ventilation rates reaching up to 2.1 air changes per hour (ACH), an improvement of approximately 0.4 ACH over the reference case. The inclusion of a polyethylene convection cover significantly enhanced the sub-ambient performance of the RC emitter by mitigating convective heat gains. Moreover, the presence of high thermal mass in building materials contributed to thermal stability, while narrower RC cavity gaps enhanced cooling performance at the expense of reduced airflow. The study further demonstrated that the SC-RC system maintained sub-ambient indoor temperatures under internal heat gains up to 4 W/m², beyond which performance began to deteriorate. Notably, in humid climates, the cooling efficacy of the RC component was substantially diminished, rendering the SC-RC system less effective than the SC-alone configuration. However, the authors acknowledge several limitations inherent in the study. These include the exclusion of wind-driven ventilation effects, the simplified assumption of uniform internal heat gains, and the idealisation of boundary insulation on certain building facades.

Gado et al. (2021) a comprehensive theoretical investigation into three distinct configurations of solar-powered hybrid cooling systems (See Figure 10) that integrate adsorption and vapour compression technologies, with the aim of enhancing both energetic performance and economic viability under the climatic conditions of Cairo, Egypt. The systems employ silica gel-water as the working pair in the adsorption cycle and R410A as the refrigerant in the compression subsystem. Configuration I integrates a solar thermal subsystem with a hybrid adsorption–compression cycle; Configuration II augments this setup with PV panels to achieve net-zero electricity consumption; and Configuration III incorporates an intermediate cold storage tank to extend operational duration. A dynamic simulation model was developed in MATLAB/Simulink and validated against experimental benchmarks, demonstrating good agreement. The findings indicate that increasing the adsorption-to-compression capacity ratio from 0.867 to 1.333 in Configuration I reduces the intermediate temperature from 15.8 °C to 5.7 °C and enhances daily electricity savings from 23% to 62.5%. Configuration II achieves complete offset of electricity demand via PV supplementation and offers the most favourable economic outcome, with an annual energy saving of 2897 kWh and a payback period of 9.65 years. Although Configuration III enables extended operation (13 vs. 12 hours), it delivers lower annual energy savings (47%) and is economically unviable due to elevated capital costs and a negative internal rate of return. The maximum overall COP of the hybrid system reaches approximately 5.59, compared to 6.9 for a standalone compression system, reflecting the intrinsic thermodynamic limitations of thermal-driven cycles. The study underscores the promise of optimally sized, solar-assisted hybrid systems, particularly those incorporating PV modules, as a viable pathway toward reducing electricity consumption in cooling applications while maintaining reasonable investment payback timelines.

Ghazy et al. (2022) explores a novel integration of a PV/T with an adsorption desalination system (ADS) to enhance the efficiency of solar cells and concurrently produce cooling and fresh water, which is showed in Figure 11. This hybrid approach targets the pressing issues of reduced photovoltaic efficiency under high temperatures and freshwater scarcity in hot, arid regions. The core innovation lies in using the chilled water generated from the evaporator of the ADS to actively cool the back of the PV module via a custom-designed sheet-and-tube collector. In turn, the heat extracted from the PV panel is used to enhance the desorption process of the ADS, thus creating a synergistic energy exchange loop between electricity generation and water desalination. This bidirectional thermal integration is tested under real-world hot weather conditions in Sohag, Egypt. The results demonstrate that the hybrid HPV/T-ADS system achieves an electrical efficiency of 11.5% and a thermal efficiency of 77.5% at 1000 W/m² solar radiation and 45 °C ambient temperature. Additionally, the system yields a specific daily water production (SDWP) of 6.31 m³/ton-day, a specific cooling power (SCP) of 152.3 W/kg, and a COP of 0.25. These figures reflect a 17.5% improvement in electrical power, 19.69% enhancement in water production, and a 9.9% increase in COP when compared to the performance of the PV module and ADS operated independently. Furthermore, the study compares this integrated system with other PV cooling technologies (e.g., water, air, nanofluids, PCM) and finds that the proposed system delivers the highest rate of electrical efficiency improvement among them. The authors also emphasise that this is the first experimental study to integrate PV/T cooling with an adsorption desalination unit, setting the foundation for subsequent development in off-grid solar-assisted polygene ration systems.

Ren and Ogura (2021) experimentally evaluates the performance of an off-grid solar-powered chemical heat pump (CHP) system capable of providing both space heating and cooling, with the objective of enabling autonomous operation in remote or infrastructure-limited regions (See Figure 12). The system comprises two fixed-bed thermochemical reactors operating in an alternating hydration–dehydration cycle, using a CaCl₂–silica gel composite as the thermochemical sorbent and water as the working fluid. Thermal energy is supplied by evacuated tube solar collectors, while auxiliary electrical demands are met via photovoltaic modules, ensuring complete off-grid functionality. Under real environmental conditions, the system demonstrated thermal COPs of 0.35 for cooling and 0.64 for heating, with corresponding energy efficiencies of 0.45 and 0.69, and exergy efficiencies of 0.18 and 0.22, respectively. The authors further conducted a performance sensitivity analysis, projecting that optimisation of the heat transfer fluid, particularly by selecting a lower-viscosity medium—and improving the circulation pump efficiency could increase the total system COP (COPₜₒₜ) from 1.6 to as high as 4.0. Despite its demonstrated viability, the system exhibits several limitations: the thermal COP, particularly in cooling mode, remains modest compared to conventional technologies. The cyclic operation is constrained by relatively long charging and discharging times (~6 hours per phase), potentially limiting responsiveness to dynamic load demands. Nonetheless, the study affirms the potential of thermochemical energy storage as a sustainable pathway for decentralised thermal energy management, particularly in solar-rich, energy-scarce contexts.

Shurafa et al. (2025) investigates hybrid photovoltaic-thermoelectric generator (PV-TEG) systems using different thermal interface materials (TIMs) under natural cooling conditions (See Figure 13). It compares pyrolytic graphite sheets (PGS) and thermal grease as TIMs, alongside a standalone PV system as a reference. PGS, known for its high thermal conductivity (1600 W/m·K in-plane), is used to enhance heat dissipation and improve overall system efficiency. An Arduino-based data logger is employed to monitor temperature, voltage, and current in real time. The PV-TEG system with PGS achieved a 17.95% efficiency, outperforming the system with thermal grease (16.87%) and the PV-only system (16.42%). The PGS-based system maintained a lower surface temperature (39.01°C) compared to thermal grease (48.88°C) and the standalone PV module (55.37°C). Power output was 4.87 W for PGS, 4.67 W for thermal grease, and 4.55 W for PV-only, showing that PGS enhances energy conversion. The temperature gradient across TEG modules was 150% higher with PGS, leading to increased thermoelectric power generation. The study highlights thermal contact resistance as a key limitation in TIMs, with thermal grease trapping heat and reducing TEG efficiency. While PGS improves performance, its manufacturing cost and durability require further study. Additionally, the natural cooling method limits heat dissipation compared to forced cooling techniques like water cooling. Future research should explore alternative TIMs, integrated cooling systems, and automation to optimise hybrid PV-TEG efficiency.

Zarei et al (2022) investigates presents the thermodynamic design and performance analysis of a novel solar-assisted cooling system that integrates a vapour compression refrigeration cycle with an ejector subsystem, both powered by a hybrid PV/T collector (See Figure 14). The system simultaneously uses electrical energy from the PV panel to operate a scroll compressor and thermal energy from the collector to preheat the refrigerant vapour entering the ejector, thereby enhancing entrainment efficiency and reducing compressor workload. Three refrigerants, R134a, R1234yf, and R290, are evaluated based on their thermodynamic behaviour and environmental impact. A validated model developed in Engineering Equation Solver (EES) is used to perform parametric simulations across a range of generator temperatures (60–90 °C), ejector efficiencies, and operating conditions. The results demonstrate that R290 achieves the highest system COP≈ 1.00, followed by R134a (0.98) and R1234yf (0.96). The ejector subsystem contributes up to 30% of the total cooling capacity, significantly improving energy efficiency and reducing reliance on electricity. However, the system faces several limitations: its performance is highly sensitive to ejector geometry and mixing efficiency, which are difficult to optimise due to complex two-phase flow interactions; the effectiveness of solar-driven thermal preheating is constrained by fluctuating irradiance, which may lead to unstable ejector operation; and while R290 delivers superior performance, its high flammability raises safety concerns that may hinder practical deployment. Furthermore, the integration of multiple subsystems requires precise thermal and control coordination, increasing system complexity and potential maintenance burdens. Despite these challenges, the proposed hybrid configuration offers a promising and environmentally sustainable pathway for reducing electricity consumption in cooling applications, particularly in regions with high solar availability.