Fostering solar hybrid cooling systems in MENA region

In recent years, there has been a significant shift in focus toward sustainable development, with particular emphasis on using renewable energy sources and reducing carbon emissions. Within sustainable development, the building sector is integral to energy conservation.¹ To mitigate the use of fossil fuels and primary energy for space heating and cooling in residential or institutional buildings, it is imperative to establish effective policies addressing greenhouse gas emissions. These policies should limit fossil fuel consumption while promoting the adoption of renewable energy sources.^2,3 The energy consumption of buildings constitutes around 32% of global energy usage, with nearly half of this energy used to meet air conditioning demands.^4,5 According to estimates, energy consumption for buildings is projected to rise by 50% by 2030, leading to a corresponding increase in carbon emissions.^6,7

Researchers have been working to enhance the energy efficiency of buildings and promote the utilization of renewable energy sources. Solar energy is widely recognized as the most abundant renewable energy among the existing range of viable renewable technologies. However, solar energy contributes to <1% of the global primary energy supply.⁸ Due to its considerable potential, solar-thermal energy has gained substantial interest. Deploying solar collectors gives a highly effective approach for harvesting the ample solar energy accessible for various purposes such as space heating and cooling, dehumidification, desalination, and several more domestic and commercial applications. This approach serves to reduce dependence on fossil fuels and GHG emissions.⁹ The global transforming energy scenario by 2050 is shown in Fig. 1.¹⁰

According to the International Energy Agency, global energy demand will increase by 38% by 2040.¹¹ Despite the enormous potential of renewable energy in the Middle East and North African countries, this region provides only 1% of total energy supply and 3.5% of total electricity generation.¹² In recent decades, there has been a substantial amount of research interest in using solar energy to meet building energy needs, such as power generation, heating, and cooling through photovoltaic (PV) panels and collectors. Singh and Das¹³ numerically compared the four air conditioning equipment’s driven by solar energy to achieve a net zero building. The results indicated that for the building area of 4981 m², around 700 m² area of solar field is required to meet the net zero target of building. Calise¹⁴ did the techno-economic analysis of solar-assisted water/LiBr absorption chiller for a cooling load of 20 kW. The simulated results showed that the proposed system can save up to 64.7% of primary energy with a payback period of 12 years. Gomri¹⁵ did the numerical study on a solar-driven 10 kW water/LiBr absorption chiller while using natural gas as an auxiliary backup. The maximum coefficient of performance (COP) achieved was 0.82, while the maximum solar fraction was 58%.

Sharma et al.¹⁶ proposed the solar powered absorption cooling system (SPACS) and analyzed its performance in summer and winter. The results showed that the proposed system can provide cooling energy of up to 2356 kW h in summer, while in winter, it reduces to 620 kW h. The maximum coefficient of performance in summer was 0.55, while in winter and monsoon, it was 0.34–0.39. The levelized cost of energy (LOCE) for the SPACS was 0.177 $/kW h, while the payback period was 12.4 years. Yildiz et al.¹⁷ conducted an experimental study on a PV-assisted cooling system’s exergetic and energy saving. The experiment lasted from 7:30 a.m. until 5:30 p.m. The results showed that the average exergetic efficiency of the PV system was 4.94, and during the test period, the proposed 0.9 kW of solar PV system could save 2.84 kW h and 31% energy. Mittal et al.¹⁸ proposed the simulation of a solar absorption chiller for Nicosia, Cyprus. They concluded that solar energy could provide around 49% of the energy necessary for cooling and water heating. The authors also emphasized the importance of sustainable energy solutions, even if the economic rewards are marginal.

Singh and Das¹⁹ simulated a triple-hybrid vapor absorption cooling system (VACS) for a high-capacity small-scale building, combining solar, natural gas, and electricity for power. Their model demonstrated energy savings and was validated against the existing literature. Importantly, they found that increasing the solar collector area led to even greater energy efficiency gains. Ibrahim et al.²⁰ proposed a solar assisted absorption air conditioning system and compared it with a vapor compression cooling system in terms of energy consumption. The results indicated that the vapor compression cooling system consumes more energy than its counterpart, while 58% energy savings can be achieved in the summer with the absorption cooling system. The payback period for the proposed setup was 5 years.

Tsoutsos et al.²¹ conducted research on the economic assessment of a solar-integrated absorption cooling system using TRNSYS. They determined that the simple payback (SBP) without financial assistance stood at 11.5 years. However, with a 40% public funding subsidy, the PBP decreased significantly to 6.9 years. Singh and Das²² conducted research on a traditional vapor compression-based building cooling system linked with a desiccant-assisted dedicated outside air system (DOAS) for warm and humid climate zones using EnergyPlus software. While the suggested design reduced the thermal load demand by roughly 13.5%, the system’s coefficient of performance (COP) was not found to be significantly impacted and as high as 5.5% electric energy savings was recorded.

Singh and Das²³ investigated a small-scale triple-hybrid air-conditioning system operated by biomass and solar energy resources. As a result of the biomass gasifier powering an electrical generator and solar collector, the current system is triple hybrid in nature, meeting all energy requirements. The system’s grid dependency can be decreased thanks to the biomass-generated electricity, allowing it to meet the net-zero energy requirement.

Yildiz et al.²⁴ analyzed three novel air-cooling designs for solar and biogas/natural gas-aided high-capacity radiant absorption-cooling systems (RACS) varying between 100 and 121 tons. Results showed that under hot and humid conditions, energy-saving potential of up to 25.4% is achievable. The proposed design reduced desiccant regeneration energy by up to 29.8%. Finally, authors advised using solar and biogas/natural gas energies for radiant absorption cooling.