Design and Analysis of a Sustainable Off-Grid Climate Refuge Shelter for Arid Climates

In hot arid climatic regions like Qatar, pedestrians can be facilitated if provided by a shelter, i.e., on the way from the public transport station to their desired building - which could provide electricity, space cooling, and freshwater in an off-grid condition. In this study, two system configurations are proposed for efficient on-site energy generation, effective space cooling, and freshwater production. System 1 consists of semi-transparent solar photovoltaic cells located on the roof integrated with batteries to keep the system running at night-time and in unfavorable irradiation conditions. An atmospheric water generator collects humid air to produce fresh water for drinking and water misting purposes, in addition to a vapor compression cooling system for higher ambient temperatures than 301.15 K. For less than 301.15 K, fan and water misting systems are operated for the comfort of pedestrians. The system is analyzed thermodynamically through energy and exergy analyses. The overall energy and exergy efficiencies of System 1 are calculated to be 19.45% and 9.58%, respectively. An hourly analysis of the proposed system for the whole year is performed to evaluate the energy profile. For System 2, which includes bifacial solar photovoltaic cells and solar thermal collectors for on-site energy generation, electrical and thermal energy storage systems are considered to support the operations during night-time or in adverse weather conditions. Ejector–based cooling system is able to use electrical as well as solar thermal energy for efficient space cooling in high ambient temperatures (more than 301.15 K). Finally, an electrodialysis system is integrated to generate freshwater from saline water to be used for drinking and water misting purposes in the off-grid sustainable shelter. The system's overall energy and exergy efficiencies are calculated to be 11.15% and 5.23%, respectively. Bi-facial PV with an efficiency of 16% can yield electricity up to 6.09 kW, contributing to the power demand for cooling. The effects of several parameters such as solar irradiance, ambient temperature, cell temperature, area of the solar PVs, and mass flow rates of refrigerants are also studied to observe the overall system efficiency and energy generated and consumed by the system. Also, considering the broad range of applications, efficient retrieval and storing electrical energy methods have been considered, which helps in balancing electricity generation and consumption to avoid voltage and frequency deviations. Comparison of two routes for electricity storage, namely, flywheels and a lithium-ion battery, is also evaluated through levelized cost of energy calculations in this study. The annual energy production by solar photovoltaics for the proposed system (System 1) is about 20 MWh. Considering the flywheel with AC configuration, it offers a 30% reduced duration of transient while interfacing to the network, and the current peak value is also lower than the battery case. The PV-battery storage system has shown the lower cost of electricity, corresponding to 0.761 $/kWh, and net present cost of $66,238 and is optimum in all sensitivity analysis cases.