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Solar photovoltaic (PV) applications are gaining a great interest worldwide and dominating the renewable energy sector. However, the solar PV panels’ performance is reduced significantly with the increase in their operating temperature, resulting in a substantial loss of energy production and poor economic scenarios. This research contributes to overcoming the PV performance degradation due to the temperature rise. This work involves experimental and theoretical studies on cooling of PV panels using the evaporative cooling (EC) principle. A new EC design to cool the bottom surface of a PV panel was proposed, fabricated, tested, and modeled. A series of experimentation readings under real conditions showed the effectiveness of the method. A steady state heat and mass transfer model was implemented and compared with the experimental data. Fair agreement between the results of the modelling and experimental work was observed. It was found that the temperature of the PV panel can be decreased by 10 °C and the power improvement achieved was 5%. Moreover, the EC helps to stabilize the panels’ temperature fluctuation, which results in a better regulation of electrical power output and reduces the uncertainty associated with solar PV systems.

We consider the development and fitting of a dynamic model for desalinated water production by a direct-contact membrane distillation (DCMD) unit. Two types of dynamic-model structures, namely, lumped parameter and spatial, were evaluated. Both the models were validated using experimental response data generated by step testing the inlet hot stream temperature of a DCMD pilot plant. Both the model structures failed to follow the dynamic response adequately. However, a modification of the model by adding a heat loss term resulted in enhanced predictions for both model structures. The overall relative error in the model-plant mismatch was approximately 3%. This is reasonable considering the random uncertainties associated with the plant operation. This observation also improves our understanding of the importance of using better correlations for heat-transfer coefficients, to develop a more reliable and accurate predictive model for a wide range of operating conditions.

The concept of integrating mechanical vapor compression (MVC) with direct contact membrane distillation (DCMD) is presented and analyzed. The hybrid system utilizes the DCMD to harvest the thermal energy of the MVC reject brine to preheat a portion of the seawater intake and simultaneously produce additional fresh water. Based on the operating temperature, the hybrid system requires specific energy consumption between 9.6 to 24.3 kWh/m3, which is equivalent to 25 to 37% less than the standalone MVC. Similarly, the freshwater production of the hybrid system can range between 1.03 and 1.1 kg/h, which is equivalent to a 3% and 10% increase relative to the standalone MVC when operating at brine temperatures of 50 and 90 °C, respectively. However, this enhancement is achieved at the expense of an average of 60% larger total surface area. This is partially due to the incorporation of the surface area of the MD modules and mostly to reduced temperature differences. Altering the permeate-to-feed ratio of the DCMD module led to a marginal change in the overall production without any enhancement in the compression power consumption. Increasing the MD module length by 50% resulted in a 3% enlargement in the overall production rate and a 10% reduction in power consumption. A modified hybrid structure that additionally utilizes the distillate heat is sought. A 5% increase in water production at the expense of a 45% rise in the specific compression energy of the modified structure over the original hybrid system is obtained.

Desalination of geothermal brackish water by membrane distillation (MD) provides a low recovery rate, but integrating MD with reverse osmosis (RO) can maximize the production rate. In this study, different design configurations of a hybrid system involving brine recycling and cascading are studied via simulations, and the performance improvement due to the process integration is substantiated via the increased recovery rate and reduced specific energy consumption. Brine recycling is also found to improve the recovery rate considerably to 40% at an energy cost of 0.9 $/m3. However, this achievement is only valid when the final brine is recycled to the RO feed: when the final brine is recycled to the MD feed, the overall performance degrades because the recycled brine cools the feed and causes a serious reduction in the driving force and the consequent production rate. Configuring the hybrid system in multiple stages connected in series increases the recovery rate to 90% and reduces the specific energy consumption to 0.9 MJ/kg. Although the specific energy cost increases dramatically because external inter-stage heating is implemented, using a free energy source (such as a geothermal or waste-energy source) for inter-stage heating could provide the optimum configuration.

This work presents a detailed thermo-economic analysis of unit water costs from dual-purpose cogeneration plants. The power levelized cost was first calculated for stand-alone steam, nuclear, and combined-cycle power plants. The cost of energy needed to operate the desalination systems connected to power plants was evaluated based on two different approaches: power- and heat-allocated methods. Numerical models based on the heat and mass balances of the power and desalination plants’ components were developed and validated. Comprehensive and updated data generated using Desaldata libraries were correlated to estimate the capital, labor, overhead, and maintenance costs for different desalination systems. The levelized water cost produced by multi-effect distillation, multi-effect distillation with vapor compression, multi-stage flash, and reverse osmosis systems connected to different power plants was estimated. The impact of various controlling parameters, including the price of natural gas, nuclear power plant installation cost, and the desalination capacity on water cost, was investigated. For all simulated cases, the levelized water cost evaluated using the heat-allocated method was found to be lower by 25–30% compared to that estimated using the power-allocated method. The cost of water produced using reverse osmosis remains below that produced by other desalination technologies. However, using the heat-allocated method to estimate the levelized water cost narrows the gap between the costs of water produced by multi-effect distillation and that produced by seawater reverse osmosis. The results also show that the use of the multi-effect distillation process in a cogeneration configuration rather than multi-effect distillation with vapor compression can result in a lower water cost. The profit analysis shows slight differences between the profit of a power plant connected to a reverse osmosis system and the profit of a power plant connected to a plain multi-effect distillation system.

Riyadh is a desert region characterized by large daily and seasonal ambient temperature variations. Air cooling using mechanical vapor compression requires high energy rates resulting in negative environmental impacts. The use of non-conventional cooling methods such as evaporative cooling is attractive and needs further investigations particularly in such critical weather conditions. This paper deals with the analysis of the performance of a direct evaporative cooling in hot and arid weather conditions. Theoretical models using heat and mass transfer, exergy and cost analysis are first developed and presented. Such models have been systematically validated using available experimental and theoretical results from previous studies. The second part of the work concerns the analysis of the performance of a direct evaporative cooler under a metropolitan central Arabian Peninsula (Riyadh, KSA) weather conditions using average hourly temperature and relative humidity of the month of July. The optimum operating parameters of the cooler have been then selected. The analysis shows that the effect of the cooler effectiveness on the exergy efficiency is not significant. The suitable value of the effectiveness of the evaporative cooler working under summer weather of the studied location is found to be between 0.7-0.8. Such a value achieves comfortable conditions at low cost.

This paper studies energy consumption management of seawater Reverse Osmosis (RO) desalination plants to maintain and enhance the Voltage Stability (VS) of Power Systems (PS) with Photovoltaic (PV) plant integration. We proposed a voltage-based management algorithm to determine the maximum power consumption for RO plants. The algorithm uses power flow study to determine the RO plant power consumption allowed within the voltage-permissible limits, considering the RO process constraints in order to maintain the desired fresh water supply. Three cases were studied for the proposed RO plant: typical operation with constant power consumption, controlled operation using ON/OFF scheduling of the High-Pressure Pumps (HPPs) and controlled operation using Variable Frequency Drive (VFD) control. A modified IEEE 30-bus system with a variable load was used as a case study with integration of three PV plants of 75 MWp total power capacity. The adopted 33.33 MW RO plant has a maximum capacity of 200,000 m3/day of fresh water production. The results reveal that while typical operation of RO plants can lead to voltage violation, applying the proposed load management algorithm can maintain the vs. of the PS. The total transmission power loss and power lines loading were also reduced. However, the study shows that applying VFD control is better than using ON/OFF control because the latter involves frequent starting up/shutting down the RO trains, which consequently requires flushing and cleaning procedures. Moreover, the specific energy consumption (SEC) and RO plant recover ratio decreases proportionally to the VFD output. Furthermore, the power consumption of the RO plant was optimized using the PSO technique to avoid unnecessary restriction of RO plant operation and water shortage likelihood.

Producing ice using adsorption systems can represent a sustainable solution and meet the recent global environmental regulations as they use natural refrigerants and can be driven by solar energy. However, the beds used in these systems still have low thermal and adsorption characteristics. This study investigates numerically the use of an emerging aluminum foamed bed packed with advanced Maxsorb adsorbent in a two-bed adsorption system and reports cases of performance improvements compared to the classical finned-tube based system used to produce ice. A comprehensive 2-D transient pressure distribution model for the two beds was developed and validated. The model considers the temporal and spatial variations of the two beds’ parameters, while the effect of the thermal mass and heat transfer effectiveness of the condenser and evaporator components are imitated at the boundary conditions for bed openings using two zero-dimensional models. The results show the interrelated effects of varying the cycle times from 400 s to 1200 s with 2, 5, and 10 mm foam thicknesses/fin heights on the overall performance of both systems. The Al-foam based system demonstrated the performance superiority at a 2 mm foam thickness with maximum ice production of 49 kgice/kgads in 8 h, an increase of 26.6% over the counterpart finned-tube based system at a 400 s cycle time. The best COP of 0.366 was attained at a 5 mm foam thickness and 1200 s with an increase of 26.7%. The effective uptake of the Al-foam based system was reduced dramatically at a 10 mm foam thickness, which deteriorated the system performance.

This work addresses retrofitting the infrastructure of multiple-effect vacuum membrane distillation (V-MEMD) units by using cross-flow configuration (CFC). In this configuration, the feed water is evenly divided and distributed over the effects. In this case, the feed water stream for each effect is kept at a high temperature and low flow rate. This will lead to an increase in the vapor pressure gradient across the hydrophobic membrane and can also maintain the thermal energy of the stream inside the individual effect. It is found that CFC improves internal and global performance indicators of productivity, energy, and exergy. A mathematical model was used to investigate the performance of such a modification as compared to the forward-flow configuration (FFC). The cross-flow configuration led to a clear improvement in the internal performance indicators of the V-MEMD unit, where specifically the mass flux, recovery ratio, gain output ratio, and heat recovery factor were increased by 2 to 3 folds. Moreover, all the global performance indicators were also enhanced by almost 2 folds, except for the performance indicators related to the heat pump, which is used to cool the cold water during the operation of the V-MEMD unit. For the heat pump system, the specific electrical energy consumption, SEEC, and the exergy destruction percentage, Ψdes, under the best-operating conditions, were inferior when the feed water flow was less than 159 L/h. This can be attributed to the fact that the heat rejected from the heat pump system is not fully harnessed.

Cogeneration of energy and clean water by incorporating direct contact membrane desalination (DCMD) and photovoltaic hybrid thermal system (PVT) into a residential building is a promising technology for addressing water and energy shortage in distant places. In this study, a microgrid integration between PVT, DCMD, and a residential building is proposed, with an end goal to meet partial electric load in the building and provide a clean water supply. A mathematical model was developed and validated to assess the system’s performance. Artificial Neural Network (ANN) and optimization techniques have been used. The performance of the proposed system was studied under the meteorological conditions of Riyadh, Saudi Arabia, and under several design and operation parameters. The optimal performance of the system is found as functions of the inlet brackish water temperature to the PVT, capital and installation cost, and the desired water productivity. Results reveal that the specific cost of water (SCW) is 23.6 $/m3 achieved with a renewable energy penetration of 25%, depending on the cost of PVT and electricity price. Thus, the proposed system meets 25% of the electric demand for the residential building, while the rest is imported from the grid. In addition, the proposed system reduced the annual greenhouse gas emission by 4300 kg for a single building. This study will contribute to a better understanding of incorporating innovative clean energy and water systems such as PVT and DCMD into a residential house.