# Sustainable Approach of Generating Water and Energy:
## 4 Results and Discussion  
The performance of the proposed system was simulated based on a typical weather condition for the city of Riyadh, Saudi Arabia. The hourly variation of the solar radiation and ambient temperature is illustrated in Figure 6. There are wide variations of the ambient temperature and solar radiation during months. It is clear from this figure that the amount of solar radiation in the month of July in the city of Riyadh is abundant. The maximum outdoor solar radiation reaches around 9000 W/m\({}^{2}\cdot\)month. Because the hybrid system is powered by solar energy, and since the amount of solar energy for the selected city is rich, this figure reveals a sustainable opportunity for the proposed system presented in this study. Figure 7 depicts the specific cost of water (SCW) for the proposed system over a wide range of the DCMD membrane surface areas. For small membrane areas, the SCW is considerably high because there is an inadequate heat transfer surface available for heat transmission across the hydrophobic membrane. It was observed that increasing the membrane surface area reduces the SCW. For a larger membrane area, the SCW is fairly stable. Thus, increasing the membrane area leads to a higher production rate, but the overall cost has a marginal impact due to the rise in operating costs. One of the parameters that influence the overall SCW is the inlet temperature of the brackish water to the collectors. Figure 8 shows the variation of inlet water temperature to the collectors and its impact on the overall SCW. Figure 8 depicts that the SCW was substantially dependent on the inlet water temperature to the collectors. With a fixed amount of flow rate, the SCW was reduced by 4.5% as a result of increasing the increment of the inlet water temperature by 5 \({}^{\circ}\)C.  
Figure 7: Effect of membrane area on Specific Cost Water (SCW) for different flow rates. Auxiliary heating was utilized in the proposed system in case the solar energy gained by the collector is not sufficient to raise the brackish water to a predetermined temperature. Figure 9 illustrates the annual auxiliary heating energy required as a function of the number of panels connected in series in two different situations. The bottom two lines (black square and blue triangle) depict the annual auxiliary during daylight for two different flow rates. In this case, the DCMD was only operating during sunlight. The other two lines (green circle and red diamond) represent the annual auxiliary heating requirement when continuous water production is required. It is clear from this figure a continuous water production increases the annual auxiliary heating for a given number of panels by 49%. Figure 10 depicts the overall performance of the proposed optimized system. It shows the monthly energy electricity produced by the PVT, monthly electricity sets to the grid, and the imported electricity from the grid. As it is shown in this figure, the energy-saving in cold months is substantially higher as compared with summer months. The reason for this is that air conditioning account for about 70% of energy consumption in residential buildings. In this case, the proposed system is producing more electricity than the house's demand in the winter seasons. For continuous water production, the proposed system costs 5% more for each cubic meter. This is illustrated in Figure 11. This figure shows the SCW of water as a function of the panels connected in series. It is clear from this figure that the best price occurs at Ns = 18. At lower panels connect in series, the SCW is high because more auxiliary heating is used to rise the water temperature to 70 \({}^{\circ}\)C. Conversely, increasing the number of panels beyond 18 rises the SCW due to the increase in operating and insulation cost. Figure 8: Effect of inlet water temperature to the collectors on SCW. The triangles represent the specific cost water values under the variation of collectors’ temperature.