Solar desalination technology is favorable due to its positive impact on environment but their cost effectiveness remains a major challenge. The two commonly used solar desalination technologies are the photovoltaic reverse osmosis (PV-RO) and solar humidification-dehumidification desalination system. While the latter requires less expertise in installation and maintenance which makes them more suitable for remote regions, unit cost of produced fresh water using PV-RO is currently lower than humidification-dehumidification desalination system.
Abd El-Aziz et al. (2016) presented an optimization of a solar-powered humidification-dehumidification HDH desalination system for remote areas where assumptions were only made on minimal external electric power. The work published in Journal of Solar Energy Engineering provided modifications on previous work, seeking to improve system performance in terms of unit cost of fresh water production. The authors modified model done on previous work by Abd El-Aziz et al. ASME, 2013 addresses problems such as negative effect of condensation performance, limitation of saline water temperature to 60°C leading to air capacity for water vapor less than 0.153Kg vapor/Kg air and expensive solar tank in solar water heater (SWH).
The modified model addressed the problems discussed above by firstly disconnecting the condenser from inlet water stream to operate on an independent coolant supply with a constant flow rate, solar air heater (SAH) added before the humidifier allows higher outlet air temperatures and higher humidity ratios and lastly, removal of the solar tank.
The authors considered a small-scale desalination plant operating near city of Hurghada in Egypt. Cost factor was assumed to be 55% while plant lifetime was assumed to be 30 years which is a typical value for the type of equipment considered.
Optimization and simulation results for a system with both large and small solar water heater area AC,W=1000m2 and AC,W=100m2 showed that unit cost of produced fresh water relative to previous work was reduced by about 75% for new cost function and by 56% for original cost function which is due to improved humidification and condensation performances. Specific energy consumption Esp was found to be in the range of 400-550 KWh/m3 depending of the system size which is still within the range reported in the literature (120-550 KWh/m3).
Disconnecting the condenser to utilize a high constant coolant flow rate increased the quantity of distilled water obtained from installed condenser which relates to a reduction in unit cost of production. The smallest system with 7.8m3/day had a unit cost of $1.7/m3 while most energy-efficient system had a unit cost of $5.7/m3 for capacity of 5m3/day. The minimum unit cost of $1.3/m3 was obtained which is 57% lower than reported range of previous systems of $3-7/m3.
For optimum 500m2 system, there was enough provision of potable water for a small town of 1000 to 3000 inhabitants and from economic point of view, it could be inferred that the system would have a payback period of 10 years in Hurghada.
Finally, Heuristic gradient projection optimization was much more efficient and required only about 10% of function evaluations required by unconstrained genetic algorithms optimization to converge.
The optimization and improved humidification and condensation performance achieved in this study have shown major cost reduction in production.
Khalid M. Abd El-Aziz 1, Karim Hamza2, Mohamed El-Morsi3, Ashraf O. Nassef4, Sayed M. Metwalli 1, Kazuhiro Saitou2. Optimum Solar Humidification–Dehumidification Desalination For Microgrids and Remote Area Communities, Sol. Energy Eng 138(2), 021005 (Feb 01, 2016) (8 pages)Show Affiliations
- Department of Mechanical, Design and Production, Cairo University, Cairo 12316, Egypt .
- Mem. ASME , Department of Mechanical Engineering, University of Michigan, Ann Arbor, .
- Mem. ASME, Department of Mechanical Engineering, American University in Cairo, New Cairo 11835, Egypt;Department of Mechanical Engineering, Ain Shams University, Cairo 11566, Egypt .
- Mem. ASME , Department of Mechanical Engineering, American University in Cairo, New Cairo 11835, Egypt .
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