**7. Conclusion**

112 Modeling and Optimization of Renewable Energy Systems

0 100 200 300 400 500

**Number of Generation**

Fig. 10. The variation of the total cost function during the GA-based optimization process

2 2,2 2,4 2,6 2,8 3 3,2 3,4 3,6 3,8

**Total Water Cost (\$/m3**

**)**

Several combinations for desalination processes driven by renewable energies (RE) can be proposed to provide water and energy in remote areas (Solar/MSF, Solar/MED, PV/RO, etc.). Reverse Osmosis (RO) is most often chosen as one of the most efficient desalination techniques in terms of energy consumption, flexibility, reliability, simple maintenance, etc.

There are a number of issues that should be taken into consideration while designing RES/RO systems as: the characteristics of water demand, the cost of water and fuel, the availability of renewable energy resources, the initial cost of the project, including the cost of each component required, the life time of the project, the interest rate subsidies, etc. A techno-economic comparison between different scenarios can be carried out to study the feasibility of the project.

In this chapter a new methodology to optimize RO desalination system driven by hybrid PV/Wind systems is presented. The proposed methodology is based on determining, among a list of commercially available system devices, the optimal number and type of units (PV modules, W/G, Batteries, etc.) such that the life time round total system cost is minimized, while simultaneously the desalinated-water demand is completely covered. The minimization of the system total cost function has been implemented using genetic algorithms (GAs) that allows considering a large number of possible configurations.

The proposed method has been applied and tested for the design of a desalination system, which cover the potable water demands of a small community in South Tunisia. The application of this methodology allows to reduce the cost of the produced water from 56 \$/m3 in the first generation to 2.62 \$/m3 for the optimal solution. The fluctuation of the

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**6** 

*China* 

**Heat Transfer Modeling of the Ground Heat** 

*Key Laboratory of Renewable Energy Utilization Technologies in Buildings, Ministry of Education, China; Shandong Jianzhu University, Jinan, Shandong,* 

Ground-coupled heat pump (GCHP) systems have been gaining increasing popularity for space air conditioning in buildings due to their reduced energy and maintenance costs. The efficiency of GCHP systems is inherently higher than that of the traditional options because it utilizes the ground which maintains a relatively stable temperature all the year round as a heat source/sink. Compared with traditional air-conditioning systems, the GCHP system features its ground heat exchanger (GHE), whether it is horizontally installed in trenches or as U-tubes in vertical boreholes. The advantages of vertical GHEs are that they require smaller plots of land areas, and can yield the most efficient GCHP system performance. The vertical GHEs are usually constructed by inserting one or two high-density polyethylene Utubes in vertical boreholes, which are referred to as single U-tube or double U-tube GHEs, respectively. The boreholes should be grouted to provide better thermal conductance and prevent groundwater from possible contamination. Borehole depths usually range from 40 to 200 meters with diameter of 100 to 150 millimeters. The schematic diagram of a borehole

a) double U-tube b) single U-tube

Fig. 1. Schematic diagram of boreholes in the vertical GHE exchanger

**1. Introduction** 

with U-tubes in vertical GHEs is illustrated in Fig. 1.

**Exchangers for the Ground-Coupled** 

**Heat Pump Systems** 

Yi Man, Ping Cui and Zhaohong Fang

