Water Desalination Using Offset Solar Parabolic Dish Concentrator: A Review

*Heman M. Pandya, C. O. Yadav and P. V. Ramana* 

### **Abstract**

 Few desalination systems exist that are not energy intensive and which do not utilize any conventional sources of energy. There is a great potential to be harnessed through solar energy and thermal desalination is one such process with little investment and the potential to produce potable water for up to 5–10 years at the least. Efforts have been made to make solar distillation systems cheaper and more capable of achieving higher yields of distilled water. An offset parabolic dish works on the principle of concentrating solar power technology, which generates higher distilled water yields with lower production costs. This review paper summarizes the optimum feasible design options available for manufacturing the offset parabolic dish concentrator for desalination purposes. The construction and performance of offset parabolic dish concentrator depends on several key features such as reflecting materials used for the concentrator, shape, size of the aperture area of the concentrator, diameter of dish concentrator, focal length of the offset parabolic dish concentrator, geometric concentration ratio (CR), and rim angle.

**Keywords:** offset parabolic dish concentrator, Scheffler dish, concentrating solar power (CSP), water distillation, desalination unit, small-scale solar still

#### **1. Introduction**

The solar water desalination process is one of the best and low-cost routes to obtain potable water through evaporation and condensation.

 There have been 400 million people who have used desalinated water in 2015 and it was reported by Dr. Md. Eaqub Ali that by 2025, 14% of the global population would be forced to use sea water. By 2030, the global water demand will be 16,900 billion m3 (Bnm3 ) and 2400 Bnm3 shortfalls of water would be generated. This water shortfall can be provided by various desalination processes [1].

There are four types of parabolic dishes: (a) Axial or front feed prime focus parabolic dish, (b) Offset parabolic dish, (c) Cassegrain, and (d) Gregorian parabolic dish.

The offset parabolic shape eliminates aperture blockage and prevents the accumulation of ice and snow by placing the receiver below the dish reflective aperture region. The offset dish is a portion of a much larger paraboloid. The reflector/concentrator is an asymmetric segment of a paraboloid, so the focus is *Water Desalination Using Offset Solar Parabolic Dish Concentrator: A Review DOI: http://dx.doi.org/10.5772/intechopen.81083* 

located on the side and does not record a shadow as in the front receiver dish. In the offset design, the receiver is positioned outside on a boom sticking out from the bottom edge of the dish.

The offset-axis dish design offers several distinct advantages over its prime focus counterpart. There is no receiver blockage and this is an important consideration when the reflecting aperture is less than 1 m in diameter. Better stability and lower wind resistance is provided by this shape (geometry).

Certain disadvantages also exist with solar based dish systems, such as these systems need tracking, they tend to be the more expensive option when compared to non-tracking desalination systems. In addition, maintenance of the system, such as timely seasonal changes in the tracking system for proper altitude tracking, also requires skilled technical personnel.

Wear and tear of the abrasive film and replacement of broken reflecting glass or regular removal of dust from the surfaces of the concentrator are a few of the issues present in almost all concentrating solar technologies.
