Introduction to the Function of a Solar Parabolic Dish
A parabolic dish is manufactured in the shape of a parabola (same shape as your satellite TV dish) and come in different sizes to suit the particular application. It is one of a number of solar energy concentrators that work on the principle that a paraboloid shape will reflect incoming light-rays from the sun and focus them at one point.
The parabolic dish has been used in number of experimental sites to produce industrial power through the linking of numerous micro-power units. However the parabolic dish has mainly been used to provide heat in the domestic sector.
This is another article in my series on the domestic use of renewable energy. We shall have a look at the design and operation of a typical parabolic dish which can produce high temperature. This can be utilized in domestic heating systems, or to power a heat engine generating electricity. The function these systems along with other uses will be covered in future articles.
We begin then with the design and operation of the parabolic dish.
Design and Operation of a Solar Parabolic Dish for Domestic Applications
A parabolic dish is fashioned into a parabola by the fixing of various mirrored sections onto the shaped template. The parabola shape is designed to have the ability to catch incoming solar light-rays, parallel to the axis of the dish.
This is the most significant property of the parabola shaped dish, as these rays arriving on earth from the sun are nearly all parallel.
Now, regardless of where the solar light-rays strike the dish the light rays will be reflected to a focal point known as the receiver point where, due to the high concentration of the solar light – rays, a high temperature is produced.
- The optimum efficiency is obtained by tracking the suns passage across the sky, which is achieved using a tracking device. This consists of a dual-axial device designed to track the sun’s azimuth in both the horizontal plane by turning longitudinally, combined with the ability to tilt in the vertical plane.
There are several disadvantages of using a Parabolic Dish solar collector,
- The sun Conversion of the thermal energy collected by the receiver into kinetic energy to drive a machine raises reliability and maintenance issues, as the machinery is usually integral to the dish.
- The tracking system must be strong enough to perform its function despite the sometimes heavy weight of the heat or electrical producing equipment. This requires a strong, rigid support frame making the tracking system more expensive to purchase, raising the operating costs, as well as being somewhat cumbersome in appearance.
The dishes come in a number of sizes,
- A small dish – just over 1m diameter and used to heat domestic water.
- A Medium dish – 1.7m diameter used to heat domestic water in commercial or industrial buildings, large propagation greenhouses, etc.
- A Large Dish – Over 4m diameter, used to heat domestic water in hotels, swimming pools in leisure centers etc.
The Current Applications of a Solar Parabolic Dish
The current applications of a solar parabolic dish are as follows,
- Supplying thermal energy to heat domestic hot water and to operate central heating systems
- Supplying thermal energy to run a heat engine such as a Sterling engine to drive a power generator producing electricity.
- Microturbine Power Generation
At present there are research and development operations in progress to produce a micro turbine which will operate on hot air. This is being designed on existing micro turbines running on natural gas
- Heat Engines
The use of Sterling engines powered by solar parabolic dishes is used in several locations throughout the world to produce power to the national grid. This is achieved by connecting numerous modules together to give a high capacity electrical output.