Concentrating Solar Power
Concentrating solar power is one of the most ancient ways of using solar energy.
An ancient Greek tale tells of how Archimedes, a great mathematician, was able to defeat a Roman fleet by using glasses which he used to concentrate the solar rays and set the Roman ships on fire. In 1973, a Greek scientist was able to reproduce the experience with the same success, although historians still doubt the original story which was dated 212 BC.
Whether the Greek tale is true or not, it really doesn’t matter. What matters is that it reveals man’s awareness of the abilities and uses of concentrating solar energy to his advantage even a thousand years ago.
In fact, man was already using glasses to concentrate solar energy hundreds of years before 212 BC. Concentrating solar power was mainly used to help start a fire – fundamental for survival. Read more about the history of solar energy.
The technologies for harnessing solar energy through concentrating the sun’s rays and making use of the concentrated heat energy to produce electricity (often using a turbine generator) is known as concentrated solar power. Concentrated solar power, which is the focus of this article, is different from the conversion of the sun’s energy (mainly light energy) directly to electricity (without a turbine generator) using photovoltaics solar panels, where the concentration of sunlight onto the solar panels is known as concentrated photovoltaics.
There are four ways of concentrating solar power.
There is the parabolic trough, which is perhaps the most common means of concentrating solar power. It consists of a large parabolic mirror (usually a silver coating or polished aluminum) on the inner surface of a long trough, with a fluid-filled tube (known as a Dewar) running along the length of the trough at the focal point. The mirror reflects and concentrates the solar energy onto the tube, heat from the sunlight is absorbed by the fluid within, and the fluid is used to produce steam in a conventional turbine generator. The trough is usually oriented on a north-south axis in the direction of the sun, and has in place mechanisms to track the sun’s movement across the sky daily.
Another way of concentrating solar power is the use of the Stirling dish, which is a parabolic mirror dish installed with a Sterling engine, which converts heat energy to mechanical energy. Like the parabolic trough, the Stirling dish focuses all the sunlight reaching it onto the focal point. However, unlike the parabolic trough, the Stirling dish tracks the sun’s rays along two axes; the focal point for the Stirling dish is where the two axes meet. A heat receiver is placed at the focal point. The fluid in the receiver is then used to generate electricity using the Sterling engine. Among the technologies to concentrate solar energy, such dishes are considered the most efficient in terms of generating electricity from solar energy.
The third way of concentrating solar power is the use of the Concentrating Linear Fresnel Reflector, which uses long rows of flat mirrors to concentrate sunlight onto an absorber positioned at the common focal point of the mirrors. Through the absorber, the heat absorbed is then channeled to a thermal liquid which has a high boiling point. This fluid then powers a steam generator using a heat exchanger. The steam generator in turn drives the turbines in a conventional generator.
The fourth way of concentrating solar power is via means of the solar power tower. The solar power tower makes use of a range of flat, adjustable mirrors to receive and reflect the rays from the sun onto another tower, known as the collector tower. The energy absorbed by the collector tower is then used to produce steam and drive turbine generators.
Today efforts to concentrate solar power is starting to grow everywhere. Spain has more than fifty such projects on the works and the European Union (EU) is planning to built a solar power station in the Sahara desert using a technology known as Desertec, which aims to use deserts to harness solar energy. By 2050, the EU aims to have 15% of its power come from the project.
While sunlight is free, harnessing solar energy requires big infrastructures to be able to gather the sunlight and transform solar power energy into electricity. In other words, the efficiency of solar energy has much to be desired. This is one of the main disadvantages of solar energy harnessing.
A station for concentrating solar power of 300 megawatts is estimated to cost between $750 million and $1100 million today. However, there are several scientific studies and projects that promise to lower these costs in future. With the advancement of technology, it is only normal that the costs will be getting lower and renewable energies like these will become more competitive with fossil fuel energy. In time to come, we will see the benefits of solar energy outweighing the disadvantages. Hopefully the day will come soon.
Read about how to build your own solar panel.
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