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Amazing energy - Part IV

One huge source of energy is the potential to exploit the difference in water temperature between the surface of the ocean and deep waters. The temperature of the water on the surface of the sea is usually significantly warmer than at the ocean depths. This temperature difference can be productively used for generation of electricity.

The technology, known as Ocean Thermal Energy Conversion (OTEC), involves pumping the warmer surface water through a heat exchanger. The heat thus captured is then used to evaporate a low boiling liquid such as ammonia, and the pressure created by the vapourised gas can then be employed to drive turbines for the production of electricity.

For this process to work efficiently, the temperature difference between the surface water and that at the ocean depths needs to be at least 20 degrees Celsius. This difference is commonly encountered in tropical oceans. If the temperature difference is greater than the energy, production can increase substantially. Indeed for every additional degree difference, a 15 percent increase in energy production is obtained. This interesting technology can provide continuous, stable and reliable energy round the clock, unlike wind or solar energy that depend on the weather.

The feasibility of this process has been demonstrated in several pilot plants, and it will soon be commercialised. Lockheed Martin, Vanuatu, Xenesys, Pacific Otec and some other companies are in the process of developing commercial projects at suitable locations where sizeable temperature differences exist between the surface of the oceans and deeper waters. The first plants with a capacity of 10-15 megawatts will be installed by 2014, and will be followed by plants of 100 megawatts or greater capacity.

There have been spectacular advances in solar cell technologies in recent years. One substance that holds great promise is ‘graphene’. This amazing substance is one of several crystalline forms of carbon that include diamond, graphite etc. It is tougher than diamond and yet stretches like rubber. It is about 200 times stronger than steel and about 150 times thinner than a human hair. It is so strong that you could suspend an elephant on a thin strand of this material and it would not break! It consists of a single layer of carbon atoms – one atom thick – in a honeycomb lattice structure. Andre Geim and Konstantin Novoselov at the University of Manchester were awarded the Nobel Prize in Physics in 2010 “for groundbreaking experiments regarding the two-dimensional material graphene”.

Normally silicon is used in the manufacture of commercial solar cells. It now turns out that graphene could prove far more efficient in transforming light into energy. This was established in a study carried out at the Institute of Photonic Sciences (ICFO) in Spain which found that solar cells made with graphene could offer up to 60 percent solar cell efficiency – this is about four times the efficiency of the present commercially available solar cells. Graphene turns out also to be an excellent conductor of electricity, even better than copper. This is leading to the development of many applications in the electronics industry.

Paper thin computers and televisions are presently under development based on this ‘miracle substance’. Indeed South Korean researchers have created a 25inch flexible touch-screen using graphene. Tomorrow your daily newspaper may be made of it too, which may be instantly updated by pressing a tab on the side. Harold H Kung at the McCormick School of Engineering and Applied Science at Northwestern University has reported a method to extend the battery life of lithium ion batteries by 10 times using a grapheme-based anode.

A considerable effort is being directed at developing better batteries and other energy storage systems. Existing batteries often fail because of the damage caused to the electrodes in them over a period of time by the movement of ions. A new electrode (made from nano-particles of copper hexacyanoferrate) has been developed by Stanford researchers and uses nanotechnology to construct an open structure for the electrode. This permits ions to move in and out without damaging it. The electrode seems to be a wonder material for use as a high-voltage cathode.

Novel ways are also being developed to utilise wind energy. In many parts of the world we find large windmills, each with three huge blades generating electricity. These wind turbines are not very efficient since about half the air does not go through the blades but around them, with a resulting loss in their capacity to generate electricity.

FloDesign, a US based company, has now developed a new generation of wind turbines that rely on the design used in jet engines. These turbines have propeller blades that are much smaller but produce more electricity as the air is directed through the turbine by a surrounding shroud. Small turbines that will produce 10 kilowatt power will be initially manufactured and they will then be followed by megawatt capacity turbines.

A problem associated with micro wind turbines is that they must work well in both light and high winds, for instance under stormy conditions when they should not spin too fast. In the case of the larger wind turbines, the design of the blades takes care of this problem, making them stall under very high speed wind. This is done through sensors that send signals to attached computers which in turn adjust the turbine speeds. This is too expensive a solution. However, nature is often the best teacher. The stability of dragonflies even under high wind conditions provided critically important clues.

The dragonfly is very stable in its flight, even under high wind speeds. This is due to the special design of its wings which are thin and flexible, and have small protrusions on their surfaces. These protrusions create a number of swirling vortices that contribute to the extraordinary aerodynamic stability of the dragonfly. Based on this, the Akira Obata of Nippon Bunri University in Japan has invented a micro turbine which is far better than those available previously.

Pakistan needs to concentrate on solving its energy problems by utilising its existing resources of coal, water, wind, and the recently discovered shale oil and shale gas.

A reader has rightly pointed out that all the electrical appliances produced in Pakistan are ‘energy inefficient’. For example our fans, tube-well motors and roadside workshop machines use heavy starting current and also consume much more electricity than American, European, or even Chinese appliances.

When one considers the millions of fans, tube-well motors and road side workshop motors in the country, one gets some idea of how much energy is being wasted because of the improper enforcement of quality standards, particularly those relating to energy efficiency, in those industries that manufacture such motors and appliances. Similarly most of our vehicles, especially locally manufactured bodies of trucks and buses, are energy inefficient.

Concluded

The writer is the president of the Pakistan Academy of Sciences and former chairman of the HEC. Email: ibne_sina@hotmail.com

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