Wednesday / Mar 15 2017
Newspaper : The News
Solar cells use the energy from the sun to produce electricity. The sun’s energy is transmitted in the form of photons. The electricity produced in this manner is a direct current (DC) that can be used to light bulbs or operate other electrical devices, such as fans.
Commercially available solar cells are normally made up of crystalline wafers of silicon and their efficiency ranges between 14 percent and 18 percent. Commercially available silicon-based solar cells have an efficiency of about 18 percent. This limits their commercial use because of the high cost of electricity production. The latest multi-junction solar cells use other materials and have a much higher efficiency – which ranges between 38 percent and 42 percent. But they are more difficult and expensive to produce. The present cost of electricity produced from solar cells comes to about 2.3 cents per kilowatt-hour. This is now becoming a more viable option as compared to electricity produced by other means.
The next generation of solar cells involves printed materials which can be mass produced at low costs. These are based on new materials, such as copper indium gallium selenide, cadmium telluride, amorphous silicon and micromorphous silicon. Their efficiency is 10 percent to 15 percent lower. However, owing to their lower production costs, these cells are considered to be competitive.
An exciting recent development has been the discovery by Swiss researchers of flexible solar cells, which are made from copper indium gallium (di)selenide (CIGS). These have about the same level of efficiency – of approximately 18.5 per cent – as the silicon wafer cells. These flexible cells can be produced cheaply and may dramatically change the solar cells market once they are mass-produced. The new generation of cells will be incorporated on rollout transparent sheets that will be placed on windows and walls to absorb and provide electricity.
Solar paints are another important development. These are paints that can generate electricity once solar cells are embedded within them. The problem with the earlier versions of such cells was that their efficiency was low and not comparable in conventional silicon-based solar cells. All this is now changing with the advancements that are being made in dye-sensitised solar cells, which have achieved an efficiency that is comparable with the efficiency of commercially available silicon cells.
A recent breakthrough in this field has been the development of low-cost quantum dot solar cells with improved efficiencies that can be sprayed on surfaces, such as roofs or windows. These cells are made of tiny particles (nanoparticles) of semiconductors and can be readily painted on surfaces. They do not need the formation of cumbersome and expensive solar panels for installation and use. The new types of solar cells developed are suspended in liquid and can, therefore, be painted or printed on glass or plastic surfaces. These cells are so small – just four nanometers in size – that you cannot see them with the naked eye. Around 250 billion cells of this nature can be fitted on the head of a needle. Since they are so tiny, they can be printed like a newspaper so that mass production is possible at a low cost. They can even be printed on a standard inkjet printer. Although the efficiency of these printed cells is lower than that of standard solar cells, the low cost of production make them highly cost-effective.
Researchers at Stanford University have devised a new method to make solar power production much more efficient as compared to conventional methods. The new process converts both heat and light into electricity whereas conventional solar cells convert only light into electricity. So these new types of cells – known as photon enhanced thermionic emission (PETE) cells work better.
Vodafone has financed the development of a solar-powered umbrella that will not only shelter you from the rain or the sun but also provide power to your mobile phone or other devices. The umbrella has been developed by PhD students at University College London and is known as Booster Brolly. It has solar panels stitched on its exterior surface and a battery that is charged by the sun’s energy on its handle. A smartphone can be charged within three hours and any excess energy can be employed to light an LED torch that is also fitted on the handle.
Another technology used to convert sun’s energy to electricity is the parabolic mirror. The solar power is generated by concentrating a large amount sunlight onto a small area which results in the production of intense heat. This can be used to run a steam turbine and produce electricity. If the heat is stored in the form of molten salt, we can generate electricity even after sunset. Spain has been a leader in such technology, followed by the US. However, the sharp drop in the prices of solar panels has made this technology economically unviable.
Solar towers are another interesting development which have harnessed the power of the sun and created energy. The solar tower technology was successfully implemented in Spain over a decade ago to produce electricity. The technology involves the sun beating down on a large surface with an area of several hundred square metres. The hot air – having a temperature of about 80 to 90 degrees Celsius – is collected and allowed to escape through the tower, thereby driving electricity turbines. Pakistan could introduce a similar initiative and produce huge amounts of electricity at a low cost. In many areas of Sindh and Balochistan, such partial, funnel-shaped structures already exist. They are created by natural erosion of mountain sides and could be readily transformed into electricity, generating solar towers at low cost.
In Pakistan, a 100-megawatt plant based on conventional solar cells was installed in the Quaid-e-Azam Solar Park in Cholistan Desert in March 2015. The contract was given to Zonergy Limited, a Chinese-owned firm, at 14.5 cents per kilowatt-hour. The international rates at that time were four cents per kilowatt-hour and have now further tumbled to 2.3 cents per kilowatt-hour.
The plant could, however, produce only 18 megawatts instead of the committed 100 megawatts, largely because of the poor quality of materials supplied. There is huge scope in this field for Pakistan if we were to install plants at the rates of about 2.5 cents per kilowatt-hour – as is being done in the UAE in a 1,000-megawatt plant. It could solve our energy problems, provided corruption or incompetence do not come in the way.