Archives

by N A C Gunatilaka

In the recent past several newspaper articles appeared suggesting various methods to overcome the present power problem. Most suggestions were thermal plants differing only in the type of fuel to be used. Coal, oil, gas (LPG and LNG) firewood and garbage were the types of fuel suggested. Of the above fuels coal, oil and gas are non-renewable finite resources.

It is common knowledge now that these resources in the world are rapidly getting depleted. Scientists forecast that all known oil and gas reserves will be exhausted within the next few decades. The known coal reserves however are large and sufficient to last several centuries at the present rate of consumption.

Turn to coal

Even this scenario might change once oil and gas reserves get exhausted and the whole world turn to coal for energy production.

Besides, huge quantities of coal are required for the extraction of metals. For this purpose coal is first converted to coke and the coal tar which is obtained as a by-product is a treasure house for a number of important chemicals so much so that coal will become too precious a substance to burn and get energy.

Another possible development is once petroleum gets exhausted is the conversion of coal to petrol. This is a known technology, which the Germans are said to have used during the second world war. Such a process is not economical now because it is cheaper to obtain petrol from petroleum. But once petroleum prices go above a certain level conversion of coal to petrol will become economical and at least some countries will definitely start doing it.

Firewood

In the light of above developments much thought has to be given in deciding what kind of power generating plants we should build as a long-term solution to the power problem. There was a suggestion to build firewood burning power plants and to use lands, which are unsuitable for growing normal crops to produce firewood.

Such a program would not only reduce our dependence on imported fossil fuels but would provide employment and a source of income to thousands of rural folk. Here again one thing that experts should consider is to find out whether it is more profitable to use such lands for producing timber instead of firewood.

Recently there was a news item about a company expressing its willingness to set up power plants using garbage. Although such plants if installed would be able to provide only a small fraction of our total power requirement it would be a very appropriate thing to do as garbage disposal is a major problem for most local bodies. Use of garbage as landfills not only pollute ground water but also create many health problems for people living in nearby areas.

All fuel burning power stations whether the fuel is coal, oil, gas, firewood or even garbage release large quantities of carbon dioxide and other gases such as sulphur dioxide and oxides of nitrogen into the atmosphere. These gases are known to cause severe environmental problems such as global warming and acid rain.

In a country where everybody wants an uninterrupted supply of electricity but nobody wants thermal power stations in their neighbourhoods selection of locations to set up thermal power plants will also be a problem. We have seen the gravity of this problem during the last few years.

Energy from sunlight

The energy in all carbon containing fuels is really the energy from sunlight which the plants have stored during photosynthesis. When we burn such fuels and produce electricity we are indirectly converting sun's energy into electricity. Even when we generate electricity in hydropower plants or wind generators the situation is the same. It is the energy from the sun that causes water to evaporate and precipitate as rain on high ground.

When producing electricity in hydroelectric plants we harness the energy of water flowing down. Similarly wind that causes wind generators to turn are caused by the unequal heating of large air masses by the heat of the sun.

From the above examples we see clearly that for all of our electricity requirements in Sri Lanka we depend indirectly on the energy from the sun. Fortunately scientists have now found a method to convert sunlight directly into electricity.

This is done by using photovoltaic cells or solar cells. These are solid-state devices, which can convert sunlight directly into electricity. Such cells were first produced in 1954. At that time solar cells were very expensive. The cost of a cell to produce one watt of power was well over a hundred thousand rupees.

Space satellites

In the late fifties and early sixties they were used mainly to power various electronic equipment in space satellites. Over the years much research and development work has been done to reduce the cost of solar cells, increase their efficiency and extend their lifetime.

Today the cost of a cell to produce one watt of power has come down to about Rs. 100. Present day cells have efficiencies over 10% and they are expected to last for more than 20 years. As a result many rural homes now use solar cells panels for lighting, radio listening and television viewing. Use of large panels makes it possible to operate refrigerators, water pumps and power tools.

Until recently solar cells were considered too expensive for their use in large-scale electricity generation. But with their costs coming down and fossil fuel prices increasing scientists, engineers and energy planners in most countries are now thinking that the use of solar cells to convert sunlight directly into electricity is the ideal solution for the power problem in future at least till such time that mankind succeeds in obtaining energy from nuclear fusion reactions.

Facts

The following facts strongly suggest that this is the method most suitable for a developing country like Sri Lanka, which lies in the tropics.

1. Every second the sun emits an incredible amount of energy in the form of electromagnetic radiation. The total radiated power has been estimated to be in the region of 4 x 10 23 kilowatts. According to astronomers the sun has been emitting this radiation for several billion years and it will continue to do so for another several billion years.

There is no evidence that the rate at which the energy is emitted is diminishing.

2. The earth receives only a tiny fraction of the energy radiated by the sun. Although tiny when compared to the total amount of energy radiated by the sun in real terms the sun's energy falling on the surface of the earth in one second is more than the total energy used by the whole of mankind in one day assuming that each man, woman and child in the world consumes at least one unit of electricity a day.

3. It is found that on a bright sunny day each square metre of the earth's surface receives sun's energy at the rate of about one kilowatt. According to data appearing in some newspapers in Sri Lanka our total daily electricity requirements is a little less than 20 gigawatt hours. This is roughly equal to the sun's energy falling one an area of about 400 hectares in 5 hours. If all this energy could be converted t electricity and stored we would not have a power problem.

4. Sri Lanka being a tropical country and being in the so-called "Sunny belt" receives enough sunshine during most part of the year.

5. Fuel burning thermal power plants are said to be economical only if they are large and producing several hundreds of megawatts. There is no such limitation for power plants using solar cells. -

They can be built to any size. Further such plants can be built in stages. If supporting structures and other secondary structures are designed and built for large power plants solar panels can be added to them as and when funds become available.

6. Installing a few large thermal power plants producing several hundreds of megawatts each, and distributing the power produced to long distances is said to cause appreciable transmission losses.

This is minimized if a large number of power plants, using solar cells each producing a few megawatts of power are built at several locations.

7. All thermal plants require cooling and they have to be located near rivers or other large bodies of water. There is no such requirement for power plant using solar cells.

8. Fuel burning power plants cause pollution and environmentalists will become more and more aggressive against the setting up of such plants. Government leaders who depend on voters to come to power will find it difficult to take decisions regarding places to set up thermal power plants. There is no need to protest against setting up power plants using solar cells, as they do not cause any pollution.

9. As photovoltaic generating plants do not have nay moving parts (unless the panels are made steerable to follow the sun) they require little maintenance. The only maintenance required would be the occasional cleaning of panel surfaces to remove dust and bird excreta.

10. Vast stretches o neglected paddy fields would be ideal sites of reinstalling solar cell power plants. When such areas are used for mounting solar panels the land underneath can be used to grow crops, which do not require direct sunlight but grow sufficiently well in diffused light.

11. Today engineers can design and build large inverters or rotary converters to handle power even in the megawatt range. Therefore the conversion of large DC currants produced in photovoltaic power plants to AC currants will not be a problem.

12. If we build a sufficient number of photovoltaic generating plants and develop our hydroelectric potential to the maximum it may be possible for us to be self sufficient in our electricity needs even without having fossil fuel burning thermal power plants.

During droughts when there is enough sunshine the photovoltaic plants will produce maximum current. Any excess electricity produced during daytime could be used to pump water back to reservoirs.

During rainy season sky is cloudy and solar cells, cannot produce much electricity. But the hydroelectric plants can work to maximum capacity because there is water in the reservoirs. Depending on the season one will compensate the other.

13. In time to come conventional fossil fuels will become prohibitively expensive. Countries like Sri Lanka will find it difficult to spend large part of their foreign exchange to buy them and transport them.

14. Many different kinds of substances are used for fabricating solar cells. The most common substance used is silicon.

As it is the second most abundant element in the earth's crust there is no fear that it will ever get exhausted. The cost of solar cells are relatively high even now because the extraction of silicon from silica and its purification to required levels of purity are expensive processes. Once chemists succeed in finding out easier and cheaper methods to extract and purify silicon the cost of solar cells will come down further.

15. As very pure silica is known to exist in Sri Lanka it may even be possible to produce solar cells for our requirements in Sri Lanka itself with foreign collaboration. In the light of above facts it seems very clear that the direct conversion of sunlight into electricity using solar cells is the most ideal long term solution to our power problem.

The writer is a retired science teacher who strongly feels that the best long-term solution to our power problem is the direct utilization of solar energy to produce electricity.

News | Business | Features | Editorial | Security
Politics | World | Letters | Sports | Obituaries |

Produced by Lake House
Copyright 2001 The Associated Newspapers of Ceylon Ltd.
Comments and suggestions to :Web Manager