Wednesday 26 July 2017 News Updated at 12:07 PM IST
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Promise of renewable energy - Deccan Herald
Promise of renewable energy
C Sivaram,
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DeccanHerald
Consternation concerning climate change and global warming, primarily due to the overuse of fossil fuels, as expressed in the United Nations Climate Change Conference that was held in Paris and other conferences has led several countries to explore renewable energy sources such as solar and wind power. Global carbon dioxide levels have already crossed the 400 ppm mark. Populous countries like China and India still generate substantial power from coal. The burning of two billion tonnes of coal every year could, in about two decades, increase the carbon dioxide by a further 30 to 40 ppm.

Moreover, the recent decision of the Trump administration to back out of the Paris Accord would further set back efforts to decarbonise energy sources, making it difficult to keep global temperature rise to less than two degrees Celsius. Unless the world’s largest economies drastically cut down on the use of coal and oil, any talk of arresting global warming would be a mirage.

High carbon emissions

However, several steps in the right direction are being taken by many countries to develop alternate energy sources. Recently, India decided to set up 10 new nuclear reactors (pressurised water reactors, or PWR) using natural uranium, each of 700 megawatts (MW), in the next decade. These reactors would produce 7 Gigawatts (GW) of power. The existing 22 nuclear reactors produce a total of about 6.7 GW. Another 2 GW would come from the additional Russian reactors (Kudankulam). India’s total installed power capacity is now above 300 GW. This is still less than two percent of the world’s total power.

These figures for nuclear reactors suggest that nuclear power would provide hardly 8% of India’s power even in the next decade. Nuclear power does not dump greenhouse gases in the atmosphere, but the uranium required is substantial. A 700 MW reactor requires about 250 tonnes of natural uranium and this has to be replaced every three years, so 20 reactors would require 5,000 tonnes. India has to import uranium and it is not a member of the Nuclear Supplies Group (NSG).

Thorium-based reactors are still in an experimental stage. Incidents like that of Chernobyl are pointers to the inherent risks involved in nuclear power. Again, decommissioning of reactors is known to be prohibitively expensive. It is for these and other reasons that many countries have opted out of nuclear power. Japan and France have reduced their nuclear power and hardly any new reactors are being built in USA or UK. If we have to generate 200 GW of nuclear power by 2035, we have to build a 700 MW reactor every three weeks!

Solar power

This leaves us with solar or wind power to be the primary power producers of the future. The advantage of solar power is that it is perennial and not intermittent or unpredictable like wind power. The total solar energy flux falling on the earth is one day is about 20,000 times of what mankind uses in the same period. Of course, much of it falls on the oceans. So, of late, there have been serious attempts in many countries to tap as much solar power as possible.

As of 2010, there was only 50 GW of solar capacity installed in the entire world. In 2015, only one percent of the world’s grid electricity was produced from solar panels. However, this is now set to change drastically. India has quadrupled its solar capacity in the last three years to 12 GW, and will add another 10 GW this year with yet another 20 GW in the pipeline.

If countries like UK can produce so much solar power, India with its tropical climate should be able to produce substantial solar power in the next decade. In fact, the world’s largest solar farm is at Kamuthi in Tamil Nadu and has structures across 2000 acres. It is planned to generate 100 GW of solar power by 2022 and, another 75 GW of wind power. If this happens, we can follow Britain’s recent example of shutting down coal plants and generate close to half of our power requirements by solar or wind energy by 2030.

The drastic rise in the use of solar power in the past few years has been partly made possible by a drastic drop in the costs of the technology involved. However, the technology as far as the development of more efficient conversion devices has not advanced much. A major drawback is that more than one-third of the sunlight is reflected off the solar panels rather than being absorbed and converted to electricity. Indeed, silicon-based solar cells have a theoretical upper limit of about one-third efficiency in the conversion of radiant solar energy into electricity. This has to do with the band gap, that is the energy required to boost the electrons to a conducting state, which results in most of them giving up their energy as heat.

Newer materials

New materials are being developed like polycrystalline perovskite thin film containing both inorganic materials like iodine or lead and organic materials like methyl ammonium. It is claimed that this can carry two-thirds of the light energy without losing it as heat. In principle, this could double the amount of electricity produced with no substantial cost increase. The hot carrier perovskite solar cell is an example. Perovskites can also be made as flexible lightweight films, both cheap and easy to install in different locations. However, they tend to disintegrate in humid conditions which are typical in the Indian context. Tesla’s Elon Musk has a new design for solar panels which resembles roof tiles, making it less cumbersome than wide solar panels, to install.

Apart from the lowered costs, what could make solar power contribute a much larger share to our total energy requirements is innovative technology that involves using many new materials to double the efficiency making the systems more compact and manageable. One hundred gigawatts of solar power by 2022, as far as India is concerned is ambitious but achievable. Unlike fossil fuels or nuclear power, solar power does not contribute waste heat as it is mining the sunlight already falling on earth, which is several thousand times the power we currently consume.

Apart from solar energy, there has also been an increased interest in tapping large scale wind flow as renewable energy. It has been estimated that land-based wind generators can provide around 100 trillion kilowatt-hour of energy per year across the world. This constitutes almost one-fourth of the power requirements of the world. However unlike solar power, wind flows are intermittent depending on factors like land topography. Wind power scales linearly with atmospheric density and the cube of the average wind speed. At higher altitudes, wind blows much faster, so this is an advantage. However, the density of air drops sharply as the altitude increases. Wind power has also emerged as a key factor in India’s quest for renewable energy. A few gigawatts of installed wind power capacity has already been placed in states like Tamil Nadu. It is expected to exceed 30 - 40 gigawatts in the next five years.
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