By Dr. P. K. Jena* in Bhubaneswar, March 10, 2022: Energy has been very important for human beings as it is one of the basic needs for better living and socio-economic developments. Energy security is therefore, imperative for sustained growth of our economy. At present, fossil fuels have become a major source of energy required for socio economic developments of mankind in most parts of the world since industrial revolution.

Fossil fuel resources such as coal, petroleum (crude oil) and natural gas take thousands of years to be formed inside earth’s crust from various organic matters and therefore these are considered as non-renewable. Nearly 80% of global energy consumption is met from various types of fossil fuels.

These conventional fuels during their combustion are highly polluting and mostly responsible for global warming due to release of large amounts of oxides of carbon, sulphur and nitrogen to the atmosphere. With increasing demand of fossil fuels all over the world and the concern for pollution of the environment due to excessive use of these, have led to global efforts in harnessing alternate clean and renewable energy resources like biomass, sun, wind and hydro power.

Another source of non renewable energy is radioactive fuels. The nuclear power plants require radioactive fuels like uranium and plutonium. Nuclear power at present provides about 6% of world’s energy and 13–14% of electricity. The high level radioactive wastes generated in nuclear reactors, are highly hazardous for human beings and other living beings and have to be disposed very carefully.

Besides, as sophisticated technology and high capital investments in nuclear plants are inevitable, the contribution of energy from this source is very limited.

In recent years, with first depletion of fossil fuels as well as nuclear fuels to meet the increasing demand of energy and concern about global warming due to the wastes and effluents generated from these, the need for developing clean, sustainable and secured energy resources, is being very much realized.

In this regard, a lot of efforts are being made in different parts of the world. As of now, only about 16% of global energy consumption comes from renewable resources with nearly 10% from traditional biomass mainly used for heating, 3% from hydro power and the rest 3% from other renewable energy sources like sun, wind, etc.

Interestingly, out of all renewable energies, solar energy is the most abundant one. In recent decades through considerable amounts of research and development, it has been found that, solar energy is a viable alternative of fossil fuels for power generation and has the highest global warming mitigation potential amongst the available clean energy sources.

The effective solar energy reaching earth’s surface ranges from about 0.06 kw/m2 at the highest latitude to 0.25 kw/m2 at the lower ones. Of late, harnessing solar energy has experienced an impressive technological advancement. In the past, solar energy in a limited amount was used in form of small scale photovoltaic cells.

However, the technologies developed recently have been able to encourage the use of solar energy in small scale in the form of concentrated solar power (CSP) and in large scale Photo Voltaic (PV) system which is able to feed into electricity grids.

It is reported that, through better technology the cost of high power band solar modules has decreased from about US $ 27000 per kw in 1982 to about $4000 per kw in 2006. Similarly, the installed cost of a PV system has declined from $16000 per kw in 1992 to about $6000 per kw in 2008.

Further developments are being made in different parts of the world to make solar energy competitive to that from fossil fuels.

Classification of Solar energy:-

The solar energy technologies can be classified into three broad categories viz., passive and active, thermal and photovoltaic, concentrating and none concentrating. The passive solar energy technology collects the energy without converting the heat and light into other forms, whereas the active solar energy technology refers to harnessing solar energy or storing or converting it for other applications. This can again be broadly divided into two groups: (i) photovoltaic (PV) and (ii) solar thermal.

(i) In photovoltaic technology, the radiant energy contained in light quanta is converted into electric energy when light falls on a semiconductor material, causing electron excitation which strongly enhances conductivity. There are two types of PV technology now available in market namely, crystalline silicon based PV cells and thin film made of different semi conductor materials including amorphous silicon, cadmium telluride and copper-indium-gallium-diselenide. I

It has been estimated that, if PV cells are installed on only 4% of the area of world’s deserts, the amount of electricity to be produced can meet the total energy needs of the world.

(ii) Solar thermal technology uses solar heat. This heat can be used directly for heating purpose or generating electricity. Therefore, it can be divided into two distinct categories viz., solar thermal non electric and solar thermal electric. The solar thermal non electric can be utilized for drying, air heater, water heater, cooking etc.

On the other hand, in the solar thermal electric system the heat is utilized to produce steam for generating electricity which is known as concentrated solar power (CSP). There are 4 types of CSP available viz., parabolic trough, Fresnel mirror, power tower and solar dish collector. It is reported that, there are many regions on earth where 1 km2 of land is sufficient to generate more than 125 Giga Watt Hours (GWH) of electricity per year through CSP technology.

Some of the merits and limitations of solar energy:

• Merits:

o The first and foremost advantage of solar energy is that, it does no emit any green house gases. The energy is produced by conducting sun’s radiation – a process free from any smoke, gas, or other chemical byproduct.
o Besides the cost for initial installation and maintenance, solar energy is available freely. Solar energy does not require expensive and ongoing raw materials like oil or coal.
o On – grid means the solar energy system remains connected to the state electricity grid, whereas off – grid solar energy has no connection to the electricity grid. So, the houses, business places or any other places being powered by solar energy are solely dependent on solar energy producing units at the respective sites.
o Unlike fossil fuels, solar energy is free from national and international politics and price volatility. The solar energy is an unlimited commodity that can be adequately and freely obtained at suitable locations.

2. Limitations:

1. Lack of Consistency and Reliability

(a) Solar systems rely on steady absorption of sunlight. The following factors limit the availability of sunlight:

i) Although solar power is an option almost anywhere on the planet with some capacity, the efficacy falls sharply as distance from the equator increases. Areas with increasing latitude get decreasing amounts of solar energy.
ii) Clouds diminish the power of solar panels, and also in habitually foggy or overcast regions.
iii) The earth’s rotation hinders the arrival of sun’s rays on most parts of it during the night.

(b) Conversion efficiency of solar energy is less than that of fossil fuels.
(c) Some pollution problems arise due to the wastes generated from the used solar PV energy systems. However, this can be avoided easily.

Nevertheless, sincere efforts are being made all over the world to use increasing amount of solar energy in place of fossil fuels, The most attractive feature of solar energy is that, it is available freely in huge quantity and produces no green house gases. Further, once the equipment is installed, there is no expenditure towards raw materials unlike fossil fuel energy sources. Another important merit of solar energy is that, it is independent of grid.

However, there are some likely uncertainty because of unfavorable weather condition and decrease of sun’s intensity at places much away from the equator. Because of a number of attractive merits of solar energy, sincere efforts should be made to further improve the technology so that it can be used extensively and replace fossil fuels to a great extent.

*(Former Director General, Council of Scientific & Industrial Research, India)