Some Notes On A Solar Energy Future For Rural India
The sun is the source of all life. Without sunlight there would be no animals, no trees, no water or oxygen - only a dead cold planet. Since ancient days people have recognised this truth. Not only the Hindus, but also the ancient Egyptians, the Druids of Europe, the Aztecs of Mexico, all worshipped the Sun.
Not only is the sun the source of life, but it also is the ultimate source of energy. The coal and mineral oils that power the modern world are products of the forests of the ‘carboniferous period,’ which flourished several hundred million years ago. These great forests would not have existed without sunlight. Nor would our planet’s weather system have existed, which enables us to produce electricity from hydro-electric stations; and set up windmills.
Simply put, when light strikes a silicon cell, electricity is produced. Packets of energy known as photons, of which light is composed, strike the silicon cell, kicking electrons out of the lattice structure of silicon crystals. This process is enhanced by doping one side of the cell surface, say, with phosphorus, which produces an excess number of electrons on the outer surface; and the other side, say, with boron, which creates a lack of electrons. The electrons are induced to flow as a current by connecting up the cells with conductors. The system is modular and arrays can be made of any size. However costs are prohibitively high at present-day cell efficiencies, which range from 8% to 14%. Amorphous silicon technology, which promises large reductions in cost, has even lower cell efficiencies ranging from 5% to 8.6%. High expenses are incurred when we purify quartzite mineral (a substance similar to common sand) to a very high grade of over 99% silicon purity. Incidentally, it is even more expensive to produce semi-conductor grade silicon chips for the computer, tele-communication, and similar high-tech industries.
The best known form of using high-grade silicon for solar energy is as crystalline cells, no more than 100 sq. cms at the largest. These silicon cells have powered all our space probes and satellites. When the Americans first started using Photovoltaic (PV) modules to produce solar energy for NASA applications, the cost was prohibitively high at over $ 1000 per peak-watt. However, as greater and more varied demands multiplied, particularly in western countries, the cost came down to around $100 per watt by 1975, and today it stands at around $3 to 4 per peak-watt. But even at this moderate cost figure photovoltaic solar energy is far more expensive than any other conventional form of energy.
However, should prices tumble even further to around $1 per peak-watt of electricity produced, or even less, solar energy would become highly competitive in price. Most scientists who have been working around the world on developing this technology are confident that at long last several technological breakthroughs have occurred which will bring down the prices quite dramatically in the next few years.
After half-a-century of struggling to escape out of a poverty trap, which the period of colonialism had led us into, we are once again at an important cross-road in our struggle to develop. Of critical concern is the energy crunch faced by the nation. We, in India consuming no more than 2% of the per capita electrical energy consumption of the United States of America, are unable to provide for the basic necessities for all our people. The UNDP Human Development Report states that high-quality electrical energy is needed in poor households if we want rural literacy, particularly girl-child literacy to improve. There is also an incalculable public health cost produced by burning low-calorific value high-ash content coal. Every million tonnes burnt releases into the air 30,000 tonnes of particulates, 10,000 tonnes of NO2, 30,000 tonnes of SO2, and 400 tonnes of hydrocarbons. Nuclear power was once thought of as an inexhaustible source of energy.
Apart from environmental hazards, their capital costs are enormous, and installed plants have never worked economically. Radioactive leakage and emergency shut downs regularly feature in the operation of these plants. Further the cost and feasibility of safely disposing of killer radioactive wastes (upto a ton of material every year from a 1000 MW plant!) are never taken into proper consideration by this military-oriented industry. These wastes take tens of thousands of years to become safe. Hence nuclear power is not a viable option for poor, well populated countries such as India.
In A.P., at least 40% of the power generated goes to the agricultural sector, (over 20% of which is lost in transmission), mostly for energising two million or so pump-sets. The government has promised free power as a palliative for ignoring the interests of the farmers and the rural sector for five decades. The same amount of power sold to industry could easily net the government around Rs.2000 crores [Rs 20 billion] per year, and this would enable industry to produce several thousand crores worth of industrial production. Taxation on industrial production alone might enable government to fund a gradual increase in power production. However, this upward spiral of increasing industrial production, and electrical generation capacity can only occur if the power needs of agriculture can be met through renewable energy programmes, coupled with watershed development and optimal utilization of water by agricultural communities.
Decentralised energy production to meet small local needs could be planned with stand-alone PV solar systems, or hybrid systems utilizing all renewable sources of energy. Such systems could incorporate some of the following components:
Photovoltaic modules, consisting of many solar cells connected together and encapsulated, say, under glass. These modules would be connected together to form an array, with a DC output.
Wind turbines connected to a generator that converts the wind energy directly into DC or AC electricity.
Micro-hydro generators, requiring a steady and reliably source of flowing water at least for several months, and connected to drive a generator.
Diesel, LPG and petrol gen-sets as a backup source of electricity when the renewable sources are insufficient.
Other system components would include:
Batteries to store excess energy generated during periods of low demand and supply electricity during periods of high demand. Rechargeable sealed lead-acid batteries would be preferable for remote location.
Inverters to convert DC electricity from a battery, solar panel or other DC energy source into AC electricity suitable for standard electrical appliances.
Regulator/controllers to interface batteries with the energy sources, to prevent overcharging, or excessive discharge of the battery.
Trackers for PV modules, which follow the sun throughout the day and hence increases their output.
More than in any other country in the world, India offers the best chance for utilizing solar energy for decentralised energy production to meet small local needs. On an average we receive 330 days of sunshine every year. Scientists have calculated that all of the energy needs of the whole world require an infinitesimal amount of the total solar energy that falls upon the earth every year as sunlight. The problem really lies in the present day cost of photo-voltaic solar energy. Cost can only come down if large-scale plants are established utilizing promising new technologies, and demand for such large-scale applications of solar energy is created by industry, government, farmers, and households. Professor Dave Irvine Halliday of Canada has won global recognition for introducing home-lighting for the poor using white-light diodes, of one watt, or even a cluster of 0.1 watt capacity, with minimal energy requirement and a life of 100,000 hours.
I should also like to mention the work taking place on CI[G]S systems at the Angstrom laboratories, Uppsala University Sweden, which are expected to be commercially available at around $ 1/peak-watt in the next few years; and on Third Generation PV Systems, at the New South Wales University, Sydney, Australia under the direction of Professor Martin Green. These Third Generation technologies are expected to exceed the theoretical solar conversion efficiency limit, calculated in 1961 by Shockley and Queisser, as 31% under 1 sun illumination and 40.8% under maximal concentration of sunlight (46,200 suns).
The routes used by Prof. Martin Green to exceed the Shockley-Queisser limit fall into three generic categories: multiple energy threshold devices; modification of the incident spectrum; and use of excess thermal generation to enhance voltages or carrier collection.
Band-gap engineering of silicon based material focuses on the fabrication of silicon nano-structures consisting of quantum well or quantum dot super-lattices to achieve such band gap control.
Modification of the solar spectrum to boost the efficiency of solar cells. Luminescent materials are being investigated that either absorb one high energy photon and emit more than one low energy photon just above the band gap of the solar cell (down-converters), or that absorb more than one low energy photon below the band gap of the cell and emit one photon just above the band gap (up-converters).
The Hot Carrier Cell slows the rate of photo-excited carrier cooling, caused by photon interaction in the lattice, to allow time for the carriers to be collected whilst they are still “hot” thus enhancing the voltage of a cell.
Professor Martin Green of Australia hopes that his third generation PV technology could even bring the cost down to between 50 to 10 US cents a peak-watt. We have to seize these options, creatively and boldly, if development of rural areas is to match the aspirations of our people.
Workshop on Distributed/Energy Efficient Power Generation
BV Raju Institute of Technology, Narsapur, Medak Dist., October 20, 2004.
Dr. Vithal Rajan Founder-Chairman, Governing Body, Confederation of Voluntary Associations
