Most of the major governments around the world, such as China and the USA, realise the need to develop solar energy as a viable source of energy. Not only it is extremely helpful in meeting their energy security challenges, but it also helps in maintaining a lead in science, technology and innovation, the calling cards of any successful economy. With generous subsidies, huge amounts of money have been invested, by China especially, in R&D efforts.
Solar power in India
Given the huge fuel import bills racked up by India each year, which is only projected to grow, there is an urgent need to meet the energy challenges posed by a growing economy, which lacks significant sources of conventional energy. Launched with much fanfare in 2009, the Jawaharlal Nehru National Solar Mission aims to increase solar power generation to 20 GW by 2020. This is a very ambitious plan, with the government allocating $19 billion to it. There is enough reason to be ambitious. Situated in the tropical belt, India is well endowed with solar energy, with a total annual solar potential of almost 5 trillion kwh. States such as Andhra Pradesh and Gujarat and regions like Ladakh receive the maximum amount of sunlight, close to 3,000 hours annually. The plan aims to increase the contribution of solar power to the total power generation from the paltry 0.4 per cent at present.
The National Solar Mission seeks to use a multi-pronged strategy to increase the use of the sun as a renewable source of energy. A number of people, especially the poor and those in the rural areas, make extensive use of biomass-based fuels (cow dung cakes, for instance) to meet their cooking and heating requirements. Burning these fuels in earthen stoves (chulhas) releases harmful particulate matter into the air, which has serious health repercussions for families. The solar mission also seeks to provide subsidies for solar cookers, lamps and water-heaters to enable families to utilise cleaner, healthier fuels for meeting their daily needs.
The National Solar Mission, in its mission document, lists the construction of a solar grid as one of its top priorities. Here, it uses a concept known as “feed-in tariffs”: A system by which tariffs for buying back power from renewable energy utility companies reduce over time; higher tariff given in the initial stages to help them tide over the high initial costs of setting up large-scale utilities.
A huge number of households in India are off the grid. In many areas inhabited by tribal communities, villages are not being provided electricity. The cost of connecting them to the grid in these cases can be prohibitive. The solar mission seeks to provide micro-credit and other subsidies to residents of these areas under the National Rural Electrification programme to enable them to buy solar lighting equipment.
Other branches of the government are also getting in on the act. The cost of ferrying fuel and other supplies to the forward posts along the Indian land border is so prohibitively high that solar power in the remote upper reaches of Leh and Kargil is being proposed. Undertaken by Pyro Power, a project has been implemented along the Leh-Kargil highway to provide power and lessen fuel requirements. According to Mayank Gupta of Pyro Power, “We are implementing a hybrid solution —where electricity from diesel generators will be augmented by solar and wind power. Fuel cells are also being added to the mix. Between October and March, the setup is being tested in the harsh environs of the Indian border.”
Selco, or the Solar Electric Light Company, is based out of Bangalore and has been providing solar electric systems to rural and urban poor for almost 15 years. Selco installs and services solar electric installations on a unique business model. Solar panels and the associated lighting systems are expensive to setup. Selco gets its customers to put up 25 per cent of the cost upfront while deferring the payment for the rest of the system on installments. Since 1995, Selco has installed almost 1,20,000 solar power systems across the country. Its founder, Harish Hande, was awarded the Ramon Magasaysay Award for 2011. All through its existence, it has served to dispel long-held myths about the affordability and serviceability of alternate technologies among the poor and about the profitability of companies that cater to such markets.
Solar cells, for all their vaunted benefits and state-of-the-art technology progressing by leaps and bounds, are worthless pieces of silicon without the sun. The sun, though shines constantly, still has to pass through clouds, fog and the occasional smog to get to the solar panel that has been pointed in its direction. This is to say nothing of the time when the sun is invisible to us at night. This raises the most troubling question for the future of solar power. During the day when our solar panels on the roof or in the backyard are busy generating electricity, most of us are in our offices, whose energy requirements are so great as to render ineffective most solar panels. At night, when the home comes alive and buzzes with activity and the steady hum of the air-conditioner, the solar panels are silent. This mismatch, it seemed, no technological marvel could overcome, almost dooming solar power to the history’s bin of have-beens. But only almost, as the recent R&D efforts have yielded significant innovations.
Research and development
As legend goes, in ancient Greece, Archimedes used mirrors to catch the sun and set the entire Roman fleet on fire. Apparently, this concentrated energy of the sun can be used for generating power. If you were driving around the Thar desert that surrounds the city of Bikaner, chances are you might come across a series of mirrors, placed in a circle, pointed, almost like chelas looking up at their guru, at a huge tower.
These installation represents the very latest in solar technology and is known as a Concentrated Solar Power (CSP) plant. Setup by ACME, a power company, at a cost of Rs 150 crore, it has a capacity of 2.5 mw, that “will be scaled to 10 mw at peak”, according to Arpita Saini, a company representative. CSP plants are constructed on a large piece of flatland, usually out in the middle of the desert (where there is no dearth of light in the day). A number of lenses (mirrors), also called heliostats, are laid out in a circle around a central tower called a receiver. The heliostats are then positioned, with the help of a computer programme, at an angle so as to maximise their ability to catch the sun’s rays and transfer maximum energy to the central tower. The central tower itself contains water or other substances, which are converted to steam with the solar energy. This steam is then used to power turbines that generate electricity. Efforts are also on to test molten salts in the central towers. These molten salts have the capability of storing energy reflected from the mirrors and lenses over long periods of time. While still an area of active research, this might go a long way in solving the problem of making solar fields productive during the nights. According to Saini, “ACME Power’s CSP plants use air receivers, and are the latest in technology being developed by eSolar, a major solar power company in the US.”
Efforts are also on for finding new materials for solar power. Professor Gurunath’s lab at IIT-Kanpur, for instance, found materials “while studying the photo-physics of fluorescent proteins found in marine organisms that can make good solar cells”. He adds, “These materials are naturally found and if the panels are broken then one does not have to worry about environmental impact, since they are completely bio-degradable.” With patents filed, Gurunath is concerned about “finding students who are interested in working in fields that are at an intersection of chemistry and electronics”. Nature also provides us with answers. Branches grow on trees in a way so as to maximise their ability to catch sunlight. This helps the lower branches to survive. These branches grow in a pattern that mimics the well-known mathematical sequence, the Fibonacci series. A 13-year old boy, Aiden Dwyer, was perceptive enough to note this and built a solar panel array using this insight. This has now been shown to produce a greater amount of power than the normal array. There are claims that this design may eventually end up revolutionising solar array design.
Some methods to produce electricity from the sun belong firmly in the realm of science fiction. For instance, a group of scientists have proposed to send up a large number of geo-stationary satellites with massive solar panels into orbit, where power of the sun increases. According to them, the electricity thus generated can be beamed to the earth with lasers or microwaves. Challenges remain in the successful execution of this idea, not the least of which is the identification of lasers or microwaves, which would not blind or kill someone who happened to cross the beam.
It becomes increasingly clear though that the need of the hour is not only to increase solar power capacity, but also to invest in the technology that will drive solar power plants across the world tomorrow. In India, especially, solar power is a promising renewable energy alternative. But we need government policies to bankroll R&D efforts as much as rolling out next generation solar grids. “Solar power is now more competitive and the rates at which solar power is generated indicate that grid parity (the cost at which generating power from solar is equal to the cost of generating power from coal) is not far away,” says Gupta.
The future for solar looks increasingly bright. And the country that manages to make the solar panels of tomorrow will control this increasingly lucrative industry.
One way of measuring the sustainability of a source of energy is the ease of its availability. In that respect, the rays of the sun are, perhaps, the easiest-to-reach fuel source. The sun derives its energy from nuclear fusion. Though the distance between the sun and the earth is large (almost 150 million km or 1 astronomical unit), it still manages to receive almost 1,000 w/m2 of energy from the sun. No wonder the ancients revered the sun.
Generation of solar power
Solar cells are the predominant way of generating electricity from the sun. A solar cell, when kept in a dark room is no more than a big chunk of silicon. Exposing the same to sunlight is electrifying, literally. A solar cell works on the principle of the photoelectric effect, which, simply put, is the name given to the movement of electrons within the atoms of the solar cell in the presence of light. All light contains energy, which is carried in the form of discrete packets called photons. When a photon strikes a solar cell, it can either be reflected, absorbed or allowed to pass through the material that makes up the solar cell. Out of these three alternatives, only those photons that are absorbed are of interest since by “absorption” of a photon, we really mean transferring of energy from the photon to the atom. The atom that absorbed this photon now has greater energy than earlier, which causes an electron within it to move (in more scientific terms, the electron moves from the valence to the conduction bands). The movement of the electron generates a small negative charge and leaves in its wake a small positive charge. Positive and negative terminals are now present within the atom, which causes a small potential difference (voltage) to be setup. When this effect is repeated across billions of atoms in the solar cell, we get solar power.
Each photon is characterised by its wavelength. Since each photon is not absorbed by the solar cell, it follows that not every wavelength is helpful in the production of electricity. While solar cells are capable of producing electricity from a range of the frequencies present in light, some parts of the solar spectrum (such as infrared, ultra-violet or diffused light) are not covered. To prevent this waste, solar cells are also often made of materials that make them respond to only a certain wavelength of light (monochromatic light). The incoming light is broken up into different wavelengths and focused on solar cells that respond to particular wavelengths. This results in an increased — sometimes as high as 50 per cent — efficiency. The most advanced commercial solar cells have an efficiency of 21 per cent. Apart from this, there are a number of other criterion, such as charge carrier separation efficiency, thermodynamic efficiency and quantum efficiency. One of the most widely used measures is the “energy conversion efficiency” metric, which measures in watts/m2 the amount of sunlight falling on a solar panel that is converted into electricity.
The materials used
Apart from the wavelength of light that strikes a solar panel, its material or manner of construction can also make a big difference to cost and efficiency of solar energy to electricity conversion. With research into solar panel technology yielding greater dividends, newer materials like cadmium and gallium arsenide have been brought into use. The most popular material, however, was — and continues to be — silicon. Different technologies exist that make use of different properties of this element. Thin-film technologies reduce the amount of silicon required to create the solar cell. “Most solar panels in India are made of crystalline silicon,” says Mayank Gupta of Pyro Power, a solar power startup based out of Delhi. Other materials such as cadmium-telluride, copper-indium-gallium-selenide (Cigs) are also increasingly being used to make solar cells. Perhaps, the most important and the most visible market for solar panels is in space exploration. The images of the international space station hovering some 400 km above the earth’s surface with its massive solar panels spread out like a soaring eagle are perhaps familiar to all of us. The power requirements of a space station are unique. The power system must not only cater to the needs of its occupants but also provide enough power to conduct experiments and operate essential life-support systems that are mission-critical. These strict requirements put the spotlight on efficiency of solar cells. Gallium-arsenide (GaAs)-based solar cells were originally developed for space exploration and similar applications. Similar materials like germanium (Ge) or gallium-indium-phosphide (GaInP2) are also being used now. GaAs-based solar cells have been used in the Mars Rover Exploration mission, which has lasted for more than 90 days that it was supposed to run. GaAs-based solar cells have also powered solar cars that have won the solar world challenge multiple times. Materials for solar cells are chosen carefully since different materials will have a different response for each wavelength.
One of the major concerns since the start of developments in solar power has been the exorbitant cost associated with installation of solar cells and the long break-even time. Since the first solar cells were invented in Bell Labs in 1954, the cost of solar cells (measured in $/watt) has come down steadily from about $250/watt to around $1/watt today. With a large number of solar power plants coming up, the cost is slated to come down further, say, about $0.33/Watt.
The cost of setting up solar panels can still be daunting for individuals with small power needs. Governments across the world, eager for their citizens to switch to greener alternatives to fossil fuels have been providing generous subsidies to home and business owners intent on switching to solar power. For instance, faced with acute land shortage to setup a power plant, the Delhi government is considering a power buyback scheme in which it will buy excess power from consumers at attractive rates. Power-buyback schemes are a hybrid solution. It makes consumers diversify the sources from where they get their electricity, while enabling them to use conventional electricity as a fall-back option in case solar does not live up to its promise (in rain or on cloudy days). This has made solar look more attractive as it allows people to recoup their investments even faster.
Sriram Shankar, www.mydigitalfc.com