| Photovoltaics |
Photovoltaics: The Future Energy Source
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The term photovoltaic comes from the Greek word “phos” meaning light and the word “voltiac” meaning electricity, the combined word means, electricity from the light. When sunlight hits a solar cell, the sun’s energy activates electrons. Though this effect was originally discovered over 164 years ago by Edmund Becquerel and initially turned into a working solar cell by Charles Fritts about 124 years ago in 1884, but as a serious source of energy, this technique has gained attention and momentum in recent years.
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 In sixty seconds the sun provides enough energy to supply the world’s energy needs for one year. In 24 hours it provides more energy than the world’s population could consume in 27 years. Sounds amazing and fairy tale like, but its true and moreover sun’s energy is free, and the supply is abundant. All one needs to do is find a way to harness it, in a cost effective manner.
The basic mechanism of PV involves, Light energy from the sun hitting a solar module, this light energy excites electrons to move away from the atom to which they are attached. The movement of electrons is an electrical current. The structure built on the silicon / silicon wafer then collects the current created by the free electrons to produce electricity. The individual wafers are wired together inside of a module and the module has electrical connections that allow the electricity to power buildings, homes, offices or any electrical device.
PV advantage
Generation of electricity utilising solar energy has many advantages over traditional electricity generation sources.
• The 89 petawatts of sunlight reaching the earth’s surface is plentiful - almost 6,000 times more than the 15 terawatts of average power consumed by humans. Solar electric generation has the highest power density among renewable energies. Solar power is pollution free during use. Production end wastes and emissions are manageable using existing pollution controls.
• PV Facilities can operate with little maintenance or intervention after initial setup. Once the initial capital cost of building a solar power plant has been spent, operating costs are extremely low compared to existing power technologies.
• Solar electric generation is economically superior where grid connection or fuel transport is difficult, costly or impossible due to geographical and logistic constraints. Such as in the cases of satellites, island communities, remote locations and ocean vessels.
• Compared to fossil and nuclear energy sources, hitherto very little research-money has been invested in the development of solar cells, so there is much room for improvement. Experimental high efficiency solar cells already have efficiencies of close to 40% and efficiencies are rapidly rising while mass production costs are rapidly falling
World of PV industry at a glance
PV industry is one of the fastest growing industries worldwide; PV production has been doubling every two years, increasing by an average of very close to 50 percent each year since year 2002. At the end of Calendar year 2007, cumulative global production was estimated to be 12,500 megawatts. Around 90% of this generating capacity consists of grid-tied electrical systems. These installations are either ground-mounted or built into the roof or walls of a building, known as BIPV (Building Integrated Photovoltaic). World solar photovoltaic (PV) market installations achieved a record high of 2,826 megawatts in Calendar year 2007, i.e. a growth of more than 60 percent over the year 2006.
Germany is the world leader in PV installation; PV market reached 3862 MW in 2007 and is the world leader in PV installations. Spain soared by over 480 percent to 655 MW, while the United States increased by 57 percent to 830 MW. It became the world’s third largest market behind Japan, once the world leader, which has an installed capacity of 1920 MW. Some other countries , which has shown great promise in coming year and ahead are Korea, Australia and Italy, in fact a few of the largest planned installations are coming up in these countries. In the Asian region, China, India, South Korea, Taiwan and Thailand are set to become the most important PV market in coming years.
In terms of PV production, World solar cell producers produced a consolidated figure of 3,436 MW in 2007, up from 2,204 MW a year earlier. Japan, which was the mainstay of PV production till a couple of years back, continues to lose ground to other emerging players, only accounting 26 percent of global production. Dubbed as the world factory, Chinese manufacturers raised their share from 20 percent in 2006 to 35 percent in 2007.
The Technology
PV cells are generally made either from crystalline silicon or thin film, deposited in thin layers on a low cost backing, such as glass or plastic. The major market share of module production has so far involved the former, but recently there has been a very strong focus on thin film technology, all over the world PV manufacturing companies has massively invested in research and production of thin film technology. Thin film technology based on silicon and other materials is expected to gain a by far larger share of the PV market in the future. This technology offers several advantages over the silicon based wafer system in terms of low material consumption, low weight, lower costs and a smooth visual appearance.
Crystalline silicon
Crystalline silicon is still the mainstay of most power modules. Although in some technical parameters it is not the ideal material for solar cells, but it has the benefit of being widely available, well understood and uses the same technology developed for the electronics industry. Efficiencies of close to 25% have been obtained with silicon cells in the laboratory, but production cells are currently averaging 13-17% efficiency. The theoretical limit for crystalline modules approaches 30%.
Thin film
Thin Film (TF) solar technology is an emerging solution for solar electricity production. Rather than using silicon wafers to build the PV device, TF is manufactured on glass. Glass substrates require less sophistication to manufacture, making them more abundant than silicon wafers and less costly. The active silicon layer is deposited using almost identical processes as those used to make LCD TFT flat panel displays.
Thin film modules are constructed by depositing extremely thin layers of photosensitive materials on a low cost backing such as glass, stainless steel or plastic. These results in lower production costs compared to the more material intensive crystalline technology. However this price advantage is counter balanced at the moment, however, by substantially lower efficiency rates and less experience of the modules’ lifetime performance.
Three types of thin film modules are commercially available. These are manufactured from amorphous silicon (a-Si), copper indium diselenide and cadmium telluride. All of these technologies have active layers in the thickness range of less than a few microns. This approach allows higher automation once a certain production volume is reached, while they all use an integrated approach to the module architecture. These technologies are less labour intensive compared to the assembly of crystalline modules by interconnecting a number of individual cells. At approximately 12% in 2007, the market share of thin film technology is still fairly low, but thin film is the “technology of future” in the nascent PV industry.
Concerns
Though PV industry has a lot of brighter aspects, but they are a few concerns, which need to be addressed, in case the PV industry has to reach to its true potential.
• Grid parity, the point at which photovoltaic electricity is equal to or cheaper than grid power, is currently a major issue for PV industry. The cost of electricity generated by PV is much higher than electricity generated by conventional means.
PV Modules, Price Per Watt, in $
• Cost may not cover lifespan savings unless a preferential feed-in tariff is offered by the grid network.
• Solar electricity is not available at night and is less available in cloudy weather conditions. Therefore, a storage or complementary power system is required.
• Limited power density: Average daily insolation in the contiguous U.S. is 3-7 kW•h/m² and on average lower in Europe.
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Photos: Web
Last review: September, 2008 |
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