Solar cells even at a low 10 percent energy conversion efficiency could satisfy the world’s energy needs with just over 0.1 percent of the earth’s surface. Solar power is poised to enter the mainstream market. Worldwide, photovoltaic installations jumped by 61.5 percent to 927 MW in 2004, up from 574 MW installed in 2003. A big advantage of solar power is that it has minimum impacts on the environment, which are mostly associated with the manufacturing processes, and do not require major changes in land use.

For houses, solar panels can be conveniently integrated into existing building structures and rooftops, and are ideal for micro-generation. There are two trends in solar cell development: bringing down manufacturing costs and boosting energy conversion efficiency, both of which are making solar energy much more affordable.

  1. Over the past decade, “second generation” thin-film technologies have been developed that do not require costly crystalline silicon wafers and can be manufactured much more cheaply. These include devices based on a range of new inorganic semi-conducting materials, as well as multi-junction amorphous (noncrystalline) silicon. Thin-film cells are fabricated using techniques such as sputtering, physical vapor deposition and plasma-enhanced chemical vapor deposition.
  2. Multi-junction cells based on amorphous silicon have been the most successful second-generation technology to-date, capturing 5-6 percent of the market not dominated by crystalline silicon. Amorphous silicon can be made from waste silicon from the computer chips industry.
  3. Organic photovoltaics are made from organic materials, which are diverse and versatile, offering endless possibilities for improving a wide range of properties. Organic molecules are cheap to make,they can have very high light absorbing capacity so that films as thin as several hundred nanometers would be sufficient for the purpose. Organic materials are compatible with plastic and other flexible substrates; and devices can therefore be fabricated with low-cost, high throughput printing techniques that consume less energy and require less capital investment than silicon-based devices and other thin-film technologies. One estimate put the reduction in cost by a factor of 10 or 20. These affordable new generations of solar devices will be a boon for the energy needs of poor countries that do not have power grids or other infrastructure support
  4. Dye sensitised solar cells (DSSCs) are among the third generation devices nearest to the market, or already in the market. These are not purely organic solar cells, but are made of a hybrid of organic and inorganic semi-conducting materials. Some of these have reached energy conversion efficiencies of about 11 percent.
  5. A study published in 2000 indicated that the N3 ruthenium dye used in the DSSCs is not mutagenic, but its other potential toxicities have not been investigated. Although conventional TiO2 may be relatively harmless, many ultrafine nanoparticles (less than 1 micron), such as those used in DSSCs, are pathogenic, and chronic exposure to the nanoparticles may result in fibrosis and airflow obstruction in the respiratory tract. It is important for proponents and developers of these very promising solar cells and applications to ensure that researchers and workers as well as the public are protected from the hazardous materials, that appropriate containment and recycling of wastes take place to prevent environmental pollution, and that research on safety and safe use goes hand in hand with development and commercial exploitation. In addition, effort should be devoted to finding safer alternatives for toxic materials.
  6. Quantum dots are offering the possibilities for improving the efficiency of solar cells in at least two respects, by extending the band gap of solar cells for harvesting more of the light in the solar spectrum, and by generating more charges from a single photon. Solar cells based on quantum dots could theoretically convert more than 65 percent of the sun’s energy into electricity, approximately doubling the efficiency of solar cells.

Extracted from the article: “Which Energy“, By Mae-Wan Ho

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