The conversion of daylight into electricity, called the photovoltaic effect, was first discovered by the French scientist Edmond Becquerel in 1839. The explanation for this effect was later provided by Albert Einstein who received for this work (and not the theory of relativity) the Nobel Prize in physics. However, the development of the first practical photovoltaic cell occurred only in 1954 at the Bell Telephone Laboratories, with the production of a silicon-based cell with 6% efficiency in converting light into electricity. The technology that was originally developed for space applications in the 1960s to power military and later commercial satellites, has since been given much attention as a potential energy source for civilian uses.
Photovoltaic (PV) systems that convert the energy of photons from sunlight directly into electricity using semiconductor devices are commonly known as solar cells. When photons enter the cell, electrons in the semiconducting material are freed, allowing them to flow and generate electricity. Solar cells are typically combined into modules in sizes from less than 1 W to 300 W to produce higher voltage and currents. If larger electricity production is required, these modules can be connected in series or parallel to form photovoltaic arrays. The modular nature of solar cells means that they can be used in applications ranging from a fraction of a Watt, such as a solar wristwatch, to large multi-MW power plants containing millions of solar cells.
Solar cells are most commonly made from mono- or polycrystalline silicon. Their efficiency in converting sunlight into electricity is constantly improving, from around 15% in the mid-1970s to more than 25% today under laboratory conditions . Other materials such as cadmium telluride, gallium arsenide, copper-indium diselenide or amorphous silica, usually in the form of deposited thin films, have also been used to produce solar cells, but their large-scale utilization has met limited success because of a shorter life-time, low efficiency or toxicity issues in production and disposal. Photocells based on organic materials are now also being designed and tested.
During the last decade, the cumulative PV capacity in the world has increased at a rate of more than 30% per year, reaching by the end of 2004 more than 2.5 GW compared to less than 0.1 GW in 1990  (Fig. 8.10). This growth is impressive, but still equals only the production capacity of two nuclear reactors. Over three-fourths of the world capacity is installed in only three major countries: Japan, Germany, and the United States. Not surprisingly, 54% of the solar cells produced in the world in 2004 came from Japan, followed by Germany as the second largest producer, and the United States.
PV technology has a wide range of applications. It can provide electricity to isolated systems far from power lines, such as telecommunication towers or water pumps in developing countries. A major future increase in solar power is, however, expected to come from the PV installed to generate all or part of the electricity needed in grid-connected buildings.
Solar cells have many advantages: they are silent, produce no emissions, have no moving parts, are easy to maintain, can be installed almost anywhere, are easily adapted to the customer's specifications, and use no fuel.
The downside of solar cells is that energy generation is limited to daylight. The Sun does not shine during the night, and even during the day cloudy conditions also reduce the energy output to only 5-20% of that of full sunlight output. The
intermittent nature of PV systems is an issue that must be addressed by the installation of supplemental conventional generating capacity or effective energy storage for cloudy or low-sunlight conditions. The main present challenge, however, is the cost of generating electricity from solar cells; this is in a range from $0.3 to $0.8 per kWh, depending on the location , and is an order of magnitude higher than the electricity production from natural gas at some $0.03 per kWh. As demand increases and larger quantities of PV are produced, the costs will decrease. However, unless a major breakthrough in solar cell production occurs that will dramatically decrease costs, its contribution to global electricity generation in the foreseeable future is likely to remain relatively limited and strongly dependent upon governmental incentives.
Was this article helpful?
Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.