Timeline of solar cells
Photovoltaics is the direct conversion of incident light into electricity (see, solar energy). The history of photovoltaic begins in 1839, when the underlying photoelectric effect was discovered. However, it still took over a hundred years until it came to a use in energy supply.
The discovery
In 1839 came Alexandre Edmond Becquerel ( 1820-1891 ) in experiments on the photoelectric effect. In experiments with the electrolytic cells in which it is used, a platinum anode and a cathode, he measured the current flowing between the electrode current. He found that the current was slightly greater in light than in the dark. He discovered the basis for photovoltaics to a practical application, it was, however, only generations later.
Basic research
Discovered in 1873 by the British engineer Willoughby Smith and his assistant Joseph May that selenium changed its electrical resistance when exposed to light. Willoughby Smith went with this discovery to the public, prompting further research of this topic.
Then in 1876 William Grylls Adams discovered together with his student Richard Evans Day that selenium produces electricity when exposing it to light. Although selenium is not likely to provide enough electrical energy to supply then used electrical components to available, the evidence was hereby furnished that a solid can convert light directly into electrical energy without having to use heat or kinetic energy. 1883 built the New York Charles Fritts, a first module ( the precursor of the photovoltaic module ) of selenium cells. Only now it came to fundamental work on the photoelectric effect, where many scientists of that time but also to grave doubts about the seriousness of this discovery. 1884 put Julius Elster ( 1854-1920 ) and Hans Friedrich Geitel ( 1855-1923 ) significant work on the photoelectric effect ( photoelectric effect ) before. Heinrich Rudolph Hertz (1857-1894) in 1887 also discovered the photoelectric effect, the exact investigation, he handed his pupil Wilhelm Ludwig Franz Hall wax ( 1859-1922 ). In the same year, and regardless of Hall wax came Augusto Righi (1850-1920) to the discovery of the electron emission of the photoelectric effect. In honor of the findings of Hall wax of the photoelectric effect was (also called external photoelectric effect ) formerly known as Hall wax effect. Also Philipp Eduard Anton Lenard (1862-1947) and Joseph John Thomson wore at the end of the 19th century further contributes to exploration of the photoelectric effect. 1907 Albert Einstein gave a theoretical explanation of the photoelectric effect, which was based on his light quantum hypothesis of 1905. For this he received the 1921 Nobel Prize in Physics.
Robert Andrews Millikan (1868-1953) was able to confirm the 1912-1916 Einstein's reflections on the photoelectric effect experimentally and has been for 1923 awards, including the Nobel Prize for physics.
Another important step for the basics of semiconductor technology and photovoltaics was the 1916 Jan Czochralski ( 1885-1953 ) discovered and named after him crystal pulling method. It was further developed until the 1940s, and came in the 1950s with the rising demand for semiconductor devices on a larger scale for practical use.
Photovoltaic cells
1940, Russell S. Ohl ( 1898-1987 ) in experiments unexpectedly found that upon illumination of a silicon sample he examined the connected meter indicated a change. He noted that a current could be generated by the illumination of the silicon. Through further investigation, the results could be confirmed. Ohl was involved at Bell Laboratories and at the discovery by targeted doping with impurities to change the electrical properties of semiconductors and to create a pn junction.
1948 there was a first concept of semiconductor photovoltaic Schottky diodes by Walter Schottky ( 1886-1976 ), and William Bradford Shockley created in 1950 ( 1910-1989 ), a theoretical model for the pn junction and thus created the conditions for understanding of today's solar cells.
The Bell Laboratories in New Jersey were in those years one of the world's most active and successful research laboratories. In 1953, there by Daryl Chapin ( 1906-1995 ), Calvin Souther Fuller ( 1902-1994 ) and Gerald Pearson ( 1905-1987 ) of crystalline silicon solar cells, each about 2 cm ², produced with efficiencies of over 4 percent. A cell even reached 6 percent efficiency - 25 April 1954, the results of the public were presented. The New York Times ran the event the next day on the front page. The solar cells had a defined pn junction and good contacting possibilities, which are important prerequisites for industrial production were given for the first time. 2002 1955 cell produced by Bell Laboratories, encapsulated and then measured with 6 percent efficiency was measured again and still had 5.1 percent efficiency. After further improvements in the efficiency of solar cells up to 11 percent could be increased.
The first industrial application in 1955 found in the power supply of telephone amplifiers.
Applications in space
On March 17, 1958, when the U.S. had already successfully launched after the Sputnik shock a satellite into orbit, flew the second satellite of the United States called Vanguard I with a chemical battery and photovoltaic cells to operate a transmitter on board into space. After much hesitation on the part of the U.S. Army, Hans Ziegler (1911-1999) was able to enforce his idea that an energy supply with solar cells would ensure the operation of the station longer than the use of batteries. Contrary to expectations, the military, the transmitter signals could be received until May 1964 before he set his signal activity. Due to the long duration of measurement, the mass distribution model of the Earth could be corrected to a hitherto not achievable accuracy based on the trajectory of Vanguard I, and it became clear that the Earth is not exactly spherical.
The success of this small satellite and the scientists involved in it laid the foundation stone for the first meaningful use of until then almost unknown and above all very expensive solar cells. For many years, solar cells were mainly developed for space applications, since they proved to be an ideal power source for satellites and space probes to Mars distance from the Sun in the sequence. The thus gained over the long battery life of the spacecraft outweighed the still high price of solar cells per kWh by far. In addition, solar cells and were compared with radioisotope generators that allow similarly long periods of use, cheaper and less risky. Most spacecraft have been and are therefore equipped with solar panels for power generation.
Today ( 2008) provided by solar cells with increased efficiency several kW of power for communications satellites with over 30 transponders, each about 150 watts transmitter power or even provide the driving energy for ion thrusters of spacecraft available. The Juno spacecraft, which was launched in August 2011, is to first obtain even in an orbit around the planet Jupiter their energy from particularly efficient and radiation resistant solar cells. Almost all of the approximately 1,000 worldwide satellites that are in use, draw their power with the help of photovoltaics. In space, a power output of 220 watts per square meter is obtained.
Use on Earth
Only in exceptional cases, for example when the next energy grid was very far away, there was initially an installation of terrestrial photovoltaic off-grid systems. With the 1973 oil crisis, interest in other sources was considerably stronger, but still large, centralized power plants were seen as the best solution for a comprehensive energy supply. Since the mid- 1970s, more solar cells for terrestrial purposes than for use in space were then prepared for the first time.
In 1976, the Australian government decided to operate the entire telecommunications network in the outback with photovoltaic battery -based stations. Establishment and operation were successful and had confidence in the solar technology to increase significantly.
1977 was developed in the USA at Sandia Laboratories (Albuquerque, New Mexico ) is a solar module with the aim to show off a potentially cost-effective technology for photovoltaic energy conversion on the ground that no longer based only on custom.
The catastrophic accident at the nuclear power plant at Three Mile Iceland at Harrisburg in the U.S. the end of March 1979 and the oil crisis in the late autumn of the same year gave the renewable energy further upwind.
From about 1980, solar panels with rechargeable batteries, a standard application for the operation of signaling systems on small unmanned oil rigs in the Gulf of Mexico. They replaced as a cheaper and lower maintenance version, the large batteries previously used, which had to be exchanged personnel consuming and expensive every few months.
Later in the 1980s were from the U.S. Coast Guard ( Coast Guard ), converted to the initiative of its employees Lloyd Lomer, all signals and navigation lights on photovoltaic energy supply. Previously, the operating costs of these systems had exceeded the cost by far. Through the photovoltaic operating costs have been dramatically reduced, and the cost for the more expensive photovoltaic systems paid for themselves quickly.
Now it came to the first major commercial activities in the U.S., which the U.S. achieved a global market share of photovoltaics of around 21 percent in 1983. Up to this time there was in the photovoltaic market solutions mainly for stand alone systems and planning for photovoltaic large systems.
The Swiss engineer Markus Real was the conviction that it is economically sensible to equip each home with its own PV system, ie to prefer a decentralized energy conversion. He came with 333 installed on individual buildings 3 kW rooftop installations in Zurich the proof. This was the beginning of a movement, in the course of which the 1000 roofs program of the Federal Republic of Germany was established. As of 1991, the utilities were obliged to purchase the electricity of small renewable power plants with the Electricity Feed Act. The mid-1990s gave Greenpeace after despite the support measures crucial parts of the photovoltaic production migrated from Germany, with a new study on Germany as a photovoltaic plant in this sector for thought. New initiatives establishing appropriate industrial companies were founded, from which emerged the Solon AG in Berlin and the solar factory in Freiburg. Later, SolarWorld AG was founded and more companies and factories emerged in this market segment.
In Japan, there was a 70,000 roofs program (1994 ), which had already reached 144,000 roofs in 2002, in the U.S., 1,000,000 Roofs Programme (1997), in Germany the 1000 roofs program (1990 ) and the 100,000 roofs program (2003 were about 65,000 roofs reached), the Renewable energy Sources Act ( EEG) came into force in 2000.
First, many small systems were installed under 5 kW peak, by the legal framework, however, large-scale systems in recent years also increasingly been built up over the 1- MWpeak - border. In 2005, the total rating of installed photovoltaic systems in Germany reached a gigawatt in 2010, the limit of ten gigawatts has been exceeded and the beginning of 2012, the 25 gigawatt limit has been exceeded.