4 SOLAR PHOTOVOLTAIC ELECTRICITY

4.1 Introduction

Photovoltaic (PV) literally means 'light-electric'. The solar PV cell is the only developed technology which can convert solar energy directly into electricity in a single step. Conceptually, it is a solar-powered battery energised by the sun. This requires special electronic materials known as semiconductors, which are also used in computer chips, and the two technologies have advanced together although in different directions. We would therefore now expect PV to be a strongly competitive method of generating electricity, but must recognise that its merits are subject to both the availability of solar irradiation and the cost of the semiconductor materials which need to cover a large area.

4.2 History

The effect of light on the electric properties of certain materials was observed well before electricity became generally available. Early PV cells made of selenium could be used for detecting light and measuring its intensity, but their conversion efficiency was too low to produce useable electric power. This had to await the postwar development of doped silicon semiconductors, on which much of our current technological culture depends. Although silicon is still the most significant PV material, several other combinations of rarer elements have been explored and found to have useful special properties.

Now known mainly for its use as an energy source for satellites, it was after the first oil price shock in the early 1970s that interest grew in the use of PV for terrestrial applications. Since then, national and international investment in R&D, demonstration and dissemination have led to important technical improvements and a drop in the price of PV modules by a factor of more than 20.

1839	photovoltaic effect discovered by Alexandre Edmond Becquerel (France)
1873	PV effects in selenium first reported (Willoughby Smith, UK)
1877	first solar cell (selenium, conversion efficiency 1%)
1918	manufacture of mono-crystalline silicon (Czochralski, Poland)
1932	photovoltaic effect discovered in Cadmium Telluride (CdTe)
1941	first silicon solar cell
1951	first germanium mono-crystalline solar cell
1954	solar cell conversion efficiency reached 6%
1955	first commercial production of solar cells
1958	first satellite with PV cells
1963	first PV module
1970	start of terrestrial PV era
1981	first PV airplane
1982	PV energy started to be used in the automotive industry
1984	first thin-film PV module (hydrogenated amorphous silicon)
1985	solar cell conversion efficiency of over 20% achieved
1986	first commercial thin-film PV module
1990s	high growth-rate of PV industry
2001	experimental PV-powered airplane Helios reached 30 km altitude

 

Source: www.pvresources.com