Photovoltaics

The amount of energy supplied to the Earth by the sun is five orders of magnitude larger than the energy needed to sustain modern civilisation. One of the most promising systems for converting this solar radiation into usable energy is the photovoltaic (PV) cell. PV materials generate direct electrical current (DC) when exposed to light. The uniqueness of PV generation is that it is based on the 'photoelectric quantum effect in semi-conductors' which means it has no moving parts and requires minimum maintenance. Silicon is, at present, the dominant PV material which is deposited on a suitable substrate such as glass. Its disadvantages are that it is expensive; it is, as yet, capable of only a relatively low output per unit of area, and, of course, only operates during daylight hours and is therefore subject to fluctuation in output due to diurnal, climate and seasonal variation. As it produces DC current, for most purposes this has to be changed to alternating current (AC) by means of an inverter.

Growth in the manufacture of PVs has been accelerating at an extraordinary pace. In 2002 it was 56 per cent in Europe and 46 per cent in Japan, greater than in 2001. We are now seeing the emergence of large plants producing PVs on an industrial scale, that is, over 200 MW per year. The result is that unit costs have almost halved between 1996 and 2002. Significant further cost reductions are confidently predicted coupled with steady improvements in efficiency.

One application of PVs is its potential radically to improve the quality of life in the rural regions of developing countries. This is certainly one area on which the industrialised countries should focus capital and technology transfer to less and least developed countries. Already rural medical facilities are being served by PV arrays, for example the rural hospital at Dire' in Mali. On a smaller scale, compact and mobile PV arrays can operate refigerators and water pumps.

PV technology will be considered further in Chapter 7.

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