Introduction

   It is assumed that the world energy demand will increase by about 70% between 2000 and 2030. Fossil fuels, supplying 80% of all energy consumed worldwide, are facing rapid resource depletion. The resource reserves of fossil fuels throughout the whole world in 2002 were projected to last 40 years for oil, 60 years for natural gas and 200 years for coal. Because of a growing demand for energy, combined with the depletion of fossil resources, global warming and its associated climate change, there is an urgent need for environmentally sustainable energy technologies[3].

    Solar energy is one of the most promising future energy resources. The direct conversion of sunlight into electric power by solar cells is of particular interest because it has many advantages over most presently used electrical power generation methods. Electricity is produced without the exhaust of green-house gases and without nuclear waste byproducts [4].

    Fortunately the supply of energy from the sun to the earth is gigantic: 3 x 1024 J a year, or about 10,000 times more than that the global population currently consumes. In other words, covering 0.1% of the earth’s surface with solar cells with an efficiency of 10% would satisfy our present needs[3].

     PV world market, market shares of different materials

   Today’s photovoltaic market is about 277 MW (in 2000) corresponding to a value of over US $ 1 billion. This is a remarkable market but still far away from constituting a noticeable contribution to the world energy consumption. Market growth in the last decade was between 15 and 25% as is shown in Fig.1 [7].

Fig. 1. Development of the world market shares in photovoltaics over the last decade in megawatts per year [7].

   This market growth would be very satisfying for any conventional product but in the case of PV it is entirely insufficient if we consider the goals. The main motivation for developing solar energy is the desire to get away from depletable fossil fuels with their adverse effect on the environment. At the present growth rate, it will take us far into the second half of this century get a relevant contribution by PV to world energy demand. Support programs in several countries are already accelerating market growth. Besides the terrestrial market there is also the space market which has entirely different boundary conditions and also different materials requirements [7].

   There are two major market sectors, grid connected and so called stand alone systems. The former delivers power directly to the grid. For this purpose the dc current from the solar modules is converted into ac by an inverter. The latter supplies power to decentralized systems and small scale consumer products. A major market currently being developed is in solar home systems supplying basic electricity demand of rural population in developing countries. The magnitude of this task can be appreciated if one is aware that about 2 billion persons are without access to electricity today. At present, both markets need subsidies, the grid connected installations because PV is much more costly than grid electricity, and solar home systems because the potential users lack the investment capital. On the other hand, there is also a significant industrial stand alone market which is today fully economical. Because of its high potential the market is hotly contested and new companies are entering constantly. It is significant that several large oil companies have now established firm footholds in photovoltaics. Indeed, a recent study of possible future energy scenarios up to the year 2060 that was published by the Shell company predicts a multigigawatt energy production by renewable energies including photovoltaics. On the other hand, the strong competition leads to very low profit margins of most participants of this market [7].

    In spite of the complicated manufacture and the high cost, crystalline silicon still dominates the market today and probably will continue to do so in the immediate future. This is mostly due to the fact that there is an abundant supply of silicon as a raw material, high efficiencies are feasible, the ecological impact is low and silicon in its crystalline form has practically no degradation. The market shares of different technologies in 2001 are shown in Fig.2.

Fig. 2. Market shares of different photovoltaic materials [7].

   The various forms of crystalline silicon have together a share of 82.7%. Single crystal and cast polymaterial had about equal share for a long time. Recently cast material has surpassed single crystals. Newer types of crystalline silicon like Ribbon and Si-film are not yet very important. A newcomer is a-Si on crystalline silicon. The dominance of the element silicon in its crystalline and amorphous form is an overwhelming 99%. Of all the other materials only CdTe has a market share but this is less than 1%[7].