Fig. 2: Estimated amount of material generated according to module technology
© Sunicon

Fig. 3: Composition of c-Si and thin-film modules (corresponding to the respective technology)
© Ökopol / Solarworld u.a.

Fig. 4: Comparison of recycling processes
© Solarworld
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Recycling is vital for sustainable photovoltaics

Not even “green technology” lasts forever. With the rapid expansion of photovoltaics, the amount of waste to be generated by PV products in the future is also increasing and it is becoming essential to set up recycling management for this waste. This is also due to the fact that strong growth and high price pressure in the industry are necessitating new, low-cost sources of solar silicon. Recycling also reduces environmental impact. Naturally, alongside saving energy and resources, it is also important to prevent the loss or release of scarce or poisonous elements and compounds. Old modules and production waste alike are available for disposal. It is difficult to determine the exact amount, because of the many factors of uncertainty. Due to the long service lives of solar modules, this technology, which is still young, has generated little waste so far. In 2008, the amount of waste which it generated in the EU was around 3,800 tonnes (corresponding to 51 MWp). By 2030, this is expected to rise to 130,000 tonnes (see Fig. 2).

PV scrap – what does it contain?

Today, around 90% of PV waste consists of crystalline silicon (c-Si) and the other 10% is accounted for by thin-film cells, which to date include CIS (Cu, In, Se), CdTe, amorphous and microcrystalline technologies. However, the proportion of thin-film cells will rise to around 20% by the year 2020 (see Fig. 2). Until then, the amount of waste generated by new developments will remain negligible. New technologies of the future could, for example, include modules with new substrate materials or organic cells – everything which to date is either still in the infancy of development, or nothing more than a concept. By 2030, the proportions of the different technologies could more or less balance out. Figure 3 shows the composition of various PV module types.

Upcycling rather than downcycling

To date, PV companies have largely failed to achieve satisfactorily pure material fractions when recycling old solar modules. This is referred to as “downcycling”, which only yields low sales returns. It entails significant costs, which go beyond those of dumping and have to be covered by acceptance fees. The cost-efficiency of module recycling depends greatly on whether high-quality recovery is achieved (“upcycling”). Recycling at product level is advantageous with regard to the energy balance and therefore should always be striven towards. Even if it were technically possible to separate all components into pure raw materials, compromises would have to be made in order to keep the costs in check. However, higher take-back costs and recycling costs must be reckoned with for thin-film solar cells, due to the low amounts of semiconductor materials which they contain. Recycling reduces the production of primary materials (which requires more energy and entails more emissions) and thus improves the ecological and economic characteristics of PV systems. Its effects on environmental impact and the CO2 balance can be determined by means of a life-cycle analysis. The so-called “yield factor” describes the ratio of harvested energy to expended energy. With the usual 25-year period of use, the factor is between 5 and 50, depending on acceptance and conditions, and is generally higher for thin-film modules than for crystalline silicon modules.

Recycling initiative in the industry

In order to establish a voluntary industry-wide take-back and recycling programme for old modules in Europe, eight companies in the PV industry founded the association PV CYCLE in July 2007. Now with over five dozen members, it represents around 85% of the European PV market. This industry association undertakes to take back and dispose of PV waste, free of charge. PV modules should deliver clean energy for at least 25 years. As the first larger photovoltaic systems were installed in the early 1990s, a significant number of PV modules will reach the end of their life cycles from 2015 onwards. By then, a programme for take-back and recycling of old modules, production waste and damaged modules should be in place. The target is to collect at least 65% of all old modules which are dismantled and to recover 85% or more of their valuable materials such as glass, aluminium and semiconductor materials.

Sustainability of recycling processes

The ecological efficiency of different recycling processes varies greatly (see Fig. 4). With shredders and waste incineration, the recycling rate for Al, Cu and glass is low, the end products are low-quality and cost reduction is unrealistic. With manual separation, the pilot system achieves a satisfactory recycling rate with low throughput. The automated system delivers high-quality end products with high throughput, thus achieving a high recycling rate in an energyefficient and cost-efficient manner. The concept of eco-efficiency takes a product's entire life cycle into account. Energy consumption, resource consumption, environmental impact and recyclability are compared with the economic value of the product, with the aim of combining environmental relief with cost reduction.

Projektinfo 02/2010:
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Sunicon AG

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TU Freiberg, AOC