8 CdTe and CuInGaSe 2 Thin-Film Solar Cells
215
toxicities of CdTe in rats found that the both median lethal concentration and lethal
dose are more than 9 times higher than that of elemental Cd [15]. Moreover, CdTe
showed no acute adverse reproductive effects in rats and low aquatic toxicity [16].
Now, if CdTe as a compound, does not represent a real harm for the environment,
then the question arises if and how this compound might release pure toxic Cd.
Different studies have been made to clarify this issue. Early works from broken modules left under rainwater showed that cadmium concentration stayed within
the limits of the law for drinking water, and similar results were obtained for
concentration in the soil when the damaged modules were left on the ground [14].
A research laboratory at the University of Arizona very recently did further studies
on the subject. Their studies concerned non-encapsulated CdTe, by examining 1.5 g
of “snipped” CdTe film together with 300 g of crushed glass, in order to maintain
the ratio between active material and encapsulant, at the same ratio as conditions
within a solar module. In this way an acidic column and a methanogenic column
were applied to test the leachate
12 produced in a municipal landfill. Even though
the material was not encapsulated, the results showed that the Cd concentration was
6.7-fold lower than the threshold limit established in the TCLP (toxic characteristic
leaching procedure) conditions and 4.6-fold lower than the one for the WET (waste
extraction test) conditions [17].
Another high risk could be in case of fires, but it has to be considered that the
melting point of CdTe is 1050 °C, a temperature normally not reached during fires of
residential houses, so that one can consider that during a fire in a residential location,
no cadmium is released into the atmosphere.
Higher temperatures are reached in fires of industrial plants. However, when
modules were subjected to temperatures of 1100 °C, the melted cadmium telluride
was captured and embedded in the melted encapsulating glass [13].
Also for CIGS the environmental impact is low, as most of the elements present
in a CIGS solar cell are not toxic, with the exception of selenium and a small amount
of Cd in the buffer layer.
Indeed, different studies have been conducted with CIGS solar cells and no significant release of toxic materials has been measured during fires, the main compound
released being CO 2 (as usual in fires).
Another issue is the presence, within CIGS and CdTe solar cells, of rare elements, such as indium and tellurium, respectively: These elements may constitute a
bottleneck for the development of these technologies on a very large scale.
However, calculations have shown that a production of several TW p of CIGS
and CdTe solar cells would be possible with the present reserves of Indium and
Tellurium—Now such a production volume may only be reached by 2050, even in
the most aggressive scenarios for the development of renewable energy.
Material-related sustainability issues can also be faced by developing recovery
during primary production, by reducing the thickness of the semiconductor layers
below 4 µm, and, most importantly by recycling modules at their end-of-life.
12 Water that has percolated through a solid and leached out some of the constituents.
215
toxicities of CdTe in rats found that the both median lethal concentration and lethal
dose are more than 9 times higher than that of elemental Cd [15]. Moreover, CdTe
showed no acute adverse reproductive effects in rats and low aquatic toxicity [16].
Now, if CdTe as a compound, does not represent a real harm for the environment,
then the question arises if and how this compound might release pure toxic Cd.
Different studies have been made to clarify this issue. Early works from broken modules left under rainwater showed that cadmium concentration stayed within
the limits of the law for drinking water, and similar results were obtained for
concentration in the soil when the damaged modules were left on the ground [14].
A research laboratory at the University of Arizona very recently did further studies
on the subject. Their studies concerned non-encapsulated CdTe, by examining 1.5 g
of “snipped” CdTe film together with 300 g of crushed glass, in order to maintain
the ratio between active material and encapsulant, at the same ratio as conditions
within a solar module. In this way an acidic column and a methanogenic column
were applied to test the leachate
12 produced in a municipal landfill. Even though
the material was not encapsulated, the results showed that the Cd concentration was
6.7-fold lower than the threshold limit established in the TCLP (toxic characteristic
leaching procedure) conditions and 4.6-fold lower than the one for the WET (waste
extraction test) conditions [17].
Another high risk could be in case of fires, but it has to be considered that the
melting point of CdTe is 1050 °C, a temperature normally not reached during fires of
residential houses, so that one can consider that during a fire in a residential location,
no cadmium is released into the atmosphere.
Higher temperatures are reached in fires of industrial plants. However, when
modules were subjected to temperatures of 1100 °C, the melted cadmium telluride
was captured and embedded in the melted encapsulating glass [13].
Also for CIGS the environmental impact is low, as most of the elements present
in a CIGS solar cell are not toxic, with the exception of selenium and a small amount
of Cd in the buffer layer.
Indeed, different studies have been conducted with CIGS solar cells and no significant release of toxic materials has been measured during fires, the main compound
released being CO 2 (as usual in fires).
Another issue is the presence, within CIGS and CdTe solar cells, of rare elements, such as indium and tellurium, respectively: These elements may constitute a
bottleneck for the development of these technologies on a very large scale.
However, calculations have shown that a production of several TW p of CIGS
and CdTe solar cells would be possible with the present reserves of Indium and
Tellurium—Now such a production volume may only be reached by 2050, even in
the most aggressive scenarios for the development of renewable energy.
Material-related sustainability issues can also be faced by developing recovery
during primary production, by reducing the thickness of the semiconductor layers
below 4 µm, and, most importantly by recycling modules at their end-of-life.
12 Water that has percolated through a solid and leached out some of the constituents.