a.
CdTe must not be confused with metallic Cadmium,
since is a highly stable product, with high melting
point and it is insoluble in water [1]. The temperature
reached in fires in the United States, where wood
is a high inflammable material, reaches a maximum
of 900°C on the roof and of 1000°C underground.
The melting point of CdTe is 1041°C and the
evaporation starts at 1050°C. The CdS melting
point is near to 1750°C. Moreover studies of
the "Brookhaven National Laboratory" and
of the "GSF Institute of Chemical Ecology"
in Germany have indicated that at typical fire temperatures
the materials in the photovoltaic modules would
remain encapsulated inside the fused glass. Finally,
in case of fire, many other common materials would
be source of risk incomparably greater that any
other emissions caused by CdTe photovoltaic systems
[2].
b. A CdTe module contains very
little cadmium, less than 0.1% in weight, and,
for thousand square meters, less than an ordinary
Ni-Cd battery. Moreover, as already mentioned, the
cadmium inside the module is in an absolutely stabile
form [3].
c.
In the photovoltaic module the Cadmium is strongly
bounded with the encapsulated Tellurium and,
therefore the photovoltaic technology supplies one
effective solution for the Cadmium confination.
d. Less than 3% of currently used
Cadmium in U.S.A. production would be enough
for large-scale manufacturing (several GW/year)
of CdTe photovoltaic modules [4].
e. It is favorable to completely
recycle the modules at the end of their life,
which is at least 25-30 years. Moreover, due to
the type of application, it is not easy for the
customer to release the modules in the environment
as it happens instead often in case of batteries.
Module recycling is the definitive solution for
any kind of environmental problem [5]
f. The Cadmium is a by-product
of the extraction of other metals like zinc, lead
and copper. The cadmium is therefore produced
in strong excess and it gets stocked. Also supposing
that the mining rubbish dumps are controlled, the
transformation of Cadmium in the stable cadmium
telluride and the control of the modules life cycle
, with the possibility of recovery through recycling,
reduces the possibility of releasing cadmium in
the atmosphere very much, even supplying environmentally
favorable cadmium applications (for example the
reduction of the emissions greenhouse tied to the
photovoltaic generation).
Finally it turns out that, paradoxically,
using CdTe modules would reduce the effects of releasing
cadmium in the environment. It must be considered
also that 41.3% of the human exposure to Cadmium
derives from the use of fertilizers, 22% from use
of fossil fuel, beyond 16% from the iron production
and steel and so on until arriving to a 2.5% due
to the cadmium applications in finished products
like the Ni-Cd batteries. CdTe photovoltaic modules
would be deliver on the market much less cadmium
than the batteries do.
In last 30 years 700 tons of Cd
have been used from 16000 to 20000 tons of Cd the
year In order to make 1GW of electricity from modules
made up of CdTe are necessary that is smaller of
4% regarding the total consumption.
The
CdTe melts at 1041°C and evaporates, in atmospheric
pressure, at 1050°C.
In fire the glass is melting first and encapsulating
the CdTe material.
Experiments
made with real fires indicate that not there is
release of Cd in the atmosphere:
CdTe
PV modules during fires 
Operation
of CdTe and CIS modules
[1]
Fthenakis V., Morris S., Moskowitz P., Morgan
D. (1999). "Toxicity of cadmium telluride,
copper indium diselenide, and copper gallium diselenide."
Progress in Photovoltaics, 7, pp. 489-497. Bohland
J., Smigielski K. (September 2000).
"First Solar's CdTe module manufacturing experience:
environmental, health, and safety results".
Proceedings of the 28th IEEE Photovoltaic Specialists
Conference, Anchorage, AK.
[2] Drysdale D. (1985). "An Introduction
to Fire Dynamics", pp. 329-330, Wiley, NY.
Moskowitz P., Fthenakis V. (1990). "Toxic
materials released from photovoltaic modules during
fires; health risks", Solar Cells, 29, pp.
63-71.
[3] Anderson B. A. (2000). "Materials
availability for large-scale thin film photovoltaics."
Progress in Photovoltaics, 8, pp. 61-76. Zweibel
K. (1997). "Reducing ES&H impacts from
thin film PV." Environmental Aspects of PV
Power Systems,Utrecht University, The Netherlands.
[4] Anderson B. A. (2000). Materials availability
for large-scale thin film photovoltaics. Progress
in Photovoltaics, 8, pp. 61-76. Cadmium Market Update
Analysis and Outlook. (1995). Roskill Information
Services Ltd., London, UK.
[5] Bohland J., Dapkus T., Kamm K., Smigielski
K. (1998). "Photovoltaics as hazardous materials:
the recycling solution." Proceedings of the
2nd IEEE World Photovoltaic Specialists Conference,
pp. 716-719.
Fthenakis V. (2002). "Could CdTe PV
modules pollute the environment?" Aug. 2002,
Brookhaven National Laboratory,
Upton, NY 11973. www.pv.bnl.gov.
