December 1, 2013

Environmental risk assessment of CdTe PV systems to be considered under catastrophic
events in Japan
Dr. Yasunari Matsuno, Associate Prof., The University of Tokyo, Japan
1. The Goal and Scope
The purpose of this report is to summarize the environmental risk assessment of CdTe PV systems to beconsidered under potential catastrophic events in Japan. Earthquakes, tsunami and big fires caused by tsunami aresome of the catastrophic events which are of most concern in Japan. So, the potential environmental risks causedby these disasters should be considered for CdTe PV systems, and the mitigation method to minimize the risks
should be clarified. This review is undertaken at the request of First Solar.
2. Huge disasters to be considered for CdTe PV systems in Japan:
An earthquake is a potential catastrophic event of particular concern in Japan. It is still fresh in our minds thata massive earthquake hit the north-east of Japan and triggered a tsunami that had caused extensive damage on
March 11th, 2011. In addition, the tsunami caused big fires at 177 places in Japan. These big fires also hadoccurred in the big earthquakes and subsequent tsunami in the past1). The main sources of the big fires were thereservoirs of fuel and liquefied petroleum gas (LPG) located along the coast that had been damaged by thetsunami2).
Since many cities are located along the coast, earthquakes, subsequent tsunami and fires are catastrophic
events of particular concern in Japan, which should be considered for CdTe PV systems.

Fig. 1 Large fire caused by tsunami in Kesenuma City on March 11, 20112)
3. Hazard map data for earthquakes and tsunami
Ministry of Land, Infrastructure and Transport and Tourism, Japan releases “Hazard Maps” for earthquakes,and tsunami, etc. which cover many regions in Japan. They are available on Web site3, 4) (in Japanese):

Fig. 2 Hazard map availability for earthquake (left) and Tsunami (right)

The details and data availability for these hazard maps vary in regions (cities and towns). Some examples ofhazard maps for earthquake and tsunami of Cities in Tohoku area are shown in Figs. 3(a)-(b).

Fig. 3(a) Earthquake Hazard Map for Higashi-Matsuyama City – Seismic Intensity Map for the case ofReoccurrence of the 1978-type Miyagiken-Oki Earthquake

Fig. 3(b) Hazard Map for Tsunami of Miyako city
4. Evaluation of environmental risks of potential catastrophic events and the mitigation methods to minimize therisks
Environmental risk assessment is the standard scientific method for evaluating potential health andenvironmental impacts from exposure to chemicals in the environment (Fig. 4).

Fig. 4 Environmental risk assessment framework
Use of heavy metals (e.g., Pb, Cr, Cd compounds) is commonplace in the PV industry. The environmental risk
related to each catastrophic event involving CdTe PV systems is discussed below.
4.1 Earthquake
Environmental risks for PV modules impacted by an earthquake would be related to the breakage of themodules in the impacted geographic area.
CdTe is classified as insoluble in water due to an extremely low solubility product (9.5×10-35). Even if
modules become broken or damaged, CdTe would not mobilize from the glass and into the environment except
under very specific conditions. One condition would be if glass modules are crushed to fine pieces (< 1 cm) andthen subjected to agitation in an acidic environment. These conditions would not occur in the field during any
project operations5).
Experimental evaluation of CdTe mobility in pure compound form has been conducted with transformationand dissolution testing. The testing is designed to determine the rate and extent to which sparingly soluble metalcompounds can produce soluble available ionic species in aqueous media under a set of standard laboratoryconditions representative of those generally occurring in the environment. Specifically, the testing measured theconcentration of Cd resulting from a 1 mg/L loading of CdTe after 28 days in a standard aqueous medium at pH 6.
15 μg/L Cd resulted from 1 mg/L CdTe loading, corresponding to approximately 1.5% solubility6).
Note that the transformation and dissolution test results are for the pure CdTe compound, whereas in CdTe PV,
CdTe is bound under high temperature to a sheet of glass by vapor transport deposition, coated with an industrial
laminate material, and covered with a second sheet of glass. The module design results in the encapsulation of thesemiconductor material between two sheets of glass thereby preventing the exposure of CdTe to the environment
under normal conditions, and greatly reducing potential exposure under broken-module conditions.
In addition, First Solar’s PV Module Performance Detection and Handling Plan that have been used in thelarge-scale CdTe PV projects in the western U.S7) may be able to identify, handle, and remove broken PV modules
after the earthquake. Specifically, routine inspections and power output monitoring can diagnose broken modules
for prompt removal. These measures will further mitigate the environmental risks of CdTe PV systems.
4.2 Tsunami
Potential risks for PV modules impacted by a tsunami would be related to the scattering of the modules overthe impacted geographic area. For metals in general, environmental mobility is a function of pH, with decreased
mobility at higher pH. Because sea water is alkaline (Fig. 5) with pH in the global ocean surface waters ranging
from 7.9 to 8.28), metal solubility would be expected to be limited for modules dispersed in sea water. In addition,even when fully dissolved (at aquatic saturation), aquatic toxicity testing of CdTe showed no ecological healtheffects on the standard zebrafish test species6). To further quantify the potential impacts of tsunami on CdTe PVmodules, First Solar conducted leaching tests with seawater as a solvent9).

Fig. 5 Variations in pH in sea water
4.2.1
Seawater Leaching Test9)
The experimental method for the seawater leaching test made use of the DIN standard batch leaching test
modified with synthetic seawater as a solvent. The potential impacts are considered for module fragments in stillsea water conditions, such as a flooded inland area of low elevation. In such condition, there is no current so
module fragments would settle and not undergo continuous tumbling. To reflect this scenario, the seawaterleaching test was conducted without tumbling. (Table 1)
In accordance with a 10:1 liquid/solid ratio, 90 grams of 9 mm by 9 mm PV module samples were subjected to900 mL of seawater solution for 24 hours. After this period, the sample solution was filtered (45 µm filter) andacidified using HNO3 to bring the solution below 2 pH, followed by analysis of Cd with ICP-MS. Five samples
were tested with results ranging from 17-37 µg Cd/L per 24 hr. (Table 1)
Table 1 Analytical results of seawater leaching test for CdTe PV modules with DIN batch leaching test modified
with synthetic seawater as a solvent and with no tumbling for closed sea water scenario
LAB #Sub ID

AA63862
AA63863AA63864
AcidBlank

130925261888
130925261885
130925261886

Cd(ppb)1737
19<10Pb(ppb)<5<5<5<5specificgravity
1.02251.02251.02151.0215

Temp before (degC)
20.7
20.720.3
20.3

pHbefore
8.17
8.18
8.17
8.17

conductivity before
(uS)

46400

PostTemp
21
20.4
20.5
20.5

postpH
8
8.22
8.22
8.18

post conductivity
(uS)
42900
43600
42800
43600

With the measured Cd concentration in seawater leachate ranging from 17-37 µg Cd/L, the percentage ofdissolved Cd to the total CdTe was estimated as approximately 0.03%/day.
4.2.2 Interpretation of potential environmental risks caused by tsunami
In the case of tsunami, broken module pieces may be dispersed in seawater. To evaluate the potential
environmental risks caused by tsunami from the results of the leaching tests, a scenario of 1 MW of PV module
fragments in closed sea water was considered.

The potential impacts were estimated based on the following equation.
C = (T×E) / V
C: Incremental Cd concentration (µg/L/day)
T: Total CdTe content (µg)
E: Cd emissions fraction (%/day)
V: Volume of seawater (L)For parameter “T” based on 13% efficient PV modules, there is approximately 0.127 g CdTe per W (1.27×1011 µg
CdTe per MW). For parameter “E”, the measured Cd concentration in seawater leachate in Table 1 corresponds toa percentage of dissolved Cd to the total CdTe of approximately 0.03%/day. For parameter “V”, a 1 MW
installation requires approximately 2 hectares (20,000 m2). If this area is flooded with 2 m of seawater, the total
volume of seawater is 40,000 m3 (40,000,000 L). Based on these parameters and the equation, the averageincremental concentration of dissolved Cd in the total volume of closed seawater is approximately 0.95 µg/L/day.
However, it should be noted that these results can be considered to reflect the worst case scenario in which all of
the PV modules would be broken into small pieces, i.e. 9 mm by 9 mm pieces, by tsunami and submerged in aclosed seawater. Therefore, it is likely that the average incremental concentration of dissolved Cd in the closed
seawater is significantly lower than 0.95 µg/L/day.
In Japan, environmental quality standards for water pollutants - environmental quality standards for the humanhealth has been set as 3.0 µg/L for Cd. This standard is based on the annual mean and can be considered forchronic (long-term) exposure. The environmental quality standard for Cd to conserve aquatic life has been
discussed, but not established in Japan10). In addition, there is no distinction in the standards for acute (short-term)
exposure and chronic (long-term) exposure. In contrast, US EPA has established national recommended water
quality criteria for the protection of aquatic life and human health in surface water for approximately 150
pollutants including Cd, in which criteria have been distinguished for acute and chronic as well as freshwater andsaltwater11). Since leaching of Cd from broken PV modules by tsunami is an accidental release, it can beconsidered as an acute (short-term) exposure. Therefore, if we compare with U.S. EPA’s acute limit of 40µg/L, Cd
concentration in sea water which contain submerged PV module after tsunami will not exceed the aquatic
screening criteria for a certain (long) period.
Nonetheless, it should be recommended that the prompt recovery of submerged PV modules should beconducted to minimize the leaching of Cd.
4.3 Big fires caused by tsunamiBeckmann and Mennenga investigated12) the effects of CdTe modules on the neighborhood and the generalpublic in the case of fire. They estimated Cd concentrations in air on the surface around the burning CdTe PV
modules. In the worst case, the Cd concentration in air from a fire with the largest area (1,000 m2) with themaximum Cd contents (66.4 g/m2) and at the shortest calculable distance (100 m) from the emission site wascalculated. However, the result (0.66 mg/m3) was still substantially below the acute exposure guideline level,AEGL-2 (10 min.) of cadmium, 1.4 mg/m3, which is the peak concentration value for the threshold to irreversible
effects or other severe, long-lasting health effects13).
It should also be noted that they assumed in their calculations that all Cd contained in the module was released
completely from the CdTe compound as Cd fumes. Reaction with CdO or a possible diffusion of cadmium in themolten glass was not considered in determining the Cd emission concentrations. Fthenakis et al. investigated CdTe
modules, which were heated to temperatures ranging from 760° C to 1,100° C, typical for fires in residences andservice buildings, and showed that more than 99% of the Cd remained within the molten glass matrix14). In
addition, as mentioned in 4.2.2, First Solar’s 13% efficient PV modules contain significantly small Cd content,
approximately 7.7 g/m2. Therefore, it is quite likely that Cd concentration in air on the surface around the burning
CdTe PV modules will be quite small compared with the acute exposure guideline level.
There are uncertainties whether and where big fires will occur after tsunami, how long they last, and whether
CdTe PV modules will be subject to the big fires or submerge in sea water. So, PV modules may not necessarily
be subject to the big fires. Therefore, the environmental risks of CdTe PV systems by big fires caused by tsunami
can be considered very small.
4.4 Other previous works related to the environmental risks of CdTe PV systems
Central Research Institute of Electric Power Industry, Japan investigated the environmental risks of CdTe PVsystems in the fiscal year of 1998 with the financial support by NEDO, in which Cd emissions in cases of fire andleaching of Cd from broken modules were investigated15).
The combustion tests were conducted to measure the volatilization rate of Cd from various CdTe thin-film PV

modules at 750-1000 centigrade. The volatilization rates of Cd from the modules were measured as <0.25% at
800-1000 centigrade. These results were used to estimate the Cd concentration in a plume generated in a wooden
house on fire as well as those on surfaces around the house. It was concluded that the estimated concentration waslower than the legally regulated value in either case.
The batch leaching tests were conducted with broken CdTe PV modules in the acid rain atmosphere (pH = 4.8,40 centigrade) with continuous tumbling for 10 minutes to 72 hours. It was found that the Cd concentrations werebelow the minimum detectable quantity in all leaching tests. So, it was concluded that Cd leaching from broken
CdTe PV modules in an ordinary atmosphere would be negligible.
From the all results mentioned above, it was concluded that there would be no problem to use CdTe PV
systems from the view point of the environmental risks.
5. Conclusion
In this report, environmental risks of CdTe PV systems under catastrophic events in Japan were consideredwith a focus on earthquakes, tsunami and big fires caused by tsunami. There is a big uncertainty on how many
CdTe PV modules will be broken in earthquakes, and in a subsequent tsunami, how many will be subject to bigfires or be submerged in sea water. However, even in the worst case scenarios, it is unlikely that the Cd
concentrations in air and sea water will exceed the environmental regulation values. So, the environmental risks ofCdTe PV systems under catastrophic events can be considered small.
For commercial reasons, power systems are not likely to be constructed in tsunami hazard areas; nevertheless,the prompt recovery of broken and submerged PV modules should be conducted to minimize the leaching of Cd
after earthquakes and tsunami.

Reference1) http://www.shimz.co.jp/theme/earthquake/fire.html
2) Kitamura, Y. Consideration to the tsunami fire in Kesennuma city 20123) http://disapotal.gsi.go.jp/bousaimap/index.html?code=14) http://disapotal.gsi.go.jp/viewer/index.html?code=15) First Solar. 2013a. Memo from P. Sinha to K. Brutsaert. Environmental Risk Assessment of Potential
Catastrophic Events. July 2.
6) Kaczmar, S., Evaluating the Read-Across Approach on CdTe Toxicity for CdTe Photovoltaics, SETAC North
America 32nd Annual Meeting, Boston, MA, November 2011
7) First Solar. 2012. Appendix 10: PV module detection and handling plan”, Topaz solar farm project.
8) Takahashi, T., and S.C. Sutherland. 2013. Climatological Mean Distribution of pH and Carbonate Ion
Concentration in Global Ocean Surface Waters in the Unified pH Scale and Mean Rate of their Changes in
Selected Areas. OCE 10- 38891. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY9) First Solar. 2013b. Memo from P. Sinha to K. Brutsaert. Environmental Risk Assessment of Potential Tsunami
Impacts. Nov. 110) http://www.env.go.jp/council/toshin/t094-h1504/houkoku_2.pdf11) http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm
12) Beckmann, J., and Mennenga A., 2011. Calculation of emissions when there is a fire in a photovoltaic system
made of cadmium telluride modules. Bavarian Environmental Agency, Augsberg, Germany.
13) http://www.epa.gov/oppt/aegl/index.htm
14) Fthenakis, V. et al (2005): Emissions and Encapsulation of Cadmium in CdTe- PV Modules During Fires.
Progress in Photovoltaics: Research and Applications
15) Central Research Institute for the Electric Power Industry (CRIEPI). 1999. Fiscal 1998 Report on the Resultsof Work Entrusted to the Renewable Energy and Industrial Technology Development Organization.