62
A. Shah
Fig. 3.20 Effect of operating temperature T on the normalized value of the output power P max ,
at MPP, of typical solar modules, for various cell technologies, based on [23] for CIGS, CdTe and
a-Si; and on datasheets for c-Si modules
The case of c-Si (wafer-based crystalline silicon) merits, for two reasons, particular attention: (1) these cells account for more than 90% of all cells produced
worldwide; (2) they have a large span of practical values of TC; in datasheets of c-Si
cells, we find values running from −0.29 up to −0.38%/°C.
When one looks at the whole picture, which results from studying datasheets
and published experimental data, one finds that there is a remarkable relationship
between the value of V oc and the magnitude of TC.
As V oc approaches its “theoretical” limit value of approximately 800 mV (see
Fig. 3.17, line 2, green), the magnitude of TC becomes smaller; thereby, TC tends
to approach its “theoretical” limit value of ≈ −0.18%/°C.
12
Conversely, cells with low values of V oc , have high magnitudes of TC, i.e. a strong
temperature dependence.
This relationship would fully explain why crystalline silicon heterojunction
modules have a remarkably low magnitude of TC.
Tijmen Slikker of Eternalsun Spire has recently done a series of measurements
on different c-Si modules and their temperature behaviour—his results are presented
here as Fig. 3.21a, b.
3. Concluding remarks
• The relative temperature coefficient TC is a parameter, which is given in the
Datasheet of the Module. It varies strongly:
– Between modules using different absorber materials, i.e. the magnitude of
TC is much larger for c-Si modules than for CdTe modules.
12 We are referring here not to the thermodynamical limit values according to Shockley and Queisser
[18], but to the semi-empirical limit values according to Green [12].
A. Shah
Fig. 3.20 Effect of operating temperature T on the normalized value of the output power P max ,
at MPP, of typical solar modules, for various cell technologies, based on [23] for CIGS, CdTe and
a-Si; and on datasheets for c-Si modules
The case of c-Si (wafer-based crystalline silicon) merits, for two reasons, particular attention: (1) these cells account for more than 90% of all cells produced
worldwide; (2) they have a large span of practical values of TC; in datasheets of c-Si
cells, we find values running from −0.29 up to −0.38%/°C.
When one looks at the whole picture, which results from studying datasheets
and published experimental data, one finds that there is a remarkable relationship
between the value of V oc and the magnitude of TC.
As V oc approaches its “theoretical” limit value of approximately 800 mV (see
Fig. 3.17, line 2, green), the magnitude of TC becomes smaller; thereby, TC tends
to approach its “theoretical” limit value of ≈ −0.18%/°C.
12
Conversely, cells with low values of V oc , have high magnitudes of TC, i.e. a strong
temperature dependence.
This relationship would fully explain why crystalline silicon heterojunction
modules have a remarkably low magnitude of TC.
Tijmen Slikker of Eternalsun Spire has recently done a series of measurements
on different c-Si modules and their temperature behaviour—his results are presented
here as Fig. 3.21a, b.
3. Concluding remarks
• The relative temperature coefficient TC is a parameter, which is given in the
Datasheet of the Module. It varies strongly:
– Between modules using different absorber materials, i.e. the magnitude of
TC is much larger for c-Si modules than for CdTe modules.
12 We are referring here not to the thermodynamical limit values according to Shockley and Queisser
[18], but to the semi-empirical limit values according to Green [12].