Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

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application of part 1 of the IEC61853 standard results instead to be a clear step forward to an energy
rating of PV modules. Most differences seem in fact to be explained by irradiance and temperature
dependencies. This is why a more extensive testing of these measurements has been implemented
within the measurement round robins performed within SP1 (see chapter 1.2.1) to further increase the
energy rating accuracy. It is not clear whether an improvement of the measurement accuracy of the in
part 2 included characterisation methods will be able to further improve the annual energy prediction
accuracy. A big hurdle remains also the modelling of un-stable and diffuse weather conditions. A
deeper validation is very difficult if not all parameters are monitored, as for example the in-plane diffuse
irradiance, the irradiance and module temperature stability as well as the on-site present albedo
conditions.
3.2.2 Second Round Robin on PV module Energy Prediction (WP4.4)
Compared to the study in chapter 3.2.1, within this study only short or long term monitoring data from
different European sites were available as input to predict the energy output, and no strict procedure
as described within IEC61853 was followed. Each round robin participant was free to use its own more
or less semi-empirical models and procedures. 7 European institutes participated at this modelling
campaign.
The described second modelling round robin (RR2), is an extension of the first one (RR1), where only
in-plane irradiance, as measured by a broad band pyranometer, and the measured back of module
temperature were available as input parameter. More details about RR1 can be found in the last
ISAAC activity report 2007. The main objective of this second round robin is: (1) to validate the modelling
of secondary effects, (2) to verify if these additional modelling steps really improves the modelling
or if they might even worsen the modelling quality and (3) to compare the more semi-empirical
procedures of this study to the more sophisticated ones of the IEC61853 approach. The 7 participating
institutes had to predict the annual energy output of four different modules (2 c-Si, 1 CdTe and 1 a-
Si). The RR followed again a systematic approach to separate, as far as possible, the validation of the
following modelling steps: hor - translation from horizontal to in-plane irradiance, tm - modelling of
module temperature, rm - reflection loss models and sm - spectral models. All results were compared
to the basic RR1 approach, with the objective to quantify the change in accuracy due to an increase in
complexity of the models. The last step was to execute all steps in once (ALL). Theoretically it is expected
that the implementation of spectral and reflection loss models improves the modeling, whereas
the translation of horizontal to in-plane irradiance as well as module temperature modeling decreases
the accuracy. This depends of course also on the availability and accuracy of the applied input parameters
as well as on the accuracy of the models itself.
Avg�Error
8%
6%
4%
2%
0%
�2%
�4%
c�Si�1 c�Si�2 CdTe
RR1 rm tm hor ALL
Figure 3: Average annual energy prediction accuracy of up to 7 institutes together with the standard
deviation. The results are seperated by module type and modelling step. Note: Not all
institutes executed all steps.
PERFORMANCE, G. Friesen, SUPSI, ISAAC-TISO
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