Dr. Günther Ebert & Dr. Christian Reise, Fraunhofer ISE 

The integrated project PERFORMANCE has been initiated in January 2006 with the aim to close the existing knowledge gaps on specific problems such as power characterization, energy yield prediction, modules service lifetimes, power degradation and better understating of new technologies properties (especially Thin Films). Moreover, the project consortium has worked to assure that scientific results are transferred and implemented prompt and easily by the industry. For these purposes, a consortium of 19 research institutes and 8 industry partners have been working at 6 specific areas in the development of norm and standards which will have an immediate positive impact in the competitiveness of the European PV industry.   

Dr. Heinz Ossenbrink, European Commission, DG Joint Research Centre -Institute for Energy (Presented by Ewan Dunlop)

This presentation dealt with the future of PV within the European Renewables Directive (RES), which sets a target of 20% renewable energy by 2020. Moreover, it is defined how much each of the member states shall contribute as well as the trajectory to reach this target, taking into account their potential. Next, the National Action Plans have to be ready by June 2010. Taking into account the different sector (transport, heating and cooling, electricity), in total, 1850 TWh of renewables need to be implemented by 2020. The JRC claims that 10% of this amount can be delivered by PV (180 TWh); this calls for a growth rate of 30-35% each year.

In order to be able to reach the targets set in the RES Directive, some challenging issues still need to be tackled, such as how to drive down the costs in order to reach grid parity, how to provide a smoother grid access, how to wave market caps and administrative barriers and most important, to assure a sustainable policy support. It is in this context that IP Performance was planned to tackle some of the above issues in order to ease the realization of the RES Directive, especially those increasing the competitiveness of PV systems. 

Dr. Werner Herrmann, TÜV Rheinland Group

With respect to power measurement at STC, recommendations were given with respect to solar simulators (class AAA solar simulators to limit the non-uniformity of the irradiance, the spectral mismatch and the temporal instability), reference devices (filtered c-Si reference devices for thin film application) and IV data acquisition parameters (segmental measurement with the multi-flash technique). Moreover, for thin films in particular, issues such as the change of electrical performance due to temperature or light/dark exposure and mismatch between the junctions of multi-junction TF technologies were identified.
Moreover, the comparability of measurement results between test labs has been investigated. For the 4 c-Si modules that were tested, less than 2% deviation in results is achievable.  With respect to thin film technologies, between 3 and 6% deviation was observed, the difference depending on the specific technology. This is due to the variation in the use of reference cells, pre-conditioning procedures and the lack of correction procedures for multi-junction TF modules.

Furthermore, recommendations for reference modules were given concerning the electrical stability, the range of modules to be covered, spectral mismatch issues, module temperature measurement, connection technique to the IV load, recalibration intervals for master references, properties of transportation and the storage environment, the frequency to use the reference module and the procedure for adjusting the solar simulator. Regarding the latter, two ways of adjustment were identified using Isc (independent from module temperature) or Pmax (compensates for non-uniformity effects) as the reference point for (re)calibration.

Recommendations for power measurements in the PV industry will be available in deliverable D1.4.4: Guidelines for PV Measurements in Industry. Further areas of research will be the development of suitable measurement and calibration procedures for TF (especially multi-junction devices and upcoming PV technologies).

Alessandro Virtuani, SUPSI–ISAAC

For power rating measurements, 2 types of measurements are possible: a slow speed one (with real sunlight or steady-state solar simulators) and a high speed measurement (with pulsed solar simulators/flashers). It has been discovered that so-called sweep-speed effects (or sweep-time effects) together with the sweep direction might influence the shape of the IV curve. A high capacitance (in particular the diffusion capacitance) of a solar cell might cause distortions in IV curve measurements (even up to 10-30% over or underestimation depending on the sweep direction) if high speed measurements are performed.

Because higher capacitances are present in high efficiency c-Si solar cells these devices are especially vulnerable for sweep-time effects. Hence, it is recommended to measure the IV curve outdoor or indoor with a long-pulse solar simulator (>100ms). Other technologies (a-Si and junctions as well as back contact cells) have lower capacitance and therefore slower-pulse solar simulators can be used. Conventional c-Si, CIS, CdTe are very low capacitive and therefore do not suffer from sweep-time effects.

Possible measurement approaches that are able to correct for the sweep-speed effect are outdoor or steady-state IV measurement or the use of multi-flash IV measurements (including point-by-point, sectional and voltage-modulated). In order to choose which method is the most appropriate the accuracy of the measurement should be assessed taking into account the cost of the equipment, the necessary time to perform the measurement and other necessary features that need to be taken into account.

In the round-robin tests performed at 6 different testing labs in Europe, it was possible to keep the spread of the fill factor within the range of ±1%.  Recommendations were made for input in a recast version of IEC 60904-1 and a test for capacitive behavior has been created at SUPSI. Further research is necessary in order to keep up with the current trends towards high efficiency c-Si solar cells.

Hans-Dieter Mohring, ZSW

In order to understand the energy yield of a specific module, it is necessary to translate the outdoor conditions into STC.  With respect to the temperature and irradiance this is feasible; though outdoor spectral conditions are much more difficult to convert into the AM1.5 spectral condition under STC. Hence, Standard Irradiance and Temperature Conditions (SIT) have been developed. Spectral mismatch can then be eliminated by spectrally matching the reference device to the module under test. Specific requirements are defined for measuring the energy yield of a module at a specific site, such as the use of a MPP tracker and self referencing.

The parameters affecting module energy yield have been defined as being the in-plane broadband irradiance, module temperature, ambient air temperature, spectral irradiance distribution, device age, irradiance and temperature exposure history, wind speed and angular irradiance distribution.

Best practices for the outdoor testing community for the characterization of the energy yield have been established taking into account the site dependency of the energy yield. Differences between technologies seem to depend on the temperature coefficient and low light level performance. Finally, long term stability of thin film is proven.

Gabi Friesen, ISAAC

This presentation dealt with the validation of PV module energy production methods. Different models will have been tested in three blind round-robin tests with data from 11 climatic zones and 5 different technologies within the scope of the project.

In the first round, the reference model has been tested for, taking into account irradiance and temperature performance. An error in prediction of maximum ±3% resulted from this; moreover this is technology and climate independent and no ranking of the models could be defined.  In a second round, module temperature has been modeled. Modeling wind effects is difficult and only leads to limited improvements in the predictions and is thus not considered. Modeling reflection losses and angle of incidence dependencies only improves the predictions for clear sky days. The measurement accuracy of diffuse and global irradiance and the translation from horizontal to in-plane irradiance seem to increase the prediction error (this seems to be the most difficult to model).

Spectral corrections will be further investigated within the third round-robin.
In conclusion, it can be said that the modeling is independent of the technology and that all the secondary effects modeled in the second round-robin did not improve the energy prediction. All models can be considered overall comparable. The main error sources are measurement errors in the in-plane irradiance and the determination of module performance.  Therefore, a simple calculation method for the energy prediction is proposed and further areas of improvement are increasing the reliability of the input parameters.

Ralph Gottschalg , CREST

This presentation focused on the IEC 61853 standard on energy rating, which has been validated within the project. The idea is that the energy rating standard should be similar to the power rating standard (IEC 60904-9); it should be done for a standardized environment. 

The development of this standard is currently still under development. It has been split into 4 parts. A first one deals with the basic irradiance and temperature measurements, whereas the second part includes spectral response, angle of incidence and module temperature. Interpolation methods should be considered with great care (especially for low irradiances). These two parts are close to becoming reality. In the third section the project outcomes have suggested to limit the complexity of the models for the calculation of the energy rating as the accuracy is considered to be more reliant on the quality of the model parameters rather than on the methodology itself. The last part deals with the definition of standard datasets; the use of standardized climatic zones rather than standard days has been proposed by the project.

Finally, it can be concluded that degradation of the modules is an important factor in determining the energy yield over time and should be carefully taken into account. Although degradation seems to be relatively technology independent, over a total lifetime of 20 years, its accumulated effect might introduce an uncertainty in the calculation of the energy rating of about 32%.

Michael Köhl, Fraunhofer Institute for Solar Energy Systems

In this presentation, the achievements of subproject 5 on the lifetime assessment of PV materials and modules were outlined. These include procedures for indoor service life testing of materials, such as accelerated lifetime tests combining UV rays, humidity and heat exposure. For outdoor lifetime testing, test benches for long-term exposure have been put up in Cadarache (France) and Freiburg (Germany). Furthermore, a non-destructive tool (confocal Raman spectroscope) has been introduced to investigate the polymer components in the encapsulation of the modules. Finally, models have been set up for service life testing of thin film modules and encapsulation materials. The outcomes serve as important inputs for further LCA and environmental impact assessments.

Due to the parallel schedule with subprojects 1 and 2, time was lost for evaluating the indoor and outdoor data that was required as inputs from these subprojects. Hence some results from accelerated indoor and long-term outdoor testing still need to be further validated and compared.

Dr. J.Merten, CEA/INES

The Variable Illumination Measurements (VIM), which is a method for the in situ monitoring of the outdoor degradation of PV modules, was explained in this presentation. With VIM, it can be investigated which parameters degrade and which don’t based on the standard equivalent circuit (enhanced with a second diode if needed and a recombination losses term for a-Si).

It seems that for thin film modules, a slight decrease in performance can be observed. Based on VIM and taking c-Si as the reference, for thin film modules the following possible sources of degradation could be defined, depending on the technology: parasitic currents, the resistances (both parallel and series). The junction diode and the photogeneration remained stable throughout the VIM analysis. However, for multijunction devices, the model is too simplified and needs to be further developed.
 

Tony Sample, European Commission, JRC, Institute for Energy, Ispra

In this presentation, the reasoning behind damp-heat testing was presented together with the results of three different damp heat tests for 7 thin film modules (of which 6 are commercially available).

For the standard damp heat test (85°C at 85 % relative humidity), the modules remain stable during the first 1000 hours, after which degradation occurs for some modules. The degradation seems to be related to the breakdown of the encapsulation system.  For the damp heat test (85/85) with applied voltage (1000V), all glass containing modules showed a rapid degradation within a relatively short time (100 hours) which can be explained by the presence or movement of Na-ions. With respect to damp heat testing with UV exposure, the greatest degradation seems to be due to delamination, though the test still needs to be continued.

It seems that the additional stress applied by UV exposure or voltage can be used to shorten the testing time required. It can be concluded that significant loss of power is due to a breakdown of the encapsulation system. It is however not yet possible to equate the loss of power to a specific number of years of outdoor exposure.

Kenneth Möller, SP

He talked about the qualification of new polymeric components as encapsulation materials and backsheet films. With respect to chemical ageing, tensile testing to determine the elongation at break and spectroscopy to investigate the transmittance of the material has been performed. Dynamic mechanical analysis in order to evaluate the elastic modulus is a way to assess the physical ageing of the material. Other relevant properties are the retention of UV absorber and the emission of corrosive degradation products (oxidation and hydrolysis products).

Standard damp-heat-testing (85°C at 85% relative humidity) seemed to be sufficient for qualification of most of the materials. If the properties remain within certain limits, the material is qualified for PV module encapsulation. Otherwise, a second damp heat test (65°C at 85%RH) is needed in order to predict the lifetime.

Frank Lenzmann

This presentation dealt with the Life Cycle Assessment (LCA) of PV modules, using Simapro software and the Ecoinvent database. The LCA studies resulted in a comparison of the environmental profile of various cell technologies (crystalline silicon, thin-film silicon, CdTe).  The determining elements for the environmental profile were highlighted, showing a particular significance of the electricity input during the production phase and the electricity output over the entire lifetime during the use phase.

First, the energy input is assessed. The largest contributor to the energy input of PV systems is the PV module (not the balance of system components). Energy input differs significantly between cell technologies. Secondly, the energy output is considered during the entire lifetime of the module (including degradation effects). Energy output is not clearly related to cell technology, but rather to module technology. Hence, the energy yield ratio (output/input) can be used to assess the environmental impact. Moreover, the energy backpack time (EPBT) can be calculated; it is in between half a year and 1 and a half years. It seems that CdTe scores well from the energy perspective. Finally, also greenhouse gas emissions are calculated; it is shown that PV (CdTe) performs well compared to other technologies like coal capture and storage (CCS).   

Nicola Pearsall, Northumbria University

This presentation talked about how the European guidelines for optimal system monitoring have been updated. Therefore, the complexity of the monitoring system needed to be balanced by the costs of a more accurate monitoring system. The system size is considered as an important differentiating parameter between the monitoring schemes. A failure mode effects analysis (based on 2 industry consultations) has been used in order to consider which faults are the most important, how often they occur, how serious they are and how to identify them.

A user questionnaire needs to be filled in, which will deliver the guidelines for the proposed system based on a ‘generic’ pre-defined coding between the answers in the questionnaire and the final guidelines. They will be available on the web for free (as an Excel tool). The guidelines are easy to update, voluntary (unless they are acknowledged by an official body). Therefore, the work of subproject 3 has been provided to IEC as input for the revision of IEC 61724 on system performance monitoring.
 

Berrie van Kampen, TNO

First of all, some figures were presented. In Europe, 60% the total available roof area should be sufficient for about 60% of the total electricity use. Currently, 90% of PV is connected to buildings, although only 1% is really integrated in the building envelope (especially in France and Italy thanks to attractive feed-in-tariffs for BIPV).

However, in order for BIPV products to be accepted (and to receive CE-marking), they should not only comply with the electro-technical standards for PV products, but also with the building standards. Hence, in subproject 6 special test methods were developed to check the mechanical and the fire resistance of BIPV products (other requirements were dealt with in other projects). Finally, also for new types of products, like flexible PV, stress tests and fire resistance tests have been developed.

Dr. Ewan D. Dunlop, European Commission JRC

First of all, the necessity of worldwide standards is highlighted as a means to abolish existing trade barriers in national legislations and standards. The work in IP Performance serves therefore as input for the creation or recast of IEC standards.

The project has supported the competitiveness of the European PV industry by acknowledging the needs of the industry. As such, outdoor measurements to determine the energy yield over the entire lifetime were of vital importance, especially from an end-user and investor point of view as they better reflect their needs.

Concrete examples of standards that were created or adapted during the project or still to be proposed during the final phase or after the project is finished are for example the new standard IEC 60904-4 on the traceability of the calibration of reference devices, the new draft standard IEC 81853 on energy rating, IEC 61724 on PV system monitoring and a new draft proposal for a European norm (CEN) for test requirements for BIPV products.