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A module’s nominal power is interesting, as is its efficiency – and, depending on the customer’s expertise, so are a few other pieces of technical module data. But the single most important factor for PV system operators is yield: how many kilowatt-hours per kW of installed power flow from the PV system to the inverter? This is exactly the question PHOTON Lab intends to answer with its module field tests.



Since 2005, a total of
over 170 different module types has been installed on a piece of property – free of shadowing – were monitored constantly using an elaborate measurement system.

One to two units of each module type are represented in the test to prevent potential faulty products or modules with below average results from distorting the results for the entire series. The modules are installed in Germany, facing south at a 28° angle and are mounted about 2.5 m above the ground, which means they have complete rear ventilation. 

PHOTON Laboratory has developed its own electronics to perform fully automated measurements at each module’s output. This eliminates the possibility of errors due to false inverter adjustment or small cable cross-sections. The test set-up’s measurement tolerance is currently +/- 1.85 percent.

Every second, each module is measured to capture an IV curve with a nominal 14 bit resolution composed of 2,000 measurement points and the maximum power point (MPP). This measurement process takes about 10 milliseconds, which means almost 99 percent of the test module’s yield can be fed into the grid via a DC-DC converter, a DC bus and an inverter.

This is important as it allows the test system to operate under real-world conditions and prevents modules from overheating due to permanent open-circuit operation.In addition to data from the solar modules, the test field employs several highly accurate pyranometers to measure solar irradiation horizontally and at the module level every second, as well as other climate data such as ambient temperature, wind speed, precipitation and barometric pressure. Module and weather data is stored in synchronized databases to ensure precise correlation.




PHOTON Laboratory Yield Measurement test site near Aachen, Germany



Real power is the decisive factor


For obvious technical reasons, the solar modules in a certain series do not all have identical powers. That’s why nominal power is always listed with a certain tolerance range, which manufacturers determine using very different methodologies. For instance, a few manufacturers list a module’s nominal power at 100 W when the actual power of the module in question actually achieves this value. Other manufacturers, by contrast, list a 100 W nominal power for a series with a true power of between 95 and 105 W. Moreover, there are some manufacturers that list module power at 100 W when their products achieve 100 W at maximum but likely display lower nominal powers. The measured yields of the individual modules installed on the PHOTON test site are standardized according to the maximum power under standard test conditions (STC), which is determined by PHOTON Lab prior to the installation using a Pasan Sun Simulator IIIb.


Sign up now for the 2015 measurement! 


This is how it works


a. Participants in this test are primarily manufacturers and distributors of crystalline PV modules as well as PV system project planners. Joining the measurement is possible at any time of the year. Monthly results will be published after exact evaluation (January results published in March, February results in April and so forth.) After completing one full calendar year, the module type will be ranked according to its overall annual performance. By contract, the participation is guaranteed for at least for one full calendar year from January to December, although, as we are interested in gaining long-term performance data, we continue testing the modules for as long as anyhow possible.


b. To establish fair conditions, test modules are selected randomly. For this purpose, the ordering party must send a list of 50 consecutive serial numbers via email to lab@photon.info. We will randomly select four modules from this list, and the ordering party will provide these modules to us along with their STC flasher results and some other details like the time of manufacturing. PHOTON will begin by comparing the test results for these modules with the results in our database for identical module types previously tested by our lab. These other modules will have come to us from third parties who have submitted test inquiries. PHOTON also reserves the right to anonymously purchase one or two modules of the exact same module type somewhere on the market (for example from distributors or wholesalers) and compare these modules to the four sent to us by the ordering party. If considerable differences in module quality arise after going through all of the indoor tests listed in point d., we will diligently discuss this issue with the manufacturer. By signing the test agreement, the ordering party promises to supply PHOTON with modules from a standard series of production. Confirmed attempts of fraud will be exposed as such.

c. Upon arrival at PHOTON Lab, the test modules may not be older than three months (based on the production date). The participant shall provide the relevant production protocols by email to lab@photon.info.


d. As soon as the modules have arrived in the lab, the following tests will be conducted: power measurement at STC, detection of the weak-light performance and temperature coefficient, and thermographic and electroluminescence imaging. Neither the ordering party nor PHOTON Lab staff shall perform any pre-treatment on the modules (exception: cleaning of the glass surface prior to testing). The ordering party confirms this by signing the order form. Light-soaking is prohibited. The above-listed tests serve primarily to ensure that the delivered goods have not been damaged during transportation and correlate with the datasheet and labels. The ordering party shall provide the flash protocols from production for reference to lab@photon.info.


e. To guarantee a timely and orderly installation, the following items should be delivered to the lab together with the module shipment: (1) installation manual in English; (2) any required mounting components such as clamps, frames or carriers; (3) connectors incl. 2 m cable each; and (4) the product datasheet. In case the manufacturer does not provide any particular mounting components, PHOTON Lab may use its standard equipment.

f. Starting on the first day of the next possible month, the yield of up to two of the provided test items will be measured, subjected to identical conditions defined for all modules on the outdoor test field. (The other modules will be kept in our storage for future reference.) At the end of each month, the measured yield is standardized to the STC power of the test modules, which was measured by PHOTON Lab as part of the incoming inspection.


g. The monthly yield data, as well as weather and irradiation data collected on the test field, will quarterly be provided to the ordering party for its own technical evaluations.


h. Each month, the standardized test results will be published online on our website and in all PHOTON magazines. 


j. A participation logo useful for the module's marketing will be provided from the very day of joining the test. A certification of the annual performance ratio will be provided in form of a logo after February each year.




• Detection of each module‘s yield (second-by-second) using sophisticated measurement devices.
• Evaluation of the module‘s yield independent of other system components.
• Performance measurement under real outdoor conditions.
• Standardization of the monthly and annual yield to the STC power measured at PHOTON Lab.
• Collection of solar irradiation and weather data for in-depth analysis.





PHOTON Laboratory








Mr. Nicolaus Yuan