PHOTON Info

SOLAR MODULE YIELD MEASUREMENT “GERMANY”

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 Lab 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. Since April 2012, PHOTON Lab has also been collecting the spectral data in the field.

For 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.

a. Participants in this test are primarily manufacturers and distributors of crystalline PV modules as well as PV system project planners. To join the measurement starting on January 1, 2013, the signed order form and test modules have to be provided by November 30, 2012 to PHOTON Lab.

b. The test modules will be selected randomly. For this purpose, the ordering party must send a list of 100 consecutive serial numbers via email to vivian.zhao@photon.info, who will randomly select four modules from this list.

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 vivian.zhao@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 vivian.zhao@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.

The installation of one to two modules in the field shall be completed by December 31, 2012.

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. 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, spectral and irradiation data collected on the test field, will quarterly be provided to the ordering party for its own technical evaluations at www.photon.info -> myPHOTON.

h. Each month, the standardized test results will be published in the following PHOTON magazines:

• Detection of each module‘s yield (second-by-second) using sophisticated measurement devices.

• Performance measurement under real outdoor conditions for a period of 12 months.

• Standardization of the monthly and annual yield to the STC power measured at PHOTON Lab.

• Collection of solar irradiation, weather and spectral data for in-depth analysis.