Electricity and Control March 2025

Measurement + instrumentation

Here Comtest, master distributor for Fluke for Southern Africa, shares Fluke’s guidelines for best practice in measuring and analysing PV circuit performance in solar photovoltaic panels and arrays. Best practice in measuring PV circuit performance

cirrus clouds are particularly problematic. One of the benefits of using I-V curve tracers for perfor mance test measurements is that the user can save critical environmental data along with the I-V data. This eliminates the risk of manual data entry errors that can cause trouble later and min imises the possibility of errors associated with rapid changes in test conditions.

Choosing a suitable sensor True pyranometers are not a good option for I-V curve testing, as they have a wide, flat spectral response that di†ers from that of crystalline and thin-film module technologies. Handheld irra diance sensors likewise are not a good choice, as it can be di†icult to orient them reliably and repeatedly in the plane of the array. Handheld irradiance sensors may also have an angular re sponse that di†ers substantially from fielded PV modules. Angular response is significant early and late in the day and on days when cloud cover scatters a significant amount of sunlight. Under these test conditions, the array and the sensor must have an equally wide sky view. Reflective light influence It is important to ensure that irradiance sensors are not influenced by strong optical reflections, as these can lead to inaccurate readings. If the irradiance sensor picks up significantly more reflected light than the PV modules under test, the model will overpredict Isc (short-circuit cur rent), and the module will appear to be underperforming. Under certain circumstances, sunlight reflected from metal surfaces can greatly exagger ate the irradiance reading. This can usually be remedied by changing the sensor mounting location. Temperature measurements in photovoltaic systems Although PV module performance is less sensitive to temperature varia

Environmental conditions, reflective light and other factors can influence the accuracy of irradiance measurement significantly.

F luke highlights that irrespective of the test method used, it is essential to know the plane of array irradiance and cell temperature to evaluate PV circuit performance. Attention should be given to environmental conditions to ensure that the I-V curves [1] can be interpreted accurately, as rapid changes in the irradiance or cell temperature can introduce errors in I-V curve tests. The use of appropriate sensor types and test methods, like the Fluke Solmetric PVA 15i-V curve tracer, will deliver reliable re sults. Environmental conditions for testing Optimal performance tests are conducted under stable weather conditions with irradiance above 700 W/m 2 . This is particularly important when establishing a performance baseline at commis sioning or recommissioning and is relevant for troubleshooting.

The standard test condition irradiance is 1 000 W/m 2 , and the closer the field test conditions are to standard test conditions, the more accurate the interpretation of I-V curves will be. Good test conditions will most likely occur during the four-hour win dow around solar noon. Irradiance measurement errors can a†ect photovoltaic performance testing signifi cantly. For instance, a small error margin in irradiance can overshadow the accura cy of even high-quality I-V curve tracers like the Fluke Solmetric PVA -1500. Fast-mov ing clouds near the sun and high-elevation Irradiance measurements and their Impact

For accurate array performance measurements, the irradiance sensor must be mounted in the plane of the array and the sensor’s spectral response should match that of the PV modules. The wireless unit shown here contains a spectrally corrected silicon photodiode irradiance sensor. It also measures backside temperature and module tilt.

MARCH 2025 Electricity + Control

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