FAQ
Frequently Asked Questions
We have collected the questions from our users.
Find the answers to our users most frequent questions,
I would like to learn more about the background of I-V curve measurement.
Are there any publications on this topic?
There isn't a lot of information available on this subject. We would highly recommend the book Photovoltaik Engineering – Handbuch für Planung, Entwicklung und Anwendung by Prof. Andreas Wagner. Another highly informative book is „Simulation der Abschattungsverluste bei solarelektrischen Systemen“ by Prof. Dr. Volker Quaschning, You can find more details about this book here.
The measuring cables of PVPM devices always consist of multiple conductors. Why is this the case?
The PVPM devices measure the voltage and current at the solar generator. When this current flows through the measuring cable (which has resistance), a portion of the voltage will drop across the cable. As a result, the measurement device would always show a lower voltage. To avoid this, a so-called four-wire cable is used: one pair of wires allows the current to flow, while the second pair is used to measure the voltage — here, practically no current flows, and the voltage remains constant. This ensures that the measurement is as precise as we require.
The PVPM devices are very large. Can’t you make them smaller?
There are compelling reasons why we cannot reduce their size: our critical factor is measurement speed. There is a direct relationship between the device size and measurement speed when using capacitive load: the smaller the device, the faster the measurement process. However, the faster the measurement, the more inaccurate the I-V curve measurement becomes, as more disturbances from capacitive and inductive elements of the PV generator and wiring interfere with the actual measurement result. We prioritize the quality and precision of the measurement over the size of the device. For this reason, we build the PVPM measuring devices in their known size.
The PVPM devices have a reference sensor with a connection cable.
Wouldn’t wireless data transmission be more practical?
While wireless connection for the reference sensor is undoubtedly a more user-friendly solution, it does have a drawback: the transmission of measurement data via radio requires some time due to the necessary protocol. We know that the irradiation can change significantly within milliseconds. To ensure the accuracy of the I-V curve measurement, we need to capture the irradiation at the exact moment of the curve measurement. For this time-critical measurement, a cable connection is required.
Can I connect other reference sensors to the PVPM devices?
You can connect any irradiance sensor to the PVPM that provides a voltage dependent on the irradiance: 0 mV at 0 W/m² and between 10 and 100 mV at 1000 W/m². The connector on the PVPM is a standard component. You can request the exact specifications and pin assignment from us. This feature is especially important when measuring modules that are not made of monocrystalline or polycrystalline cells. According to EN 60904, the reference sensor must have the same spectral properties as the module being measured—meaning you need a suitable sensor. Compatible reference sensors are available for common photovoltaic technologies and can be connected to the PVPM.
Are additional devices required for measurements with the PVPM?
No, the PVPM devices are fully independent of other devices. In addition to the measuring device (which has its own battery), you only need the reference sensor, connection cables, and the safety disconnect switch. Since the power supply, computer, and graphic display are all integrated into the device, the on-site work is straightforward and simple.
What is the significance of the Rs (series resistance) value?
The series resistance RsRs is a key indicator of the quality of a PV generator’s wiring. Issues such as connector corrosion, cable damage, or undersized wiring can cause RsRs to be higher than expected for a given module. Since manufacturers typically do not specify the RsRs value of a module, you can calculate it using the PVPM.disp software, which is included with the PVPM. If the measured RsRs is higher than the calculated value, the wiring should be inspected for potential faults.
