PROFITEST PV

• Measurement of characteristic I-U curves at PV modules and strings up to 1000 V DC, 20 A DC and 20 kW
• The acquired characteristic I-U curve is highly accurate thanks to steady measurement at the capacitive load.
• Measurement of short-circuit current Isc, open circuit voltage Uoc, instantaneous peak power of a solar cell Pmax, series resistance Rs and internal parallel resistance Rp
• Automatic conversion of momentary measured values to STC
  
• Patented calculation process for evaluating PV generators without knowledge of the manufacturer’s specifications
• Patented calculation process for determining the generator’s internal series resistance based solely on a single characteristic IU curve
  
• Integrated customer database with bidirectional data exchange
• Integrated module database with bidirectional data exchange • High level of intrinsic safety thanks to included load disconnector (1000 V / 32 A DC)
  
• Power and temperature measurement via 4-wire cable for error-free results
• Separate measurement of temperatures at the irradiation sensor and the back of the module (Pt100) for increased measuring accuracy
• Continuous display of momentary irradiation and temperature provides information regarding measuring conditions
• Easy touch-screen operation
• Highly luminous, high resolution color TFT display with energy-saving LED illumination (suitable for use in sunlight!)
• External power pack with broad-range input for charging the batteries, and for continuous operation of the measuring instrument
  
• Software for graphic representation, evaluation and documentation with integrated database
• Operation via a PC with direct import of measurements is also possible (e.g. for long-term measurements).
• Open interfaces allow for operation of the instrument in special applications as well

The differences ...

Why is measurement with capacitive load necessary?

On the one hand, measurement of characteristic curves for PV generators (modules, strings, arrays) must not be conducted too quickly (high dV/dt), because the measured characteristic curve may be changed in the case of rapid measurement (< 20 ms) due to the capacitive/inductive attributes of the generator or the test setup, in which case not only the characteristics of the PV generator are reflected in the measurement results. On the other hand, measurement must not be too slow either (> 1 sec.), because the danger of fluctuating radiant exposure is otherwise significantly increased, which would influence measurement results. This affects module temperature as well, which reacts relatively sluggishly but nevertheless can change within a matter of seconds.

Patented calculation process for determining the generator’s internal series resistance based solely on a single characteristic IU curve

This resistance is the physical result of the material used to manufacture the module, as well as its layout and wiring connections, and normally has a constant value. For example, it amounts to roughly 1 Ω for crystalline modules and more than 2 Ω for thin-film modules. As of recently, measurement of internal series resistance can be performed with instruments from the Profitest PV product range. Only a single characteristic I-U curve has to be traced at the module for this purpose. On the basis of this characteristic curve, the instrument automatically calculates RS, as well as peak power PPK and parallel resistance RP.

Theoretically anticipated internal series resistance RS can be calculated. For example, this is possible with the software if the following characteristic STC values are known for the module: Uoc, Isc, UMpp and IMpp.

The calculated RS value can then be compared with the measured value, which is read out by a Profitest PV after curve tracing. If the measured value is too high, wiring must be inspected for interruptions, corrosion, connection errors and underdimensioning.