HT instruments SOLAR I-V - Manual (Page 74)

I-V400 - SOLAR I-V
EN - 72
The reason why MPPTs are used is simple: a photovoltaic system without MPPTs may
operate anyway; however, with the same solar irradiation, it provides less energy.
There are inverters with 1, 2 or also 3 inbuilt MPPTs available on the market. Typically, the
inverters with more than one MPPT are used in systems where:
- the different photovoltaic systems it consists of “forcibly” have different inclinations
or directions. In this way, each single MPPT manages its own photovoltaic field,
maximizing its performance for the corresponding irradiation and temperature
characteristics (without being influenced by the other photovoltaic fields).
- a greater service continuity is sought. With more MPPTs it is possible to put one
single photovoltaic field out of service, while the others continue producing energy
towards the remaining MPPTs.
11.3. THEORETICAL ASPECTS OF THE I-V CURVE MEASUREMENT
The I-V curve test is performed as described below:
 The meter performs the I-V curve measurement of the PV module connected to it,
further to the real time measurement of irradiance and module temperature
 The results of measurements are automatically “translated” to the standard conditions
(STC) of irradiance at 1000 W/m
2
and module temperature at 25°C. The accuracy
indicated in this manual is granted under condition indicated in § 10.2.
 The meter performs a comparison between the maximum nominal power, with the
margin of percentage tolerance declared by the module’s manufacturer, which is
included in the kind of module selected on the meter from the database (§ 5.3.1), and
the measured value
 If the comparison of power is within the declared tolerance, the final response of the
meter will be “OK” or will be “NO OK” in the opposite case, and the module will not be
complying with the specifications declared by the manufacturer (§ 6.2.3)
11.3.1. Theoretical aspects of Rs measurement
The test about serial resistance Rs is used in order to perform an exact measurement in
real time of this parameter and then add this value to the definition of the PV module’s
specifications in the internal database of the meter, in compliance with the IEC/EN60891
standard.