Economic system design with
Fronius Symo Hybrid
White Paper
© Fronius International GmbH
Version 1, 10/2016
Fronius reserves all rights, in particular rights of reproduction, distribution and translation.
No part of this work may be reproduced in any way without the written consent of Fronius. It must not be saved, edited,
reproduced or distributed using any electrical or electronic system.
You are hereby reminded that the information published in this document, despite exercising the greatest of care in its
preparation, is subject to change and that neither the author nor Fronius can accept any legal liability
Gender-specific wording refers equally to female and male form.
1/4
INTRODUCTION AND EXECUTIVE SUMMARY
Nowadays the amortization of a newly installed PV system depends on the initial investment as well as
the self-consumption ratio. The feed-in limitations as well as non-existing feed-in tariffs resulted the
max. efficiency rate becoming less important.
This paper addresses the question whether the max. DC current from the PV generator (I
higher than the max. input current of the inverter (I
) and what kind of effect can be expected.
dc,max
) can be much
pv,sc
Even if the max. DC current is much higher than the max. input current of the inverter according to the
data sheets, the yield losses are insignificant. The explanation for this is simple:
Due to the relatively low radiation in Central Europe plus the rare occurrence of radiation higher
than 900 W/m² directly on the module surface, the max. input current of the inverter is not
exceeded. Even on a PV system with oversized array this happens on very rare occasions only.
However, if the DC current is exceeding the max. input current of the inverter, the inverter will
react by shifting the operating point (MPP). In fact the DC current will be restricted to the max.
input current of the inverter and at the same time the voltage of the new operating point will
increase. This behaviour compensates most of the initially assumed losses of current limitation.
CURRENT OVERSIZING OF THE INVERTER
RESPECTIVELY THE MPP-TRACKER
The DC inputs of inverter/MPP-trackers (MPPT) are characterized resp. limited by various different parameters.
It is not uncommon that the max. MPP-current of the PV generator exceeds the max. input current of the inverter
resp. the MPP-tracker when multiple strings are connected in parallel. In that case, we talk about current
oversizing. (I
The Fronius SnapINverter series (Fronius Galvo / Symo / Symo Hybrid / Primo / Eco) shows an extremely high
resilience regarding current and power oversizing. The current oversizing can be at least 50%, some types can
handle even more (see data sheets “max. short-circuit current module” = I
of the PV-generator (I
the inverter.
Current oversizing does not necessarily lead to dramatic yield losses. This kind of system design actually makes
economically sense because its losses are negligible.
of PV-generator > I
mpp,stc
sc,stc
of inverter/MPPTs).
cd,max
) can be 50% over the I
). So the max. short-circuit current
pv,max
of the inverter without voiding the warranty or damaging
dc,max
Example: Fronius Symo Hybrid 5.0-3-S (I
The PV current with 19A is therefore 18,75% higher than the max. input current of the inverter (I
= 16A) with 2 module strings with an I
dc,max
= 9,5A each
mpp,stc
dc,max
= 16A).
But this design reduces the annual yield by less than 0,75%.
The same calculation for a module with I
= 8,8A (2 strings are 17,6A) reduces the annual yield by only
mpp,stc
0,25%.
2/4
Loading...