Optimizing PV Systems July 2014 - Part 1: Inverters | Page 11

Fronius Case Study:
MMP trackers
The benefits of using two MMP trackers for partial
shading: a working example at SALUS GmbH
The issue of static partial shading can be inescapable
without restricting the size of the array. The challenge of
shading presents itself particularly on commercial buildings
with obstructions such as air conditioning units and
irregularly shaped roofs, causing output losses of up to as
much as 25%. Output is reduced if shading occurs on any
part of an array, even if all other modules remain in direct
sunlight. How much the output is reduced depends on how
the array is configured. This is because modules are
connected in series and shading on one or more of them will
cause variances in the MPP voltage from the modules.
Normally the inverter cannot find the optimal MPP point as it
is stuck on the global MPP, but instead the new local MPP
would generate more power.

When one of Germany’s leading manufacturers of natural
medicines, SALUS GmbH, took the decision in May to add a
further 300kW to their existing system, installers at
Elektrotechnik Pichleer were presented with the challenge of
shading. The 96m2 east/west roof-mounted system, which is
located on the hydroelectric plant, has a large number of
chimneys on the roof, so multistring inverters were required.
The installation uses 42 string inverters including 40 Fronius
IG Plus inverters plus 2 new Fronius Symos to tackle the
shading issues. The Fronius Symo inverters total 14.8 kW of
the installation and were selected for their flexibility due to
the high system voltage (1,000 V), wide input voltage range
(150 V to 800 V) and twin MPP trackers.
Separating an array into two segments, each on their own
MPPT, as has been done at SALUS GmbH, increases
system harvesting. This is because shaded modules no
longer have to be connected in the same string as those

that are fully exposed - which keeps MPP performance in
the non-shaded array high - therefore maximising output.
This eliminates the need for an additional inverter (with
associated labour time and costs) to do effectively the same
job. What further enhances the benefits of the two MPP
trackers in the Fronius Symo is the very broad voltage range
of their input, allowing connection of highly asymmetric
configurations. This enables the system designer to solve
most shading issues. In some cases even a 1:9 ratio
between MPPT1 and MPPT2 is possible.

To generate maximum yield, MPPT performance is of
critical importance. The Fronius Symo offers a new MPP
tracking algorithm which dynamically adapts its behaviour
when searching for the optimal operating point. This
Dynamic Peak Manager allows the inverter to deliver the
maximum output in all circumstances. What’s particularly
impressive about this is that it automatically checks the
entire characteristic at regular intervals to ensure it can
always find the maximum operating point, even when
partially shaded therefore no longer are there hidden Local
MPP points. The two MPP trackers in the Fronius Symo
work completely independently of each other, which
guarantees maximum power and yields, even under difficult
conditions such as (partial) shade, foggy weather, module
failure and so on.
The east/west system at SALUS that took just 2 days to
install is set to produce 12,070kWh per year, of which 800 –
900kW will be used for manufacturing natural medicines.
Bernard Pichler, installer of the 100% self-consumption
system, found a solution for the shaded areas of the roof
that would not only maximize yield, but save time and
money and therefore increase profitability of the installation.

Fronius UK Ltd | Maidstone Road | Kingston, Milton Keynes | MK10 0BD, United Kingdom
Tel: [phone] | Fax: [phone] | http://www.fronius.co.uk