USE OF STRING INVERTERS
IN UTILITY-SCALE PV SYSTEMS
REFUsol GMBH 02/2013
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REFUsol TECHNOLOGY
STRING INVERTERS
IN UTILITY-SCALE SYSTEMS
Examination
Depending on the
application, it is
also worthwhile to
use string inverters
in many utility-scale
PV systems.
In large-scale PV projects worldwide, central inverters are
mainly used. Switching cabinets are usually combined in large
concrete stations and installed as central units in the PV park.
A detailed examination of this practice is worthwhile, however,
as it also makes sense in many cases to plan specific large
projects with string inverters.
As well as very high transport and installation outlay,
switching cabinets in these concrete stations also require costly
cooling and on-site servicing, and put a large section of the
whole PV system out of action if they break down.
Instead of a central inverter, it can definitely be advantageous to install smaller inverter units in the PV park on a
decentralized basis. This significantly reduces transport and
installation outlay, eliminates the need for costly cooling systems, and the maintenance-free string inverters can be quickly
and easily replaced if they fail. This also considerably reduces
the risk of a breakdown, as string inverters can be easily repaired while a replacement inverter ensures that yields are
maintained.
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Reasons for string inverters in
utility-scales PV projects
QQ Simplified
project planning or re-planning compared to central inverters
QQ Partial delivery of inverters possible, or partial commissioning of the park (depending on progress of construction)
QQ Easy transportation to the construction site, no 40-ton truck
or provision of special routes for a truck or a crane required
in the park, therefore better use of space
QQ Outdoor inverters, easy installation on the module frame,
no housing and no external cooling needed
QQ Integrated data logger, no external string boxes/generator
junction boxes or monitoring systems required
QQ Easy installation (by 1 person) and commissioning with few
settings, no commissioning by manufacturer required
QQ Cheap standard transformers instead of double-wound
transformers
QQ Flexibility for east/west-oriented PV systems
QQ Lower cabling costs on the DC side fully compensate for the
increased cabling work on the AC side
Increased yield with string inverters
QQ Higher
efficiency (incl. DC supply)
QQ Individual MPP tracking for each individual string inverter in-
stead of central MPP tracking for the central inverter (shade/
clouds, snow, dirt, module mismatch etc.)
QQ Detailed string monitoring due to high number of inverters
without cost-intensive generator junction boxes safeguards
yield at string level and enables module faults to be isolated to one of 4-5 strings
QQ More efficient control and longer feed-in duration thanks to
broader voltage range than with central inverter
QQ Flexible system planning on sites with rough terrain, different gradients and non-rectangular boundaries
Advantages of string inverters with regard to
breakdown risk and servicing
QQ In the event of a breakdown, only a small area of the system
is affected (e.g. 20 kW)
availability of the whole system thanks to simple replacement process
QQ Easy replacement of string inverters safeguards yields during a repair
QQ More flexibility throughout the whole service life of the
PV system (e.g. variable module degradation, replacement
modules, replacement inverters etc.)
QQ Higher
Quality and durability
QQ Convection
cooling of the string inverters prevents contamination inside the devices and minimizes wearing parts so
that no maintenance whatsoever is required
QQ Exhaust air and heat are expelled directly from outdoor
string inverters because of their compact design, so there
is no need for a fragile and high-maintenance cooling system
QQ With their IP65 housing and condensation protection, REFUsol string inverters are designed for all climate zones (dust,
sand, salt mist, air humidity and temperature cycles)
QQ All REFUsol string inverters are built to last over 20 years,
as verified by MTBF calculations in accordance with EN/IEC
61709
QQ Experience from almost 50 years in the inverter manufacturing business and over 15 years in the photovoltaics industry
guarantees quality at the highest level.
REFUsol GmbH | Uracher Straße 91 | 72555 Metzingen | Germany | Тel. +49 7123 969-0 | Fax +49 7123 969-165 | info@refusol.com | www.refusol.com
REFUsol_WP_20130218
Reduced investment costs
with string inverters