Information

4.3 Manufacturer recommendation
Manufacturers shall provide more information in the
datasheet of its charge controllers. Besides that the
given values must be correct and reproducible.
Especially the DC-DC conversion efficiency shall be
given as a whole surface plor depending on all relevant
input and output voltage relations. As a valid alternative
the newly defined REW efficiency can be used to
provide a realistic figure of the conversion efficiency.
All DC-DC conversion efficiencies shall not be given as
peak values, but as representative European weighted
values. The thermal derating performance shall be
mentioned clearly.
Manufacturers should provide information on the
static and dynamic MPPT algorithm according to DIN
EN50530.
By designing a product manufacturers shall leave
enough room to easily connect cables to the charge
controllers.
4.4 System design
MPPT charge controllers offer a wide input voltage
range and allow to use solar modules with more than
36/72-cells, which is similar to the input configuration
of comparable grid-connected inverters. According to
the system properties it is recommended to design the
solar module array in an adequateway.
The maximum open circuit voltage of the module
string is seen as a highly critical design criterion and
must always be below the manufacturer’s value given in
the datasheet. This must also be valid for minimum
temperature system conditions (the lower the ambient
temperature gets, the higher the modules open circuit
voltage is). According to the datasheet of the PV
module and according to the minimum temperature
specification, the maximum possible open circuit
voltage must be calculated in order to fit the MPPT
voltage range of the charge controller and its given
figures in its datasheet.
The maximum Watt peak rating of the used module
strings can exceed the nominal continuous power of the
MPPT charge controller by about 15% which is a
common practice for grid connected systems. This
reflects the fact that the output power of solar modules
is dependent on the temperature and that it is
significantly reduced by increasing ambient
temperature.
5. CONCLUSION
To improve the performance of MPPT charge
controllers a manufacturer neutral test procedure has
been developed and should be used as a benchmark
during MPPT charge controller development. A new
conversion efficiency rating has been defined to :
η
REW
= η
DC-DC
· η
mpp_stat
· η
mpp_dyn
taking into
account the European weighted DC-DC conversion
efficiency as well as MPP tracking efficiencies accordin
to DIN EN50530.
The test showed in an obvious way that there is
especially weak MPPT tracking performance in many
products.
A world wide manufacturer representative test of
MPPT charge controllers shows according to graph 9
that there is still improvement of such products
necessary to finally offer products suitable for
sustainable and quality driven off-grid systems. The best
test candidate shows typical efficiency of η
REW
< 93%,
while the bottom quality reaches η
REW
< 78%.
Just by choosing an MPP tracker the customer can
gain or loose a lot of energy in the system.
6. REFERENCES
[1] DIN EN 50530 VDE 0126-12:2011-04 - Overall efficiency of
grid connected photovoltaic inverters,
http://www.vde- verlag.de/standards/0126035/din-en-50530-
vde-0126-12-2011-04.html
[2] EU Project DERRI – TA Project “TESCABI”, testing scheme
for MPPT charge controllers and battery inverters.
[3] EU weighted efficiency definition, H. Häberlin et al.,
Total Efficiency η-tot – A new Quantity for better Characterisation
of Grid-Connected PV Inverters, 20
th
European Photovoltaic Solar
Energy,Conference, Barcelona, 2005
[4] AIT inverter test laboratoy, http://www.ait.ac.at