Information

80%
82%
84%
86%
88%
90%
92%
94%
96%
98%
100%
1 2 3 4 5 6 7 8 9
Test candidate
MPPT efficiency in %
Static Dynamic
Graph 8: Comparison of average weighted static and
dynamic MPPT efficiencies for the different test
candidates
As it is visualized clearly, the average performance
of some samples is unsatisfactory. In combination with
a given low static MPPT efficiency and an additional
low DC-DC conversion efficiency such devices will
transfer less energy to the battery than switching shunt-
type of series controllers, which feature beneficial
overall performance results.
3.6 Efficiency considerations
As a result of the 5 testing categories it can be seen
that there are significant differences in the test results
among the all tested devices. Especially the DC-DC
conversion efficiency in combination with the static and
dynamic MPP tracking efficiency and the self-
consumption figures represent the most important
criteria.
The average performance of the test candidates
according to the the Realistic Equally Weighted
efficiency - REW can be seen in graph 9.
Efficiency in % Test candidate
Graph 9: REW efficiency in % of all test candidates
The outcome of this test shows clearly that there is a
significant difference between well designed MPPT
charge controllers and low performing products. Even
the best available products perform below η
REW
< 93%,
which is a non-satisfactory figure. All well known
brands are part of the test and the outcome clearly
shows that there is no guaranty to buy a brand product
to finally use a good performing charge controller. Five
out of nine products show acceptable performance and
can be effectively used in off-grid systems. Some of the
test candidates reach less than 85% and will bring less
energy to the battery as standard switching controllers.
All samples show a weak performance in static and
especially dynamic MPPT algorithm. Taking the low
DC-DC conversion efficiency under consideration none
of the mentioned products is able to meet the
manufacturer’s specifications.
4. SUMMARY
Off-grid systems using MPPT charge controllers
dominate the market more and more. Due to significant
module price reduction in the last years the average off-
grid system size is rising as it is now economically
feasible to built off-grid systems in areas in which such
systems have been too expensive up to now. Especially
non off-grid modules with about 40-70 cells per module
are used more and more in off-grid installations. MPPT
charge controllers must be used then. The tests of this
work show that variously specified products are
available on the market, but it is nearly impossible for
the users to find out, whether the selected MPPT charge
controller shows good performance in the field or not.
4.1 Test procedure
A suitable test procedure is hereby developed and it
benchmarks the performance of MPPT charge
controllers into 6 categories: Installation and usage, self-
consumption, an equally weighted DC-DC conversion
efficiency based on the European weighted efficiencies
among all input and output voltages. Furthermore
derating performance, Static and dynamic MPPT
efficiency.
4.2 User recommendation
For end users and system integrating companies it is
not possible to perform the tests described in this paper.
For each single installation it should be carefully
checked, whether MPPT charge controllers are
necessary and in which extent. In the case that it is
possible to use standard 36-cells or 72-cells modules
switching controllers can also be integrated in an
efficient and effective way.
Users are definitely asked to gain detailed self
consumption information from the manufacturer, as
well as confirmed figures for the DC-DC conversion
efficiency calculated on the base of European efficiency
rules and finally MPP tracking efficiency according to
DIN EN50530.