While the electricity supply system is undergoing a
major change with an increasing penetration of
renewable energy sources, the exact composition of the
energy mix will mainly depend on the costs evolution of
the various technologies. The costs of photovoltaic
electricity generation can mainly be reduced by
decreasing the manufacturing costs of PV modules and
inverters, by improving the reliability and last but not
least by enhancing the system performance. In this
context, increasing attention is paid to the efficiency of
PV inverters.
The detailed characterisation of inverters’ efficiency
consisting in measuring the inverter efficiency for
various maximum power point (MPP) powers and
voltages has been introduced some years ago. On the
other hand, new techniques for optimising the
dimensioning of PV plants through MPP voltage
monitoring have also been proposed [1].
In the meantime, extensive experiences have been
gained [2]. Until the recent developments, the European
efficiency as introduced in the nineties was still used as
the most important figure to compare inverters or to
observe trends on the market. While the introduction of
this European efficiency more than one decade ago as a
simple widely acknowledged figure probably contributed
to the significant improvement of inverters’ performance
in the past ten years (by more than five percent points
[3]), recent discussions question its adequacy to provide
a representative picture. The main concerns in this
context relate to the influence of the irradiation
distribution depending on the location, the well known
dependency of the conversion efficiency on the DC-input
voltage [1] [2], and last but not least the influence of the
MPP Tracking [4] [5] [6] [7]. All these factors which
have been recently investigated are still not taken into
account by the current definition of the European
efficiency. This paper introduces a new way of
computing the European efficiency which is a good
compromise between simplicity and accuracy.
In the first part, the operation conditions for inverters
are compared for various locations. In the second part,
the concept of maximal reachable efficiency is
introduced and illustrated. A comparison between
products and locations is provided. Finally, the adequacy
of the proposed concept to compare the performance of
inverters is discussed