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54 EINBLICKE
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The "Energielabor" at the University of Oldenburg can be seen
as symbolic of Oldenburg‘s energy research. It was planned
back in the 1970s,when the oil crisis triggered a search for new
forms of energy. Rather than expanding the use of nuclear
power the Oldenburg scientists set their sights on harnes-
sing the wind and sun as energy sources.The research group
"Physics of Renewable Energies" set out to prove that it was
possible to run a laboratory powered entirely by renewable
energy sources. In 1982 it became the first building to go into
operation on the University‘sWechloy campus.Until the early
1990s, the "Energielabor" was the subject of almost all research
in the field of renewable energies in Oldenburg. Today the
building is used for practical training, lectures and office space.
In a fewmonths‘ time the "Energielabor" will celebrate its 30th
anniversary, but some of its installations have been operating
for considerably longer. A number of the photovoltaic panels
there have been in use for 36 years – a record time in Germany.
The solar panels weremanufactured by the firmAEG-Telefun-
ken under the product name "TSG MQ 36/0". At the time the
electricity company‘s headquarters were located in Wedel,
near Hamburg. Over the years the company changed names
several times,passed into the hands of Daimler-Benz and RWE
and now forms part of the technology group Schott AG and is
called Schott Solar GmbH.Before the 336modules with a total
rated output of 3.5 kilowatts were installed at the "Energie-
labor" in 1981 they had already
been operating for five years as
part of a project funded by the
Federal Ministry of Education
and Research. Today, the modules at the "Energielabor" con-
stitute the oldest photovoltaic array of such size in Germany.
The "Energielabor" therefore offers ideal conditions for ob-
serving the lifetime of solar cells. Because there are hardly
any other installations of this size and age in Germany, there
is a lack of information about the economic efficiency of
photovoltaic arrays. They are generally assumed to have an
average lifespan of 25 years. Almost all economic efficiency
calculations used for planning the financing of photovoltaic
systems are based on this figure. If a photovoltaic array falls
short of the operating life guaranteed by the manufacturer
the operator of the system faces considerable financial and
economic problems.The solar panels at the Oldenburg "Ener-
gielabor" have already exceeded the expected operating life
by more than ten years. And they still provide operating data
that on the basis of precisemeasurements testify to unaltered
quality regarding electricity production.
But what can limit the lifespan of photovoltaic arrays? There
are essentially two factors. On the one hand the characteristics
of the semiconductor materials can alter while the system is
in operation. This process is referred to as degradation. The
degradation process depends on the materials that are used.
For the production of the solar cells at the "Energielabor" sili-
conwas used: a classic semiconductor metal that is extremely
durable and barely changes its characteristics over time. On
the other hand – and this is the main factor limiting their life-
span – solar cells need to be protected against environmental
influences and connected to the electric system. This entails
the use of components such as glass coverings, frames and
cable connections which can corrode or crack and therefore
constitute the main weak points in a photovoltaic array.
The quality of a photovoltaic array that has been in operation
for some time can be measured in several ways. At first there
is the visual inspection, which reveals external signs of aging.
Frequent problems are corrosion andbleaching of the cells, the
so-called "browning" phenomenon inwhich the plasticmate-
rial encapsulating the cells becomes discoloured as a result of
UV radiation. Solar panels can also be damaged as a result of
bubbles forming in the plastic encasements or degradation of
the plastic, as well as cracks in the glass and corroded cables.
But only careful measurements carried out in the laboratory
can provide detailed information about the true state of a
module.The solar panels are examined under conditions that
are precisely defined e.g.as regards amount and spectral distri-
bution of irradiance on the
module level,as well as cell
temperature. Continuous
measurements assessing
the total output of the array at the "Energielabor" had indica-
ted that it still had a very good operating performance when
compared with the manufacturer‘s specifications. In 2010,
the researchers of the "Energy and Semiconductor Research
Laboratory" decided to investigate further, and in November
they detached individual modules and measured their per-
formance in the laboratory.
The resultswere astounding: providing for the usual deviations
from the manufacturer‘s specifications, which are aimed at a
hardly realistic ideal operating performance, after 35 years in
operation themodules still displayed onlyminimal alterations
regarding the key parameters. Both the short-circuit current
and the open-circuit voltage were just three percent below
the original values, while the fill factor was actually two per-
cent above it.The efficiency,ultimately the decisive factor,was
four percent below the values specified by the manufacturer.
Photovoltaik-Modul AEG-Telefunken TSG MQ 36/0
(temperature 25°C)
1976
2011
rated power
10,3 W 9,9 W
open circuit voltage
21,0 V
20,3 V
short circuit voltage 685 mA 664 mA
MPP-voltage
16,6 V
16,6 V
MPP-current
630 mA 607 mA
efficiency
8,55 % 8,2 %
total number of mudules
336
total power
3460 W
The oldest photovoltaic
array still in operation.
Photovoltaics: "An energy
source with huge potential."
Hardly any variations after 35 years in operation: the manufacturer‘s specifi-
cations in comparison to the Oldenburg measurement data.