Hi guys,
I want to reassure
everyone that all my samples are yet on my roof (proof in Figure 1).
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| Figure 1 - Proof |
For sure you are wondering: why did you put your samples there? Well, the reason is that I’m studying the effect of the weather changes on my semi-transparent layer and in particular I want to investigate the reduction of transparency because of the aging of the polyurethane glue.
For this purpose, with the help of the technicians of IFSTTAR, I realized a low cost device for the
measurement of the power reduction of the solar cell because of the presence of
the top layer. The idea is to simulate the sunlight in a controlled environment
and, as a good engineer, I made some simplifications.
The sun is replaced by
an halogen lamp which is able to generate an irradiance power of about 300-400
W/m2. The lamp is placed in a dark box (basically is an
old bedside table with sliding doors) and the distance between the sample for
the test and the lamp is about 60 cm (Figure 2).
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| Figure 2 - Very low cost device for the measurement of the power reduction of the solar cell |
The electrical
instrumentation is composed by:
- a solar cell having a peak power of 15W, an open circuit voltage Voc of 19.5V and a short circuit current Isc of 0.97A (these values are measured in the standard conditions of 1000W/m2 of irradiance and 25°C and they are useful for discriminating the different characteristics of the solar cells in the market);
- a solarimeter to measure the radiation of the lamp and to verify that it is always constant during all the test;
- a set of resistances between 2 and 5000 Ω;
- two mutlimeters in order to measure at the same time the intensity and the voltage of the solar cell for each value of resistance;
- a thermometer to check the temperature and verify that the box is not becoming a pizza oven;
- a plate for the connection of all the devices.
Once all the equipment
is installed, the test can be performed. The idea is to measure simultaneously the
current intensity and the voltage of the solar cell for different values of
resistances.
The data can be plotted
in a graph having for abscissa the voltage and for ordinate the current
intensity. With a miserable effort of
fantasy we will call this plot intensity-voltage curve.
The goal is to find the highest power output of the solar panel (P max),
which is given by the product of the intensity and the voltage (Figure 3).
Now the question is: what happens to the Maximum Power Point when the
solar cell is covered by the semi-transparent layer? As you can expect, the
maximum power point decreases and the reduction depends on the phenomena of
absorption, reflection and diffraction between the solar radiation and the
sample.
In order to well-quantify the power reduction, we are going to introduce
a novel term called ‘’performance loss’’ (please, appreciate again the
originality of the name).
where:
-
Pmax,unc is the maximum power point
of the solar cell;
-
Pmax,c is the maximum power point of the solar cell
covered by the semi-transparent layer.
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| Figure 3 - Example of Intensity-Voltage curve |
The performance loss ranges theoretically between 0% (sample perfectly
transparent) and 100% (sample totally black). My first samples had a value
around 70%, but after the optimization of the mixture, I reached a value of
46%.
In terms of aging effect due the exposition to the weather
changes, I observed an average increase of the performance loss of about 10%.
Recently I also studied the effect of each variable (thickness, glue content,
grading curve) on the transparency and I quantified their impact through the
factorial design, an experimental method commonly used in chemistry able to
measure the effect of a variable on the outcome. Regarding this, I will
probably dedicate a new post because it’s a very interesting topic and also
because my blog will be more attractive with some matrices and formulas!
Bye for now and see you soon!
Domenico
“The research presented in this
report/paper/deliverable was carried out as part of the H2020-MSCA-ETN-2016.
This project has received funding from the European Union’s H2020 Programme for
research, technological development and demonstration under grant agreement
number 721493”