In 2013, I started with my Maxun One solar bike project. For the development of very lightweight solar cell encapsulation materials, I needed to measure the wear due to atmospheric influence. This requires a measurement system with high long-term reproducibility. By using error corrections, the long-term reproducibility of the solar cell curve tracer is 0.2%.
Matching solar cells
With this curve tracer you can measure the characteristic curves of a single solar cell. Because the reproducibility is high, the curve tracer can be used very well for matching solar cells. The generated power of the solar cell, at the MPP, can be measured accurately by averaging a large number of samples:
The curve tracer is based on an Arduino Uno microcontroller board. The solar cell is loaded with a power MOSFET BUZ10 which is used as a variable resistance. The gate is driven slowly by an increasing voltage so that the drain current increases from zero to the maximum current that the solar cell delivers. During this process the voltage and current are measured and printed to the screen. We need a 12V adaptor for the supply.
To do reproducible measurements independent of the varying sunlight, a high-power light source is needed. In 2013, LEDs with sufficient power had not yet been invented. That is why I used a slide projector, which light intensity is about 1/3 sun.
The sun is always tilted at a certain angle to the PV panels. Therefore, the reflection of the encapsulation materials has to be measured also. Because, in the Netherlands the average sun angle in the summer is 30 degrees we take this tilt for the measurements.
Measuring wear and different encapsulation materials require high long-term reproducibility. By using error corrections, the long-term reproducibility of the recent version of the solar cell curve tracer is 0.2%.
The high reproducibility is obtained by
You can download the code at GitHub. Several libraries had changed since 2013, which I have fixed. But I haven't tested the program again, so I don't know if everything works 100%.
The hardware must be calibrated first, see below.
bool printCurve = 1; // 0 = without curve, 1 = with curve
The hardware must be calibrated first. Required instruments:
The calibration procedure is included in Curvetracer.pde. Use this Excel file for automatic calculation of the values.
Doing reproducible measurements with the sun is difficult and we have to wait for the summer to do tests. The measurements have to be corrected for the current sun irradiation [W/m2]. This can be done with a solar irradiance meter.
The light intensity is about 1/3 sun. This not the recent version with the long-term reproducibility of 0.2%.