In order to get the best out of your vehicle it is important to know what power your panel is delivering. For the student designed cars there is strict limits, the regulations stipulate that the panel power produced at standardised AIM 1.5 sun level must not exceed 10 Watts. And when the car is presented for race scrutineering the panel is checked using calibrated equipment.
While this may seem a complicated process your can perform a Power Test using some relatively simple equipment and still estimate the power your solar panel is generating to within less than 10% of what a calibrated system would measure.
If you also use a Calibrated solar panel at the same time you test you can adjust your measure values to correct the reading to the AIM 1.5 standard to generate a more accurate maximum panel power value.
What is a Solar Panel?
A solar panel is one or more solar cells, or photovoltaic (PV) cells, that coverts the energy in light waves into electrical power.
These cells all share a same trait, they generate a voltage and current flow when a photon of energy in light is absorbed by the cell. This powers devices.
There are MANY different types of construction technique for creating a PV cell and they range from the relatively cheap and common Silicon based unit all the way to the very expensive and uncommon Gallium arsenide devices that are used to power satellites and even the International Space Station.
Practice Solar Panel to AIMSC & VMSVC 2017 Regulations
The 2017 regulations governing the student designed car event have changed significantly from all previous regulations in the area of the solar panel used to drive these cars.
Under the 2017 regulations the car must race with a panel provided by the organisers, however for practice the competitors must provide their own solar panel.
This should not present any problems to most previous competitors as the panel to be provided by the organisers is a single Scorpio No. 26 panel (14 cells) calibrated to output 5.5 watts in full Sun. The majority of competitors have been using two such panels in past competitions, a simple reconfiguring of their existing panels will give them a practice panel.
To make a practice panel that exactly matches the panel to be provided by the organisers two actions are necessary, firstly mount the single Scorpio panel to an aluminium backing identical to the backing the organisers will be providing and secondly, calibrate the panel to produce 5.5 watts at full Sun.
The aluminium panel backing
Details of the wiring and connectors is provided in the regulations, the aluminium backing will be manufactured to the following sketch.
Calibrating the panel
Without a calibrated light box, it is difficult to achieve exact calibration, however the simple process described below detailing how calibration can be performed in Sunlight will give reasonable accuracy.
To calibrate the panel in Sunlight it is necessary to know the Sun level prevailing, this can be measured using a Scorpio No. 10 calibrated cell. For accuracy, it is essential to have the calibration cell and panel being measured in the same plane when measurements are being taken.
At a known Sun level measure the panel’s open circuit voltage (OCV) and short circuit current in amps (ISC). Make these measurements with the solar panel at 25 Degrees C and at a Sun level greater than 70% for best accuracy.
Approximate power can be calculated by multiplying voltage and current together then multiplying by 0.7 which is an average fill factor for these panels.
OCV × ISC × 0.7 = Power in watts
Having calculated the power at a specific Sun level as described above, ratio the power obtained up to the power expected at full Sun.
To calibrate the panel to produce 5.5 watts at full Sun, mask a portion of the panel with a light excluding covering to reduce the power produced to 5.5 watts. Note this covering should cover the same proportion of every cell in the panel. The approximate size of the mask can be calculated using the calculated full Sun power and the desired 5.5 watt maximum and using the ratio of these powers to reduce the panel surface area by the same ratio.
Always recheck the panel power after masking to ensure the correct size of masking has been applied.
(Special note: Not all Scorpio No.26 panels will produce 5.5 watts, some panels may only produce 5.2 watts. In past years Scorpio provided “standard panels” with a power output of from 5.2 to 5.8 watts at a lower cost than their “premium panels” which had power output above 5.8 watts.)