https://en.wikipedia.org/wiki/Theory_of_solar_cells#Equivalent_circuit_of_a_solar_cell
This circuit is very easy to create with discrete circuit components. To get higher panel voltage, we can just connect a bunch of these circuits in series, or just put a bunch of diodes in series and adjust the other values as appropriate.
Let’s try and come up with a reasonable design a component selection for it.
Parameter | Component | Value | Reason |
|---|---|---|---|
IL | Power supply in CC mode | 10A min. | Isc of solar cells is about 7A. If the power supply is able to provide 10A then we are able to hit all operation points. |
ID | Diodes in series | Vf of diode string = 30V | 30V = max input voltage for Nomura MPPTs. We can connect others in series if we want to expand and test at higher voltages for other MPPTs. |
Rsh | Resistor | 100k Ohms or so. | Guess for shunt resistances in solar cell |
Rs | Resistor | 0.2 Ohms or so. | Guess for connection resistances in solar panel |
10A 30V programmable supply: https://www.digikey.ca/en/products/detail/b-k-precision/9103/7056819
We have one of these in the bay already.
Diode string - 30 of these in series should be reasonable: https://www.digikey.ca/en/products/detail/vishay-general-semiconductor-diodes-division/VS-E4TU2006FP-N3/8269295
We can connect all the diodes in series, but have a movable connection so that the string length can be adjusted for different numbers of solar panels.
Heatsink - diodes will get hot. Need a heatsink and fan to keep them cool.
2 of these heatsinks, with half of the diodes on each one, mounted so that it forms a channel for the fins in the middle and the flat base on the outside: https://www.amazon.ca/Awxlumv-Amplifier-Transistor-Semiconductor-300mm69mm36mm/dp/B07TJZ2MYZ/ref=sr_1_3?crid=BBU8JQU8V7FI&keywords=300*69*36&qid=1667273517&qu=eyJxc2MiOiIxLjM4IiwicXNhIjoiMC4wMCIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=300%2B69%2B36%2Caps%2C168&sr=8-3&th=1
Rough heat sink calculator: https://celsiainc.com/resources/calculators/heat-sink-size-calculator/#:~:text=Heat%20Sink%20Sizing%20Calculator%20%2D%20Rough,(Tjunction%20%2D%20maximum%20ambient%20temperature)
2 of these fans, one on each end of the heatsink module should be good: https://www.digikey.ca/en/products/detail/delta-electronics/AFB0824GHE/5799833
Fan power supply: https://www.digikey.ca/en/products/detail/mean-well-usa-inc/GST60A24-P1JR/10659909
Diode Temp rise
1.4V (diode datasheet) * 10A = 14W.
14W * 3C/W (diode datasheet) = 52C rise.
If we keep the heatsink under 100C, the diodes should be fine. A few fans for lots of forced air should be able to do this.
Adding a few thermocouples to monitor temperature of the diodes would be a good idea though.
A few forum threads on building these:
https://diysolarforum.com/threads/bench-power-supply-to-simulate-solar-panel.11564/page-2
Before jumping into a purchase to make one of these, we can make a small model of one with regular diodes and test the IV curve. Just need to make sure to keep the tests quick so the diodes don’t heat up too much.