Good idea- I will do some investigation
That requires logging illumination levels as well. Keep in mind that the MPP varies with illumination.
Yes it's illogical. Think of panel, when just tiny amount of power is drawn, it's voltage gets much higher than Vmpp but current and power is almost 0. If you put a huge load on it, the current raises above Impp but voltage drops towards zero. The purpose of MPPT is to regulate the load to get max W out of the panel.
Thank you- yes I understand the principles, I guess in my mind the purpose of a mppt is to actually keep the panel at mppt, even if it means it cannot provide to the load, or if there is excess power that needs to go somewhere. I appreciate that you are saying that is not what the waveshare is doing so I will find an alternative. I think my requirements are obviously different than typical, in that I don't care about what is going to the load, I just want to keep a panel at mpp for study purposes
Programmable power supply and dumb load could do it.
The MPP only comes into play when the load wants to draw more current than the current produced at the MPP. The tracker is supposed to prevent that, and keep the current at the MPP. If the load is drawing less than the MPP current, then it just draws what it draws, and the MPP is irrelevant. But it seems to me that MPP is only relevant if the load is some kind of switching device. For a linear battery charger, more current is more current so long as the voltage is high enough to charge the battery, and reducing the current to the MPP just, well, reduces the current.
Anyway, you might want to check with the Waveshare people about exactly how their device follows the MPP. I don't think there's anything that automatically tracks the MPP, so the tracker may just constantly vary the current a tiny bit either way, then calculate whether the resulting power produced is greater or less. But there are approximations that do pretty well but aren't really tracking MPP. One alternative is to just track voltage, and try to keep it at 85% of the OC voltage. But you would want to know exactly how they are doing the tracking.
Could you explain what data you intend to log, and what you expect it to tell you?
Thank you, this makes sense to me, I will check with Waveshare about how their setup works.
I think keeping it at an approximation of mpp would work- especially because I can take real current-voltage sweeps on a separate piece of kit periodically (e.g. once a month) to update my mpp estimation. Something like this maybe but with a more appropriately rated pot/rheostat?
The data logging is really about the lifetime of the cell/panel over time. Keeping a panel at mpp is best to approximate how it would be deployed in the real world, but I want to know how its performance (for example what this mpp wattage is, or just the peak power output or associated voltage & current) changes over time (accounting for irradiance). I would expect to see a decrease in the average/peak power output over time, as the efficiency of the cell reduces.
Exactly.
But if you want to measure/log mppt current and voltage, that situation would obviously not give them to you.
I think you would need to account for temperature as well as irradiance.
Anyway, here's a description of the various algorithms used to track the MPPT.
https://www.mathworks.com/discovery/mppt-algorithm.html
P&O is what I was trying to remember. Ideally you want to stay at the point on the power curve at which its slope is zero (the line is flat).
So are you going to have a normal solar panel right next to yours? That would make irradiance and temperature the same for both, which would make for a more valid comparison.
I've never thought of it before, but is the life of a solar panel affected by how much current it supplies on average? In other words, would two identical panels sitting side by side age differently if one is open circuit and the other short circuit?
Thanks Sherman, the algorithms link is very interesting, I will have a think about how to implement P&O, but I am leaning towards just measuring & setting it periodically.
I hadn't though about including a reference panel, but it is a good idea, thank you.
I don't know about silicon, but certainly in some other types of solar (I work on organic solar cells, and this also applies to perovskites) the voltage it is maintained at influences lifetime- for organics usually they will have a better lifetime if kept at Jsc instead of Voc, due to some of the reactions at play.
I tried to find answer to that several years ago and read all researches I found, without conclusion. My idea is that they mainly age from temperature and UV-temp-humidity degradation of plastic laminates and adhesives. So keeping them at mpp condition would be the best for temperature and as a consequence less aging.
If panels are partially shaded, the case is different.