Hey everyone, I've set up a 30W solar panel that produces a maximum current of 1.67 A. I've connected it to an MPPT controller, and I'm measuring its output with a multimeter while charging a 3S Li-ion (12.6V) battery. Currently, in the weak winter sunlight here in Germany, I'm seeing a charging current of only about 0.2 A, with the battery voltage hovering around 11V. When I skip the MPPT and measure the solar panel directly, it shows around 22V output. I'm really confused about what the MPPT is doing for me if it's not helping maximize the current. Any insights?
2 Answers
It sounds like your MPPT might not be fully harnessing the solar panel's potential under the current conditions. The output you see from your panel (22V) is nice, but the key here is how much current it can provide at that voltage. Remember, with panels, the 30W rating is the max output under ideal conditions, not your average. In weak sunlight, you're likely only utilizing a fraction of that, which is why you're seeing low current for charging. The MPPT works to optimize this, but if the panel can only give so much in weak light, that's your limiting factor. You're definitely experiencing the effect of winter sun!
You're right to question the MPPT's role here. It’s designed to find the maximum power point of the solar panel, but that’s dependent on the conditions. Too often, panels output high voltages with low currents when the sunlight is weak. The MPPT will adjust the charging voltage to match the battery, but if the panel isn't producing much power, the MPPT can't magically increase it. In essence, it's doing its job, but the conditions are limiting the maximum current it can pull in from the solar panel.
So, if I'm charging a 5200mAh 3S Li-Ion battery, would I get better results with a 50W panel instead of the 30W? Would that help under low light?
Exactly, even during low light, your panel can show voltage but may not provide enough current to make a difference. The MPPT will still do its best to optimize the power it gets, but it can't create power out of nothing.