Hey everyone! I'm new to solar setups and I'm trying to get everything configured correctly. I've connected a Victron 75/15 MPPT charge controller to a 12V lithium battery and have two 100W solar panels. Right now, it's cloudy and getting late in the day, and I'm only seeing between 4 to 6 watts of output from the panels, but nothing seems to be charging the battery. Shouldn't the panels trickle charge the battery with whatever they produce? Is there a specific threshold that needs to be met before the charge controller starts sending power to the battery? Also, I thought the output would be a bit higher even on a cloudy day. I'm using bigger wires than necessary; could that affect the efficiency?
2 Answers
Yes, when it's cloudy or late in the day, you're not going to see much output from your solar panels—that's pretty normal. It's essential to check if your charge controller is set up for lithium batteries; if it's still configured for AGM or lead-acid, it might not be delivering enough voltage to charge your battery, which typically needs around 14.4 volts. So, if you're not seeing any charging activity, that might be your culprit.
Exactly! The efficiency can drop significantly with cloud cover, especially near sunset. You might get almost nothing during light drizzle. To answer your other question, if you're getting 4-6 watts, you should ideally see at least some trickle charging into the battery. It's worth checking your charge controller settings and looking for any output info to confirm if anything is making its way into the battery.