Hi,
Dumb question:
I have 3x 305W blue solar panels, 1.5 yr old, last year I regularly got 700 to 800W going via the MPPT into my 2x 200ah LifePo4 batteries.
This year, same period, similar sun conditions, clean panels never over 600W… Batteries are not full, would this mean 1 panel is defective?
Thank you, Pieter
Similar sun condition is a very relative thing… Even a slight haze can affect their production.
Or maybe a bypass diode is malfunctioning if you want to go on the “problem” path, although on full light condition the diodes are not influencing production. Additional shade/vegetation issue, because after a year some things grow… 
In contrast, in my situation, after 2 years, I have the feeling that sometimes the production is bigger than in the first year… 
Although, different panel type and manufacturer/seller.
You are certainly correct on the conditions but am on the med and been monitoring for a month and really seems like I get 30% less, need the juice… Is there a way to test for a faulty diode? PS no shade or dirt, on a boat.
Like I said, if the panels are fully illuminated, without shades, then the diodes are not the problem.
Do you have some references from last year?
Is the total production voltage the same?
Is the current the same?
If the current is the same but the voltage lower, then there is a problem with a section.
If the current is lower but the same voltage, then is a problem with transparency/wear.
I am going to assume you have 3 panels in parallel. You could have one panel failing or a poor connector on one panel. A quick test if you can access the panels is get a sheet of cardboard or a thick blanket. Then cover the panels one at a time, if you cover one and the power stays the same then that panel or the connectors are not making contact.
A tester for up to 1600w costs around 75€. Always good to have something like this in your toolbox. But a blanket shadowing single panels works too.
Right, easy peasy, my middle panel doesn’t do anything✔️
Thank you gentlemen, much appreciated!
Now to work out if it is the panel, or wiring or connectors.
I’m seeing a voltage drop of .72v and .49v between the mppt and BMV in the first 2 photos.
That amount of voltage drop requires investigation, and if possible rectification.
Will check tomorrow with a friend who is smarter if connectors or panel🫣
If its the connectors, its a very easy job to chop off the connector (both the panel lead side, and the other side - that might be on the cable going back to the controller, or to another panel) and attach new connectors.
Always replace connectors on both sides at the same time so that the mating surfaces (where all the current passes) are new, clean, and matching.
Also if your supply of MC4 connectors (and therefore the connectors on the cable going back to the controller) are brand X, and the panel is using brand Y, always chop off the first and last connector of the array and replace with your own brand - that way the panels always connect to each other with matching connectors (brand Y) and your final connection to the cable going back to the controller will also be with matching connectors (brand X). MC4 brands may often look the same, but they are not matching spec. Most regs will say that the connectors must be not just matching spec, but matching brand.
Make sure you report back with the solution - it all adds to our collective experience. Also mark your final report as the solution so that everyone/system knows the thread is solved.
So got new connectors but same issue, connected panel by panel separately to the MPPT and now found 1 to deliver only half of the watts of the 2 other ones so this would mean I measured wrong and it is broken I assume…?
Yes it looks like the one panel is not working properly. It would be useful.to compare the SmartSolar status screens to see the PV voltage and current on a good and poor panel. I am assuming that the poor panel is producing half the voltage so in parallel, the other 2 panels are at full voltage stopping all production from the poor panel.
That’s why it can also be useful to have more than one MPPT controller so you can compare the outputs.
I have two through necessity since the boat roof has 13 panels on it, split into 3 strings, 5S1P on one MPPT and 4S2P on the other – which should therefore have 60% higher power output. I spotted it had 20% lower output instead, because of a connection problem to one of the two parallel strings… 
Ian, absolutely right, wanna swap boats?
Not enough room here unfortunately 
If you have a multimeter that has DC current capabilities greater than the panel specs;
This will remove any uncertainty of whether the MPPT has actually reached Pmax or not, i.e. it gives you a number that is only dependant on 2 variables; [panel, lead and connector quality], and [solar radiation level]. If you do the tests quickly, you can eliminate the 2nd, provided the solar angles are comparable.
That leaves leads, connectors, and panels - as you have replaced the connectors - presumably correctly - you just have leads and panels, and leads are almost always fine if a visual inspection shows no damage. Pay particular attention to where the lead joins the panel - if the lead has been yanked, you could have damage there.
