A client emails me and says a couple of their solar panels look like they are slacking. Most of the time, they are right that something is off. What they are almost never right about is why. An underperforming solar panel on an Enphase system could be sitting in the shade of a tree, or it could have a genuine hardware failure that qualifies for a free warranty replacement. On a phone app, those two problems look nearly identical. Telling them apart is the entire job, and it is where a lot of solar companies get lazy.
Here in Southwest Florida, we keep an eye on a lot of Enphase systems, so I want to walk you through how we actually diagnose an underproducing panel. Not the guesswork version. The version that holds up when we file a warranty claim on your behalf.
One Weak Panel Is Not Always a Broken Panel
Enphase systems use microinverters, which means every panel reports its production individually. That is a real advantage. On an older string inverter, one weak panel hides in the crowd and drags down the whole string quietly. With Enphase, each panel stands on its own.
The catch is that seeing a number is not the same as understanding it. A panel producing less on a given day might be perfectly healthy. It might be shaded for two hours every morning. It might catch a passing cloud the others missed. The raw number alone does not tell you whether you have a maintenance problem or a non-issue that costs you nothing.
Why Enphase Enlighten Only Tells You Half the Story
Enphase Enlighten is the app you were handed when your system was commissioned, and Enlighten Manager is the more detailed version we use on the back end. Both are good tools. You can pull up a single microinverter and chart its power, DC voltage, DC current, and AC voltage across the day. If you want to see it for yourself, Enphase’s monitoring platform is where that data lives.
What Enlighten does not do well is comparison. It shows you what one panel did. It does not automatically stack that panel against its neighbors on the same roof, at the same angle, under the same sky, at the same moment. And comparison is the only honest way to separate a healthy panel having a slow day from a panel that is genuinely sick. If you want the background on how these systems report, we cover it in our overview of Enphase microinverter systems.
The Real Trick Is Comparing a Panel to Its Peers
When we diagnose a lagging panel, the first thing we do is find its peers. Peers are the other panels in the same array, on the same roof plane, with the same azimuth and tilt, wired to the same kind of module. Those panels see the same weather and the same sun as the suspect panel, minute for minute.
We pick a few healthy peers, take their median production, and measure the suspect panel against it. If a panel is producing 54 percent of what its peers are producing, that is not a rounding error. That is a flag. This peer to peer comparison removes weather, season, and cloud cover from the equation, because every panel in the group experienced the exact same conditions. Whatever is left is specific to that one panel.
Read the Curve, Not Just the Total
Here is the part most people skip. The daily total tells you how much a panel lost. The shape of the curve tells you why. A shaded panel does not underproduce evenly. It produces low during the shaded hours, then climbs back up and matches its peers once the shadow moves off.
We see this constantly. A panel on the east edge of a south-facing roof runs low every morning, then catches up and tracks its peers by mid to late afternoon. That is a tree to the east throwing morning shade. A panel on a west-facing array does the opposite. It keeps pace all morning, then falls off a cliff around 1:30 in the afternoon, every single day. That is afternoon shade.
The tell is the recovery. When a panel converges back onto its peers later in the day, it is proving that the hardware is perfectly healthy. It hits full output the moment the sun is clear. That is a site condition, usually a tree or a vent stack, not a defect. In Florida this also shifts with the seasons. A morning shade problem often eases in winter as the sun tracks farther south, then returns hard in late spring and summer when the sun climbs high and swings north.
When It Is Not Shading: A Genuine Hardware Fault
Now the other case. We had a system with one microinverter running about a third below its peers, and the curve told a completely different story. It was not low in the morning or low in the afternoon. It was low all day, sunrise to sunset, every single day.
When you look at the DC voltage, it sits about one third below the healthy peers from the moment the sun comes up until it goes down. A panel is built from three sub-strings of cells, each protected by a bypass diode. When one of those sub-strings drops out, from a failed bypass diode or a damaged run of cells, you lose roughly a third of the panel’s voltage, all day, in every kind of weather. That is a DC-side panel fault, and it is exactly the kind of thing a manufacturer warranty is supposed to cover.
Shading recovers. A dead sub-string never does. That single distinction is the difference between calling a tree service and filing a warranty claim.
Ruling Out the Usual Suspects
Good diagnosis is as much about what you rule out as what you rule in. Before we blame a panel, we confirm the microinverter itself is converting normally, that the operating temperature is in range, and that grid voltage is not the culprit.
Grid voltage is worth a special note, because it gets blamed for a lot of things it did not do. A high line voltage reading of 250 or 255 volts does not trip a microinverter off. The voltage has to run much higher than that, and even then the giveaway is that production only drops during the exact moments the voltage spikes. If the voltage is high but the panel is producing right alongside its peers, the grid is not your problem. We check for that specifically so we do not send you chasing a ghost.
Southwest Florida heat is another one people assume. Microinverters do derate when they get hot enough, but that shows up as a midday softening across the whole array on the hottest days, not as one panel that lags every hour of every day. Ruling these out matters.
Why This Matters for Your Warranty and Your Power Bill
Two reasons this is worth getting right. First, the money. Under FPL net metering, every kilowatt-hour your system makes offsets a kilowatt-hour you would otherwise buy. A panel stuck at a third of its output is quietly shrinking your bill credits month after month. It is not a catastrophe, but it adds up, and it is money you already paid for when you bought the system.
Second, the warranty. Enphase microinverters carry a long factory warranty, and your solar modules carry their own manufacturer warranty, typically around 25 years. But a manufacturer is not going to ship a replacement on your say-so. They want evidence: proof that the panel underperforms its matched peers under identical conditions, with shading, grid, and temperature ruled out, and the hardware cause isolated. That is precisely what a proper diagnostic report delivers. When we open a claim, we can hand the manufacturer a document that leaves very little to argue with.
I Built Software to Do This
I will tell you a little secret about where this comes from. Doing this diagnosis by hand in Enlighten Manager means clicking one panel at a time, pulling up peers one at a time, and comparing charts in your head. It works, but it is slow, and slow means problems sit unnoticed.
So I built a custom fleet monitoring software that compares every microinverter to its peers automatically. It lets us scrub through production day by day, flags the underperformers, and generates the warranty report in one click. It does the tedious part so we can spend our time on the diagnosis that actually needs a human. The point for you is simple. We have tools that almost nobody else has, and we can prove what we find efficiently and convincingly.
The Bottom Line
If you have an Enphase system and one panel looks like it is underproducing, do not panic and do not ignore it. An underperforming solar panel is either a shading problem you fix at the site or a hardware fault you fix under warranty, and the only way to know which is to compare that panel to its peers and read the shape of the curve, not just the daily total. Shading recovers later in the day. A real hardware fault drags all day, every day. If you are in Southwest Florida and you want a straight answer instead of a shrug, reach out to Florida Solar Design Group. We will diagnose it remotely first, tell you exactly what is going on, and if it is a warranty item, we will build the case to get it replaced.
