Your solar installer looked at the array after the storm and said the panels survived. Six weeks later, your monitoring app shows one string down 18 percent and a single panel running 40 degrees hotter than its neighbors. That’s not a glitch. That’s the classic signature of solar panel hot spots, and along the Front Range they show up after hail more than any other cause.
Hot spots are one of the sneakiest kinds of hail damage because the glass usually looks fine. The panel keeps producing, just less. Then the damage compounds quietly until you’ve got a panel that’s cooking itself, and sometimes the wiring around it too.
If you’re mid reroof or mid claim right now, this matters, because hot spots that get missed during the adjuster’s inspection are hard to get paid for later. Here’s what’s actually happening inside the panel, why hail is the usual trigger in Weld and Larimer counties, and what it costs to deal with. If you’d rather just have someone put a thermal camera on your roof this week, call us at (970) 286-3417. The inspection conversation is free.
What Solar Panel Hot Spots Actually Are
A solar panel is a string of cells wired in series, usually 60 or 72 of them. In series wiring, current has to flow through every cell. When one cell gets damaged and can’t pass as much current as the others, the healthy cells push current through it anyway. That damaged cell stops acting like a generator and starts acting like a resistor.
A resistor turns electricity into heat. So the damaged cell heats up while the rest of the panel stays at normal temperature. That localized heating is the hot spot. On a thermal camera it looks like a bright square or blotch on an otherwise even panel, sometimes 30 to 60 degrees Fahrenheit hotter than the cells around it.
Panels have bypass diodes that are supposed to route current around damaged sections. They help, but each diode typically covers a third of the panel. When a diode kicks in, you lose that whole third of the panel’s output. And diodes fail too, especially ones cycling constantly over a damaged cell, and a stuck diode can make a hot spot worse instead of better.
Left alone, hot spots don’t heal. The heat degrades the encapsulant around the cell, browns the backsheet, and in bad cases melts solder joints or scorches the junction box. The National Renewable Energy Laboratory here in Colorado has documented cell cracking and hot spot formation as major drivers of panel degradation, and their research is worth a skim if you want the deep technical version: nrel.gov/pv.
Why Hail Creates Hot Spots on Solar Panels Weeks Later
Here’s the part that catches homeowners off guard. Hail rarely shatters panel glass. Tempered solar glass is rated to take 1 inch hail at highway speeds. What hail does instead is flex the glass, and that flexing transmits force into the silicon cells underneath.
Silicon cells are about as thick as two sheets of paper. When they flex, they crack. These micro cracks are invisible from the ground and usually invisible up close too. We wrote a full breakdown of that mechanism in our post on micro cracks from hail, but the short version is this: the crack severs some of the tiny fingers that collect current from the cell surface.
Right after the storm, the cracked cell may still perform close to normal because the cracked pieces are still touching. Then Colorado weather does its thing. Hot afternoons, cold nights, wind loading, snow loading. The panel expands and contracts, the crack edges separate, and the cell’s output drops. That’s when the series wiring problem starts and the cell begins running hot.
This is why hot spots show up weeks or months after hail, and why a visual inspection right after a storm misses them. The damage is real on day one. The symptom takes a season to develop.
The timing problem has an insurance consequence. In Colorado, most policies give you a limited window to report storm damage, often one year, sometimes less. If your hail event was in June and your hot spots don’t get diagnosed until the following spring, you can end up outside the window. That’s a big reason we push for thermal inspections during the claim, not after it closes. Our page on solar hail damage in Greeley covers how we document this for adjusters.
What a Hot Spot Looks Like From the Ground
You usually can’t see the hot spot itself, but you can see its side effects if you know where to look:
- A brown or yellowed patch on the back of the panel, visible from the attic side on some installs
- Snail trails, which are dark squiggly lines on the panel face where moisture got into a crack
- A burnt or bubbled spot on the panel surface in advanced cases
- One panel consistently underperforming in your monitoring app
- Melted or discolored areas near the junction box on the panel’s back
If you’re seeing any of that, stay off the roof and skip ahead to the section on when to call a pro.
The Marisol Problem: When the Adjuster Says the Panels Are Fine
Marisol in Windsor had a roof claim from the Memorial Day hail last year. The adjuster approved the shingles but wrote the solar array up as undamaged because the glass was intact. Standard outcome. Her roofer scheduled the reroof and called us for the detach and reset.
Before we pulled the panels, we ran a thermal scan as part of our pre detach documentation. Three panels showed clear hot spots, and one had visible backsheet browning that lined up with the thermal image. We photographed everything, matched the damage pattern to the hail direction, and sent the package to her adjuster as a supplement.
The carrier added $2,850 to her scope to replace the three panels. Without the scan, she’d have paid us to reinstall three panels that were quietly dying, and by the time her production numbers made the problem obvious, the claim would’ve been closed. If your reroof is coming up and nobody has put a thermal camera on your array yet, reach out through our contact form and we’ll fold the scan into your detach quote.
How Pros Find Hot Spots on Solar Panels
You can’t diagnose hot spots by eye, and production data alone won’t do it either, since shading, soiling, and inverter issues mimic the same output drop. Real diagnosis uses a few tools together.
Thermal imaging is the workhorse. A technician scans the array with an infrared camera, ideally on a sunny day when the panels are under load, because hot spots only appear when current is flowing. A healthy array shows an even temperature across every panel. Hot spots jump out as bright squares.
String level testing comes next. We measure voltage and current on each string to figure out how much output the damaged panels are costing you, which matters for the insurance math, since a panel that’s lost 25 percent of its output has a real dollar value attached.
Electroluminescence imaging is the lab grade option, a dark room technique that makes cracks glow on camera. It’s mostly reserved for disputes, but it settles arguments. The Department of Energy has a plain English primer on how PV cells work that helps all of this make sense: energy.gov solar photovoltaic cell basics.
The mistake we see most often is homeowners trying to diagnose this with a $60 phone thermal camera from a ladder. The resolution isn’t there, glass reflections create false readings, and the ladder work isn’t worth it. This is a hire it out situation.
What Hot Spot Problems Cost in Northern Colorado
Here’s the honest range of what you’re looking at, based on what these jobs actually run in the Greeley area. Your numbers will vary with roof height, panel brand, and how your system is wired.
| Service | Typical Cost | When You Need It |
|---|---|---|
| Thermal inspection with report | $150 to $400, often free with a detach quote | After any hail event, before a claim closes |
| Single panel replacement, labor and panel | $450 to $900 per panel | Confirmed hot spot on an in production panel |
| Bypass diode or junction box repair | $150 to $350 | Diode failure without cell damage, less common after hail |
| String troubleshooting and rewire | $250 to $600 | Output drop with no visible panel damage |
| Full detach and reset during reroof | $1,500 to $4,500 for a typical home array | Roof replacement with panels coming off anyway |
Two notes on that table. First, panel replacement pricing depends on whether your panel model is still made, since discontinued panels can force a partial array redesign and a bigger supplement. Second, if your roof is being replaced anyway, replacing hot spot panels during the reset is dramatically cheaper than mobilizing a crew twice, because the labor overlaps.
Gary in Eaton learned the second point the expensive way. His array came down and went back up during his reroof in April, and he waved off the thermal scan to save a little money. By August his monitoring showed one panel down hard, and the backsheet had scorched. Because the crew had to come back out for a single panel swap, he paid $1,150 all in, when catching it during the reset would’ve cost him about $600 and one less service call.
Hot Spots and Your Hail Claim
Insurance is where hot spots get contentious, because the damage is invisible in the adjuster’s photos. Here’s what actually moves a claim.
Documentation beats argument. A thermal image timestamped during the claim window, paired with string test data showing the output loss, is very hard for a desk reviewer to dismiss. A homeowner saying “my production seems low” is very easy to dismiss.
The hail correlation matters. Adjusters look for damage patterns consistent with the storm, so we map hot spot locations against hail direction and size reports for your address. When four hot spots line up on the windward slope, that’s not a coincidence, and we say so in the report.
Supplements are normal, not adversarial. If hot spots surface after your initial scope was written but before the claim closes, your contractor submits a supplement with the new evidence. Carriers handle these every day. We walked through the whole coverage question, including detach and reset line items, in our post on insurance and detach reset work.
One caution in the other direction. Not every underperforming panel is hail damage, and claiming hot spots that turn out to be soiling or a bad optimizer burns your credibility with the carrier. Get the diagnosis first, then make the claim. If you’re not sure whether what you’re seeing is storm related, our rundown of the signs of hail damage on solar panels is a good place to start.
Ray in Evans is the version of this story that goes right. Post storm thermal scan found hot spots on seven panels across his 24 panel array. We documented everything while his roof claim was open, the carrier paid $6,400 for the panel replacements on top of the detach and reset, and his out of pocket for the solar side was his deductible and nothing else. Timeline was the whole game. The scan happened in week two of the claim, not month eight.
When to Stop DIY and Call Someone
There’s real homeowner work here, and then there’s a hard line.
You can and should watch your monitoring app monthly and screenshot anything odd. You can look at the array from the ground with binoculars after a storm. You can check panel backs from inside the attic if your install makes that visible. You can pull your hail date and claim number together so a contractor can move fast.
Stop there. Don’t get on the roof, because hail damaged shingles are slippery and a panel with a hot spot can have compromised wiring. Don’t open junction boxes or disconnect connectors, because a residential string can run over 400 volts DC in full sun, and DC arcs don’t self extinguish the way household AC does. Don’t pry at a browned backsheet to look underneath. And don’t run a panel with visible scorching while you wait for a convenient appointment, because that’s how electrical fires start. Shut the system down at the disconnect and make the call.
We handle thermal scans, hot spot documentation for claims, panel swaps, and full detach and reset for reroofs across Greeley, Evans, Windsor, Johnstown, Eaton, Firestone, and Fort Lupton. If a storm just hit and something on your array looks or smells wrong, our emergency line answers around the clock at (970) 286-3417. For everything else, send us the details and we’ll get you a free written estimate.
Frequently Asked Questions
Can a solar panel with a hot spot still be used?
Technically it will keep producing at reduced output, but running it is a bad bet. The heat accelerates degradation of the surrounding cells and the encapsulant, so the problem spreads, and in the worst cases a hot spot can scorch the backsheet or start a fire. If a thermal scan confirms a hot spot, plan on replacing that panel rather than riding it out.
How soon after hail do solar panel hot spots appear?
Sometimes immediately, but more often weeks to months later. The hail creates micro cracks that barely affect output at first, then thermal cycling through Colorado’s hot days and cold nights opens the cracks up and the hot spot develops. That delay is exactly why we recommend a thermal scan while your insurance claim is still open instead of waiting for production to visibly drop.
Will my insurance pay to replace panels with hot spots?
Often yes, if the hot spots are documented as hail related while the claim is open. Carriers respond to thermal images, string test data, and a damage pattern that matches the storm, and that evidence usually goes in as a supplement to your roof claim. What they don’t respond well to is an undocumented complaint filed after the claim has closed, so timing and paperwork decide most of these.
Can hot spots be repaired without replacing the panel?
Usually no. A hot spot caused by cracked cells is permanent physical damage inside the laminate, and there’s no field repair for a broken cell. The exception is when the root cause is a failed bypass diode rather than cell damage, which a technician can sometimes fix at the junction box for a few hundred dollars, but after hail the cell damage scenario is far more common.