Bird streaking vs. uniform dust soiling in thermal scans
A thermal scan of a solar array doesn't hand you a diagnosis. It hands you a pattern, and the pattern is only useful if whoever's reading it knows the difference between a cell that's hot because a bird sat on it and a module that's hot because nobody's washed the array since spring. Mix those up and you send a cleaning crew to fix a problem that needs a tech with a multimeter, or you send the tech out for a row that just needs a rinse.
What bird streaking looks like on a thermal pass
Bird droppings create what techs usually call a localized hot spot, and it's a specific kind of localized. The deposit sits on a handful of cells, sometimes just one, and because it's opaque and uneven, it blocks irradiance unevenly across that small area. The cells under the mess heat up relative to their neighbors because they're working harder to push the same current through a partially shaded string segment. On a thermal image this reads as a tight, irregular blob, often trailing in a streak shape from wind or rain runoff, with sharp edges against the surrounding cells that are running at normal operating temperature.
The giveaway is the contrast. A bird strike doesn't care about row orientation or row position. You'll see it on table 14 and nowhere near table 15, on the leading edge of an array near a transmission line or a perch point, and nowhere in any particular pattern otherwise. If you walk the array afterward, you'll usually find the deposit, assuming it hasn't washed off, right where the thermal signature pointed.
What uniform dust soiling looks like instead
Uniform soiling is the opposite kind of problem. Dust, agricultural drift, pollen in the spring, whatever's settling on the array over weeks or months, builds up evenly across whole sections rather than concentrating on individual cells. The thermal effect is real but it's diffuse: a gradual temperature rise across an entire table or an entire row, sometimes the whole south-facing edge of a block, with soft boundaries instead of the sharp ones a bird strike produces. The signature you're looking for is a wash: a section running a degree or two warmer than the rest of the field, consistently, table after table.
Soiling loss also tends to correlate with site geography in a way droppings don't. Rows closer to an access road or a gravel lot soil faster than rows tucked behind a tree line. Low-tilt arrays pick up dust that steep-tilt arrays shed on their own. If the warm pattern tracks with those physical features of the site rather than with perch points or power lines, that's soiling, not birds.
Why the distinction decides who you dispatch
This is the part that actually matters for scheduling. A bird strike is a spot problem, a handful of cells on a handful of modules, and it's often tied to the output of just those cells rather than the whole string. Depending on severity it might call for a quick wipe-down, or if the droppings have been baking on for a season it can start affecting string performance and warrant a closer look at that combiner's output before you write it off as cosmetic.
Uniform soiling is a different conversation. It's a wash job, usually scoped by section rather than by panel, and it's the kind of finding that changes a cleaning crew's route for the week rather than sending a single tech down one row. Treating a soiling section like a spot repair wastes a truck roll. Treating a bird strike like it needs a full-table wash wastes water and time on 23 clean modules to deal with one dirty one.
Reading a raw thermal export to make that call, row by row, is exactly the kind of squinting most O&M teams are trying to get out of. Panel Soiling pairs the thermal pass with RGB and ranks what gets found, so the findings come back sorted by what they are and what they need, not as a heat map you have to interpret yourself.
If your crews are still guessing which pattern they're looking at before they roll a truck, it might be worth seeing what a ranked findings dossier looks like for your site.