6 min read
Soiling, a fault, or curtailment? Why your solar output dropped
In short: When a solar system underperforms in Cyprus, the cause is almost always one of three things: soiling (dust), an equipment fault, or grid curtailment. They look similar on a summary dashboard but need completely different responses. The job is to tell them apart before spending money, because the fix for one does nothing for the others.
Why this is the question that matters
A monitoring portal usually shows you a number: yesterday’s kWh, a performance ratio, a red or green dot. What it rarely shows is why the number is low. Owners lose real money not because they lack data, but because they act on the wrong cause: cleaning panels that have an inverter fault, or raising a service ticket for what was actually the grid curtailing output.
Get the diagnosis right and the fix is usually cheap and fast. Get it wrong and you pay twice.
The three causes, side by side
| Soiling loss | Equipment fault | Curtailment | |
|---|---|---|---|
| What it is | Dust and deposition on the glass | A failing string, inverter, connector or hot-spot | The grid operator capping how much you can export |
| How the loss looks | Gradual, creeps up over dry weeks | A step-change: output drops and stays down | Output flat-topped or clipped during specific hours |
| Weather link | Worse in long dry spells; recovers after rain | None; independent of weather | Often tied to high-generation, low-demand periods |
| Does cleaning fix it? | Yes | No | No |
| The right response | Schedule a clean (on economics) | Diagnose and repair the component | Confirm it’s grid-side; adjust expectations, not the asset |
The trap is that all three can show up as “lower than expected kWh.” Only the pattern and the right instruments separate them.
How we actually separate them
- Soiling is quantified by comparing measured output against available irradiance. If the gap grows over dry weeks and closes after rain or a clean, it’s dust. We covered the economics of that in how often to clean solar panels in Cyprus.
- Equipment faults show a step-change and, very often, a thermal signature. Drone thermography finds hot-spots, bypass-diode failures and cell-level anomalies that no summary number reveals; string-level monitoring pins the loss to a specific part of the array.
- Curtailment is grid-side clipping: the operator limiting export, not a problem with your system. We flag curtailment windows explicitly, so lost generation during those hours is never misread as a fault (and never triggers an unnecessary clean or callout).
A simple diagnostic order
- Rule out curtailment first. Check whether the shortfall lines up with known curtailment windows or an export cap. If it does, the asset is healthy. The limit is external.
- Check for a step-change. A sudden, sustained drop points to equipment, not dust. Dust is gradual.
- Compare output to irradiance over time. A widening gap through dry weather, recoverable by cleaning, is soiling.
- Look at the thermal and string-level picture. Hot-spots and single-string losses localise a fault to the component to repair.
- Only then act (clean, repair, or adjust expectations), matched to the cause you actually found.
Bottom line
“My solar is underperforming” is not one problem; it’s three, and they don’t share a fix. The value of good O&M is not more data. It’s the correct diagnosis, so every euro you spend goes at the real cause.
Distinguishing soiling, faults and curtailment is core to our solar PV operations & maintenance in Cyprus. If your output isn’t what it should be and you’re not sure why, book an O&M assessment and we’ll find out.
← All posts