Why Is My Solar Generation Lower Than Expected?
If your solar panels are producing less than you hoped, the most common reason in Ireland is simply the season — output swings hugely between June and December. Before assuming a fault, compare this month against the same month last year in your monitoring app, then rule out shading and dirt. Our maintenance guide and winter output guide cover what is normal versus what needs a closer look.
Quick Answer
The most likely cause is normal seasonal variation: an Irish solar array makes far more in summer than winter, so low output may be expected. First, open your monitoring app and compare this month to the same month last year, not to summer. If output has genuinely dropped year-on-year, check for new shading, dirt, or one underperforming string before calling your installer.
Last updated June 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
Common reasons solar generation is lower than expected
Solar output in Ireland varies enormously through the year. A 4kWp array makes far more electricity in June than in December, and the Irish average is around 867 kWh per kWp installed per year. Most "low output" worries turn out to be normal seasonal variation. The causes below are ordered roughly from most to least common, so work down the list before assuming a fault.
1. Season and weather — usually normal
This is by far the most common reason. Short, overcast Irish winter days produce a fraction of what long summer days do. A drop from summer to winter is expected, not a fault. Always compare against the same month a year ago, never against your best summer figures. Our winter solar guide sets realistic month-by-month expectations.
2. Shading that has grown or changed
Trees grow, hedges thicken, and a neighbour's extension, a chimney, a dormer or an aerial can throw new shadows across your panels. Even partial shade on one panel can drag down a whole string. If output dipped after a season of growth or building work, shading is a strong suspect.
3. Soiling — dirt, moss, bird droppings and lichen
Ireland's damp climate encourages moss and lichen growth, and bird droppings, pollen and general grime build up over time, especially on low-tilt panels. Soiling can shave several percent off output. See our maintenance guide for safe cleaning advice.
4. Orientation and tilt that is not optimal
East or west-facing arrays, or a shallow or steep roof pitch, generate less than a well-angled south-facing roof. This is not a fault — it is just the physics of your roof — but it does mean your realistic ceiling is lower than a textbook south-facing system. Our efficiency guide explains how orientation affects yield.
5. Inverter clipping or a string offline
On a bright day an undersized inverter can clip the peak (a minor, often deliberate trade-off). More serious is a string that has gone offline — if part of your array stops reporting, output can fall sharply. The monitoring app or inverter display will usually flag this.
6. A faulty optimiser or microinverter on one panel
If you have panel-level optimisers or microinverters, a single failed unit shows up as one panel producing much less than its neighbours. This is easy to spot in per-panel monitoring and is a clear sign to involve your installer.
7. Gradual degradation over the years
Panels lose a small amount of output each year, usually around 0.4–0.5%. Over a decade that is a noticeable but modest decline and is completely normal. A sudden year-on-year drop is not degradation and is worth investigating.
8. Temperature on hot days — minor in Ireland
Panels are slightly less efficient when very hot, so a heatwave peak can be marginally lower than a cool, bright day. In the Irish climate this effect is small and rarely the real cause of disappointing output.
| Cause | How likely | Tell-tale sign |
|---|---|---|
| Season / weather | Very common | Low in winter, recovers in spring — normal |
| New or grown shading | Common | Output dips at certain times of day |
| Soiling (dirt, moss, lichen) | Common | Visible grime; gradual decline |
| Orientation / tilt | Built-in | Always lower than a south-facing array |
| String offline / clipping | Occasional | Sudden step-down; fault flag in app |
| Faulty optimiser / microinverter | Occasional | One panel far below its neighbours |
| Degradation | Slow | ~0.4–0.5% per year, gradual |
| High temperature | Minor in IE | Slightly lower peak on very hot days |
What you can safely check yourself
Before paying for a call-out, there are several safe, app-level and ground-level checks any homeowner can do. None of these involve opening equipment or touching wiring. Work through them in order.
Safe to do
- Open your monitoring app and compare this month to the same month last year
- Look at the daily curve for a sudden step-down on a clear day
- Check per-panel data if you have optimisers or microinverters
- Look for one underperforming string or panel versus the others
- Glance at the inverter display for a green light versus a red/orange light or error code
- Look from ground level for dirt, moss, droppings or new shadows
Never do
- Never open the inverter casing — it carries lethal voltage
- Never touch, disconnect or probe DC wiring or panel connectors
- Never climb onto the roof without proper safety gear
- Never attempt electrical repairs or rewiring yourself
- Never bypass or reset protective devices beyond a normal consumer-unit breaker reset
A five-minute diagnostic
- Open your app and switch the view to year-on-year for this same month.
- If output is broadly in line with last year, it is almost certainly seasonal — no fault.
- If it has genuinely dropped, check per-panel data for one weak panel or string.
- Look at the inverter: green light good, red/orange or an error code needs attention.
- Step into the garden and check for new shade or visible dirt on the panels.
Safety first: solar DC wiring and inverters carry lethal voltage. You may safely check things at app, breaker and display level, but you must never open an inverter or touch DC wiring. For anything electrical, use a registered professional — see below.
When to call an installer or electrician
Some symptoms point to a genuine fault that needs a qualified professional. Anything inside the inverter or on the DC side is off limits to homeowners. In Ireland, use a RECI or Safe Electric registered electrician for electrical work, or go back to your original SEAI-registered installer while the system is still under warranty.
Call sooner rather than later
- A clear year-on-year drop you cannot explain with shade or dirt
- One panel or string persistently far below the rest
- Inverter showing a red/orange light or repeating error code
- Zero generation in the middle of a bright day
- Unusual buzzing, burning smell, or visible damage near the inverter
Who to call in Ireland
- Your original SEAI-registered installer first if you are still under warranty
- A RECI or Safe Electric registered electrician for any electrical fault
- The inverter manufacturer's support line for firmware or monitoring issues
- Keep your install paperwork handy — warranty claims usually need it
Persistent, unexplained drops in output that are not seasonal, shading or soiling almost always warrant a professional check. Catching a failed optimiser or an offline string early avoids months of lost generation.
Irish context: metering, export and the grid
Sometimes the panels are fine and the issue is with how generation or export is being measured or paid. A few Ireland-specific points are worth ruling out.
Metering and export
Your generation (what the panels make) is separate from your export (what you send to the grid). Under the National Smart Metering Programme (NSMP), a smart meter records export, and your supplier pays the Clean Export Guarantee (CEG). If your bill or export figures look off, the panels may be generating fine while the metering or supplier side needs checking.
Connection and the grid
Domestic solar in Ireland connects under the ESB Networks NC6 notification process. If you have recently had work done or a connection issue, that can affect export rather than raw generation. For grid or metering questions, ESB Networks and your electricity supplier are the right contacts, not the panel installer.
In short: low generation points to panels, shading, soiling or the inverter. Low export payments with healthy generation usually points to the smart meter, CEG tariff or your supplier.
Low Solar Output FAQ
Why is my solar generation so low in winter?
Low winter output is normal in Ireland. Days are short and overcast, so a 4kWp array makes far less in December than in June. Compare your figures to the same month last year rather than to summer. If they are broadly similar year-on-year, there is no fault to fix.
How do I know if my solar panels are underperforming or just seasonal?
Open your monitoring app and compare this month to the same month a year ago. Seasonal dips repeat every year and recover in spring. A genuine year-on-year drop that you cannot explain with new shading or dirt is the sign of a real problem worth investigating.
Can dirt really reduce my solar output in Ireland?
Yes. Ireland's damp climate encourages moss, lichen and algae, and bird droppings and pollen add to it, especially on low-tilt panels. Soiling can cost several percent of output. Rain handles a lot of it, but visible build-up is worth a safe, ground-level clean or a professional cleaner.
One of my panels is producing much less than the others. What does that mean?
If you have optimisers or microinverters and one panel reads far below its neighbours, that usually points to a faulty optimiser or microinverter, or heavy localised shading or soiling on that panel. Rule out shade and dirt, then contact your installer, as it is likely a warranty issue.
Is it safe to open my inverter to check it myself?
No. Solar DC wiring and inverters carry lethal voltage. You can safely check the app, the inverter's external display and lights, and your consumer-unit breaker, but never open the inverter or touch DC wiring. For electrical faults use a RECI or Safe Electric registered electrician, or your SEAI-registered installer.
Related Guides
Solar Troubleshooting
Diagnose common solar faults: generation, inverter, battery, export.
Maintenance Guide
Cleaning, monitoring, warranties, and lifespan.
Solar Panels in Winter
Winter output data, monthly breakdown, and performance tips.
Solar Panels Not Generating
No output? Inverter, isolator and breaker checks first.
Sources
- SEAI — Solar Electricity Grant
- ESB Networks — Microgeneration & NC6 connection
- Safe Electric — find a registered electrician
Last updated 11 June 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
John Rooney is the founder of Solar Info and has been covering the Irish solar energy market since 2023. He fact-checks all content against official SEAI data and maintains relationships with SEAI-registered installers across Ireland.
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