Irish weather is not the solar killer many assume. This guide gives you county-level irradiance data, seasonal output tables, and the real factors that determine your annual solar panel output — from roof angle to shading to panel quality.
Solar panel output in Ireland is frequently underestimated. The country’s reputation for rain and cloud has led many homeowners to dismiss solar PV before investigating the numbers. But measured solar irradiance data from SEAI and the European Commission’s PVGIS tool tells a more encouraging story — one that explains why over 100,000 Irish households have installed solar PV systems.
Ireland receives between 900 and 1,150 kWh of global horizontal irradiance (GHI) per square metre per year. This is the total solar energy hitting a flat surface, and it’s the baseline from which your system’s tilted, south-facing output is calculated.
The specific yield (kWh per kWp per year) for an optimally oriented south-facing roof at 30–40° tilt ranges from roughly 820–1,050 kWh/kWp/yr across Ireland, with a national median around 900–950 kWh/kWp/yr.
For a 4 kWp system, this translates to 3,280–4,200 kWh per year depending on location.
Output in Ireland is highly seasonal. Understanding this pattern helps you plan self-consumption strategy, battery sizing, and expectations for winter bills.
Approximate monthly output for a 4 kWp south-facing 35° tilt system in Dublin:
Summer months (May–August) account for roughly 55–60% of annual output. Winter months (November–February) contribute only 15–18%. This seasonal imbalance is why battery storage alone cannot solve the winter energy problem — batteries sized for summer surpluses can’t store enough for the winter shortfall. See our analysis of solar and battery storage economics.
The direction your roof faces has the biggest impact on annual yield. Using 100% as the baseline for a perfect south-facing roof:
An east-west split array (panels on both east and west slopes) is a good solution for ridged roofs with no south face. While individual panels produce less, the array generates a flatter production curve across the day rather than a sharp midday peak — which often improves self-consumption.
The optimal tilt for Ireland is approximately 30–40° from horizontal. Most Irish pitched roofs fall in the 25–45° range, which is near-optimal. Flat roofs can use ballasted tilt frames, typically set at 10–15° for wind load reasons (lower profile) while sacrificing some annual output.
Even partial shading causes disproportionate output losses with standard string inverter systems. A single shaded panel in a string can reduce the entire string’s output to match the shaded panel’s level. Key shading sources on Irish roofs:
A shading loss of 10–20% is not unusual on constrained Dublin suburban roofs. Power optimisers or microinverters eliminate most string-level shading losses. Read our power optimisers guide for detail.
Solar panels lose approximately 0.35–0.45% of output for every degree above 25°C. Ireland’s mild climate is an advantage here. While a panel in Spain might reach 70°C on a clear day (losing 20% of rated output), an Irish panel on a warm July day typically reaches 45–55°C, losing only 7–13%. On cool, bright spring days when panels might be 15–20°C, they can actually exceed their rated output because the temperature coefficient works in reverse below 25°C.
Ireland’s frequent rainfall is an unlikely benefit — it keeps panels naturally clean. Dust accumulation (the main soiling issue in dryer climates) is minimal. Annual cleaning is generally not required in most of Ireland, unlike in southern Europe. Bird droppings near nesting sites can cause localised shading and should be removed. See our solar panel maintenance guide.
No PV system converts 100% of the solar energy hitting the panels into usable electricity. Typical system losses include:
This is why a 4 kWp panel array doesn’t produce 4 × peak sun hours × 365 days of electricity. Industry standard modelling uses a performance ratio (PR) of 0.75–0.85 for Irish residential systems, meaning 75–85% of theoretical maximum output is delivered to your meter.
Before committing to a system size and investment, it’s worth modelling expected output using:
Real-world monitoring data from Irish residential PV systems consistently shows output within 5–10% of well-modelled projections. Larger deviations usually indicate:
After your system is installed, your inverter’s monitoring app (SolarEdge monitoring, Fronius Solar.web, or Enphase Enlighten) will show daily, monthly, and annual output. Most homeowners find the actual figures meet or exceed installer projections when the system was correctly specified.
Solar panel output in Ireland averages 850–1,050 kWh per kWp per year for a well-oriented south-facing system, with southern counties outperforming northern ones. A 4 kWp system in Dublin generates roughly 3,600–4,200 kWh/year; in Cork or Wexford, the same system might produce 4,000–4,600 kWh. The key variables are orientation, tilt, shading, and system design — all things a competent installer will account for in their proposal.
Want to understand what these numbers mean for your electricity bills? See our solar panel payback period guide for a worked financial example.
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Home Solar guides Solar Panel Output in Irish Weather: Real Numbers for Every County Solar Panel Output in Irish Weather: Real Numbers for Every County
Solar advisor team
Published 15 May 2026
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