How Much Electricity Do Solar Panels Generate in Ireland?

How Much Electricity Do Solar Panels Generate in Ireland?

Around 910 kWh a year for every 1kWp of panels on a south-facing Irish roof. That’s the national average from PVGIS, the European Commission’s solar database, and it’s the one number worth remembering before you read any quote.

Scale it up and the sums are quick. A 4kWp system produces roughly 3,600 kWh a year. A 6kWp system lands near 5,500 kWh. A single 430W panel makes somewhere between 340 and 420 kWh, depending on where in the country it’s bolted down.

Those figures assume a clear south-facing roof at a sensible pitch. Point the panels east, put a chimney in front of them or fit them in Donegal rather than Cork, and the number shifts, sometimes by a lot. This guide covers what moves it and by how much.

How Much Does One Panel Produce in a Year?

Start with the panel itself. Most residential panels fitted in Ireland today are rated between 420W and 450W. That rating is lab output under test conditions, a comparison tool rather than a promise.

In the real world, a 430W panel on a good Irish roof makes roughly 390 kWh over a year. Ten of them, which is a common 4.3kWp install on a three-bed semi, give you around 3,900 kWh. Sixteen on a bigger roof, close to 7kWp, give you around 6,200 kWh.

For context, the CSO puts median household use at 3,228 kWh a year, and the CRU’s typical domestic customer is 4,200 kWh. So a 10 to 12 panel system produces about as much as an ordinary house uses, over a year. Working out exactly how many you need is covered in SPV’s guide to how many solar panels an Irish home needs, which sizes it by bedrooms and usage rather than by roof space alone.

Does the County Make a Difference?

More than most people expect, and not in the direction they’d guess. The south coast and the east do best. The north-west does worst. The midlands sit in the middle.

PVGIS estimates for a south-facing roof at 30 degrees put Cork at about 986 kWh per kWp a year and Dublin at about 972. Wexford is close behind at 957. Galway, Cavan and the midlands counties land between 880 and 920. Donegal, at the bottom, comes in around 782.

That’s a 20 per cent spread between the best and worst county. A 4kWp system in Cork makes nearly 4,000 kWh a year. The same system in Letterkenny makes about 3,100. Both are worth having, but the payback is a year or two apart. SPV’s rundown of Ireland’s best counties for solar goes county by county if you want to see where yours sits.

These are satellite estimates rather than readings from your roof, and local weather varies year to year. Treat them as a guide rather than a guarantee.

How Much Does Roof Direction and Pitch Cost You?

The numbers above assume a south-facing roof pitched around 30 to 35 degrees, which is close to ideal for Irish latitudes. Most roofs aren’t that.

Facing East or West

An east or west roof produces about 15 to 20 per cent less than a south one over the year. That’s less of a loss than it sounds, and an east-west split has a real advantage. The east side makes power in the morning, the west side in the evening, which is when the kettle and the cooker are on. Many homes use more of what they generate on an east-west roof than on a south one, even though the total is lower.

Facing North

A north-facing roof loses 40 per cent or more, and SPV will usually tell you not to bother with it. If north is all you have, a ground mount or a flat-roof frame tilted south is the better route.

Pitch

Pitch matters less than direction. Anything between 20 and 45 degrees is within a few per cent of the best case. A flat roof with panels laid flat is where the loss gets noticeable, which is why flat-roof systems use tilted frames. The detail is in SPV’s post on the best roof angle for solar panels, including what to do with a shallow bungalow roof.

What Does a Typical Month Look Like?

Very uneven. A 4kWp system in the midlands makes around 500 kWh in June and around 100 kWh in December. Roughly three quarters of the year’s electricity arrives between April and September.

That matters because it changes what the annual figure means for your bill. In June the panels make more than the house can use and the surplus goes to the grid. In December they cover the fridge and the lights and not much else. SPV’s breakdown of solar panel performance in winter versus summer has the month-by-month numbers, and the gap is wider than most first-time buyers expect.

Cloudy days still produce. A panel under thick Irish cloud typically makes 10 to 25 per cent of its clear-sky output, because it’s working from diffuse light rather than direct sun. A bright overcast day in May can out-produce a clear day in January, because the day is twice as long.

What Quietly Cuts Output on a Real Roof?

The county and the direction are fixed. These aren’t, and they’re where a system that should make 3,900 kWh ends up making 3,200.

• Shading from a chimney, a tree or a neighbour’s extension. On a string inverter, one shaded panel drags down the whole row for as long as the shadow sits there.
• Dirt and moss. Irish rain keeps panels fairly clean, but a roof under trees or near a farmyard can lose 5 per cent or more by midsummer.
• Inverter sizing. An inverter smaller than the array clips the peaks on bright days. Common on cheap quotes.
• Heat. Panels lose output as they warm up, which is one reason a cool, bright April day often beats a hot one in July.
• Age. Panels lose roughly half a per cent of output per year, so a system makes about 88 to 90 per cent of its day-one figure after 20 years.

Across SPV’s 3,000-plus installs, shading is the one that bites most often, and it’s the one a proper site survey catches before the panels go up. Optimisers or microinverters fix it where a tree can’t be cut back.

How Do You Check What Your Own Roof Will Make?

Two ways. The first is a desk estimate. Put your address, roof direction and pitch into PVGIS, which is free and public, and it’ll give you a monthly kWh figure for a system of any size. The tool is at the European Commission’s PVGIS site, and it’s the same data every honest installer uses.

The second is a site survey, where someone stands on the roof or flies a drone over it, measures the shading through the day and sizes the inverter to match. That’s what turns a desk estimate into a quote you can hold the installer to.

Once the system is in, the monitoring app shows real output against the estimate, month by month. A system running 10 per cent under its PVGIS figure in its first summer has a problem worth raising.

A solar system in Ireland makes a predictable amount of electricity, good enough to plan a budget around. What’s unpredictable is a roof nobody has looked at. If you’d like a figure for your own house rather than a national average, request a free quote through the contact page or ring 049 489 1207, and SPV will have a survey-based estimate back to you within 24 hours.

FAQs

How much electricity does a 4kW solar system generate in Ireland?

Around 3,600 kWh a year on a south-facing roof, based on the PVGIS national average of about 910 kWh per kWp. In Cork or Dublin it’s closer to 3,900, and in Donegal closer to 3,100.

How much electricity does one solar panel produce per day in Ireland?

A 430W panel averages about 1 kWh a day across the year, but that hides a huge swing. The same panel makes around 2 kWh on a clear June day and under half a kWh on a short December one.

Do solar panels work on cloudy days in Ireland?

Yes, at 10 to 25 per cent of their clear-sky output, because they generate from diffuse light as well as direct sun. Long overcast summer days still produce useful electricity, and short winter ones produce very little whatever the weather.

Which direction is best for solar panels in Ireland?

South, at a pitch of 30 to 35 degrees. East or west loses 15 to 20 per cent over the year but often matches household usage better, and north is usually not worth fitting.

How much does the location in Ireland affect solar output?

PVGIS puts the spread at about 20 per cent between the best county, Cork, at around 986 kWh per kWp and the worst, Donegal, at around 782. Dublin and the south-east sit near the top, the midlands in the middle and the north-west at the bottom.

How much output do solar panels lose over time?

Roughly half a per cent a year, so a system still makes about 88 to 90 per cent of its original output after 20 years. Most panel warranties guarantee a figure in that range.