Solar Panel Types Ireland 2026 — Mono, TOPCon, HJT & Bifacial Compared

The Irish Number That Changes the Whole Comparison

Most panel comparisons you will read were written for markets with a lot of direct sun. Ireland is not one of those markets, and the gap is bigger than people assume.

Using the European Commission's PVGIS database (SARAH2 satellite record, 16-year average from 2005 to 2020), here is how the light actually arrives:

Annual solar radiation on a horizontal surface, and how much of it is diffuse

Location	Annual radiation (kWh/m²)	Diffuse share
Dublin	1,002	57.5%
Cork	1,033	58.4%
Belfast	955	59.3%
Madrid	1,785	31.2%

Nearly 58% of the light reaching a Dublin roof over a year is diffuse: scattered through cloud and haze rather than arriving as a direct beam. In Madrid that figure is 31%. Even in the brightest month of the Irish year, May, the diffuse share in Dublin only drops to about 53%. In December it is 62%.

That single statistic reshuffles the priority list. Specs that pay off under a hard, hot, direct beam matter less here. Specs that govern how a panel behaves in weak, scattered light and mild temperatures matter more. Keep it in mind as you read the rest of this page, because it is the reason some genuinely impressive panel technology is worth less on an Irish roof than the brochure suggests.

The Four Panel Types You Will Actually Be Quoted

Every panel a registered Irish installer will put on your roof is crystalline silicon. What changes is the cell architecture inside.

Mono PERC (P-type)

The workhorse of the last decade. PERC stands for Passivated Emitter and Rear Cell, a rear-surface layer that reflects unabsorbed light back through the cell for a second chance. Panel efficiency lands around 20% to 21.5%. PERC modules are still perfectly good hardware and there are hundreds of thousands of them on Irish roofs working exactly as intended. They are simply no longer the default on new quotes, because the technology that replaced them costs about the same.

N-type TOPCon

This is what replaced PERC, and it did so quickly. TOPCon stands for Tunnel Oxide Passivated Contact, and the change that matters is underneath the acronym: it is built on N-type silicon rather than P-type. That buys a higher efficiency ceiling, better behaviour as the panel heats up, slower long-term degradation, and immunity to the light-induced degradation that affected P-type cells early in their life. Efficiency typically runs 21.5% to 23%. It is now the mainstream residential panel across Europe, Ireland included, and it is what most SEAI-registered installers will quote you by default in 2026.

HJT (Heterojunction)

HJT sandwiches thin amorphous silicon layers around a crystalline wafer. It has the best temperature coefficient of the three, excellent low-light response and very low degradation, with efficiency reaching 23% to 24.5% on residential modules. It also costs meaningfully more per watt and is harder to source through Irish installers. It makes sense in one specific situation, covered below.

Polycrystalline

The blue, speckled panels of the 2010s, made from multiple silicon crystals. Efficiency around 17% to 18%. They are not sold for new Irish residential installs any more and you should treat a poly quote in 2026 as a reason to ask questions about where the stock came from.

If you want to know which manufacturers Irish installers actually specify within these categories, that is a separate question and we cover it in our guide to the best solar panels in Ireland. This page is about the technology; that page is about the brands.

Two Real Datasheets, Side by Side

Abstract efficiency ranges are less useful than two actual products. Below are the published specifications for a widely-installed N-type TOPCon module and a widely-installed mono PERC module of the same physical format, so the comparison is like for like.

Published datasheet specifications: TOPCon vs mono PERC

Specification	JinkoSolar Tiger Neo (N-type TOPCon)	JA Solar Deep Blue 3.0 (mono PERC)
Cell type	N-type monocrystalline, 108 half-cells	P-type mono PERC, half-cell
Module efficiency	22.27%	21.00%
Temperature coefficient (Pmax)	−0.29% per °C	−0.35% per °C
NOCT	45°C	45°C
Product warranty	25 years	12 years
Performance warranty	30 years	25 years
First-year degradation	1.00%	2.00%
Annual degradation after year one	0.40%	0.55%
Guaranteed output at end of warranty	87.4% at year 30	84.8% at year 25

Read that table again and notice where the real gap sits. It is not the efficiency line, which is worth about one percentage point. It is the warranty and degradation block: 25 years of product cover against 12, and a guarantee that still holds at year 30 rather than expiring at year 25. On a system you expect to own for two decades, that is the difference that compounds. Our guide to how long solar panels last in Ireland goes into what those warranty terms actually oblige a manufacturer to do.

Does the Temperature Coefficient Matter in Ireland?

Less than you would think, and this is where southern-European reasoning gets imported without adjustment.

Every panel is rated at a cell temperature of 25°C. The temperature coefficient tells you what you lose for each degree above that. Both panels above carry an NOCT of 45°C, measured at 800 W/m² with 20°C ambient air, so panels do run hot even here on a bright day.

Do the arithmetic at that 20-degree rise. The PERC panel loses about 7.0% of its rated output. The TOPCon panel loses about 5.8%. That gap of roughly 1.2 percentage points is the very best case for TOPCon on temperature, and it only applies while the panel is that hot.

Now consider how often that happens. Met Éireann recorded a mean temperature of 16.59°C for July 2025, which it noted was 1.21°C above the 1991 to 2020 long-term average. In other words, a warm Irish July. A Spanish system spends whole summers in conditions where the temperature coefficient bites hard. An Irish system spends most of its generating hours nowhere near it. Averaged across an Irish year, the temperature advantage is worth a fraction of a percent, not the headline figure.

The low-light behaviour is the more relevant advantage here, given that diffuse share of 58%. N-type cells do hold their efficiency better at low irradiance, which is the sort of light Ireland supplies in bulk. Worth being straight with you, though: the specific percentages quoted for low-light gains almost always come from manufacturer testing or vendor-commissioned field trials, and we are not aware of independent long-term Irish field data comparing the technologies side by side. Treat the direction of the claim as sound and the size of it as marketing until someone measures it here.

Bifacial Panels on an Irish Roof: Usually Pointless

Bifacial modules generate from both faces, picking up light reflected off the surface beneath them. That is a real effect and it can add 5% to 15% in the right setting.

A pitched, tiled Irish roof is not the right setting. The rear of the panel faces a dark slate or concrete tile a few centimetres away. There is almost no light down there to reflect and almost no gap for it to travel through. You pay a premium for a rear face that does close to nothing.

Bifacial earns its money where the back of the panel can see something bright and open: a ground-mounted array over pale gravel, or a flat roof with a light-coloured membrane and a proper mounting height. If an installer proposes bifacial for a standard pitched roof, ask what rear-side gain they are actually modelling and how. A good answer will reference the surface below the panels. A vague answer tells you the premium is going somewhere other than your generation figures.

Does the Panel Type Change Your SEAI Grant?

No. This surprises people, so it is worth being precise about how the grant works.

The SEAI Solar Electricity Grant is paid purely on installed capacity: €700 per kWp for the first 2 kWp, then €200 for every additional kWp up to 4 kWp, capping at €1,800 in 2026. A 2 kWp system draws €1,400 and a 4 kWp system draws the full €1,800, whether those kilowatts come from TOPCon, PERC or HJT.

SEAI also does not run an approved-panel list. What SEAI registers is companies and installers, who commit to working to the SEAI Domestic Technical Standards and Specification and the Solar PV Code of Practice. SEAI states plainly on its own registration pages that it "does not approve, guarantee or warranty a company/installer or their works." So if a salesperson tells you a particular panel is "SEAI approved," they are describing something that does not exist. The registration attaches to the installer, not the module.

The rest of the grant conditions are equally panel-agnostic. Your home must have been built and lived in before 2021, the work must be done by a company from the SEAI registered list with the electrical work by a Safe Electric Ireland electrician, an NC6 connection application goes to ESB Networks, your installer signs a Declaration of Works, and a post-works BER assessment has to be completed and published by a registered BER assessor before the grant can be drawn down. You have eight months from grant approval to complete the work. And since May 2023 the 0% VAT rate applies to the supply and installation of solar panels on private residences, which again does not vary by panel technology.

What Actually Decides Your Output in Ireland

If you want the honest ranking of what moves your annual kWh, panel type is not near the top of it.

PVGIS modelling puts a 1 kWp crystalline system at an optimal 41° tilt and near-due-south azimuth at about 977 kWh a year in Dublin and 979 kWh in Cork, allowing 14% system losses. Real Irish roofs, at whatever pitch and orientation the builder chose, more commonly deliver around 850 to 900 kWh per kWp. That gap between the ideal and the typical is roughly 10%, and it exists before anyone has picked a panel brand.

Shading is bigger still. A chimney or a neighbouring gable clipping one string can cost far more than the entire mono-to-TOPCon efficiency difference, which is why panel-level optimisers are sometimes worth more than a panel upgrade. Roof direction moves output by tens of percent between a south-facing and a north-facing plane. And system size, covered in how many solar panels you need, sets the ceiling on everything else.

Then there is what happens to the DC power after the panels. A mismatched or undersized inverter will quietly cap a good array. Panel type sits below all of these in the order of things that decide your annual kWh.

None of which means panel type is irrelevant. It means you should settle orientation, shading and sizing with your installer first, then pick the panel, rather than letting the panel spec sheet drive a conversation it was never going to win.

How to Read a Quote's Panel Line

Quotes tend to give you a brand, a model number and a wattage. Ask for four more things:

• The cell technology, named. "N-type TOPCon" or "P-type mono PERC," not "high-efficiency monocrystalline," which describes both.
• Both warranty numbers. Product years and performance years, separately, plus the guaranteed output percentage at the end of the performance term.
• First-year and annual degradation. The difference between 2.00% and 1.00% in year one is real money over twenty years.
• The datasheet itself. Every reputable manufacturer publishes a PDF with the temperature coefficient and NOCT printed on it. An installer who cannot produce it for the exact model they are quoting is a flag.

Comparing that block across three quotes tells you far more than comparing headline wattages, because a 440W panel and a 425W panel of different physical sizes are not the comparison you think they are. Our guide to solar panel sizes and dimensions explains why watts per square metre is the number that matters on a fixed roof.

So Which Type Should You Buy?

For a standard Irish home with a reasonable amount of usable roof, N-type TOPCon in 2026. It is what most SEAI-registered installers quote as standard, the price premium over PERC has largely gone, and the warranty terms are materially better.

Choose HJT only if your usable roof is genuinely constrained and you need every watt out of a small area, and only after you have priced it against simply accepting a slightly smaller system. Accept mono PERC without complaint if the price is clearly better and the warranty terms are comparable, because the hardware is proven and the output difference is small. Skip bifacial on a pitched roof. Walk away from polycrystalline on a new install.

Then spend the attention you saved on the things that actually move the number: where the panels face, what shades them, how many there are, and whether the installer has the SEAI registration and the Safe Electric credentials to sign the Declaration of Works that releases your grant.

Frequently Asked Questions