Solar Panels & Inverters Explained (UK 2026)

The marketing around solar panels and inverters reads like a tech sheet for a different industry. Half a quote's value is hidden in the data sheets nobody opens. Here's what the terms actually mean, what's mainstream in 2026, and how to tell whether the kit on your quote is appropriate for your roof.

The panel technology landscape

Almost every panel sold for UK residential roofs in 2026 is monocrystalline silicon. The differences are in the cell architecture:

• PERC (Passivated Emitter Rear Cell) — the previous mainstream, now being phased out. Mid-20% efficiency. Still fine, but you should be buying TOPCon or back-contact in 2026.
• TOPCon (Tunnel Oxide Passivated Contact) — the current volume technology. ~22–23% efficiency, less degradation over time, better low-light performance than PERC. The default for mainstream brands like Jinko, Trina, JA, LONGi.
• HJT (Heterojunction) — higher efficiency (~22–24%) and better temperature coefficient than TOPCon. More expensive. REC Alpha and some premium tiers use HJT.
• Back-contact / IBC (Interdigitated Back Contact) — all the wiring is on the back of the cell, so the front of the panel is uniformly black with no busbars. ~23–24% efficiency. Premium tier: SunPower/Maxeon, LONGi HPBC, REC Alpha Pure-R. Most expensive.

What "475 W" really tells you

The 440 W panel of 2024 has been displaced. 475 W is the new mainstream for residential rooftop solar in 2026, with 500W+ panels common on premium roofs. Same panel footprint, more output. For roof-area-constrained homes, this is the biggest single development of the last few years.

Wattage matters, but efficiency matters more for tight roofs:

• 20% efficient panels — typical 2026 budget option, ~390 W per square metre
• 22% efficient panels — mainstream TOPCon, ~430 W per square metre
• 24% efficient panels — premium back-contact, ~470 W per square metre

On a 20 m² roof, that's the difference between a 7.8 kWp and a 9.4 kWp system. For larger roofs the efficiency premium doesn't pay back; for small roofs it usually does.

The 2026 panel league table

Warranties

Industry standard in 2026:

• Product warranty: 25 years on Maxeon and REC; 12–15 years on mainstream TOPCon. The product warranty covers manufacturing defects (cell failure, frame separation, etc.).
• Performance warranty: 25–30 years. Guarantees the panel retains a stated percentage of original output. Premium panels typically guarantee 87–92% retained at year 25; mainstream guarantees 80–85%.

The inverter — usually overlooked, often the bottleneck

The inverter converts the DC from the panels into AC for your home and the grid. There are three architectures:

String inverter

One inverter handling all panels in a "string" (a series chain). Cheapest, simplest, most proven. Downside: the whole string drops to the output of the weakest panel under shade, soiling, or partial obstruction. Fine for simple unshaded roofs. Typical UK price £600–£1,200. Brands: SMA Sunny Boy, Fronius Primo, Solis, Growatt, GoodWe.

Hybrid inverter

A string inverter with a built-in battery connection. Future-proofs your install — fit a hybrid now even if you don't have a battery, and adding one later is much simpler than swapping a non-hybrid inverter. The 2026 UK default for any new install where battery is on the horizon. Typical UK price £800–£1,400. Brands: GivEnergy Gen 3, Fronius GEN24, GoodWe ET, Solis S6 Hybrid, Sunsynk, Growatt SPH, Huawei SUN2000.

Microinverters

A small inverter on each panel, doing per-panel MPPT (maximum power point tracking). Each panel operates independently — shading or soiling on one doesn't pull down the others. 25-year product warranties are standard. Real-time panel-level monitoring through the app. Downside: cost and complexity. Adds £100–£140 per panel — on a 12-panel system that's £1,500+ above a string inverter. Worth it for heavily shaded, multi-pitch, or complex roofs. Industry leader: Enphase IQ8+.

DC power optimisers (SolarEdge)

A middle option — small optimisers on each panel doing per-panel MPPT, but a central inverter doing the DC-to-AC conversion. Per-panel monitoring, less impact from partial shade than a pure string inverter, lower cost than microinverters. SolarEdge had quality issues 2023–25 and has restructured; the technology is solid but the brand picture is mixed in 2026.

How an inverter "clips" — important for sizing

Inverters have a maximum AC output. If you have 5 kWp of panels and a 3.68 kW inverter, on a bright June day the panels will try to produce 4.5+ kW but the inverter will cap output at 3.68 kW. That capped energy is lost. This is called inverter clipping.

A small amount of clipping (5–10%) is actually fine and can save money on the inverter. But aggressive clipping wastes generation. The DC:AC ratio that matters: aim for around 1.0–1.25 (i.e. a 4 kW inverter with 4–5 kWp of panels). On east-west splits where peak generation is flatter, you can run higher DC:AC ratios.

Why the 3.68 kW threshold matters

Above 3.68 kW per phase, you cross the threshold from G98 (fit-and-notify) to G99 (DNO pre-approval). That's why so many residential string inverters are sized at 3.68 kW — inverters can be installed without pre-approval. If your panels exceed 3.68 kWp, your installer can either: clip slightly (often fine), upsize the inverter and go G99 (2–8 week wait), or split into two inverters.

Three-phase supplies (rare in UK domestic, common in some rural and period properties) have 3.68 kW per phase, so 11.04 kW total before G99 kicks in. If you have three-phase, this massively simplifies upsizing.