How to choose solar panels for a UK roof: six metrics that matter in 2026
Last updated: Written by Anthony Bushen-GarvieReviewed by a Geko MCS-certified engineer 8 min
How to choose solar panels UK in one line: pick the panel that fits your roof, not the one with the biggest wattage on the datasheet. Module efficiency, shade behaviour, bifacial gain, temperature coefficient, warranty terms and whole-system value decide how much electricity you actually get over 25 years.
Geko Energy is MCS-certified. We fit Aiko and DMEGC with our own employed engineers after a free 30-minute video consultation. No doorstep sales.
- 01Module efficiencyWatts per m² of roof
- 02Shade handlingOutput kept under shadows
- 03Bifacial gainLight used from the rear
- 04Temperature coefficientPower lost as cells heat up
- 05WarrantiesProduct, performance, workmanship
- 06Whole-system valueLifetime kWh against installed cost
Quick answer: the six metrics
| Metric | What it tells you | Why it matters on a UK roof |
|---|---|---|
| Module efficiency | Watts produced per m² under lab test | Small or awkward roofs need more power per tile |
| Shade handling | Output kept when chimneys, trees or dormers cast shadows | Few UK roofs are completely unshaded |
| Bifacial gain | Extra generation from light on the rear | Useful on flat roofs and ground mounts; usually tiny on close-coupled pitched tiles |
| Temperature coefficient | Power lost as cells heat up | Hot summer roofs and in-roof installs run well above the 25°C lab test |
| Warranty | Product defects + guaranteed output over time | A long number only helps if manufacturer and installer still stand behind it |
| Whole-system value | Lifetime kWh and bill savings vs installed cost | Scaffolding, labour, inverter, battery and design usually dwarf the module price |
Swipe to see the full table
Not sure which panel fits?
1. Module efficiency
Module efficiency is how much of the light hitting a panel becomes electricity under Standard Test Conditions (STC): 1,000 W of light per square metre and a cell temperature of 25°C. Convert a quarter of that light and the module is 25% efficient.
Your roof area is fixed. Higher efficiency means more kilowatts from the same footprint. It's most useful when space is tight, when you want fewer panels on a street-facing elevation, or when you need a target system size without covering every free tile.
Modern residential modules commonly sit in the low-to-mid 20% range; premium N-type ABC panels go higher. Aiko's Neostar 3S+60 datasheet lists up to 24.6% at STC for the top wattage in that series. We confirm the exact model on your quote. Efficiency is not everything: a well-designed unshaded array can beat a flagship module stuck behind a chimney.
2. Shade handling
The Energy Saving Trust is clear: nearby buildings, trees or chimneys cut performance. An unshaded south-facing roof is ideal. East- and west-facing roofs still work, typically generating around 15–20% less than due south. North-facing is rarely recommended.
When shade is unavoidable, ask about:
- Bypass diodes: modules split into zones; a diode bypasses a shaded zone so the rest keeps working.
- ABC cell layouts: rear contacts can limit partial-shade losses; they do not make panels immune to shade.
- Optimisers or microinverters: can stop one shaded panel dragging a string; the Energy Saving Trust notes they help when shade is present.
A proper MCS design includes shade analysis. If a quote ignores trees that will grow for 25 years, walk away.
3. Bifacial gain
Bifacial panels can generate from front and rear when light reaches the backsheet. Datasheet rear uplifts are lab or best-case figures, not a promise for every UK roof. On close-coupled pitched tiles rear gain is usually negligible; on flat roofs and ground mounts with spaced, tilted rows it can matter. If a quote credits bifacial uplift without modelled rear irradiance for your mounting height, ignore it in the savings figure.
4. Temperature coefficient
Panels are rated at 25°C cell temperature; real roofs run hotter. Dark tiles and in-roof installs with poor airflow can push cells toward 60–70°C. The Pmax temperature coefficient is power lost per °C above 25°C (lower magnitude is better). At 70°C, −0.26%/°C costs about 11.7% of peak power; −0.30%/°C costs about 13.5%. Aiko's Neostar 3S+60 datasheet lists −0.26%/°C.
Try your own numbers
- −0.26%/°C11.7% of peak power468 W lost
- −0.30%/°C13.5% of peak power540 W lost
- −0.35%/°C15.8% of peak power630 W lost
Illustrative: peak power lost on a 4 kW array at that cell temperature. Real output also depends on light, wiring and the inverter.
5. Warranties
“25-year warranty” can mean three things: product (defects), performance (minimum output after 25–30 years under STC), and workmanship / insurance-backed guarantee (installer labour, ideally insured). Aiko's Neostar 3S+60 datasheet lists 25-year product cover and a 30-year performance curve to 88.85% at year 30. DMEGC on our page carries 25-year product and performance cover. Match warranty text to the exact model on your quote. Fine print: warranty traps. Geko adds a 6-year IAA insurance-backed guarantee and uses 100% in-house employed installers across England and Wales.
6. Whole-system value
Pounds-per-watt compares modules, not quotes. Scaffolding, labour, inverter, mounting, DNO paperwork and any battery usually dwarf panel price.
Optimise for modelled annual kWh (south-facing myth); self-consumption with battery and tariff (battery guide, SEG); VAT timing: qualifying residential solar/battery installs are zero-rated until 31 March 2027, then 5% from 1 April 2027 (VAT Notice 708/6, VAT window); and MCS products plus installer (Product Directory, Find an Installer).
How Geko matches panels to your roof
On the free consultation we review roof, shade, usage and budget, then specify Aiko Neostar (N-type ABC, all-black, high W/m²) or DMEGC (Tier-1 value). Both pair with Fox ESS and Sigenergy. We handle DNO G98/G99 and SEG registration. Call 07700 140545 (Mon–Fri, 9am–6pm).
Or compare quotes you already have.
Common mistakes
- 1Buying on wattage alone. A larger 500 W panel can deliver similar or worse watts per square metre than a smaller high-efficiency module.
- 2Ignoring shade in the savings spreadsheet.
- 3Crediting bifacial uplift on a pitched tiled roof without a model.
- 4Treating “25-year warranty” as one number instead of product, performance and workmanship.
- 5Choosing the cheapest modules while the quote is vague on who climbs the roof.
FAQs
What is the best solar panel for a UK home in 2026?
- There is no single winner. The best panel maximises lifetime generation and value on your roof after shade, orientation, mounting and warranty are modelled. Geko typically specifies Aiko Neostar or DMEGC after a design review.
How efficient should a residential solar panel be?
- Most modern residential modules sit in the low-to-mid 20% range under STC. Premium ABC modules can exceed 24%. Higher efficiency helps most when roof space is limited.
Do solar panels work on cloudy UK days?
- Yes. The Energy Saving Trust notes that cells do not need direct sunlight and still generate in cloudy weather, though output is lower than in clear sun.
Are bifacial solar panels worth it in the UK?
- Often on flat roofs and ground mounts with reflected light behind the array. On close-coupled pitched tiled roofs rear gain is typically small.
What temperature coefficient should I look for?
- Lower magnitude is better (for example −0.26%/°C is stronger than −0.30%/°C). It matters more for hot roofs and in-roof systems.
Do I need MCS-certified panels and an MCS installer?
- Not legally required, but without an MCS-certified install you typically lose Smart Export Guarantee access and important consumer protections. Verify panels and installers on mcscertified.com.
Will solar panel VAT stay at 0%?
- For qualifying residential installations the temporary zero rate runs to 31 March 2027. From 1 April 2027 it reverts to 5% under HMRC's VAT Notice 708/6. Confirm on GOV.UK before you sign.
How do I get a design that uses these metrics properly?
- Speak to an MCS-certified engineer who will model your roof. Start with Geko's free 30-minute video consultation, or call 07700 140545 (Mon–Fri 9am–6pm).
Get panels chosen for your roof
A free 30-minute video consultation with one of our engineers, then one total price with the exact panel, inverter and warranty on it.
Phone lines open Mon–Fri, 9am–6pm
Sources
- Energy Saving Trust: Solar panels
- GOV.UK: VAT Notice 708/6
- MCS: Solar PV for consumers
- MCS: Product Directory
- MCS: Find an Installer
- Aiko Solar: Neostar 3S+60 manufacturer datasheet (efficiency, temperature coefficient, warranty curve; opened November 2026)
- Geko Energy: Aiko, DMEGC, warranty traps, MCS explained
Geko Energy designs and installs solar PV, battery storage and EV charging. We are not affiliated with panel or battery manufacturers beyond the products we specify. Equipment availability and datasheet figures change, so we confirm the exact model on your quotation.
