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Plug-in solar on a flat roof (extension, garage or dormer)

A flat roof gives an unshaded spot with no climbing ladders onto a pitched roof. Low-tilt frames (around 10–15°) keep the panels out of the wind and still make around 90% of an ideal setup facing south.

How much a two-panel kit makes here

FacingPer yearvs idealSaving
South788 kWh90%£120
South-east771 kWh88%£118
South-west766 kWh88%£118
East723 kWh83%£113
West717 kWh82%£112
North648 kWh74%£104

920W kit with an 800W inverter, middle of England, someone home part of the day, 26.32p/kWh. “Ideal” = garden frame facing south at 35°. Data: PVGIS.

Tips

Best-value kits for a flat roof

KitPriceSavingPayback
Worldwide Solar 800W (2 × 535W, HMS-800-2WB)
Worldwide Solar		£498£1254.0 yrsSee deal
Worldwide Solar 800W (2 × 460W, HMS-800-2WB)
Worldwide Solar		£484£1204.0 yrsSee deal
Solarfy Duo 910W (flat mount)
Solarfy		£549£1194.6 yrsSee deal
Thunder Bolt 920W kit
Thunder Energy		£749.99£1206.3 yrsSee deal
Thunder Bolt 460W kit
Thunder Energy		£549.99£797.0 yrsSee deal

What would a kit save you?

No postcode – using the UK average (Birmingham).
Where would the panels go?
Which way do they face?
Use a phone compass, standing with your back to the wall or rail.
Shade during the day
Who's home in the daytime?
Solar only saves money when it powers something as it's made.
Space for
Your electricity price
Default: Ofgem price cap average, 1 Oct – 31 Dec 2026.
Only Octopus pays for plug-in export so far, and only on kits bought from them.
£125 a yearestimated saving
4.0 yrspayback
853 kWhmade per year
474 kWh (56%)used in your home

Based on the Worldwide Solar 800W (2 × 535W, HMS-800-2WB) (£498), the fastest payback for this spot.

Jan: 23 kWh madeJan: 17 kWh used at homeJanFeb: 37 kWh madeFeb: 25 kWh used at homeFebMar: 69 kWh madeMar: 40 kWh used at homeMarApr: 99 kWh madeApr: 51 kWh used at homeAprMay: 116 kWh madeMay: 59 kWh used at homeMayJun: 119 kWh madeJun: 61 kWh used at homeJunJul: 118 kWh madeJul: 61 kWh used at homeJulAug: 101 kWh madeAug: 53 kWh used at homeAugSep: 78 kWh madeSep: 43 kWh used at homeSepOct: 48 kWh madeOct: 31 kWh used at homeOctNov: 27 kWh madeNov: 20 kWh used at homeNovDec: 19 kWh madeDec: 15 kWh used at homeDec

made used at home (the part that saves money)

Best kits for this spot

Fastest payback

Worldwide Solar 800W (2 × 535W, HMS-800-2WB)

£498 at Worldwide Solar · saves about £125/yr · pays back in 4.0 yrs

See deal at Worldwide Solar
Runner-up

Worldwide Solar 800W (2 × 460W, HMS-800-2WB)

£484 at Worldwide Solar · saves about £120/yr · pays back in 4.0 yrs

See deal at Worldwide Solar
Also good

Solarfy Duo 910W (flat mount)

£549 at Solarfy · saves about £119/yr · pays back in 4.6 yrs

See deal at Solarfy