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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SW9 (Lambeth)

See if solar pays off for you in Lambeth — price, savings and payback in under a minute (official UK data).

Solar Calculator

Change the settings below to see how costs and savings work for your situation.

System Size

Roof Direction

Battery Storage

Export Value

Your Numbers

Break-even
12.6 years
After this, it's pure profit
Upfront Cost
£6,104
What you pay to get started
Annual Benefit
£483
What you save every year
Profit Over 25 Years
£5,971
After paying itself off, you're this much ahead

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How we calculate this

Solar generation: Based on typical south-facing roof at 35° angle. We account for weather, dirt, and system losses (14%).

How much you'll use directly:

  • Without battery: You'll use about 40% of what you generate. The rest gets sold back to the grid.
  • With 5 kWh battery: You'll use about 70% (battery stores extra for evening use).
  • With 10 kWh battery: You'll use about 75% (more storage means less exported).
  • Panel-only payback: Bigger systems don’t shorten payback—cost and savings rise together per kW.
  • Battery & payback: Batteries raise self-use and cut bills, but added hardware cost often lengthens break-even at typical UK rates.
  • When a battery can still make sense:
    • Evening-heavy usage patterns
    • Time-of-use tariffs / cheap night rates
    • Low export rate vs. high unit rate
    • Heat pump or EV charging synergy
    • Optional backup/resilience (system-dependent)
    • Lower evening-hour CO₂ vs. grid

Costs: Battery prices are typically £700 per kWh. Export tariffs vary by supplier (usually 5–15p per kWh).

Grid connection: Systems up to about 3.7 kW typically need just a notification (G98). Larger systems may need permission (G99).

These are typical values based on average usage patterns. Your actual results will vary based on your roof, shading, and how you use electricity.

Your area in context

In London, the current unit rate is 25.63p/kWh with a 46.06p/day standing charge. Your postcode’s south-facing sunshine yield is 991 kWh/kW — 0 above the regional median (991).

Read the full story

A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 991 kWh per year on a south-facing roof. We value self-used electricity at 25.6p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
25.6p/kWh
Standing charge
46.1p/day
Sunshine yield (south)
991 kWh/kW
Export price (baseline)
10p/kWh

Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.

No battery 5 kW example → Annual benefit: £805, Upfront: £10,173, Break-even: 12.6 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 792 kWh 1189 kWh £203 £119 £322 £4,069 12.6 yrs £2,371
3 kW 2972 kWh 1189 kWh 1783 kWh £305 £178 £483 £6,104 12.6 yrs £3,556
4 kW 3962 kWh 1585 kWh 2377 kWh £406 £238 £644 £8,138 12.6 yrs £4,741
5 kW 4953 kWh 1981 kWh 2972 kWh £508 £297 £805 £10,173 12.6 yrs £5,927
6 kW 5944 kWh 2377 kWh 3566 kWh £609 £357 £966 £12,207 12.6 yrs £7,112
7 kW 6934 kWh 2774 kWh 4161 kWh £711 £416 £1,127 £14,242 12.6 yrs £8,298
8 kW 7925 kWh 3170 kWh 4755 kWh £812 £475 £1,288 £16,276 12.6 yrs £9,483

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

3 kWh battery 5 kW example → Annual benefit: £960, Upfront: £12,273, Break-even: 12.8 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 1189 kWh 792 kWh £305 £79 £384 £6,169 16.1 yrs £1,509
3 kW 2972 kWh 1783 kWh 1189 kWh £457 £119 £576 £8,204 14.2 yrs £3,314
4 kW 3962 kWh 2377 kWh 1585 kWh £609 £158 £768 £10,238 13.3 yrs £5,119
5 kW 4953 kWh 2972 kWh 1981 kWh £762 £198 £960 £12,273 12.8 yrs £6,923
6 kW 5944 kWh 3566 kWh 2377 kWh £914 £238 £1,152 £14,307 12.4 yrs £8,728
7 kW 6934 kWh 4161 kWh 2774 kWh £1,066 £277 £1,344 £16,342 12.2 yrs £10,533
8 kW 7925 kWh 4755 kWh 3170 kWh £1,219 £317 £1,536 £18,376 12.0 yrs £12,338

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

5 kWh battery 5 kW example → Annual benefit: £1,037, Upfront: £13,673, Break-even: 13.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 1387 kWh 594 kWh £355 £59 £415 £7,569 18.2 yrs £729
3 kW 2972 kWh 2080 kWh 892 kWh £533 £89 £622 £9,604 15.4 yrs £2,843
4 kW 3962 kWh 2774 kWh 1189 kWh £711 £119 £830 £11,638 14.0 yrs £4,957
5 kW 4953 kWh 3467 kWh 1486 kWh £889 £149 £1,037 £13,673 13.2 yrs £7,072
6 kW 5944 kWh 4161 kWh 1783 kWh £1,066 £178 £1,245 £15,707 12.6 yrs £9,186
7 kW 6934 kWh 4854 kWh 2080 kWh £1,244 £208 £1,452 £17,742 12.2 yrs £11,301
8 kW 7925 kWh 5547 kWh 2377 kWh £1,422 £238 £1,660 £19,776 11.9 yrs £13,415

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

7.5 kWh battery 5 kW example → Annual benefit: £1,060, Upfront: £15,423, Break-even: 14.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 1446 kWh 535 kWh £371 £53 £424 £9,319 22.0 yrs £-835
3 kW 2972 kWh 2169 kWh 802 kWh £556 £80 £636 £11,354 17.8 yrs £1,372
4 kW 3962 kWh 2893 kWh 1070 kWh £741 £107 £848 £13,388 15.8 yrs £3,579
5 kW 4953 kWh 3616 kWh 1337 kWh £927 £134 £1,060 £15,423 14.5 yrs £5,786
6 kW 5944 kWh 4339 kWh 1605 kWh £1,112 £160 £1,273 £17,457 13.7 yrs £7,994
7 kW 6934 kWh 5062 kWh 1872 kWh £1,297 £187 £1,485 £19,492 13.1 yrs £10,201
8 kW 7925 kWh 5785 kWh 2140 kWh £1,483 £214 £1,697 £21,526 12.7 yrs £12,408

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

10 kWh battery 5 kW example → Annual benefit: £1,076, Upfront: £17,173, Break-even: 16.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 1486 kWh 495 kWh £381 £50 £430 £11,069 25.7 yrs £-2,462
3 kW 2972 kWh 2229 kWh 743 kWh £571 £74 £646 £13,104 20.3 yrs £-192
4 kW 3962 kWh 2972 kWh 991 kWh £762 £99 £861 £15,138 17.6 yrs £2,077
5 kW 4953 kWh 3715 kWh 1238 kWh £952 £124 £1,076 £17,173 16.0 yrs £4,346
6 kW 5944 kWh 4458 kWh 1486 kWh £1,143 £149 £1,291 £19,207 14.9 yrs £6,615
7 kW 6934 kWh 5201 kWh 1734 kWh £1,333 £173 £1,506 £21,242 14.1 yrs £8,884
8 kW 7925 kWh 5944 kWh 1981 kWh £1,523 £198 £1,721 £23,276 13.5 yrs £11,154

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

13.5 kWh battery 5 kW example → Annual benefit: £1,091, Upfront: £19,623, Break-even: 18.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1981 kWh 1526 kWh 456 kWh £391 £46 £437 £13,519 31.0 yrs £-4,788
3 kW 2972 kWh 2288 kWh 684 kWh £586 £68 £655 £15,554 23.8 yrs £-2,457
4 kW 3962 kWh 3051 kWh 911 kWh £782 £91 £873 £17,588 20.1 yrs £-125
5 kW 4953 kWh 3814 kWh 1139 kWh £977 £114 £1,091 £19,623 18.0 yrs £2,206
6 kW 5944 kWh 4577 kWh 1367 kWh £1,173 £137 £1,310 £21,657 16.5 yrs £4,537
7 kW 6934 kWh 5339 kWh 1595 kWh £1,368 £159 £1,528 £23,692 15.5 yrs £6,868
8 kW 7925 kWh 6102 kWh 1823 kWh £1,564 £182 £1,746 £25,726 14.7 yrs £9,199

Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.

Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.

Insights for SW9

Figures below are tailored to SW9 — click through for full league tables.

Big-Roof Britain Rank #2131 of 2182
3.8 kWp (UK avg 5.1 kWp)
~8 panels (≈430 W)
Solar Payback Index Rank #1304 of 2997
11.0 years (UK avg 11.3 years)
~£921 /yr • £10,173 upfront
Standing-Charge Drag Rank #1080 of 2997
18.3% (UK avg 21.7%) drag on savings
£168 fixed • ~£921 /yr value

Your Area at a Glance

Your Electricity Rate
25.63p/kWh
Daily Fixed Charge
46.06p/day
Local Sunshine
991kWh/kW
A 1 kW system generates ~991 kWh per year. A typical home uses ~2,700 kWh per year.
Typical System Size
3.0kW
For eligible homes in this area

⚠️ This area is predominantly flats. Many residents require freeholder approval for solar installations. System size shown reflects houses and bungalows only.

Local Property Data

Property Types

Houses: 12% • Flats: 74% • Bungalows: 0% Based on 16,223 properties

Coverage

Lambeth (100%)

Areas Covered

Brixton North, Myatt's Fields, Stockwell East, Brixton Windrush, Clapham East, Brixton Acre Lane, Oval, Herne Hill & Loughborough Junction + 3 more

Data Sources & Assumptions

Solar yield: PVGIS (EU Joint Research Centre), January 2025 data

Electricity rates: Ofgem price cap, Q4 2025

Installation costs: MCS certified installer data, March 2025

Property data: EPC open data (Open Government Licence), aggregated

All estimates are typical values. Actual results vary based on your specific situation, roof characteristics, and usage patterns.

Compare nearby areas

Nearby in London

SW99 (Lambeth)
≈0.4 km away
Local sunshine: ~991 kWh/kWp · +0% vs SW9
SE5 (Southwark)
≈1.3 km away
Local sunshine: ~993 kWh/kWp · +0% vs SW9
SW8 (Lambeth)
≈1.4 km away
Local sunshine: ~991 kWh/kWp · +0% vs SW9
SW2 (Lambeth)
≈1.7 km away
Local sunshine: ~990 kWh/kWp · -0% vs SW9
SE24 (Lambeth)
≈1.8 km away
Local sunshine: ~993 kWh/kWp · +0% vs SW9
SW4 (Lambeth)
≈1.9 km away
Local sunshine: ~990 kWh/kWp · -0% vs SW9

Similar sunshine across the UK

N21 (Enfield)
~991 kWh/kWp · -0% vs SW9
HP8 (Buckinghamshire)
~991 kWh/kWp · -0% vs SW9
SG4 (North Hertfordshire)
~991 kWh/kWp · +0% vs SW9