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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SW1A (Westminster)

See if solar pays off for you in Westminster — 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
£5,976
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 1982 kWh 793 kWh 1189 kWh £203 £119 £322 £4,069 12.6 yrs £2,373
3 kW 2973 kWh 1189 kWh 1784 kWh £305 £178 £483 £6,104 12.6 yrs £3,560
4 kW 3964 kWh 1586 kWh 2378 kWh £406 £238 £644 £8,138 12.6 yrs £4,747
5 kW 4955 kWh 1982 kWh 2973 kWh £508 £297 £805 £10,173 12.6 yrs £5,933
6 kW 5946 kWh 2378 kWh 3568 kWh £610 £357 £966 £12,207 12.6 yrs £7,120
7 kW 6937 kWh 2775 kWh 4162 kWh £711 £416 £1,127 £14,242 12.6 yrs £8,307
8 kW 7928 kWh 3171 kWh 4757 kWh £813 £476 £1,288 £16,276 12.6 yrs £9,493

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 1982 kWh 1189 kWh 793 kWh £305 £79 £384 £6,169 16.1 yrs £1,512
3 kW 2973 kWh 1784 kWh 1189 kWh £457 £119 £576 £8,204 14.2 yrs £3,319
4 kW 3964 kWh 2378 kWh 1586 kWh £610 £159 £768 £10,238 13.3 yrs £5,125
5 kW 4955 kWh 2973 kWh 1982 kWh £762 £198 £960 £12,273 12.8 yrs £6,931
6 kW 5946 kWh 3568 kWh 2378 kWh £914 £238 £1,152 £14,307 12.4 yrs £8,737
7 kW 6937 kWh 4162 kWh 2775 kWh £1,067 £277 £1,344 £16,342 12.2 yrs £10,544
8 kW 7928 kWh 4757 kWh 3171 kWh £1,219 £317 £1,536 £18,376 12.0 yrs £12,350

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: £1,038, 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 1982 kWh 1387 kWh 595 kWh £356 £59 £415 £7,569 18.2 yrs £732
3 kW 2973 kWh 2081 kWh 892 kWh £533 £89 £623 £9,604 15.4 yrs £2,848
4 kW 3964 kWh 2775 kWh 1189 kWh £711 £119 £830 £11,638 14.0 yrs £4,964
5 kW 4955 kWh 3469 kWh 1487 kWh £889 £149 £1,038 £13,673 13.2 yrs £7,080
6 kW 5946 kWh 4162 kWh 1784 kWh £1,067 £178 £1,245 £15,707 12.6 yrs £9,196
7 kW 6937 kWh 4856 kWh 2081 kWh £1,245 £208 £1,453 £17,742 12.2 yrs £11,312
8 kW 7928 kWh 5550 kWh 2378 kWh £1,422 £238 £1,660 £19,776 11.9 yrs £13,428

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: £1,061, 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 1982 kWh 1447 kWh 535 kWh £371 £54 £424 £9,319 22.0 yrs £-832
3 kW 2973 kWh 2170 kWh 803 kWh £556 £80 £637 £11,354 17.8 yrs £1,377
4 kW 3964 kWh 2894 kWh 1070 kWh £742 £107 £849 £13,388 15.8 yrs £3,586
5 kW 4955 kWh 3617 kWh 1338 kWh £927 £134 £1,061 £15,423 14.5 yrs £5,795
6 kW 5946 kWh 4341 kWh 1605 kWh £1,113 £161 £1,273 £17,457 13.7 yrs £8,004
7 kW 6937 kWh 5064 kWh 1873 kWh £1,298 £187 £1,485 £19,492 13.1 yrs £10,213
8 kW 7928 kWh 5787 kWh 2141 kWh £1,483 £214 £1,697 £21,526 12.7 yrs £12,422

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 1982 kWh 1487 kWh 496 kWh £381 £50 £431 £11,069 25.7 yrs £-2,458
3 kW 2973 kWh 2230 kWh 743 kWh £571 £74 £646 £13,104 20.3 yrs £-187
4 kW 3964 kWh 2973 kWh 991 kWh £762 £99 £861 £15,138 17.6 yrs £2,084
5 kW 4955 kWh 3716 kWh 1239 kWh £952 £124 £1,076 £17,173 16.0 yrs £4,355
6 kW 5946 kWh 4460 kWh 1487 kWh £1,143 £149 £1,292 £19,207 14.9 yrs £6,626
7 kW 6937 kWh 5203 kWh 1734 kWh £1,333 £173 £1,507 £21,242 14.1 yrs £8,897
8 kW 7928 kWh 5946 kWh 1982 kWh £1,524 £198 £1,722 £23,276 13.5 yrs £11,167

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: £1,092, 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 1982 kWh 1526 kWh 456 kWh £391 £46 £437 £13,519 31.0 yrs £-4,784
3 kW 2973 kWh 2289 kWh 684 kWh £587 £68 £655 £15,554 23.7 yrs £-2,451
4 kW 3964 kWh 3052 kWh 912 kWh £782 £91 £873 £17,588 20.1 yrs £-118
5 kW 4955 kWh 3815 kWh 1140 kWh £978 £114 £1,092 £19,623 18.0 yrs £2,214
6 kW 5946 kWh 4578 kWh 1368 kWh £1,173 £137 £1,310 £21,657 16.5 yrs £4,547
7 kW 6937 kWh 5342 kWh 1596 kWh £1,369 £160 £1,529 £23,692 15.5 yrs £6,880
8 kW 7928 kWh 6105 kWh 1823 kWh £1,565 £182 £1,747 £25,726 14.7 yrs £9,213

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 SW1A

Figures below are tailored to SW1A — click through for full league tables.

Solar Payback Index Rank #1290 of 2997
11.0 years (UK avg 11.3 years)
~£1,106 /yr • £12,207 upfront
Standing-Charge Drag Rank #317 of 2997
15.2% (UK avg 21.7%) drag on savings
£168 fixed • ~£1,106 /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: 4% • Flats: 91% • Bungalows: 0% Based on 343 properties

Coverage

Westminster (92%)|Wandsworth (8%)

Areas Covered

St James's, Vincent Square, Nine Elms

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

SW1Y (Westminster)
≈0.3 km away
Local sunshine: ~987 kWh/kWp · -0% vs SW1A
W1J (Westminster)
≈0.7 km away
Local sunshine: ~987 kWh/kWp · -0% vs SW1A
W1X (Westminster)
≈0.7 km away
Local sunshine: ~988 kWh/kWp · -0% vs SW1A
SW1H (Westminster)
≈0.7 km away
Local sunshine: ~991 kWh/kWp · -0% vs SW1A
W1S (Westminster)
≈0.8 km away
Local sunshine: ~988 kWh/kWp · -0% vs SW1A
W1B (Westminster)
≈0.9 km away
Local sunshine: ~988 kWh/kWp · -0% vs SW1A

Similar sunshine across the UK

RG41 (Wokingham)
~991 kWh/kWp · -0% vs SW1A
NN6 (West Northamptonshire)
~991 kWh/kWp · -0% vs SW1A
LU4 (Luton)
~991 kWh/kWp · +0% vs SW1A