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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SW1X (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
£484
What you save every year
Profit Over 25 Years
£5,992
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 992 kWh/kW — 2 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 992 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)
992 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: £806, 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 1985 kWh 794 kWh 1191 kWh £203 £119 £323 £4,069 12.6 yrs £2,382
3 kW 2977 kWh 1191 kWh 1786 kWh £305 £179 £484 £6,104 12.6 yrs £3,573
4 kW 3969 kWh 1588 kWh 2382 kWh £407 £238 £645 £8,138 12.6 yrs £4,764
5 kW 4962 kWh 1985 kWh 2977 kWh £509 £298 £806 £10,173 12.6 yrs £5,955
6 kW 5954 kWh 2382 kWh 3572 kWh £610 £357 £968 £12,207 12.6 yrs £7,146
7 kW 6946 kWh 2779 kWh 4168 kWh £712 £417 £1,129 £14,242 12.6 yrs £8,337
8 kW 7939 kWh 3175 kWh 4763 kWh £814 £476 £1,290 £16,276 12.6 yrs £9,528

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: £961, 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 1985 kWh 1191 kWh 794 kWh £305 £79 £385 £6,169 16.0 yrs £1,523
3 kW 2977 kWh 1786 kWh 1191 kWh £458 £119 £577 £8,204 14.2 yrs £3,334
4 kW 3969 kWh 2382 kWh 1588 kWh £610 £159 £769 £10,238 13.3 yrs £5,145
5 kW 4962 kWh 2977 kWh 1985 kWh £763 £198 £961 £12,273 12.8 yrs £6,957
6 kW 5954 kWh 3572 kWh 2382 kWh £916 £238 £1,154 £14,307 12.4 yrs £8,768
7 kW 6946 kWh 4168 kWh 2779 kWh £1,068 £278 £1,346 £16,342 12.1 yrs £10,580
8 kW 7939 kWh 4763 kWh 3175 kWh £1,221 £318 £1,538 £18,376 11.9 yrs £12,391

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: £1,039, 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 1985 kWh 1389 kWh 595 kWh £356 £60 £416 £7,569 18.2 yrs £743
3 kW 2977 kWh 2084 kWh 893 kWh £534 £89 £623 £9,604 15.4 yrs £2,865
4 kW 3969 kWh 2779 kWh 1191 kWh £712 £119 £831 £11,638 14.0 yrs £4,986
5 kW 4962 kWh 3473 kWh 1488 kWh £890 £149 £1,039 £13,673 13.2 yrs £7,108
6 kW 5954 kWh 4168 kWh 1786 kWh £1,068 £179 £1,247 £15,707 12.6 yrs £9,229
7 kW 6946 kWh 4862 kWh 2084 kWh £1,246 £208 £1,455 £17,742 12.2 yrs £11,351
8 kW 7939 kWh 5557 kWh 2382 kWh £1,424 £238 £1,662 £19,776 11.9 yrs £13,473

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: £1,062, 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 1985 kWh 1449 kWh 536 kWh £371 £54 £425 £9,319 21.9 yrs £-821
3 kW 2977 kWh 2173 kWh 804 kWh £557 £80 £637 £11,354 17.8 yrs £1,394
4 kW 3969 kWh 2898 kWh 1072 kWh £743 £107 £850 £13,388 15.8 yrs £3,609
5 kW 4962 kWh 3622 kWh 1340 kWh £928 £134 £1,062 £15,423 14.5 yrs £5,823
6 kW 5954 kWh 4346 kWh 1608 kWh £1,114 £161 £1,275 £17,457 13.7 yrs £8,038
7 kW 6946 kWh 5071 kWh 1876 kWh £1,300 £188 £1,487 £19,492 13.1 yrs £10,252
8 kW 7939 kWh 5795 kWh 2143 kWh £1,485 £214 £1,700 £21,526 12.7 yrs £12,467

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: £1,078, Upfront: £17,173, Break-even: 15.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1985 kWh 1488 kWh 496 kWh £382 £50 £431 £11,069 25.7 yrs £-2,447
3 kW 2977 kWh 2233 kWh 744 kWh £572 £74 £647 £13,104 20.3 yrs £-170
4 kW 3969 kWh 2977 kWh 992 kWh £763 £99 £862 £15,138 17.6 yrs £2,107
5 kW 4962 kWh 3721 kWh 1240 kWh £954 £124 £1,078 £17,173 15.9 yrs £4,383
6 kW 5954 kWh 4465 kWh 1488 kWh £1,145 £149 £1,293 £19,207 14.9 yrs £6,660
7 kW 6946 kWh 5210 kWh 1737 kWh £1,335 £174 £1,509 £21,242 14.1 yrs £8,937
8 kW 7939 kWh 5954 kWh 1985 kWh £1,526 £198 £1,724 £23,276 13.5 yrs £11,213

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: £1,093, Upfront: £19,623, Break-even: 17.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1985 kWh 1528 kWh 456 kWh £392 £46 £437 £13,519 30.9 yrs £-4,773
3 kW 2977 kWh 2292 kWh 685 kWh £588 £68 £656 £15,554 23.7 yrs £-2,434
4 kW 3969 kWh 3056 kWh 913 kWh £783 £91 £875 £17,588 20.1 yrs £-95
5 kW 4962 kWh 3820 kWh 1141 kWh £979 £114 £1,093 £19,623 17.9 yrs £2,244
6 kW 5954 kWh 4585 kWh 1369 kWh £1,175 £137 £1,312 £21,657 16.5 yrs £4,582
7 kW 6946 kWh 5349 kWh 1598 kWh £1,371 £160 £1,531 £23,692 15.5 yrs £6,921
8 kW 7939 kWh 6113 kWh 1826 kWh £1,567 £183 £1,749 £25,726 14.7 yrs £9,260

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 SW1X

Figures below are tailored to SW1X — click through for full league tables.

Big-Roof Britain Rank #100 of 2182
6.6 kWp (UK avg 5.1 kWp)
~14 panels (≈430 W)
Solar Payback Index Rank #1296 of 2997
11.0 years (UK avg 11.3 years)
~£1,107 /yr • £12,207 upfront
Standing-Charge Drag Rank #348 of 2997
15.2% (UK avg 21.7%) drag on savings
£168 fixed • ~£1,107 /yr value

Your Area at a Glance

Your Electricity Rate
25.63p/kWh
Daily Fixed Charge
46.06p/day
Local Sunshine
992kWh/kW
A 1 kW system generates ~992 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: 18% • Flats: 74% • Bungalows: 0% Based on 3,520 properties

Coverage

Westminster (57%)|Kensington and Chelsea (38%)|Wandsworth (5%)

Areas Covered

Knightsbridge & Belgravia, Brompton & Hans Town, Vincent Square, Royal Hospital, Nine Elms, St James's

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

SW1W (Westminster)
≈0.7 km away
Local sunshine: ~991 kWh/kWp · -0% vs SW1X
SW1E (Westminster)
≈1.1 km away
Local sunshine: ~991 kWh/kWp · -0% vs SW1X
SW7 (Kensington and Chelsea)
≈1.3 km away
Local sunshine: ~992 kWh/kWp · +0% vs SW1X
W1J (Westminster)
≈1.3 km away
Local sunshine: ~987 kWh/kWp · -0% vs SW1X
SW3 (Kensington and Chelsea)
≈1.3 km away
Local sunshine: ~989 kWh/kWp · -0% vs SW1X
W1Y (Westminster)
≈1.4 km away
Local sunshine: ~987 kWh/kWp · -0% vs SW1X

Similar sunshine across the UK

SA33 (Carmarthenshire)
~992 kWh/kWp · -0% vs SW1X
AL2 (St Albans)
~992 kWh/kWp · -0% vs SW1X
LL71 (Isle of Anglesey)
~992 kWh/kWp · -0% vs SW1X