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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SW20 (Merton)

See if solar pays off for you in Merton — 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
£12,207
What you pay to get started
Annual Benefit
£972
What you save every year
Profit Over 25 Years
£12,084
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 996 kWh/kW — 6 above the regional median (991).

Read the full story

A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 996 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)
996 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: £810, 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 1993 kWh 797 kWh 1196 kWh £204 £120 £324 £4,069 12.6 yrs £2,409
3 kW 2989 kWh 1196 kWh 1794 kWh £306 £179 £486 £6,104 12.6 yrs £3,613
4 kW 3986 kWh 1594 kWh 2391 kWh £409 £239 £648 £8,138 12.6 yrs £4,817
5 kW 4982 kWh 1993 kWh 2989 kWh £511 £299 £810 £10,173 12.6 yrs £6,022
6 kW 5979 kWh 2391 kWh 3587 kWh £613 £359 £972 £12,207 12.6 yrs £7,226
7 kW 6975 kWh 2790 kWh 4185 kWh £715 £419 £1,134 £14,242 12.6 yrs £8,430
8 kW 7972 kWh 3189 kWh 4783 kWh £817 £478 £1,296 £16,276 12.6 yrs £9,635

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: £965, Upfront: £12,273, Break-even: 12.7 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1993 kWh 1196 kWh 797 kWh £306 £80 £386 £6,169 16.0 yrs £1,555
3 kW 2989 kWh 1794 kWh 1196 kWh £460 £120 £579 £8,204 14.2 yrs £3,382
4 kW 3986 kWh 2391 kWh 1594 kWh £613 £159 £772 £10,238 13.3 yrs £5,209
5 kW 4982 kWh 2989 kWh 1993 kWh £766 £199 £965 £12,273 12.7 yrs £7,036
6 kW 5979 kWh 3587 kWh 2391 kWh £919 £239 £1,159 £14,307 12.3 yrs £8,864
7 kW 6975 kWh 4185 kWh 2790 kWh £1,073 £279 £1,352 £16,342 12.1 yrs £10,691
8 kW 7972 kWh 4783 kWh 3189 kWh £1,226 £319 £1,545 £18,376 11.9 yrs £12,518

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: £1,043, Upfront: £13,673, Break-even: 13.1 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1993 kWh 1395 kWh 598 kWh £358 £60 £417 £7,569 18.1 yrs £778
3 kW 2989 kWh 2093 kWh 897 kWh £536 £90 £626 £9,604 15.3 yrs £2,916
4 kW 3986 kWh 2790 kWh 1196 kWh £715 £120 £835 £11,638 13.9 yrs £5,055
5 kW 4982 kWh 3488 kWh 1495 kWh £894 £149 £1,043 £13,673 13.1 yrs £7,194
6 kW 5979 kWh 4185 kWh 1794 kWh £1,073 £179 £1,252 £15,707 12.5 yrs £9,333
7 kW 6975 kWh 4883 kWh 2093 kWh £1,251 £209 £1,461 £17,742 12.1 yrs £11,471
8 kW 7972 kWh 5580 kWh 2391 kWh £1,430 £239 £1,669 £19,776 11.8 yrs £13,610

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: £1,067, 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 1993 kWh 1455 kWh 538 kWh £373 £54 £427 £9,319 21.8 yrs £-786
3 kW 2989 kWh 2182 kWh 807 kWh £559 £81 £640 £11,354 17.7 yrs £1,447
4 kW 3986 kWh 2910 kWh 1076 kWh £746 £108 £853 £13,388 15.7 yrs £3,679
5 kW 4982 kWh 3637 kWh 1345 kWh £932 £135 £1,067 £15,423 14.5 yrs £5,911
6 kW 5979 kWh 4364 kWh 1614 kWh £1,119 £161 £1,280 £17,457 13.6 yrs £8,143
7 kW 6975 kWh 5092 kWh 1883 kWh £1,305 £188 £1,493 £19,492 13.1 yrs £10,376
8 kW 7972 kWh 5819 kWh 2152 kWh £1,491 £215 £1,707 £21,526 12.6 yrs £12,608

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: £1,082, 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 1993 kWh 1495 kWh 498 kWh £383 £50 £433 £11,069 25.6 yrs £-2,411
3 kW 2989 kWh 2242 kWh 747 kWh £575 £75 £649 £13,104 20.2 yrs £-116
4 kW 3986 kWh 2989 kWh 996 kWh £766 £100 £866 £15,138 17.5 yrs £2,178
5 kW 4982 kWh 3737 kWh 1246 kWh £958 £125 £1,082 £17,173 15.9 yrs £4,473
6 kW 5979 kWh 4484 kWh 1495 kWh £1,149 £149 £1,299 £19,207 14.8 yrs £6,767
7 kW 6975 kWh 5231 kWh 1744 kWh £1,341 £174 £1,515 £21,242 14.0 yrs £9,062
8 kW 7972 kWh 5979 kWh 1993 kWh £1,532 £199 £1,732 £23,276 13.4 yrs £11,356

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: £1,098, 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 1993 kWh 1535 kWh 458 kWh £393 £46 £439 £13,519 30.8 yrs £-4,736
3 kW 2989 kWh 2302 kWh 688 kWh £590 £69 £659 £15,554 23.6 yrs £-2,380
4 kW 3986 kWh 3069 kWh 917 kWh £787 £92 £878 £17,588 20.0 yrs £-23
5 kW 4982 kWh 3836 kWh 1146 kWh £983 £115 £1,098 £19,623 17.9 yrs £2,334
6 kW 5979 kWh 4604 kWh 1375 kWh £1,180 £138 £1,317 £21,657 16.4 yrs £4,691
7 kW 6975 kWh 5371 kWh 1604 kWh £1,377 £160 £1,537 £23,692 15.4 yrs £7,048
8 kW 7972 kWh 6138 kWh 1833 kWh £1,573 £183 £1,757 £25,726 14.6 yrs £9,405

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 SW20

Figures below are tailored to SW20 — click through for full league tables.

Big-Roof Britain Rank #1426 of 2182
4.7 kWp (UK avg 5.1 kWp)
~10 panels (≈430 W)
Solar Payback Index Rank #1298 of 2997
11.0 years (UK avg 11.3 years)
~£1,112 /yr • £12,207 upfront
Standing-Charge Drag Rank #272 of 2997
15.1% (UK avg 21.7%) drag on savings
£168 fixed • ~£1,112 /yr value

Your Area at a Glance

Your Electricity Rate
25.63p/kWh
Daily Fixed Charge
46.06p/day
Local Sunshine
996kWh/kW
A 1 kW system generates ~996 kWh per year. A typical home uses ~2,700 kWh per year.
Typical System Size
6.0kW
For houses & bungalows in this area

Local Property Data

Property Types

Houses: 48% • Flats: 45% • Bungalows: 1% Based on 8,225 properties

Coverage

Merton (99%)|Kingston upon Thames (1%)

Areas Covered

Hillside, Raynes Park, Village, West Barnes, Cannon Hill, Wimbledon Town & Dundonald, Merton Park, Lower Morden + 1 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

SW19 (Merton)
≈0.8 km away
Local sunshine: ~996 kWh/kWp · -0% vs SW20
SM4 (Merton)
≈2.6 km away
Local sunshine: ~999 kWh/kWp · +0% vs SW20
KT3 (Kingston upon Thames)
≈2.8 km away
Local sunshine: ~996 kWh/kWp · -0% vs SW20
SW17 (Wandsworth)
≈4.2 km away
Local sunshine: ~996 kWh/kWp · -0% vs SW20
SW18 (Wandsworth)
≈4.3 km away
Local sunshine: ~992 kWh/kWp · -0% vs SW20
CR4 (Merton)
≈4.7 km away
Local sunshine: ~993 kWh/kWp · -0% vs SW20

Similar sunshine across the UK

BA4 (Somerset)
~996 kWh/kWp · +0% vs SW20
PE37 (Breckland)
~996 kWh/kWp · +0% vs SW20
BS9 (Bristol, City of)
~996 kWh/kWp · -0% vs SW20