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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SE8 (Lewisham)

See if solar pays off for you in Lewisham — 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
£485
What you save every year
Profit Over 25 Years
£6,014
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 994 kWh/kW — 4 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 994 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)
994 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: £808, 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 1988 kWh 795 kWh 1193 kWh £204 £119 £323 £4,069 12.6 yrs £2,394
3 kW 2983 kWh 1193 kWh 1790 kWh £306 £179 £485 £6,104 12.6 yrs £3,591
4 kW 3977 kWh 1591 kWh 2386 kWh £408 £239 £646 £8,138 12.6 yrs £4,788
5 kW 4971 kWh 1988 kWh 2983 kWh £510 £298 £808 £10,173 12.6 yrs £5,985
6 kW 5965 kWh 2386 kWh 3579 kWh £612 £358 £969 £12,207 12.6 yrs £7,182
7 kW 6959 kWh 2784 kWh 4176 kWh £713 £418 £1,131 £14,242 12.6 yrs £8,379
8 kW 7953 kWh 3181 kWh 4772 kWh £815 £477 £1,293 £16,276 12.6 yrs £9,576

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: £963, 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 1988 kWh 1193 kWh 795 kWh £306 £80 £385 £6,169 16.0 yrs £1,537
3 kW 2983 kWh 1790 kWh 1193 kWh £459 £119 £578 £8,204 14.2 yrs £3,355
4 kW 3977 kWh 2386 kWh 1591 kWh £612 £159 £771 £10,238 13.3 yrs £5,174
5 kW 4971 kWh 2983 kWh 1988 kWh £764 £199 £963 £12,273 12.7 yrs £6,992
6 kW 5965 kWh 3579 kWh 2386 kWh £917 £239 £1,156 £14,307 12.4 yrs £8,811
7 kW 6959 kWh 4176 kWh 2784 kWh £1,070 £278 £1,349 £16,342 12.1 yrs £10,629
8 kW 7953 kWh 4772 kWh 3181 kWh £1,223 £318 £1,541 £18,376 11.9 yrs £12,448

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: £1,041, 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 1988 kWh 1392 kWh 597 kWh £357 £60 £416 £7,569 18.2 yrs £759
3 kW 2983 kWh 2088 kWh 895 kWh £535 £89 £625 £9,604 15.4 yrs £2,888
4 kW 3977 kWh 2784 kWh 1193 kWh £713 £119 £833 £11,638 14.0 yrs £5,017
5 kW 4971 kWh 3480 kWh 1491 kWh £892 £149 £1,041 £13,673 13.1 yrs £7,146
6 kW 5965 kWh 4176 kWh 1790 kWh £1,070 £179 £1,249 £15,707 12.6 yrs £9,276
7 kW 6959 kWh 4871 kWh 2088 kWh £1,249 £209 £1,457 £17,742 12.2 yrs £11,405
8 kW 7953 kWh 5567 kWh 2386 kWh £1,427 £239 £1,666 £19,776 11.9 yrs £13,534

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: £1,064, 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 1988 kWh 1451 kWh 537 kWh £372 £54 £426 £9,319 21.9 yrs £-805
3 kW 2983 kWh 2177 kWh 805 kWh £558 £81 £639 £11,354 17.8 yrs £1,418
4 kW 3977 kWh 2903 kWh 1074 kWh £744 £107 £851 £13,388 15.7 yrs £3,640
5 kW 4971 kWh 3629 kWh 1342 kWh £930 £134 £1,064 £15,423 14.5 yrs £5,863
6 kW 5965 kWh 4354 kWh 1611 kWh £1,116 £161 £1,277 £17,457 13.7 yrs £8,085
7 kW 6959 kWh 5080 kWh 1879 kWh £1,302 £188 £1,490 £19,492 13.1 yrs £10,308
8 kW 7953 kWh 5806 kWh 2147 kWh £1,488 £215 £1,703 £21,526 12.6 yrs £12,530

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: £1,080, 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 1988 kWh 1491 kWh 497 kWh £382 £50 £432 £11,069 25.6 yrs £-2,431
3 kW 2983 kWh 2237 kWh 746 kWh £573 £75 £648 £13,104 20.2 yrs £-146
4 kW 3977 kWh 2983 kWh 994 kWh £764 £99 £864 £15,138 17.5 yrs £2,139
5 kW 4971 kWh 3728 kWh 1243 kWh £956 £124 £1,080 £17,173 15.9 yrs £4,423
6 kW 5965 kWh 4474 kWh 1491 kWh £1,147 £149 £1,296 £19,207 14.8 yrs £6,708
7 kW 6959 kWh 5219 kWh 1740 kWh £1,338 £174 £1,512 £21,242 14.1 yrs £8,993
8 kW 7953 kWh 5965 kWh 1988 kWh £1,529 £199 £1,728 £23,276 13.5 yrs £11,277

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: £1,095, 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 1988 kWh 1531 kWh 457 kWh £392 £46 £438 £13,519 30.9 yrs £-4,756
3 kW 2983 kWh 2297 kWh 686 kWh £589 £69 £657 £15,554 23.7 yrs £-2,410
4 kW 3977 kWh 3062 kWh 915 kWh £785 £91 £876 £17,588 20.1 yrs £-63
5 kW 4971 kWh 3828 kWh 1143 kWh £981 £114 £1,095 £19,623 17.9 yrs £2,284
6 kW 5965 kWh 4593 kWh 1372 kWh £1,177 £137 £1,314 £21,657 16.5 yrs £4,631
7 kW 6959 kWh 5359 kWh 1601 kWh £1,373 £160 £1,533 £23,692 15.4 yrs £6,978
8 kW 7953 kWh 6124 kWh 1829 kWh £1,570 £183 £1,753 £25,726 14.7 yrs £9,325

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 SE8

Figures below are tailored to SE8 — click through for full league tables.

Big-Roof Britain Rank #2123 of 2182
3.8 kWp (UK avg 5.1 kWp)
~8 panels (≈430 W)
Solar Payback Index Rank #1277 of 2997
11.0 years (UK avg 11.3 years)
~£924 /yr • £10,173 upfront
Standing-Charge Drag Rank #1060 of 2997
18.2% (UK avg 21.7%) drag on savings
£168 fixed • ~£924 /yr value

Your Area at a Glance

Your Electricity Rate
25.63p/kWh
Daily Fixed Charge
46.06p/day
Local Sunshine
994kWh/kW
A 1 kW system generates ~994 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: 78% • Bungalows: 0% Based on 13,344 properties

Coverage

Lewisham (89%)|Greenwich (9%)|Southwark (2%)

Areas Covered

Deptford, Evelyn, Greenwich Creekside, Brockley, Rotherhithe, Lewisham Central, Greenwich Park

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

SE14 (Lewisham)
≈1.5 km away
Local sunshine: ~994 kWh/kWp · -0% vs SE8
SE10 (Greenwich)
≈2.0 km away
Local sunshine: ~1,006 kWh/kWp · +1% vs SE8
SE4 (Lewisham)
≈2.1 km away
Local sunshine: ~994 kWh/kWp · -0% vs SE8
E22 (Tower Hamlets)
≈2.2 km away
Local sunshine: ~991 kWh/kWp · -0% vs SE8
SE16 (Southwark)
≈2.5 km away
Local sunshine: ~994 kWh/kWp · +0% vs SE8
SE13 (Lewisham)
≈2.6 km away
Local sunshine: ~993 kWh/kWp · -0% vs SE8

Similar sunshine across the UK

RG15 (Basingstoke and Deane)
~994 kWh/kWp · -0% vs SE8
RG5 (Wokingham)
~994 kWh/kWp · -0% vs SE8
EN11 (Broxbourne)
~994 kWh/kWp · +0% vs SE8