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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in TN13 (Sevenoaks)

See if solar pays off for you in Sevenoaks — 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
12.0 years
After this, it's pure profit
Upfront Cost
£12,207
What you pay to get started
Annual Benefit
£1,021
What you save every year
Profit Over 25 Years
£13,323
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 South East, the current unit rate is 26.92p/kWh with a 47.60p/day standing charge. Your postcode’s south-facing sunshine yield is 1015 kWh/kW — 14 below the regional median (1029).

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 1015 kWh per year on a south-facing roof. We value self-used electricity at 26.9p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
26.9p/kWh
Standing charge
47.6p/day
Sunshine yield (south)
1015 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: £851, Upfront: £10,173, Break-even: 12.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 812 kWh 1218 kWh £219 £122 £340 £4,069 12.0 yrs £2,739
3 kW 3045 kWh 1218 kWh 1827 kWh £328 £183 £511 £6,104 12.0 yrs £4,108
4 kW 4060 kWh 1624 kWh 2436 kWh £437 £244 £681 £8,138 12.0 yrs £5,478
5 kW 5075 kWh 2030 kWh 3045 kWh £546 £305 £851 £10,173 12.0 yrs £6,847
6 kW 6090 kWh 2436 kWh 3654 kWh £656 £365 £1,021 £12,207 12.0 yrs £8,217
7 kW 7105 kWh 2842 kWh 4263 kWh £765 £426 £1,191 £14,242 12.0 yrs £9,586
8 kW 8120 kWh 3248 kWh 4872 kWh £874 £487 £1,362 £16,276 12.0 yrs £10,956

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: £1,023, Upfront: £12,273, Break-even: 12.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 1218 kWh 812 kWh £328 £81 £409 £6,169 15.1 yrs £2,013
3 kW 3045 kWh 1827 kWh 1218 kWh £492 £122 £614 £8,204 13.4 yrs £4,069
4 kW 4060 kWh 2436 kWh 1624 kWh £656 £162 £818 £10,238 12.5 yrs £6,126
5 kW 5075 kWh 3045 kWh 2030 kWh £820 £203 £1,023 £12,273 12.0 yrs £8,182
6 kW 6090 kWh 3654 kWh 2436 kWh £984 £244 £1,227 £14,307 11.7 yrs £10,239
7 kW 7105 kWh 4263 kWh 2842 kWh £1,148 £284 £1,432 £16,342 11.4 yrs £12,295
8 kW 8120 kWh 4872 kWh 3248 kWh £1,312 £325 £1,636 £18,376 11.2 yrs £14,351

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: £1,109, Upfront: £13,673, Break-even: 12.3 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 1421 kWh 609 kWh £383 £61 £443 £7,569 17.1 yrs £1,300
3 kW 3045 kWh 2132 kWh 914 kWh £574 £91 £665 £9,604 14.4 yrs £3,700
4 kW 4060 kWh 2842 kWh 1218 kWh £765 £122 £887 £11,638 13.1 yrs £6,100
5 kW 5075 kWh 3553 kWh 1523 kWh £956 £152 £1,109 £13,673 12.3 yrs £8,500
6 kW 6090 kWh 4263 kWh 1827 kWh £1,148 £183 £1,330 £15,707 11.8 yrs £10,899
7 kW 7105 kWh 4974 kWh 2132 kWh £1,339 £213 £1,552 £17,742 11.4 yrs £13,299
8 kW 8120 kWh 5684 kWh 2436 kWh £1,530 £244 £1,774 £19,776 11.1 yrs £15,699

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: £1,134, Upfront: £15,423, Break-even: 13.6 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 1482 kWh 548 kWh £399 £55 £454 £9,319 20.5 yrs £-244
3 kW 3045 kWh 2223 kWh 822 kWh £598 £82 £681 £11,354 16.7 yrs £2,259
4 kW 4060 kWh 2964 kWh 1096 kWh £798 £110 £907 £13,388 14.8 yrs £4,762
5 kW 5075 kWh 3705 kWh 1370 kWh £997 £137 £1,134 £15,423 13.6 yrs £7,265
6 kW 6090 kWh 4446 kWh 1644 kWh £1,197 £164 £1,361 £17,457 12.8 yrs £9,768
7 kW 7105 kWh 5187 kWh 1918 kWh £1,396 £192 £1,588 £19,492 12.3 yrs £12,271
8 kW 8120 kWh 5928 kWh 2192 kWh £1,596 £219 £1,815 £21,526 11.9 yrs £14,774

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: £1,152, Upfront: £17,173, Break-even: 14.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 1523 kWh 508 kWh £410 £51 £461 £11,069 24.0 yrs £-1,857
3 kW 3045 kWh 2284 kWh 761 kWh £615 £76 £691 £13,104 19.0 yrs £715
4 kW 4060 kWh 3045 kWh 1015 kWh £820 £102 £921 £15,138 16.4 yrs £3,287
5 kW 5075 kWh 3806 kWh 1269 kWh £1,025 £127 £1,152 £17,173 14.9 yrs £5,858
6 kW 6090 kWh 4568 kWh 1523 kWh £1,230 £152 £1,382 £19,207 13.9 yrs £8,430
7 kW 7105 kWh 5329 kWh 1776 kWh £1,435 £178 £1,612 £21,242 13.2 yrs £11,002
8 kW 8120 kWh 6090 kWh 2030 kWh £1,639 £203 £1,842 £23,276 12.6 yrs £13,573

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: £1,169, Upfront: £19,623, Break-even: 16.8 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2030 kWh 1563 kWh 467 kWh £421 £47 £467 £13,519 28.9 yrs £-4,169
3 kW 3045 kWh 2345 kWh 700 kWh £631 £70 £701 £15,554 22.2 yrs £-1,529
4 kW 4060 kWh 3126 kWh 934 kWh £842 £93 £935 £17,588 18.8 yrs £1,111
5 kW 5075 kWh 3908 kWh 1167 kWh £1,052 £117 £1,169 £19,623 16.8 yrs £3,752
6 kW 6090 kWh 4689 kWh 1401 kWh £1,262 £140 £1,402 £21,657 15.4 yrs £6,392
7 kW 7105 kWh 5471 kWh 1634 kWh £1,473 £163 £1,636 £23,692 14.5 yrs £9,032
8 kW 8120 kWh 6253 kWh 1868 kWh £1,683 £187 £1,870 £25,726 13.8 yrs £11,673

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 TN13

Figures below are tailored to TN13 — click through for full league tables.

Big-Roof Britain Rank #744 of 2182
5.3 kWp (UK avg 5.1 kWp)
~11 panels (≈430 W)
Solar Payback Index Rank #458 of 2997
10.4 years (UK avg 11.3 years)
~£1,176 /yr • £12,207 upfront
Standing-Charge Drag Rank #223 of 2997
14.8% (UK avg 21.7%) drag on savings
£174 fixed • ~£1,176 /yr value

Your Area at a Glance

Your Electricity Rate
26.92p/kWh
Daily Fixed Charge
47.60p/day
Local Sunshine
1015kWh/kW
A 1 kW system generates ~1015 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: 62% • Flats: 31% • Bungalows: 4% Based on 6,392 properties

Coverage

Sevenoaks (100%)

Areas Covered

Sevenoaks Town and St John's, Dunton Green and Riverhead, Sevenoaks Kippington, Sevenoaks Eastern, Brasted, Chevening and Sundridge, Sevenoaks Northern, Seal and Weald + 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 South East

TN14 (Sevenoaks)
≈3.3 km away
Local sunshine: ~1,023 kWh/kWp · +1% vs TN13
TN15 (Sevenoaks)
≈6.1 km away
Local sunshine: ~1,023 kWh/kWp · +1% vs TN13
TN11 (Tonbridge and Malling)
≈8.9 km away
Local sunshine: ~1,042 kWh/kWp · +3% vs TN13
TN10 (Tonbridge and Malling)
≈9.2 km away
Local sunshine: ~1,034 kWh/kWp · +2% vs TN13
TN9 (Tonbridge and Malling)
≈10.9 km away
Local sunshine: ~1,028 kWh/kWp · +1% vs TN13
TN16 (Bromley)
≈11.7 km away
Local sunshine: ~1,009 kWh/kWp · -1% vs TN13

Similar sunshine across the UK

CB23 (South Cambridgeshire)
~1,015 kWh/kWp · +0% vs TN13
SO24 (Winchester)
~1,015 kWh/kWp · -0% vs TN13
EX4 (Exeter)
~1,015 kWh/kWp · -0% vs TN13