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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in TR23 (Isles of Scilly)

See if solar pays off for you in Isles of Scilly — price, savings and payback in under a minute (official UK data).

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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
11.0 years
After this, it's pure profit
Upfront Cost
£12,207
What you pay to get started
Annual Benefit
£1,105
What you save every year
Profit Over 25 Years
£15,415
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 Southern Western, the current unit rate is 26.82p/kWh with a 54.03p/day standing charge. Your postcode’s south-facing sunshine yield is 1101 kWh/kW — 87 above the regional median (1013).

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 1101 kWh per year on a south-facing roof. We value self-used electricity at 26.8p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
26.8p/kWh
Standing charge
54.0p/day
Sunshine yield (south)
1101 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: £921, Upfront: £10,173, Break-even: 11.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2202 kWh 881 kWh 1321 kWh £236 £132 £368 £4,069 11.0 yrs £3,297
3 kW 3303 kWh 1321 kWh 1982 kWh £354 £198 £552 £6,104 11.0 yrs £4,945
4 kW 4403 kWh 1761 kWh 2642 kWh £472 £264 £737 £8,138 11.0 yrs £6,594
5 kW 5504 kWh 2202 kWh 3303 kWh £590 £330 £921 £10,173 11.0 yrs £8,242
6 kW 6605 kWh 2642 kWh 3963 kWh £709 £396 £1,105 £12,207 11.0 yrs £9,891
7 kW 7706 kWh 3082 kWh 4624 kWh £827 £462 £1,289 £14,242 11.0 yrs £11,539
8 kW 8807 kWh 3523 kWh 5284 kWh £945 £528 £1,473 £16,276 11.0 yrs £13,188

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: £1,106, Upfront: £12,273, Break-even: 11.1 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2202 kWh 1321 kWh 881 kWh £354 £88 £442 £6,169 13.9 yrs £2,678
3 kW 3303 kWh 1982 kWh 1321 kWh £531 £132 £664 £8,204 12.4 yrs £5,067
4 kW 4403 kWh 2642 kWh 1761 kWh £709 £176 £885 £10,238 11.6 yrs £7,457
5 kW 5504 kWh 3303 kWh 2202 kWh £886 £220 £1,106 £12,273 11.1 yrs £9,846
6 kW 6605 kWh 3963 kWh 2642 kWh £1,063 £264 £1,327 £14,307 10.8 yrs £12,235
7 kW 7706 kWh 4624 kWh 3082 kWh £1,240 £308 £1,548 £16,342 10.6 yrs £14,624
8 kW 8807 kWh 5284 kWh 3523 kWh £1,417 £352 £1,769 £18,376 10.4 yrs £17,013

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: £1,198, Upfront: £13,673, Break-even: 11.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2202 kWh 1541 kWh 661 kWh £413 £66 £479 £7,569 15.8 yrs £2,019
3 kW 3303 kWh 2312 kWh 991 kWh £620 £99 £719 £9,604 13.4 yrs £4,778
4 kW 4403 kWh 3082 kWh 1321 kWh £827 £132 £959 £11,638 12.1 yrs £7,538
5 kW 5504 kWh 3853 kWh 1651 kWh £1,033 £165 £1,198 £13,673 11.4 yrs £10,297
6 kW 6605 kWh 4624 kWh 1982 kWh £1,240 £198 £1,438 £15,707 10.9 yrs £13,057
7 kW 7706 kWh 5394 kWh 2312 kWh £1,447 £231 £1,678 £17,742 10.6 yrs £15,816
8 kW 8807 kWh 6165 kWh 2642 kWh £1,653 £264 £1,918 £19,776 10.3 yrs £18,576

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: £1,226, Upfront: £15,423, 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 2202 kWh 1607 kWh 594 kWh £431 £59 £491 £9,319 19.0 yrs £491
3 kW 3303 kWh 2411 kWh 892 kWh £647 £89 £736 £11,354 15.4 yrs £3,362
4 kW 4403 kWh 3214 kWh 1189 kWh £862 £119 £981 £13,388 13.6 yrs £6,232
5 kW 5504 kWh 4018 kWh 1486 kWh £1,078 £149 £1,226 £15,423 12.6 yrs £9,103
6 kW 6605 kWh 4822 kWh 1783 kWh £1,293 £178 £1,472 £17,457 11.9 yrs £11,973
7 kW 7706 kWh 5625 kWh 2081 kWh £1,509 £208 £1,717 £19,492 11.4 yrs £14,844
8 kW 8807 kWh 6429 kWh 2378 kWh £1,724 £238 £1,962 £21,526 11.0 yrs £17,715

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: £1,245, Upfront: £17,173, Break-even: 13.8 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2202 kWh 1651 kWh 550 kWh £443 £55 £498 £11,069 22.2 yrs £-1,111
3 kW 3303 kWh 2477 kWh 826 kWh £664 £83 £747 £13,104 17.5 yrs £1,834
4 kW 4403 kWh 3303 kWh 1101 kWh £886 £110 £996 £15,138 15.2 yrs £4,779
5 kW 5504 kWh 4128 kWh 1376 kWh £1,107 £138 £1,245 £17,173 13.8 yrs £7,723
6 kW 6605 kWh 4954 kWh 1651 kWh £1,329 £165 £1,494 £19,207 12.9 yrs £10,668
7 kW 7706 kWh 5779 kWh 1926 kWh £1,550 £193 £1,743 £21,242 12.2 yrs £13,612
8 kW 8807 kWh 6605 kWh 2202 kWh £1,771 £220 £1,992 £23,276 11.7 yrs £16,557

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: £1,263, Upfront: £19,623, Break-even: 15.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2202 kWh 1695 kWh 506 kWh £455 £51 £505 £13,519 26.8 yrs £-3,413
3 kW 3303 kWh 2543 kWh 760 kWh £682 £76 £758 £15,554 20.5 yrs £-394
4 kW 4403 kWh 3391 kWh 1013 kWh £909 £101 £1,011 £17,588 17.4 yrs £2,625
5 kW 5504 kWh 4238 kWh 1266 kWh £1,137 £127 £1,263 £19,623 15.5 yrs £5,643
6 kW 6605 kWh 5086 kWh 1519 kWh £1,364 £152 £1,516 £21,657 14.3 yrs £8,662
7 kW 7706 kWh 5934 kWh 1772 kWh £1,591 £177 £1,769 £23,692 13.4 yrs £11,681
8 kW 8807 kWh 6781 kWh 2026 kWh £1,819 £203 £2,021 £25,726 12.7 yrs £14,700

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 TR23

Figures below are tailored to TR23 — click through for full league tables.

Big-Roof Britain Rank #230 of 2182
6.1 kWp (UK avg 5.1 kWp)
~13 panels (≈430 W)
Solar Payback Index Rank #76 of 2997
9.6 years (UK avg 11.3 years)
~£1,272 /yr • £12,207 upfront
Standing-Charge Drag Rank #474 of 2997
15.5% (UK avg 21.7%) drag on savings
£197 fixed • ~£1,272 /yr value

Your Area at a Glance

Your Electricity Rate
26.82p/kWh
Daily Fixed Charge
54.03p/day
Local Sunshine
1101kWh/kW
A 1 kW system generates ~1101 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: 70% • Flats: 10% • Bungalows: 20% Based on 20 properties

Coverage

Isles of Scilly (100%)

Areas Covered

Bryher

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 Southern Western

TR24 (Isles of Scilly)
≈1.1 km away
Local sunshine: ~1,096 kWh/kWp · -0% vs TR23
TR25 (Isles of Scilly)
≈4.6 km away
Local sunshine: ~1,092 kWh/kWp · -1% vs TR23
TR21 (Isles of Scilly)
≈5.3 km away
Local sunshine: ~1,066 kWh/kWp · -3% vs TR23
TR22 (Isles of Scilly)
≈6.7 km away
Local sunshine: ~1,099 kWh/kWp · -0% vs TR23
TR19 (Cornwall)
≈52.1 km away
Local sunshine: ~1,083 kWh/kWp · -2% vs TR23
TR18 (Cornwall)
≈60.9 km away
Local sunshine: ~1,066 kWh/kWp · -3% vs TR23

Similar sunshine across the UK

PO41 (Isle of Wight)
~1,101 kWh/kWp · +0% vs TR23
CO16 (Tendring)
~1,101 kWh/kWp · +0% vs TR23
CT13 (Dover)
~1,100 kWh/kWp · -0% vs TR23