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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in TR25 (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).

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
11.1 years
After this, it's pure profit
Upfront Cost
£12,207
What you pay to get started
Annual Benefit
£1,096
What you save every year
Profit Over 25 Years
£15,181
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 1092 kWh/kW — 78 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 1092 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)
1092 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: £913, Upfront: £10,173, 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 2183 kWh 873 kWh 1310 kWh £234 £131 £365 £4,069 11.1 yrs £3,234
3 kW 3274 kWh 1310 kWh 1965 kWh £351 £196 £548 £6,104 11.1 yrs £4,852
4 kW 4366 kWh 1746 kWh 2620 kWh £468 £262 £730 £8,138 11.1 yrs £6,469
5 kW 5458 kWh 2183 kWh 3274 kWh £585 £327 £913 £10,173 11.1 yrs £8,086
6 kW 6549 kWh 2620 kWh 3929 kWh £703 £393 £1,096 £12,207 11.1 yrs £9,703
7 kW 7640 kWh 3056 kWh 4584 kWh £820 £458 £1,278 £14,242 11.1 yrs £11,320
8 kW 8732 kWh 3493 kWh 5239 kWh £937 £524 £1,461 £16,276 11.1 yrs £12,938

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: £1,097, Upfront: £12,273, Break-even: 11.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2183 kWh 1310 kWh 873 kWh £351 £87 £439 £6,169 14.1 yrs £2,603
3 kW 3274 kWh 1965 kWh 1310 kWh £527 £131 £658 £8,204 12.5 yrs £4,955
4 kW 4366 kWh 2620 kWh 1746 kWh £703 £175 £877 £10,238 11.7 yrs £7,306
5 kW 5458 kWh 3274 kWh 2183 kWh £878 £218 £1,097 £12,273 11.2 yrs £9,658
6 kW 6549 kWh 3929 kWh 2620 kWh £1,054 £262 £1,316 £14,307 10.9 yrs £12,009
7 kW 7640 kWh 4584 kWh 3056 kWh £1,230 £306 £1,535 £16,342 10.6 yrs £14,361
8 kW 8732 kWh 5239 kWh 3493 kWh £1,405 £349 £1,754 £18,376 10.5 yrs £16,713

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: £1,188, Upfront: £13,673, Break-even: 11.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2183 kWh 1528 kWh 655 kWh £410 £65 £475 £7,569 15.9 yrs £1,938
3 kW 3274 kWh 2292 kWh 982 kWh £615 £98 £713 £9,604 13.5 yrs £4,656
4 kW 4366 kWh 3056 kWh 1310 kWh £820 £131 £951 £11,638 12.2 yrs £7,375
5 kW 5458 kWh 3820 kWh 1637 kWh £1,025 £164 £1,188 £13,673 11.5 yrs £10,094
6 kW 6549 kWh 4584 kWh 1965 kWh £1,230 £196 £1,426 £15,707 11.0 yrs £12,813
7 kW 7640 kWh 5348 kWh 2292 kWh £1,434 £229 £1,664 £17,742 10.7 yrs £15,531
8 kW 8732 kWh 6112 kWh 2620 kWh £1,639 £262 £1,901 £19,776 10.4 yrs £18,250

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: £1,216, Upfront: £15,423, 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 2183 kWh 1594 kWh 589 kWh £427 £59 £486 £9,319 19.2 yrs £408
3 kW 3274 kWh 2390 kWh 884 kWh £641 £88 £730 £11,354 15.6 yrs £3,237
4 kW 4366 kWh 3187 kWh 1179 kWh £855 £118 £973 £13,388 13.8 yrs £6,066
5 kW 5458 kWh 3984 kWh 1474 kWh £1,069 £147 £1,216 £15,423 12.7 yrs £8,895
6 kW 6549 kWh 4781 kWh 1768 kWh £1,282 £177 £1,459 £17,457 12.0 yrs £11,723
7 kW 7640 kWh 5578 kWh 2063 kWh £1,496 £206 £1,702 £19,492 11.5 yrs £14,552
8 kW 8732 kWh 6374 kWh 2358 kWh £1,710 £236 £1,945 £21,526 11.1 yrs £17,381

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: £1,234, Upfront: £17,173, Break-even: 13.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2183 kWh 1637 kWh 546 kWh £439 £55 £494 £11,069 22.4 yrs £-1,195
3 kW 3274 kWh 2456 kWh 819 kWh £659 £82 £741 £13,104 17.7 yrs £1,707
4 kW 4366 kWh 3274 kWh 1092 kWh £878 £109 £987 £15,138 15.3 yrs £4,609
5 kW 5458 kWh 4093 kWh 1364 kWh £1,098 £136 £1,234 £17,173 13.9 yrs £7,512
6 kW 6549 kWh 4912 kWh 1637 kWh £1,317 £164 £1,481 £19,207 13.0 yrs £10,414
7 kW 7640 kWh 5730 kWh 1910 kWh £1,537 £191 £1,728 £21,242 12.3 yrs £13,316
8 kW 8732 kWh 6549 kWh 2183 kWh £1,756 £218 £1,975 £23,276 11.8 yrs £16,219

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: £1,253, Upfront: £19,623, Break-even: 15.7 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2183 kWh 1681 kWh 502 kWh £451 £50 £501 £13,519 27.0 yrs £-3,498
3 kW 3274 kWh 2521 kWh 753 kWh £676 £75 £752 £15,554 20.7 yrs £-523
4 kW 4366 kWh 3362 kWh 1004 kWh £902 £100 £1,002 £17,588 17.6 yrs £2,453
5 kW 5458 kWh 4202 kWh 1255 kWh £1,127 £126 £1,253 £19,623 15.7 yrs £5,429
6 kW 6549 kWh 5043 kWh 1506 kWh £1,352 £151 £1,503 £21,657 14.4 yrs £8,405
7 kW 7640 kWh 5883 kWh 1757 kWh £1,578 £176 £1,754 £23,692 13.5 yrs £11,380
8 kW 8732 kWh 6724 kWh 2008 kWh £1,803 £201 £2,004 £25,726 12.8 yrs £14,356

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 TR25

Figures below are tailored to TR25 — click through for full league tables.

Big-Roof Britain Rank #335 of 2182
5.8 kWp (UK avg 5.1 kWp)
~12 panels (≈430 W)
Solar Payback Index Rank #107 of 2997
9.7 years (UK avg 11.3 years)
~£1,261 /yr • £12,207 upfront
Standing-Charge Drag Rank #498 of 2997
15.6% (UK avg 21.7%) drag on savings
£197 fixed • ~£1,261 /yr value

Your Area at a Glance

Your Electricity Rate
26.82p/kWh
Daily Fixed Charge
54.03p/day
Local Sunshine
1092kWh/kW
A 1 kW system generates ~1092 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: 69% • Flats: 0% • Bungalows: 28% Based on 36 properties

Coverage

Isles of Scilly (100%)

Areas Covered

St Martin'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 Southern Western

TR24 (Isles of Scilly)
≈3.5 km away
Local sunshine: ~1,096 kWh/kWp · +0% vs TR25
TR23 (Isles of Scilly)
≈4.6 km away
Local sunshine: ~1,101 kWh/kWp · +1% vs TR25
TR21 (Isles of Scilly)
≈5.6 km away
Local sunshine: ~1,066 kWh/kWp · -2% vs TR25
TR22 (Isles of Scilly)
≈8.6 km away
Local sunshine: ~1,099 kWh/kWp · +1% vs TR25
TR19 (Cornwall)
≈47.5 km away
Local sunshine: ~1,083 kWh/kWp · -1% vs TR25
TR18 (Cornwall)
≈56.3 km away
Local sunshine: ~1,066 kWh/kWp · -2% vs TR25

Similar sunshine across the UK

BH8 (Bournemouth, Christchurch and Poole)
~1,092 kWh/kWp · +0% vs TR25
CT8 (Thanet)
~1,092 kWh/kWp · +0% vs TR25
CT7 (Thanet)
~1,091 kWh/kWp · -0% vs TR25