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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in NP12 (Caerphilly)

See if solar pays off for you in Caerphilly — 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
13.1 years
After this, it's pure profit
Upfront Cost
£10,173
What you pay to get started
Annual Benefit
£775
What you save every year
Profit Over 25 Years
£9,197
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 Wales, the current unit rate is 26.83p/kWh with a 51.69p/day standing charge. Your postcode’s south-facing sunshine yield is 926 kWh/kW — 42 below the regional median (968).

Read the full story

A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 926 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
51.7p/day
Sunshine yield (south)
926 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: £775, Upfront: £10,173, 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 1852 kWh 741 kWh 1111 kWh £199 £111 £310 £4,069 13.1 yrs £2,129
3 kW 2778 kWh 1111 kWh 1667 kWh £298 £167 £465 £6,104 13.1 yrs £3,194
4 kW 3704 kWh 1482 kWh 2223 kWh £398 £222 £620 £8,138 13.1 yrs £4,259
5 kW 4631 kWh 1852 kWh 2778 kWh £497 £278 £775 £10,173 13.1 yrs £5,323
6 kW 5557 kWh 2223 kWh 3334 kWh £596 £333 £930 £12,207 13.1 yrs £6,388
7 kW 6483 kWh 2593 kWh 3890 kWh £696 £389 £1,085 £14,242 13.1 yrs £7,453
8 kW 7409 kWh 2964 kWh 4445 kWh £795 £445 £1,240 £16,276 13.1 yrs £8,517

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: £931, Upfront: £12,273, Break-even: 13.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1852 kWh 1111 kWh 741 kWh £298 £74 £372 £6,169 16.6 yrs £1,276
3 kW 2778 kWh 1667 kWh 1111 kWh £447 £111 £558 £8,204 14.7 yrs £2,964
4 kW 3704 kWh 2223 kWh 1482 kWh £596 £148 £745 £10,238 13.8 yrs £4,652
5 kW 4631 kWh 2778 kWh 1852 kWh £745 £185 £931 £12,273 13.2 yrs £6,341
6 kW 5557 kWh 3334 kWh 2223 kWh £895 £222 £1,117 £14,307 12.8 yrs £8,029
7 kW 6483 kWh 3890 kWh 2593 kWh £1,044 £259 £1,303 £16,342 12.5 yrs £9,717
8 kW 7409 kWh 4445 kWh 2964 kWh £1,193 £296 £1,489 £18,376 12.3 yrs £11,405

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: £1,009, Upfront: £13,673, 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 1852 kWh 1297 kWh 556 kWh £348 £56 £403 £7,569 18.8 yrs £500
3 kW 2778 kWh 1945 kWh 834 kWh £522 £83 £605 £9,604 15.9 yrs £2,500
4 kW 3704 kWh 2593 kWh 1111 kWh £696 £111 £807 £11,638 14.4 yrs £4,499
5 kW 4631 kWh 3241 kWh 1389 kWh £870 £139 £1,009 £13,673 13.6 yrs £6,499
6 kW 5557 kWh 3890 kWh 1667 kWh £1,044 £167 £1,210 £15,707 13.0 yrs £8,499
7 kW 6483 kWh 4538 kWh 1945 kWh £1,218 £194 £1,412 £17,742 12.6 yrs £10,499
8 kW 7409 kWh 5186 kWh 2223 kWh £1,391 £222 £1,614 £19,776 12.3 yrs £12,499

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: £1,032, Upfront: £15,423, 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 1852 kWh 1352 kWh 500 kWh £363 £50 £413 £9,319 22.6 yrs £-1,063
3 kW 2778 kWh 2028 kWh 750 kWh £544 £75 £619 £11,354 18.3 yrs £1,030
4 kW 3704 kWh 2704 kWh 1000 kWh £726 £100 £826 £13,388 16.2 yrs £3,123
5 kW 4631 kWh 3380 kWh 1250 kWh £907 £125 £1,032 £15,423 14.9 yrs £5,217
6 kW 5557 kWh 4056 kWh 1500 kWh £1,088 £150 £1,238 £17,457 14.1 yrs £7,310
7 kW 6483 kWh 4732 kWh 1750 kWh £1,270 £175 £1,445 £19,492 13.5 yrs £9,404
8 kW 7409 kWh 5409 kWh 2000 kWh £1,451 £200 £1,651 £21,526 13.0 yrs £11,497

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: £1,048, Upfront: £17,173, Break-even: 16.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1852 kWh 1389 kWh 463 kWh £373 £46 £419 £11,069 26.4 yrs £-2,689
3 kW 2778 kWh 2084 kWh 695 kWh £559 £69 £629 £13,104 20.8 yrs £-533
4 kW 3704 kWh 2778 kWh 926 kWh £745 £93 £838 £15,138 18.1 yrs £1,623
5 kW 4631 kWh 3473 kWh 1158 kWh £932 £116 £1,048 £17,173 16.4 yrs £3,779
6 kW 5557 kWh 4168 kWh 1389 kWh £1,118 £139 £1,257 £19,207 15.3 yrs £5,934
7 kW 6483 kWh 4862 kWh 1621 kWh £1,305 £162 £1,467 £21,242 14.5 yrs £8,090
8 kW 7409 kWh 5557 kWh 1852 kWh £1,491 £185 £1,676 £23,276 13.9 yrs £10,246

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: £1,063, Upfront: £19,623, Break-even: 18.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1852 kWh 1426 kWh 426 kWh £383 £43 £425 £13,519 31.8 yrs £-5,014
3 kW 2778 kWh 2139 kWh 639 kWh £574 £64 £638 £15,554 24.4 yrs £-2,796
4 kW 3704 kWh 2852 kWh 852 kWh £765 £85 £851 £17,588 20.7 yrs £-578
5 kW 4631 kWh 3566 kWh 1065 kWh £957 £107 £1,063 £19,623 18.5 yrs £1,640
6 kW 5557 kWh 4279 kWh 1278 kWh £1,148 £128 £1,276 £21,657 17.0 yrs £3,858
7 kW 6483 kWh 4992 kWh 1491 kWh £1,339 £149 £1,488 £23,692 15.9 yrs £6,076
8 kW 7409 kWh 5705 kWh 1704 kWh £1,531 £170 £1,701 £25,726 15.1 yrs £8,295

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 NP12

Figures below are tailored to NP12 — click through for full league tables.

Big-Roof Britain Rank #1205 of 2182
4.9 kWp (UK avg 5.1 kWp)
~10 panels (≈430 W)
Solar Payback Index Rank #1710 of 2997
11.4 years (UK avg 11.3 years)
~£892 /yr • £10,173 upfront
Standing-Charge Drag Rank #1648 of 2997
21.2% (UK avg 21.7%) drag on savings
£189 fixed • ~£892 /yr value

Your Area at a Glance

Your Electricity Rate
26.83p/kWh
Daily Fixed Charge
51.69p/day
Local Sunshine
926kWh/kW
A 1 kW system generates ~926 kWh per year. A typical home uses ~2,700 kWh per year.
Typical System Size
5.0kW
For houses & bungalows in this area

Local Property Data

Property Types

Houses: 82% • Flats: 10% • Bungalows: 8% Based on 7,925 properties

Coverage

Caerphilly (100%)

Areas Covered

Blackwood, Pontllanfraith, Cefn Fforest and Pengam, Penmaen, Argoed, St Cattwg, Ynysddu, Maesycwmmer + 4 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 Wales

CF82 (Caerphilly)
≈3.5 km away
Local sunshine: ~934 kWh/kWp · +1% vs NP12
CF81 (Caerphilly)
≈3.9 km away
Local sunshine: ~935 kWh/kWp · +1% vs NP12
NP11 (Caerphilly)
≈4.5 km away
Local sunshine: ~930 kWh/kWp · +0% vs NP12
NP2 (Caerphilly)
≈4.6 km away
Local sunshine: ~918 kWh/kWp · -1% vs NP12
CF8 (Caerphilly)
≈6.4 km away
Local sunshine: ~988 kWh/kWp · +7% vs NP12
NP24 (Caerphilly)
≈6.7 km away
Local sunshine: ~881 kWh/kWp · -5% vs NP12

Similar sunshine across the UK

CW7 (Cheshire West and Chester)
~926 kWh/kWp · -0% vs NP12
LS14 (Leeds)
~926 kWh/kWp · -0% vs NP12
DD11 (Angus)
~926 kWh/kWp · -0% vs NP12