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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in NP15 (Monmouthshire)

See if solar pays off for you in Monmouthshire — 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
£12,207
What you pay to get started
Annual Benefit
£968
What you save every year
Profit Over 25 Years
£11,997
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 964 kWh/kW — 4 below the regional median (968).

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 964 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)
964 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: £807, 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 1929 kWh 771 kWh 1157 kWh £207 £116 £323 £4,069 12.6 yrs £2,385
3 kW 2893 kWh 1157 kWh 1736 kWh £310 £174 £484 £6,104 12.6 yrs £3,578
4 kW 3857 kWh 1543 kWh 2314 kWh £414 £231 £645 £8,138 12.6 yrs £4,771
5 kW 4822 kWh 1929 kWh 2893 kWh £517 £289 £807 £10,173 12.6 yrs £5,963
6 kW 5786 kWh 2314 kWh 3472 kWh £621 £347 £968 £12,207 12.6 yrs £7,156
7 kW 6751 kWh 2700 kWh 4050 kWh £724 £405 £1,130 £14,242 12.6 yrs £8,349
8 kW 7715 kWh 3086 kWh 4629 kWh £828 £463 £1,291 £16,276 12.6 yrs £9,541

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: £969, 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 1929 kWh 1157 kWh 771 kWh £310 £77 £388 £6,169 15.9 yrs £1,584
3 kW 2893 kWh 1736 kWh 1157 kWh £466 £116 £581 £8,204 14.1 yrs £3,426
4 kW 3857 kWh 2314 kWh 1543 kWh £621 £154 £775 £10,238 13.2 yrs £5,267
5 kW 4822 kWh 2893 kWh 1929 kWh £776 £193 £969 £12,273 12.7 yrs £7,109
6 kW 5786 kWh 3472 kWh 2314 kWh £931 £231 £1,163 £14,307 12.3 yrs £8,951
7 kW 6751 kWh 4050 kWh 2700 kWh £1,087 £270 £1,357 £16,342 12.0 yrs £10,793
8 kW 7715 kWh 4629 kWh 3086 kWh £1,242 £309 £1,551 £18,376 11.9 yrs £12,635

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: £1,050, Upfront: £13,673, Break-even: 13.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1929 kWh 1350 kWh 579 kWh £362 £58 £420 £7,569 18.0 yrs £833
3 kW 2893 kWh 2025 kWh 868 kWh £543 £87 £630 £9,604 15.2 yrs £2,999
4 kW 3857 kWh 2700 kWh 1157 kWh £724 £116 £840 £11,638 13.9 yrs £5,166
5 kW 4822 kWh 3375 kWh 1447 kWh £906 £145 £1,050 £13,673 13.0 yrs £7,332
6 kW 5786 kWh 4050 kWh 1736 kWh £1,087 £174 £1,260 £15,707 12.5 yrs £9,499
7 kW 6751 kWh 4725 kWh 2025 kWh £1,268 £203 £1,470 £17,742 12.1 yrs £11,665
8 kW 7715 kWh 5400 kWh 2314 kWh £1,449 £231 £1,680 £19,776 11.8 yrs £13,832

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: £1,075, Upfront: £15,423, Break-even: 14.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1929 kWh 1408 kWh 521 kWh £378 £52 £430 £9,319 21.7 yrs £-722
3 kW 2893 kWh 2112 kWh 781 kWh £567 £78 £645 £11,354 17.6 yrs £1,542
4 kW 3857 kWh 2816 kWh 1042 kWh £756 £104 £860 £13,388 15.6 yrs £3,805
5 kW 4822 kWh 3520 kWh 1302 kWh £944 £130 £1,075 £15,423 14.4 yrs £6,069
6 kW 5786 kWh 4224 kWh 1562 kWh £1,133 £156 £1,290 £17,457 13.5 yrs £8,333
7 kW 6751 kWh 4928 kWh 1823 kWh £1,322 £182 £1,504 £19,492 13.0 yrs £10,597
8 kW 7715 kWh 5632 kWh 2083 kWh £1,511 £208 £1,719 £21,526 12.5 yrs £12,861

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: £1,091, Upfront: £17,173, 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 1929 kWh 1447 kWh 482 kWh £388 £48 £436 £11,069 25.4 yrs £-2,342
3 kW 2893 kWh 2170 kWh 723 kWh £582 £72 £654 £13,104 20.0 yrs £-14
4 kW 3857 kWh 2893 kWh 964 kWh £776 £96 £873 £15,138 17.3 yrs £2,315
5 kW 4822 kWh 3616 kWh 1205 kWh £970 £121 £1,091 £17,173 15.7 yrs £4,644
6 kW 5786 kWh 4340 kWh 1447 kWh £1,164 £145 £1,309 £19,207 14.7 yrs £6,973
7 kW 6751 kWh 5063 kWh 1688 kWh £1,358 £169 £1,527 £21,242 13.9 yrs £9,301
8 kW 7715 kWh 5786 kWh 1929 kWh £1,552 £193 £1,745 £23,276 13.3 yrs £11,630

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: £1,107, Upfront: £19,623, Break-even: 17.7 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1929 kWh 1485 kWh 444 kWh £398 £44 £443 £13,519 30.5 yrs £-4,663
3 kW 2893 kWh 2228 kWh 665 kWh £598 £67 £664 £15,554 23.4 yrs £-2,269
4 kW 3857 kWh 2970 kWh 887 kWh £797 £89 £886 £17,588 19.9 yrs £125
5 kW 4822 kWh 3713 kWh 1109 kWh £996 £111 £1,107 £19,623 17.7 yrs £2,519
6 kW 5786 kWh 4455 kWh 1331 kWh £1,195 £133 £1,328 £21,657 16.3 yrs £4,912
7 kW 6751 kWh 5198 kWh 1553 kWh £1,395 £155 £1,550 £23,692 15.3 yrs £7,306
8 kW 7715 kWh 5941 kWh 1774 kWh £1,594 £177 £1,771 £25,726 14.5 yrs £9,700

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 NP15

Figures below are tailored to NP15 — click through for full league tables.

Big-Roof Britain Rank #154 of 2182
6.3 kWp (UK avg 5.1 kWp)
~13 panels (≈430 W)
Solar Payback Index Rank #1252 of 2997
11.0 years (UK avg 11.3 years)
~£1,114 /yr • £12,207 upfront
Standing-Charge Drag Rank #700 of 2997
16.9% (UK avg 21.7%) drag on savings
£189 fixed • ~£1,114 /yr value

Your Area at a Glance

Your Electricity Rate
26.83p/kWh
Daily Fixed Charge
51.69p/day
Local Sunshine
964kWh/kW
A 1 kW system generates ~964 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: 75% • Flats: 12% • Bungalows: 13% Based on 1,856 properties

Coverage

Monmouthshire (100%)

Areas Covered

Llanbadoc and Usk, Raglan, Gobion Fawr, Llangybi Fawr, Devauden, Llantilio Crossenny, Mitchel Troy and Trellech United, Shirenewton + 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 Wales

NP4 (Torfaen)
≈9.6 km away
Local sunshine: ~966 kWh/kWp · +0% vs NP15
NP44 (Torfaen)
≈10.5 km away
Local sunshine: ~971 kWh/kWp · +1% vs NP15
NP18 (Newport)
≈11.4 km away
Local sunshine: ~997 kWh/kWp · +3% vs NP15
NP5 (Monmouthshire)
≈12.7 km away
Local sunshine: ~964 kWh/kWp · -0% vs NP15
NP19 (Newport)
≈14.1 km away
Local sunshine: ~1,000 kWh/kWp · +4% vs NP15
NP6 (Monmouthshire)
≈14.2 km away
Local sunshine: ~996 kWh/kWp · +3% vs NP15

Similar sunshine across the UK

EX37 (North Devon)
~964 kWh/kWp · -0% vs NP15
GL51 (Cheltenham)
~964 kWh/kWp · -0% vs NP15
PL34 (Cornwall)
~964 kWh/kWp · -0% vs NP15