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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in NP25 (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
12.7 years
After this, it's pure profit
Upfront Cost
£12,207
What you pay to get started
Annual Benefit
£958
What you save every year
Profit Over 25 Years
£11,738
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 954 kWh/kW — 14 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 954 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)
954 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: £798, Upfront: £10,173, 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 1908 kWh 763 kWh 1145 kWh £205 £114 £319 £4,069 12.7 yrs £2,316
3 kW 2862 kWh 1145 kWh 1717 kWh £307 £172 £479 £6,104 12.7 yrs £3,474
4 kW 3816 kWh 1526 kWh 2290 kWh £410 £229 £639 £8,138 12.7 yrs £4,633
5 kW 4770 kWh 1908 kWh 2862 kWh £512 £286 £798 £10,173 12.7 yrs £5,791
6 kW 5724 kWh 2290 kWh 3435 kWh £614 £343 £958 £12,207 12.7 yrs £6,949
7 kW 6678 kWh 2671 kWh 4007 kWh £717 £401 £1,117 £14,242 12.7 yrs £8,107
8 kW 7632 kWh 3053 kWh 4579 kWh £819 £458 £1,277 £16,276 12.7 yrs £9,265

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: £959, Upfront: £12,273, Break-even: 12.8 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1908 kWh 1145 kWh 763 kWh £307 £76 £383 £6,169 16.1 yrs £1,501
3 kW 2862 kWh 1717 kWh 1145 kWh £461 £114 £575 £8,204 14.3 yrs £3,301
4 kW 3816 kWh 2290 kWh 1526 kWh £614 £153 £767 £10,238 13.3 yrs £5,102
5 kW 4770 kWh 2862 kWh 1908 kWh £768 £191 £959 £12,273 12.8 yrs £6,902
6 kW 5724 kWh 3435 kWh 2290 kWh £922 £229 £1,150 £14,307 12.4 yrs £8,703
7 kW 6678 kWh 4007 kWh 2671 kWh £1,075 £267 £1,342 £16,342 12.2 yrs £10,503
8 kW 7632 kWh 4579 kWh 3053 kWh £1,229 £305 £1,534 £18,376 12.0 yrs £12,303

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: £1,039, Upfront: £13,673, 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 1908 kWh 1336 kWh 572 kWh £358 £57 £416 £7,569 18.2 yrs £743
3 kW 2862 kWh 2004 kWh 859 kWh £538 £86 £623 £9,604 15.4 yrs £2,865
4 kW 3816 kWh 2671 kWh 1145 kWh £717 £114 £831 £11,638 14.0 yrs £4,986
5 kW 4770 kWh 3339 kWh 1431 kWh £896 £143 £1,039 £13,673 13.2 yrs £7,108
6 kW 5724 kWh 4007 kWh 1717 kWh £1,075 £172 £1,247 £15,707 12.6 yrs £9,229
7 kW 6678 kWh 4675 kWh 2004 kWh £1,254 £200 £1,455 £17,742 12.2 yrs £11,351
8 kW 7632 kWh 5343 kWh 2290 kWh £1,433 £229 £1,662 £19,776 11.9 yrs £13,473

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: £1,063, Upfront: £15,423, Break-even: 14.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1908 kWh 1393 kWh 515 kWh £374 £52 £425 £9,319 21.9 yrs £-814
3 kW 2862 kWh 2089 kWh 773 kWh £561 £77 £638 £11,354 17.8 yrs £1,404
4 kW 3816 kWh 2786 kWh 1030 kWh £747 £103 £850 £13,388 15.7 yrs £3,622
5 kW 4770 kWh 3482 kWh 1288 kWh £934 £129 £1,063 £15,423 14.5 yrs £5,840
6 kW 5724 kWh 4179 kWh 1546 kWh £1,121 £155 £1,276 £17,457 13.7 yrs £8,057
7 kW 6678 kWh 4875 kWh 1803 kWh £1,308 £180 £1,488 £19,492 13.1 yrs £10,275
8 kW 7632 kWh 5572 kWh 2061 kWh £1,495 £206 £1,701 £21,526 12.7 yrs £12,493

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: £1,079, Upfront: £17,173, Break-even: 15.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1908 kWh 1431 kWh 477 kWh £384 £48 £432 £11,069 25.6 yrs £-2,436
3 kW 2862 kWh 2147 kWh 716 kWh £576 £72 £647 £13,104 20.2 yrs £-154
4 kW 3816 kWh 2862 kWh 954 kWh £768 £95 £863 £15,138 17.5 yrs £2,129
5 kW 4770 kWh 3578 kWh 1193 kWh £960 £119 £1,079 £17,173 15.9 yrs £4,411
6 kW 5724 kWh 4293 kWh 1431 kWh £1,152 £143 £1,295 £19,207 14.8 yrs £6,693
7 kW 6678 kWh 5009 kWh 1670 kWh £1,344 £167 £1,511 £21,242 14.1 yrs £8,975
8 kW 7632 kWh 5724 kWh 1908 kWh £1,536 £191 £1,727 £23,276 13.5 yrs £11,257

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: £1,095, Upfront: £19,623, Break-even: 17.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1908 kWh 1469 kWh 439 kWh £394 £44 £438 £13,519 30.9 yrs £-4,757
3 kW 2862 kWh 2204 kWh 658 kWh £591 £66 £657 £15,554 23.7 yrs £-2,411
4 kW 3816 kWh 2939 kWh 878 kWh £788 £88 £876 £17,588 20.1 yrs £-65
5 kW 4770 kWh 3673 kWh 1097 kWh £986 £110 £1,095 £19,623 17.9 yrs £2,282
6 kW 5724 kWh 4408 kWh 1317 kWh £1,183 £132 £1,314 £21,657 16.5 yrs £4,628
7 kW 6678 kWh 5142 kWh 1536 kWh £1,380 £154 £1,533 £23,692 15.5 yrs £6,975
8 kW 7632 kWh 5877 kWh 1755 kWh £1,577 £176 £1,752 £25,726 14.7 yrs £9,321

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 NP25

Figures below are tailored to NP25 — click through for full league tables.

Big-Roof Britain Rank #527 of 2182
5.6 kWp (UK avg 5.1 kWp)
~12 panels (≈430 W)
Solar Payback Index Rank #1441 of 2997
11.1 years (UK avg 11.3 years)
~£1,102 /yr • £12,207 upfront
Standing-Charge Drag Rank #748 of 2997
17.1% (UK avg 21.7%) drag on savings
£189 fixed • ~£1,102 /yr value

Your Area at a Glance

Your Electricity Rate
26.83p/kWh
Daily Fixed Charge
51.69p/day
Local Sunshine
954kWh/kW
A 1 kW system generates ~954 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: 72% • Flats: 16% • Bungalows: 12% Based on 4,156 properties

Coverage

Monmouthshire (95%)|Herefordshire, County of (3%)|Forest of Dean (2%)

Areas Covered

Town, Mitchel Troy and Trellech United, Osbaston, Wyesham, Overmonnow, Llantilio Crossenny, Drybridge, St Arvans + 3 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

NP5 (Monmouthshire)
≈4.6 km away
Local sunshine: ~964 kWh/kWp · +1% vs NP25
NP15 (Monmouthshire)
≈17.2 km away
Local sunshine: ~964 kWh/kWp · +1% vs NP25
NP16 (Monmouthshire)
≈19.3 km away
Local sunshine: ~996 kWh/kWp · +4% vs NP25
NP7 (Monmouthshire)
≈20.9 km away
Local sunshine: ~939 kWh/kWp · -2% vs NP25
NP6 (Monmouthshire)
≈21.8 km away
Local sunshine: ~996 kWh/kWp · +4% vs NP25
NP26 (Monmouthshire)
≈25.1 km away
Local sunshine: ~998 kWh/kWp · +5% vs NP25

Similar sunshine across the UK

LE41 (Leicester)
~954 kWh/kWp · -0% vs NP25
DN14 (East Riding of Yorkshire)
~954 kWh/kWp · -0% vs NP25
NG70 (Mansfield)
~954 kWh/kWp · -0% vs NP25