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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in SA31 (Carmarthenshire)

See if solar pays off for you in Carmarthenshire — 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
£10,173
What you pay to get started
Annual Benefit
£801
What you save every year
Profit Over 25 Years
£9,850
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 957 kWh/kW — 11 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 957 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)
957 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: £801, 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 1915 kWh 766 kWh 1149 kWh £205 £115 £320 £4,069 12.7 yrs £2,338
3 kW 2872 kWh 1149 kWh 1723 kWh £308 £172 £481 £6,104 12.7 yrs £3,507
4 kW 3829 kWh 1532 kWh 2298 kWh £411 £230 £641 £8,138 12.7 yrs £4,676
5 kW 4787 kWh 1915 kWh 2872 kWh £514 £287 £801 £10,173 12.7 yrs £5,845
6 kW 5744 kWh 2298 kWh 3446 kWh £616 £345 £961 £12,207 12.7 yrs £7,014
7 kW 6701 kWh 2680 kWh 4021 kWh £719 £402 £1,121 £14,242 12.7 yrs £8,183
8 kW 7658 kWh 3063 kWh 4595 kWh £822 £460 £1,281 £16,276 12.7 yrs £9,352

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: £962, 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 1915 kWh 1149 kWh 766 kWh £308 £77 £385 £6,169 16.0 yrs £1,527
3 kW 2872 kWh 1723 kWh 1149 kWh £462 £115 £577 £8,204 14.2 yrs £3,340
4 kW 3829 kWh 2298 kWh 1532 kWh £616 £153 £770 £10,238 13.3 yrs £5,154
5 kW 4787 kWh 2872 kWh 1915 kWh £771 £191 £962 £12,273 12.8 yrs £6,967
6 kW 5744 kWh 3446 kWh 2298 kWh £925 £230 £1,154 £14,307 12.4 yrs £8,781
7 kW 6701 kWh 4021 kWh 2680 kWh £1,079 £268 £1,347 £16,342 12.1 yrs £10,594
8 kW 7658 kWh 4595 kWh 3063 kWh £1,233 £306 £1,539 £18,376 11.9 yrs £12,408

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: £1,043, Upfront: £13,673, 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 1915 kWh 1340 kWh 574 kWh £360 £57 £417 £7,569 18.2 yrs £771
3 kW 2872 kWh 2010 kWh 862 kWh £539 £86 £626 £9,604 15.4 yrs £2,907
4 kW 3829 kWh 2680 kWh 1149 kWh £719 £115 £834 £11,638 14.0 yrs £5,043
5 kW 4787 kWh 3351 kWh 1436 kWh £899 £144 £1,043 £13,673 13.1 yrs £7,179
6 kW 5744 kWh 4021 kWh 1723 kWh £1,079 £172 £1,251 £15,707 12.6 yrs £9,314
7 kW 6701 kWh 4691 kWh 2010 kWh £1,259 £201 £1,460 £17,742 12.2 yrs £11,450
8 kW 7658 kWh 5361 kWh 2298 kWh £1,438 £230 £1,668 £19,776 11.9 yrs £13,586

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: £1,067, 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 1915 kWh 1398 kWh 517 kWh £375 £52 £427 £9,319 21.8 yrs £-785
3 kW 2872 kWh 2097 kWh 775 kWh £562 £78 £640 £11,354 17.7 yrs £1,447
4 kW 3829 kWh 2795 kWh 1034 kWh £750 £103 £853 £13,388 15.7 yrs £3,680
5 kW 4787 kWh 3494 kWh 1292 kWh £937 £129 £1,067 £15,423 14.5 yrs £5,912
6 kW 5744 kWh 4193 kWh 1551 kWh £1,125 £155 £1,280 £17,457 13.6 yrs £8,144
7 kW 6701 kWh 4892 kWh 1809 kWh £1,312 £181 £1,493 £19,492 13.1 yrs £10,377
8 kW 7658 kWh 5591 kWh 2068 kWh £1,500 £207 £1,707 £21,526 12.6 yrs £12,609

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: £1,083, 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 1915 kWh 1436 kWh 479 kWh £385 £48 £433 £11,069 25.6 yrs £-2,406
3 kW 2872 kWh 2154 kWh 718 kWh £578 £72 £650 £13,104 20.2 yrs £-109
4 kW 3829 kWh 2872 kWh 957 kWh £771 £96 £866 £15,138 17.5 yrs £2,187
5 kW 4787 kWh 3590 kWh 1197 kWh £963 £120 £1,083 £17,173 15.9 yrs £4,484
6 kW 5744 kWh 4308 kWh 1436 kWh £1,156 £144 £1,299 £19,207 14.8 yrs £6,781
7 kW 6701 kWh 5026 kWh 1675 kWh £1,348 £168 £1,516 £21,242 14.0 yrs £9,078
8 kW 7658 kWh 5744 kWh 1915 kWh £1,541 £191 £1,733 £23,276 13.4 yrs £11,375

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: £1,099, 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 1915 kWh 1474 kWh 440 kWh £396 £44 £440 £13,519 30.8 yrs £-4,727
3 kW 2872 kWh 2211 kWh 661 kWh £593 £66 £659 £15,554 23.6 yrs £-2,366
4 kW 3829 kWh 2949 kWh 881 kWh £791 £88 £879 £17,588 20.0 yrs £-5
5 kW 4787 kWh 3686 kWh 1101 kWh £989 £110 £1,099 £19,623 17.9 yrs £2,356
6 kW 5744 kWh 4423 kWh 1321 kWh £1,187 £132 £1,319 £21,657 16.4 yrs £4,718
7 kW 6701 kWh 5160 kWh 1541 kWh £1,384 £154 £1,539 £23,692 15.4 yrs £7,079
8 kW 7658 kWh 5897 kWh 1761 kWh £1,582 £176 £1,758 £25,726 14.6 yrs £9,440

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 SA31

Figures below are tailored to SA31 — click through for full league tables.

Big-Roof Britain Rank #1254 of 2182
4.9 kWp (UK avg 5.1 kWp)
~10 panels (≈430 W)
Solar Payback Index Rank #1259 of 2997
11.0 years (UK avg 11.3 years)
~£922 /yr • £10,173 upfront
Standing-Charge Drag Rank #1505 of 2997
20.5% (UK avg 21.7%) drag on savings
£189 fixed • ~£922 /yr value

Your Area at a Glance

Your Electricity Rate
26.83p/kWh
Daily Fixed Charge
51.69p/day
Local Sunshine
957kWh/kW
A 1 kW system generates ~957 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: 64% • Flats: 22% • Bungalows: 12% Based on 5,408 properties

Coverage

Carmarthenshire (100%)

Areas Covered

Carmarthen Town North and South, Llangunnor, Carmarthen Town West, Abergwili, Llangyndeyrn, Trelech, St Clears and Llansteffan, Whitland

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

SA32 (Carmarthenshire)
≈9.9 km away
Local sunshine: ~950 kWh/kWp · -1% vs SA31
SA33 (Carmarthenshire)
≈10.3 km away
Local sunshine: ~992 kWh/kWp · +4% vs SA31
SA17 (Carmarthenshire)
≈11.9 km away
Local sunshine: ~985 kWh/kWp · +3% vs SA31
SA39 (Carmarthenshire)
≈18.6 km away
Local sunshine: ~888 kWh/kWp · -7% vs SA31
SA16 (Carmarthenshire)
≈19.0 km away
Local sunshine: ~1,012 kWh/kWp · +6% vs SA31
SA34 (Carmarthenshire)
≈21.3 km away
Local sunshine: ~995 kWh/kWp · +4% vs SA31

Similar sunshine across the UK

LE7 (Charnwood)
~957 kWh/kWp · -0% vs SA31
B61 (Bromsgrove)
~957 kWh/kWp · +0% vs SA31
DE73 (Derby)
~957 kWh/kWp · -0% vs SA31