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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in WD18 (Watford)

See if solar pays off for you in Watford — 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
12.4 years
After this, it's pure profit
Upfront Cost
£6,104
What you pay to get started
Annual Benefit
£491
What you save every year
Profit Over 25 Years
£6,163
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 Eastern, the current unit rate is 26.53p/kWh with a 48.25p/day standing charge. Your postcode’s south-facing sunshine yield is 985 kWh/kW — 25 below the regional median (1009).

Read the full story

A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 985 kWh per year on a south-facing roof. We value self-used electricity at 26.5p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
26.5p/kWh
Standing charge
48.2p/day
Sunshine yield (south)
985 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: £818, Upfront: £10,173, Break-even: 12.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 788 kWh 1181 kWh £209 £118 £327 £4,069 12.4 yrs £2,473
3 kW 2954 kWh 1181 kWh 1772 kWh £313 £177 £491 £6,104 12.4 yrs £3,710
4 kW 3938 kWh 1575 kWh 2363 kWh £418 £236 £654 £8,138 12.4 yrs £4,946
5 kW 4923 kWh 1969 kWh 2954 kWh £522 £295 £818 £10,173 12.4 yrs £6,183
6 kW 5907 kWh 2363 kWh 3544 kWh £627 £354 £981 £12,207 12.4 yrs £7,419
7 kW 6892 kWh 2757 kWh 4135 kWh £731 £414 £1,145 £14,242 12.4 yrs £8,656
8 kW 7876 kWh 3151 kWh 4726 kWh £836 £473 £1,308 £16,276 12.4 yrs £9,892

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: £981, Upfront: £12,273, Break-even: 12.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 1181 kWh 788 kWh £313 £79 £392 £6,169 15.7 yrs £1,675
3 kW 2954 kWh 1772 kWh 1181 kWh £470 £118 £588 £8,204 13.9 yrs £3,563
4 kW 3938 kWh 2363 kWh 1575 kWh £627 £158 £784 £10,238 13.1 yrs £5,450
5 kW 4923 kWh 2954 kWh 1969 kWh £784 £197 £981 £12,273 12.5 yrs £7,338
6 kW 5907 kWh 3544 kWh 2363 kWh £940 £236 £1,177 £14,307 12.2 yrs £9,225
7 kW 6892 kWh 4135 kWh 2757 kWh £1,097 £276 £1,373 £16,342 11.9 yrs £11,113
8 kW 7876 kWh 4726 kWh 3151 kWh £1,254 £315 £1,569 £18,376 11.7 yrs £13,000

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: £1,062, Upfront: £13,673, Break-even: 12.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 1378 kWh 591 kWh £366 £59 £425 £7,569 17.8 yrs £926
3 kW 2954 kWh 2068 kWh 886 kWh £549 £89 £637 £9,604 15.1 yrs £3,139
4 kW 3938 kWh 2757 kWh 1181 kWh £731 £118 £850 £11,638 13.7 yrs £5,352
5 kW 4923 kWh 3446 kWh 1477 kWh £914 £148 £1,062 £13,673 12.9 yrs £7,565
6 kW 5907 kWh 4135 kWh 1772 kWh £1,097 £177 £1,274 £15,707 12.3 yrs £9,778
7 kW 6892 kWh 4824 kWh 2068 kWh £1,280 £207 £1,487 £17,742 11.9 yrs £11,991
8 kW 7876 kWh 5513 kWh 2363 kWh £1,463 £236 £1,699 £19,776 11.6 yrs £14,204

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: £1,086, Upfront: £15,423, Break-even: 14.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 1437 kWh 532 kWh £381 £53 £435 £9,319 21.4 yrs £-629
3 kW 2954 kWh 2156 kWh 797 kWh £572 £80 £652 £11,354 17.4 yrs £1,682
4 kW 3938 kWh 2875 kWh 1063 kWh £763 £106 £869 £13,388 15.4 yrs £3,993
5 kW 4923 kWh 3594 kWh 1329 kWh £953 £133 £1,086 £15,423 14.2 yrs £6,303
6 kW 5907 kWh 4312 kWh 1595 kWh £1,144 £159 £1,304 £17,457 13.4 yrs £8,614
7 kW 6892 kWh 5031 kWh 1861 kWh £1,335 £186 £1,521 £19,492 12.8 yrs £10,924
8 kW 7876 kWh 5750 kWh 2127 kWh £1,525 £213 £1,738 £21,526 12.4 yrs £13,235

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: £1,103, Upfront: £17,173, Break-even: 15.6 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 1477 kWh 492 kWh £392 £49 £441 £11,069 25.1 yrs £-2,249
3 kW 2954 kWh 2215 kWh 738 kWh £588 £74 £662 £13,104 19.8 yrs £127
4 kW 3938 kWh 2954 kWh 985 kWh £784 £98 £882 £15,138 17.2 yrs £2,503
5 kW 4923 kWh 3692 kWh 1231 kWh £979 £123 £1,103 £17,173 15.6 yrs £4,879
6 kW 5907 kWh 4430 kWh 1477 kWh £1,175 £148 £1,323 £19,207 14.5 yrs £7,254
7 kW 6892 kWh 5169 kWh 1723 kWh £1,371 £172 £1,544 £21,242 13.8 yrs £9,630
8 kW 7876 kWh 5907 kWh 1969 kWh £1,567 £197 £1,764 £23,276 13.2 yrs £12,006

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: £1,119, Upfront: £19,623, Break-even: 17.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1969 kWh 1516 kWh 453 kWh £402 £45 £448 £13,519 30.2 yrs £-4,568
3 kW 2954 kWh 2274 kWh 679 kWh £603 £68 £671 £15,554 23.2 yrs £-2,127
4 kW 3938 kWh 3032 kWh 906 kWh £804 £91 £895 £17,588 19.6 yrs £313
5 kW 4923 kWh 3790 kWh 1132 kWh £1,006 £113 £1,119 £19,623 17.5 yrs £2,754
6 kW 5907 kWh 4549 kWh 1359 kWh £1,207 £136 £1,343 £21,657 16.1 yrs £5,195
7 kW 6892 kWh 5307 kWh 1585 kWh £1,408 £159 £1,566 £23,692 15.1 yrs £7,636
8 kW 7876 kWh 6065 kWh 1812 kWh £1,609 £181 £1,790 £25,726 14.4 yrs £10,077

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 WD18

Figures below are tailored to WD18 — click through for full league tables.

Big-Roof Britain Rank #2085 of 2182
3.9 kWp (UK avg 5.1 kWp)
~8 panels (≈430 W)
Solar Payback Index Rank #1091 of 2997
10.8 years (UK avg 11.3 years)
~£752 /yr • £8,138 upfront
Standing-Charge Drag Rank #2106 of 2997
23.4% (UK avg 21.7%) drag on savings
£176 fixed • ~£752 /yr value

Your Area at a Glance

Your Electricity Rate
26.53p/kWh
Daily Fixed Charge
48.25p/day
Local Sunshine
985kWh/kW
A 1 kW system generates ~985 kWh per year. A typical home uses ~2,700 kWh per year.
Typical System Size
3.0kW
For houses & bungalows in this area

⚠️ This area is predominantly flats. Many residents require freeholder approval for solar installations. System size shown reflects houses and bungalows only.

Local Property Data

Property Types

Houses: 37% • Flats: 59% • Bungalows: 0% Based on 8,522 properties

Coverage

Watford (88%)|Three Rivers (12%)

Areas Covered

Holywell, Vicarage, Park, Central, Moor Park & Eastbury, Dickinsons, Oxhey, Oxhey Hall & Hayling

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 Eastern

WD99 (Watford)
≈0.0 km away
Local sunshine: ~991 kWh/kWp · +1% vs WD18
WD1 (Watford)
≈1.6 km away
Local sunshine: ~991 kWh/kWp · +1% vs WD18
WD17 (Watford)
≈1.8 km away
Local sunshine: ~985 kWh/kWp · +0% vs WD18
WD19 (Three Rivers)
≈3.1 km away
Local sunshine: ~992 kWh/kWp · +1% vs WD18
WD24 (Watford)
≈3.1 km away
Local sunshine: ~985 kWh/kWp · +0% vs WD18
WD2 (Watford)
≈3.7 km away
Local sunshine: ~992 kWh/kWp · +1% vs WD18

Similar sunshine across the UK

RG45 (Bracknell Forest)
~984 kWh/kWp · -0% vs WD18
LN2 (Lincoln)
~985 kWh/kWp · +0% vs WD18
SA17 (Carmarthenshire)
~985 kWh/kWp · +0% vs WD18