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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in L35 (Knowsley)

See if solar pays off for you in Knowsley — 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
13.0 years
After this, it's pure profit
Upfront Cost
£8,138
What you pay to get started
Annual Benefit
£625
What you save every year
Profit Over 25 Years
£7,479
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 North Wales and Mersey, the current unit rate is 27.72p/kWh with a 69.95p/day standing charge. Your postcode’s south-facing sunshine yield is 914 kWh/kW — 16 below the regional median (930).

Read the full story

A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 914 kWh per year on a south-facing roof. We value self-used electricity at 27.7p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
27.7p/kWh
Standing charge
70.0p/day
Sunshine yield (south)
914 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: £781, Upfront: £10,173, 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 1828 kWh 731 kWh 1097 kWh £203 £110 £312 £4,069 13.0 yrs £2,178
3 kW 2742 kWh 1097 kWh 1645 kWh £304 £165 £469 £6,104 13.0 yrs £3,267
4 kW 3656 kWh 1462 kWh 2193 kWh £405 £219 £625 £8,138 13.0 yrs £4,356
5 kW 4570 kWh 1828 kWh 2742 kWh £507 £274 £781 £10,173 13.0 yrs £5,445
6 kW 5484 kWh 2193 kWh 3290 kWh £608 £329 £937 £12,207 13.0 yrs £6,533
7 kW 6397 kWh 2559 kWh 3838 kWh £709 £384 £1,093 £14,242 13.0 yrs £7,622
8 kW 7311 kWh 2925 kWh 4387 kWh £811 £439 £1,249 £16,276 13.0 yrs £8,711

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: £943, Upfront: £12,273, 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 1828 kWh 1097 kWh 731 kWh £304 £73 £377 £6,169 16.4 yrs £1,373
3 kW 2742 kWh 1645 kWh 1097 kWh £456 £110 £566 £8,204 14.5 yrs £3,110
4 kW 3656 kWh 2193 kWh 1462 kWh £608 £146 £754 £10,238 13.6 yrs £4,847
5 kW 4570 kWh 2742 kWh 1828 kWh £760 £183 £943 £12,273 13.0 yrs £6,583
6 kW 5484 kWh 3290 kWh 2193 kWh £912 £219 £1,131 £14,307 12.6 yrs £8,320
7 kW 6397 kWh 3838 kWh 2559 kWh £1,064 £256 £1,320 £16,342 12.4 yrs £10,057
8 kW 7311 kWh 4387 kWh 2925 kWh £1,216 £292 £1,508 £18,376 12.2 yrs £11,794

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: £1,024, Upfront: £13,673, Break-even: 13.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1828 kWh 1279 kWh 548 kWh £355 £55 £410 £7,569 18.5 yrs £621
3 kW 2742 kWh 1919 kWh 823 kWh £532 £82 £614 £9,604 15.6 yrs £2,682
4 kW 3656 kWh 2559 kWh 1097 kWh £709 £110 £819 £11,638 14.2 yrs £4,742
5 kW 4570 kWh 3199 kWh 1371 kWh £887 £137 £1,024 £13,673 13.4 yrs £6,803
6 kW 5484 kWh 3838 kWh 1645 kWh £1,064 £165 £1,229 £15,707 12.8 yrs £8,863
7 kW 6397 kWh 4478 kWh 1919 kWh £1,241 £192 £1,433 £17,742 12.4 yrs £10,924
8 kW 7311 kWh 5118 kWh 2193 kWh £1,419 £219 £1,638 £19,776 12.1 yrs £12,985

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: £1,048, Upfront: £15,423, Break-even: 14.7 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1828 kWh 1334 kWh 494 kWh £370 £49 £419 £9,319 22.2 yrs £-934
3 kW 2742 kWh 2001 kWh 740 kWh £555 £74 £629 £11,354 18.1 yrs £1,223
4 kW 3656 kWh 2669 kWh 987 kWh £740 £99 £838 £13,388 16.0 yrs £3,381
5 kW 4570 kWh 3336 kWh 1234 kWh £925 £123 £1,048 £15,423 14.7 yrs £5,539
6 kW 5484 kWh 4003 kWh 1481 kWh £1,110 £148 £1,258 £17,457 13.9 yrs £7,697
7 kW 6397 kWh 4670 kWh 1727 kWh £1,295 £173 £1,467 £19,492 13.3 yrs £9,854
8 kW 7311 kWh 5337 kWh 1974 kWh £1,479 £197 £1,677 £21,526 12.8 yrs £12,012

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: £1,064, Upfront: £17,173, Break-even: 16.1 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1828 kWh 1371 kWh 457 kWh £380 £46 £426 £11,069 26.0 yrs £-2,555
3 kW 2742 kWh 2056 kWh 685 kWh £570 £69 £639 £13,104 20.5 yrs £-332
4 kW 3656 kWh 2742 kWh 914 kWh £760 £91 £851 £15,138 17.8 yrs £1,890
5 kW 4570 kWh 3427 kWh 1142 kWh £950 £114 £1,064 £17,173 16.1 yrs £4,113
6 kW 5484 kWh 4113 kWh 1371 kWh £1,140 £137 £1,277 £19,207 15.0 yrs £6,335
7 kW 6397 kWh 4798 kWh 1599 kWh £1,330 £160 £1,490 £21,242 14.3 yrs £8,558
8 kW 7311 kWh 5484 kWh 1828 kWh £1,520 £183 £1,703 £23,276 13.7 yrs £10,780

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: £1,080, Upfront: £19,623, Break-even: 18.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1828 kWh 1407 kWh 420 kWh £390 £42 £432 £13,519 31.3 yrs £-4,875
3 kW 2742 kWh 2111 kWh 631 kWh £585 £63 £648 £15,554 24.0 yrs £-2,588
4 kW 3656 kWh 2815 kWh 841 kWh £780 £84 £864 £17,588 20.3 yrs £-301
5 kW 4570 kWh 3519 kWh 1051 kWh £975 £105 £1,080 £19,623 18.2 yrs £1,987
6 kW 5484 kWh 4222 kWh 1261 kWh £1,170 £126 £1,297 £21,657 16.7 yrs £4,274
7 kW 6397 kWh 4926 kWh 1471 kWh £1,365 £147 £1,513 £23,692 15.7 yrs £6,561
8 kW 7311 kWh 5630 kWh 1682 kWh £1,561 £168 £1,729 £25,726 14.9 yrs £8,848

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 L35

Figures below are tailored to L35 — click through for full league tables.

Big-Roof Britain Rank #1537 of 2182
4.7 kWp (UK avg 5.1 kWp)
~10 panels (≈430 W)
Solar Payback Index Rank #1603 of 2997
11.3 years (UK avg 11.3 years)
~£722 /yr • £8,138 upfront
Standing-Charge Drag Rank #2874 of 2997
35.4% (UK avg 21.7%) drag on savings
£255 fixed • ~£722 /yr value

Your Area at a Glance

Your Electricity Rate
27.72p/kWh
Daily Fixed Charge
69.95p/day
Local Sunshine
914kWh/kW
A 1 kW system generates ~914 kWh per year. A typical home uses ~2,700 kWh per year.
Typical System Size
4.0kW
For houses & bungalows in this area

Local Property Data

Property Types

Houses: 80% • Flats: 13% • Bungalows: 5% Based on 8,213 properties

Coverage

Knowsley (63%)|St. Helens (37%)

Areas Covered

Rainhill, Whiston and Cronton, Prescot South, Prescot North, St Gabriels, Halewood North, Eccleston, Thatto Heath + 2 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 North Wales and Mersey

L34 (Knowsley)
≈1.7 km away
Local sunshine: ~922 kWh/kWp · +1% vs L35
L36 (Knowsley)
≈3.5 km away
Local sunshine: ~919 kWh/kWp · +1% vs L35
L27 (Liverpool)
≈4.6 km away
Local sunshine: ~921 kWh/kWp · +1% vs L35
WA10 (St. Helens)
≈4.8 km away
Local sunshine: ~911 kWh/kWp · -0% vs L35
WA9 (St. Helens)
≈5.2 km away
Local sunshine: ~911 kWh/kWp · -0% vs L35
L28 (Knowsley)
≈5.4 km away
Local sunshine: ~926 kWh/kWp · +1% vs L35

Similar sunshine across the UK

LS2 (Leeds)
~914 kWh/kWp · +0% vs L35
BD4 (Bradford)
~914 kWh/kWp · +0% vs L35
LS6 (Leeds)
~914 kWh/kWp · +0% vs L35