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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in BT8 (Lisburn and Castlereagh)

See if solar pays off for you in Lisburn and Castlereagh — 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
38.1 years
After this, it's pure profit
Upfront Cost
£12,207
What you pay to get started
Annual Benefit
£321
What you save every year
Profit Over 25 Years
£-4,188
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 Northern Ireland, the current unit rate is 0.00p/kWh with a 0.00p/day standing charge. Your postcode’s south-facing sunshine yield is 891 kWh/kW — 100 below the regional median (991).

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 891 kWh per year on a south-facing roof. We value self-used electricity at 0.0p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.

Unit rate
0.0p/kWh
Standing charge
0.0p/day
Sunshine yield (south)
891 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: £267, Upfront: £10,173, Break-even: 38.1 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 713 kWh 1069 kWh £0 £107 £107 £4,069 38.1 yrs £-1,931
3 kW 2673 kWh 1069 kWh 1604 kWh £0 £160 £160 £6,104 38.1 yrs £-2,896
4 kW 3564 kWh 1426 kWh 2138 kWh £0 £214 £214 £8,138 38.1 yrs £-3,861
5 kW 4455 kWh 1782 kWh 2673 kWh £0 £267 £267 £10,173 38.1 yrs £-4,826
6 kW 5346 kWh 2138 kWh 3208 kWh £0 £321 £321 £12,207 38.1 yrs £-5,792
7 kW 6237 kWh 2495 kWh 3742 kWh £0 £374 £374 £14,242 38.1 yrs £-6,757
8 kW 7128 kWh 2851 kWh 4277 kWh £0 £428 £428 £16,276 38.1 yrs £-7,722

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: £178, Upfront: £12,273, Break-even: 68.9 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 1069 kWh 713 kWh £0 £71 £71 £6,169 86.5 yrs £-4,743
3 kW 2673 kWh 1604 kWh 1069 kWh £0 £107 £107 £8,204 76.7 yrs £-6,065
4 kW 3564 kWh 2138 kWh 1426 kWh £0 £143 £143 £10,238 71.8 yrs £-7,387
5 kW 4455 kWh 2673 kWh 1782 kWh £0 £178 £178 £12,273 68.9 yrs £-8,708
6 kW 5346 kWh 3208 kWh 2138 kWh £0 £214 £214 £14,307 66.9 yrs £-10,030
7 kW 6237 kWh 3742 kWh 2495 kWh £0 £249 £249 £16,342 65.5 yrs £-11,352
8 kW 7128 kWh 4277 kWh 2851 kWh £0 £285 £285 £18,376 64.4 yrs £-12,673

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: £134, Upfront: £13,673, Break-even: 102.3 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 1247 kWh 535 kWh £0 £53 £53 £7,569 141.6 yrs £-6,500
3 kW 2673 kWh 1871 kWh 802 kWh £0 £80 £80 £9,604 119.8 yrs £-8,000
4 kW 3564 kWh 2495 kWh 1069 kWh £0 £107 £107 £11,638 108.8 yrs £-9,500
5 kW 4455 kWh 3119 kWh 1337 kWh £0 £134 £134 £13,673 102.3 yrs £-10,999
6 kW 5346 kWh 3742 kWh 1604 kWh £0 £160 £160 £15,707 97.9 yrs £-12,499
7 kW 6237 kWh 4366 kWh 1871 kWh £0 £187 £187 £17,742 94.8 yrs £-13,999
8 kW 7128 kWh 4990 kWh 2138 kWh £0 £214 £214 £19,776 92.5 yrs £-15,499

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: £120, Upfront: £15,423, Break-even: 128.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 1301 kWh 481 kWh £0 £48 £48 £9,319 193.7 yrs £-8,357
3 kW 2673 kWh 1951 kWh 722 kWh £0 £72 £72 £11,354 157.3 yrs £-9,910
4 kW 3564 kWh 2602 kWh 962 kWh £0 £96 £96 £13,388 139.1 yrs £-11,463
5 kW 4455 kWh 3252 kWh 1203 kWh £0 £120 £120 £15,423 128.2 yrs £-13,017
6 kW 5346 kWh 3903 kWh 1443 kWh £0 £144 £144 £17,457 120.9 yrs £-14,570
7 kW 6237 kWh 4553 kWh 1684 kWh £0 £168 £168 £19,492 115.7 yrs £-16,123
8 kW 7128 kWh 5204 kWh 1925 kWh £0 £192 £192 £21,526 111.8 yrs £-17,677

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: £111, Upfront: £17,173, Break-even: 154.2 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 1337 kWh 446 kWh £0 £45 £45 £11,069 248.5 yrs £-10,178
3 kW 2673 kWh 2005 kWh 668 kWh £0 £67 £67 £13,104 196.1 yrs £-11,767
4 kW 3564 kWh 2673 kWh 891 kWh £0 £89 £89 £15,138 169.9 yrs £-13,356
5 kW 4455 kWh 3341 kWh 1114 kWh £0 £111 £111 £17,173 154.2 yrs £-14,945
6 kW 5346 kWh 4010 kWh 1337 kWh £0 £134 £134 £19,207 143.7 yrs £-16,534
7 kW 6237 kWh 4678 kWh 1559 kWh £0 £156 £156 £21,242 136.2 yrs £-18,123
8 kW 7128 kWh 5346 kWh 1782 kWh £0 £178 £178 £23,276 130.6 yrs £-19,712

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: £102, Upfront: £19,623, Break-even: 191.5 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 1782 kWh 1372 kWh 410 kWh £0 £41 £41 £13,519 329.8 yrs £-12,699
3 kW 2673 kWh 2058 kWh 615 kWh £0 £61 £61 £15,554 253.0 yrs £-14,324
4 kW 3564 kWh 2744 kWh 820 kWh £0 £82 £82 £17,588 214.6 yrs £-15,949
5 kW 4455 kWh 3430 kWh 1025 kWh £0 £102 £102 £19,623 191.5 yrs £-17,573
6 kW 5346 kWh 4117 kWh 1230 kWh £0 £123 £123 £21,657 176.1 yrs £-19,198
7 kW 6237 kWh 4803 kWh 1435 kWh £0 £143 £143 £23,692 165.1 yrs £-20,822
8 kW 7128 kWh 5489 kWh 1639 kWh £0 £164 £164 £25,726 156.9 yrs £-22,447

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.

Your Area at a Glance

Your Electricity Rate
0.00p/kWh
Daily Fixed Charge
0.00p/day
Local Sunshine
891kWh/kW
A 1 kW system generates ~891 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

No EPC data available for this outcode

Coverage

Lisburn and Castlereagh (78%)|Belfast (22%)

Areas Covered

Belvoir, Beechill, Newtownbreda, Galwally, Knockbracken, Carryduff West, Cairnshill, Carryduff East + 4 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 Northern Ireland

BT6 (Belfast)
≈3.6 km away
Local sunshine: ~892 kWh/kWp · +0% vs BT8
BT9 (Belfast)
≈3.7 km away
Local sunshine: ~893 kWh/kWp · +0% vs BT8
BT7 (Belfast)
≈4.1 km away
Local sunshine: ~893 kWh/kWp · +0% vs BT8
BT5 (Belfast)
≈4.9 km away
Local sunshine: ~892 kWh/kWp · +0% vs BT8
BT2 (Belfast)
≈5.2 km away
Local sunshine: ~893 kWh/kWp · +0% vs BT8
BT10 (Belfast)
≈5.2 km away
Local sunshine: ~884 kWh/kWp · -1% vs BT8

Similar sunshine across the UK

AB43 (Aberdeenshire)
~891 kWh/kWp · -0% vs BT8
PR26 (South Ribble)
~891 kWh/kWp · -0% vs BT8
M31 (Trafford)
~891 kWh/kWp · -0% vs BT8