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Big Roof Britain Solar Payback Index Standing Charge Drag

Solar Panels in TW19 (Spelthorne)

See if solar pays off for you in Spelthorne — 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
12.3 years
After this, it's pure profit
Upfront Cost
£10,173
What you pay to get started
Annual Benefit
£830
What you save every year
Profit Over 25 Years
£10,580
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 Southern, the current unit rate is 26.48p/kWh with a 44.62p/day standing charge. Your postcode’s south-facing sunshine yield is 1001 kWh/kW — 1 below the regional median (1001).

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 1001 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
44.6p/day
Sunshine yield (south)
1001 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: £830, Upfront: £10,173, Break-even: 12.3 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2001 kWh 800 kWh 1201 kWh £212 £120 £332 £4,069 12.3 yrs £2,572
3 kW 3002 kWh 1201 kWh 1801 kWh £318 £180 £498 £6,104 12.3 yrs £3,858
4 kW 4002 kWh 1601 kWh 2401 kWh £424 £240 £664 £8,138 12.3 yrs £5,144
5 kW 5003 kWh 2001 kWh 3002 kWh £530 £300 £830 £10,173 12.3 yrs £6,430
6 kW 6004 kWh 2401 kWh 3602 kWh £636 £360 £996 £12,207 12.3 yrs £7,715
7 kW 7004 kWh 2802 kWh 4203 kWh £742 £420 £1,162 £14,242 12.3 yrs £9,001
8 kW 8005 kWh 3202 kWh 4803 kWh £848 £480 £1,328 £16,276 12.3 yrs £10,287

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: £995, Upfront: £12,273, Break-even: 12.3 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2001 kWh 1201 kWh 800 kWh £318 £80 £398 £6,169 15.5 yrs £1,791
3 kW 3002 kWh 1801 kWh 1201 kWh £477 £120 £597 £8,204 13.7 yrs £3,737
4 kW 4002 kWh 2401 kWh 1601 kWh £636 £160 £796 £10,238 12.9 yrs £5,682
5 kW 5003 kWh 3002 kWh 2001 kWh £795 £200 £995 £12,273 12.3 yrs £7,628
6 kW 6004 kWh 3602 kWh 2401 kWh £954 £240 £1,194 £14,307 12.0 yrs £9,573
7 kW 7004 kWh 4203 kWh 2802 kWh £1,113 £280 £1,393 £16,342 11.7 yrs £11,519
8 kW 8005 kWh 4803 kWh 3202 kWh £1,272 £320 £1,592 £18,376 11.5 yrs £13,464

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: £1,077, Upfront: £13,673, 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 2001 kWh 1401 kWh 600 kWh £371 £60 £431 £7,569 17.6 yrs £1,051
3 kW 3002 kWh 2101 kWh 901 kWh £556 £90 £646 £9,604 14.9 yrs £3,326
4 kW 4002 kWh 2802 kWh 1201 kWh £742 £120 £862 £11,638 13.5 yrs £5,601
5 kW 5003 kWh 3502 kWh 1501 kWh £927 £150 £1,077 £13,673 12.7 yrs £7,877
6 kW 6004 kWh 4203 kWh 1801 kWh £1,113 £180 £1,293 £15,707 12.1 yrs £10,152
7 kW 7004 kWh 4903 kWh 2101 kWh £1,298 £210 £1,508 £17,742 11.8 yrs £12,427
8 kW 8005 kWh 5603 kWh 2401 kWh £1,484 £240 £1,724 £19,776 11.5 yrs £14,703

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: £1,102, Upfront: £15,423, Break-even: 14.0 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2001 kWh 1461 kWh 540 kWh £387 £54 £441 £9,319 21.1 yrs £-501
3 kW 3002 kWh 2191 kWh 810 kWh £580 £81 £661 £11,354 17.2 yrs £1,873
4 kW 4002 kWh 2922 kWh 1081 kWh £774 £108 £882 £13,388 15.2 yrs £4,247
5 kW 5003 kWh 3652 kWh 1351 kWh £967 £135 £1,102 £15,423 14.0 yrs £6,621
6 kW 6004 kWh 4383 kWh 1621 kWh £1,161 £162 £1,323 £17,457 13.2 yrs £8,996
7 kW 7004 kWh 5113 kWh 1891 kWh £1,354 £189 £1,543 £19,492 12.6 yrs £11,370
8 kW 8005 kWh 5844 kWh 2161 kWh £1,547 £216 £1,764 £21,526 12.2 yrs £13,744

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: £1,119, Upfront: £17,173, Break-even: 15.4 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2001 kWh 1501 kWh 500 kWh £397 £50 £447 £11,069 24.7 yrs £-2,120
3 kW 3002 kWh 2251 kWh 750 kWh £596 £75 £671 £13,104 19.5 yrs £321
4 kW 4002 kWh 3002 kWh 1001 kWh £795 £100 £895 £15,138 16.9 yrs £2,761
5 kW 5003 kWh 3752 kWh 1251 kWh £994 £125 £1,119 £17,173 15.4 yrs £5,201
6 kW 6004 kWh 4503 kWh 1501 kWh £1,192 £150 £1,342 £19,207 14.3 yrs £7,641
7 kW 7004 kWh 5253 kWh 1751 kWh £1,391 £175 £1,566 £21,242 13.6 yrs £10,082
8 kW 8005 kWh 6004 kWh 2001 kWh £1,590 £200 £1,790 £23,276 13.0 yrs £12,522

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: £1,135, Upfront: £19,623, Break-even: 17.3 yrs
System Annual output Self-use Exported Bill saving Export income Annual benefit Upfront cost Break-even 20-year net
2 kW 2001 kWh 1541 kWh 460 kWh £408 £46 £454 £13,519 29.8 yrs £-4,438
3 kW 3002 kWh 2311 kWh 690 kWh £612 £69 £681 £15,554 22.8 yrs £-1,931
4 kW 4002 kWh 3082 kWh 921 kWh £816 £92 £908 £17,588 19.4 yrs £575
5 kW 5003 kWh 3852 kWh 1151 kWh £1,020 £115 £1,135 £19,623 17.3 yrs £3,081
6 kW 6004 kWh 4623 kWh 1381 kWh £1,224 £138 £1,362 £21,657 15.9 yrs £5,587
7 kW 7004 kWh 5393 kWh 1611 kWh £1,428 £161 £1,589 £23,692 14.9 yrs £8,093
8 kW 8005 kWh 6164 kWh 1841 kWh £1,632 £184 £1,816 £25,726 14.2 yrs £10,599

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 TW19

Figures below are tailored to TW19 — click through for full league tables.

Big-Roof Britain Rank #1382 of 2182
4.8 kWp (UK avg 5.1 kWp)
~10 panels (≈430 W)
Solar Payback Index Rank #893 of 2997
10.7 years (UK avg 11.3 years)
~£954 /yr • £10,173 upfront
Standing-Charge Drag Rank #751 of 2997
17.1% (UK avg 21.7%) drag on savings
£163 fixed • ~£954 /yr value

Your Area at a Glance

Your Electricity Rate
26.48p/kWh
Daily Fixed Charge
44.62p/day
Local Sunshine
1001kWh/kW
A 1 kW system generates ~1001 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: 57% • Flats: 28% • Bungalows: 9% Based on 4,837 properties

Coverage

Spelthorne (61%)|Windsor and Maidenhead (26%)|Runnymede (12%)|Hounslow (1%)

Areas Covered

Stanwell North, Datchet, Horton & Wraysbury, Ashford North and Stanwell South, Egham Hythe, Staines, Bedfont, Heathrow Villages + 1 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 Southern

TW6 (Hillingdon)
≈2.8 km away
Local sunshine: ~1,007 kWh/kWp · +1% vs TW19
TW18 (Spelthorne)
≈2.9 km away
Local sunshine: ~998 kWh/kWp · -0% vs TW19
TW15 (Spelthorne)
≈3.5 km away
Local sunshine: ~1,001 kWh/kWp · +0% vs TW19
TW14 (Hounslow)
≈4.6 km away
Local sunshine: ~1,001 kWh/kWp · +0% vs TW19
TW20 (Runnymede)
≈4.9 km away
Local sunshine: ~999 kWh/kWp · -0% vs TW19
TW13 (Hounslow)
≈5.5 km away
Local sunshine: ~1,001 kWh/kWp · +0% vs TW19

Similar sunshine across the UK

NR2 (Norwich)
~1,001 kWh/kWp · +0% vs TW19
NR3 (Norwich)
~1,001 kWh/kWp · +0% vs TW19
CB6 (East Cambridgeshire)
~1,001 kWh/kWp · +0% vs TW19