Solar panels in Derry/Londonderry, Northern Ireland
Roofs in Derry/Londonderry get about 785 hours of usable sunlight a year — less than 100% of the cities we've measured. Here's what that means in cost, savings and payback, using real rooftop data rather than a national average.
Check your specific roof in Derry/Londonderry → City averages are a starting point; your own roof's size, pitch and shading change the answer a lot.
What a typical Derry/Londonderry solar system costs
A 10-panel system (4 kW) is about right for an average Derry/Londonderry home using 2,500 kWh a year. It would produce roughly 2,669 kWh annually and offset 100% of that usage.
| System | Size | kWh/yr | Net cost | Saves/yr | Payback |
|---|---|---|---|---|---|
| 8 panels | 3.2 kW | 2,135 | £5,440 | £380 | 14.3 yrs |
| 12 panels | 4.8 kW | 3,203 | £8,160 | £508 | 16.1 yrs |
| 16 panels | 6.4 kW | 4,270 | £10,880 | £636 | 17.1 yrs |
| 20 panels | 8 kW | 5,338 | £13,600 | £764 | 17.8 yrs |
| 26 panels | 10.4 kW | 6,939 | £17,680 | £956 | 18.5 yrs |
How we worked this out for Derry/Londonderry
Every number on this page comes from these seven steps. Nothing is a national average — the sunlight figure is measured from Derry/Londonderry rooftops.
| # | Step | Result |
|---|---|---|
| 1 | What one panel makes here 400W ÷ 1000 × 785 sun hrs × 0.85 system losses |
267 kWh/yr |
| 2 | Panels needed to cover typical usage 2,500 kWh ÷ 267 kWh per panel |
10 panels |
| 3 | System size 10 panels × 400W |
4.00 kW |
| 4 | Annual production 4.00 kW × 785 hrs × 0.85 |
2,669 kWh/yr |
| 5 | Installed cost 4,000 W × £1.70 per watt (VAT is 0% on UK installs) |
£6,800 |
| 6 | Annual saving 875 kWh used as generated × 26.1p + 1,794 kWh exported × 12p |
£444/yr |
| 7 | Payback £6,800 ÷ £444 per year |
15.3 years |
Step 6 is where most calculators quietly overstate things. Only 33% of what a system this size produces in Derry/Londonderry is used the moment it is generated; the other 1,794 kWh is exported and paid at the Smart Export Guarantee rate, not your import price. Valuing every kWh at the full 26.1p retail rate — which many calculators do — would show a payback of 9.8 years instead of the 15.3 we show. That 5.5-year difference is the single biggest reason our figures look worse than other sites' for Derry/Londonderry.
Assumptions: 400W panels, 15% system losses (inverter, wiring, heat, soiling), £1.70/W installed, 2,500 kWh typical annual household use, 26.1p/kWh electricity. Change any of those and every figure above moves — which is exactly why a single national "solar costs X" number is misleading.
Notice that payback barely improves as systems get bigger, and eventually gets worse. That's because you can only save money on electricity you were going to buy anyway. Once a system covers your usage, extra panels mostly generate exports at a much lower rate.
Why Derry/Londonderry gets 785 sun hours
That figure comes from Google's analysis of real rooftops across Derry/Londonderry — it already accounts for shading from trees, chimneys and neighbouring buildings, which is why it's lower than the raw "hours of daylight" figures you'll see elsewhere. An unusually open, unshaded roof in Derry/Londonderry reaches about 801 hours, roughly 2% better than typical.
The numbers behind this page
| Typical usable sunlight | 785 hrs/yr |
|---|---|
| Unshaded roof | 801 hrs/yr |
| Electricity rate (Northern Ireland avg) | 26.1p/kWh |
| Installed cost assumed | £1.70/W |
| Panel size assumed | 400 W |
| Typical household usage | 2,500 kWh/yr |
| Power used as generated | 33% |
| Paid for exported power | 12p/kWh (SEG) |
| Rooftops sampled here | 4 |
| Google imagery from | 2014 |
When Derry/Londonderry actually produces
Annual totals hide the thing that catches people out: 44% of Derry/Londonderry's yearly sunlight arrives in May–July, and just 7% across November–January.
| Month | Sun hrs | Share of year |
|---|---|---|
| Jan | 18 | |
| Feb | 34 | |
| Mar | 58 | |
| Apr | 87 | |
| May | 110 | |
| Jun | 121 | |
| Jul | 116 | |
| Aug | 96 | |
| Sep | 68 | |
| Oct | 41 | |
| Nov | 22 | |
| Dec | 14 |
That is a severe seasonal swing — Derry/Londonderry produces roughly 8.5× as much in Jun as in Dec. A system sized to cover your annual usage will overproduce badly in summer and fall well short in winter, so how your utility credits exported power matters more here than in most places.
The annual total is measured from Google's rooftop imagery. Its split across months is calculated from solar geometry at Derry/Londonderry's latitude, not separately measured, so treat the monthly figures as the shape of a typical year rather than a forecast.
How Derry/Londonderry compares to the other 788 cities
| Measure | Derry/Londonderry | Rank of 788 |
|---|---|---|
| Usable sunlight | 785 hrs | 787th |
| Sunlight lost to shade | 2% | 721st most |
| Median roof size | 239 m² | 247th largest |
| Electricity rate | 26.1p | 144th highest |
| Payback | 15.3 yrs | 728th fastest |
| Grid carbon | 479 kg/MWh | 544th dirtiest |
What actually stands out about Derry/Londonderry:
- Unusually open roofs. Only 2% of available sunlight is lost to obstruction in Derry/Londonderry — better than all but 67 of the 788 cities measured. Most roofs here get close to their theoretical maximum.
- Plenty of roof to work with. Typical roofs here fit around 65 panels — roughly 6× what an average home needs. Roof size will not be what limits your system in Derry/Londonderry.
- Dimmer than the rest of Northern Ireland. Derry/Londonderry roofs get 6% less usable sunlight than the typical Northern Ireland city we've measured — statewide averages will overstate what you can expect here.
- Older imagery. Google's aerial capture of Derry/Londonderry dates from 2014. Tree growth and new construction since then are not reflected.
Cities with almost the same sunlight
The closest matches to Derry/Londonderry's 785 usable sun hours elsewhere in the UK. Sunlight varies far more across Britain than electricity prices do, so these are the places where a system of the same size produces roughly the same amount.
| City | Sun hrs | Rate | Payback |
|---|---|---|---|
| Glasgow, Scotland | 797 | 26.1p | 15.2 yrs |
| Inverness, Scotland | 759 | 26.1p | 15.7 yrs |
| Falkirk, Scotland | 811 | 26.1p | 15 yrs |
| Kendal, North West | 832 | 26.1p | 14.3 yrs |
Nearby cities
See all of Northern Ireland → statewide sunlight, rates, incentives and every city we've measured.
Derry/Londonderry solar questions
How many solar panels do I need in Derry/Londonderry?
About 10 panels for an average home using 2,500 kWh a year. Derry/Londonderry roofs get 785 usable sun hours, so each 400W panel produces roughly 267 kWh annually. A typical Derry/Londonderry roof fits about 65 panels, so roof space is unlikely to be your limit.
Is solar worth it in Derry/Londonderry?
At 26.1p/kWh and 785 sun hours, a typical system pays for itself in about 15.3 years and returns roughly £4,294 over a 25-year panel life. That is slower than average, so compare several quotes before committing. Exported power earns 12p/kWh under the Smart Export Guarantee, well below the 26.1p you pay to import.
How much do solar panels cost in Derry/Londonderry?
A 4 kW system costs about £6,800 before incentives. That works out near £1.70 per watt installed. Roof pitch, shading, electrical panel upgrades and equipment choice move the price most, which is why quotes for the same house can differ by thousands.
Worth reading before you buy
Estimates only, generated 2026-08-22 from Google Solar API rooftop samples and average Northern Ireland electricity rates. Not a quote and not financial advice. Your roof, usage, utility plan and local incentives will change these numbers — get real quotes before buying.