Solar panels in Carmarthen, Wales

Roofs in Carmarthen get about 970 hours of usable sunlight a year — less than 93% 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 Carmarthen → City averages are a starting point; your own roof's size, pitch and shading change the answer a lot.

What a typical Carmarthen solar system costs

A 8-panel system (3.2 kW) is about right for an average Carmarthen home using 2,500 kWh a year. It would produce roughly 2,638 kWh annually and offset 100% of that usage.

How we worked this out for Carmarthen

Every number on this page comes from these seven steps. Nothing is a national average — the sunlight figure is measured from Carmarthen rooftops.

Step 6 is where most calculators quietly overstate things. Only 33% of what a system this size produces in Carmarthen is used the moment it is generated; the other 1,763 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 7.9 years instead of the 12.4 we show. That 4.5-year difference is the single biggest reason our figures look worse than other sites' for Carmarthen.

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 Carmarthen gets 970 sun hours

That figure comes from Google's analysis of real rooftops across Carmarthen — 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 Carmarthen reaches about 1,035 hours, roughly 7% better than typical.

The numbers behind this page

When Carmarthen actually produces

Annual totals hide the thing that catches people out: 42% of Carmarthen's yearly sunlight arrives in May–July, and just 8% across November–January.

That is a severe seasonal swing — Carmarthen produces roughly 6.3× 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 Carmarthen's latitude, not separately measured, so treat the monthly figures as the shape of a typical year rather than a forecast.

How Carmarthen compares to the other 788 cities

What actually stands out about Carmarthen:

• Plenty of roof to work with. Typical roofs here fit around 38 panels — roughly 4× what an average home needs. Roof size will not be what limits your system in Carmarthen.
• Older imagery. Google's aerial capture of Carmarthen dates from 2021. Tree growth and new construction since then are not reflected.

Cities with almost the same sunlight

The closest matches to Carmarthen's 970 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.

Nearby cities

See all of Wales → statewide sunlight, rates, incentives and every city we've measured.

Carmarthen solar questions

Worth reading before you buy

Estimates only, generated 2026-08-22 from Google Solar API rooftop samples and average Wales 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.