Every month, UrbanVolt publishes a solar generation update for our clients across the UK and Ireland, so you always know how the weather has affected your system’s output.
United Kingdom
May 2026 started poorly for solar generation and finished in record-breaking fashion.
The opening two weeks were largely written off in generation terms. Unsettled conditions, persistent cloud cover, occasional heavy showers and below-average temperatures across the UK suppressed output from the start of the month. Frosts were reported in some northwestern areas as late as 5th May, a sign of just how cold and unsettled the airmass was. Cold air alone doesn’t prevent solar generation – panels don’t need warmth to produce electricity – but the cloud and rain that accompanied these conditions does. For sites across the UK, generation during the first fortnight will have tracked below what a typical May day would deliver.
Things began to shift around 19th May. High pressure started to assert itself, temperatures rose, and by 24th May some stations were already recording temperatures above 30°C. What followed over the next few days was genuinely exceptional. Kew Gardens in London set a new UK May maximum temperature record of 35.1°C on 26th May, beating the previous record of 32.8°C that had stood since 1944. More than 20 other stations also exceeded that 1944 benchmark, with many recording new station records for May. Heatwave thresholds were met across much of central and southern England and Wales. In Camborne, Cornwall, temperatures on the night of 27th May didn’t drop below 21.4°C – a new UK record for the highest daily minimum temperature in May.
From a solar generation perspective, this period was as productive as any you’ll see in a UK May. Intense high pressure means clear skies, and clear skies in late May means long daylight hours and strong irradiance hitting panels at some of the best sun angles of the year. Occasional thundery showers broke through the heat, causing brief dips in output in some areas, but these were short-lived against the backdrop of an otherwise settled and sunny spell.
Rainfall across the UK came in at just 78% of the long-term average – good news for generation, as drier months mean fewer cloud-bearing weather systems. The regional picture is stark: Essex and Suffolk recorded just 31% of their average May rainfall, making the southeast the driest part of the country and reinforcing what the sunshine data suggests about where generation was strongest. At the other end of the scale, Tyne and Wear came in at 140% of average and Shetland at 137%, so Scotland and the northeast will have seen a more muted month.
The UK mean temperature for the month was 12.0°C, 1.3°C above the long-term average, making it the joint third warmest May on record. England provisionally recorded its second warmest May and its warmest May on record for maximum temperatures. These are indicators of the kind of high-pressure, low-cloud-cover conditions that drive strong solar output.
If you’re reviewing your monitoring data, look for this pattern: a suppressed first fortnight followed by a sharp step-up from around 19th May, peaking in the final week. For sites in central and southern England, that final week alone will have been responsible for a disproportionate share of the month’s total generation.
Source: https://www.metoffice.gov.uk/research/climate/maps-and-data/summaries
Ireland
May 2026 followed a similar pattern to April – a cooler, more variable opening period giving way to an exceptional finish.
The first two thirds of the month were largely driven by high pressure sitting to the west of Ireland, steering Arctic air down from the north. Cool temperatures, some rain and showers from the northwest, and a generally unsettled spell around 18th–21st May meant generation during this period was steady rather than spectacular. The cooler Arctic air does, however, tend to arrive with relatively clear skies – high pressure conditions even in cool air suppress cloud cover, so panels were still generating through much of this period.
Everything changed in the final third of the month. An intense area of high pressure built across western and central Europe and pushed north over Ireland from around 22nd May. A tropical continental airmass followed on 24th May. Therefore, between 25th and 27th May, Ireland experienced some of the hottest temperatures ever recorded in May. Shannon Airport hit 30.6°C on 26th – the highest May temperature ever recorded at a synoptic station in Ireland. Eighteen stations set new May maximum temperature records during this three-day period, and seven of those also provisionally broke the national May maximum air temperature record. The date 26th May also produced the highest single day of sunshine for the month – 15.2 hours at Johnstown Castle, Co Wexford.
For solar generation, this was as good as it gets in May. Intense high pressure, clear skies, long days and strong irradiance all converging at the same time. May already has some of the longest days of the year, so the solar window in that final week was close to the maximum possible for Ireland. Thunderstorms broke out across the south on the evening of 27th, which will have briefly disrupted generation there, and a cooler Atlantic airflow closed out the month – but the damage to the overall monthly total was minimal.
Sunshine figures for the month were variable by region, which is worth understanding in terms of what your system’s monitoring data may show. The east performed best – Casement Aerodrome in Co Dublin topped the table at 207.0 hours, reaching 108% of its long-term average. Shannon Airport, despite hosting Ireland’s hottest ever May day, came in at 96% of normal (177.0 hours), partly because the intense heat event was brief and the west and south saw more cloud earlier in the month. Cork Airport was the dullest station nationally at 150.3 hours. If your site is in the east or southeast, May will have been a stronger month than if you’re in the west.
For most UrbanVolt customers in Ireland, May will have been a good month, particularly in the east. The final week alone will have contributed a disproportionate share of the monthly total. If you want to understand your site’s specific performance, your monitoring data will tell the story clearly.
Source: https://www.met.ie/climate-statement-for-may-2026