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
Like May, June 2026 solar generation finished in record-breaking fashion after a relatively slow start
During the first two weeks, a westerly Atlantic flow kept dragging cloud and rain across the country, and daily temperatures through much of this period barely reached the high teens. For solar systems, it’s the cloud that matters more than the cold – panels don’t need warmth, they need irradiance – and with overcast skies dominating from the 1st through to around the 14th, output was below what June should deliver. To give you a sense of just how active it was: 122.6mm of rain fell in a single day at Honister Pass in Cumbria on 4th June, and 74mph gusts were recorded at the Isle of Wight on both the 3rd and the 6th. Not the June anyone ordered.
From around mid-month, a heatwave developing on the near continent started pushing high pressure north and west across the UK. Temperatures in the southeast began climbing first, and by the third week the Met Office had issued Red Warnings for Extreme Heat – their highest level – across three consecutive days. On 26th June, Lingwood in Norfolk hit 37.7°C, a new provisional UK record for June. Cardiff reached 35.9°C on the 25th, a new Wales maximum. On the night of the 25th, Cardiff also didn’t drop below 23.5°C – a new UK record for the warmest June overnight minimum. And on the 26th, the Central England Temperature series – which goes back to 1772 – provisionally recorded its highest ever daily mean temperature anomaly, at 26.5°C against a long-term average of around 14.7°C for that date.
For generation, the second half of June was about as good as it gets in the UK. June already has the longest days of the year, so the solar window each day is at its annual peak. Add clear high-pressure skies on top of that and systems across England and Wales were running optimally.
A quick note on how temperatures impact solar panels: panel efficiency does drop slightly when ambient temperatures reach above around 25°C, because the cells themselves get hot. At 37°C outside, panel surface temperatures will have been higher still. In practice, the irradiance gains from clear skies at this time of year far outweigh that efficiency dip, so generation will still have been very strong. But, it does mean the output wasn’t quite as proportional to the temperature as you might expect.
Rainfall for the UK came in above average overall, which might seem odd given everything that happened in the second half of the month. The reason is that a lot of rain fell early on. Parts of Northern Ireland, northwest England and southern England had already hit their entire monthly average by mid-month, and the second half brought some heavy thunderstorms breaking through the heat in places. These will have caused short-lived dips in generation in affected areas.
June was also the fifth month in a row where the UK mean temperature came in more than 1°C above the long-term average. Whether that continues through July and August remains to be seen, but it has been a strong summer so far for solar generation.
Source: https://www.metoffice.gov.uk/research/climate/maps-and-data/summaries
Ireland
June was again a varied month, delivering some strong generation numbers, particularly in the east.
The first ten days were dominated by Atlantic low pressure. Widespread frontal rain, thundery showers and cool polar maritime air kept skies overcast across most of the country, especially in the west. From a solar perspective, persistent cloud cover suppresses irradiance regardless of how long the days are. June has the longest days of the year, with the solstice falling on the 21st, so the lost generation potential during this cloudy opening period is particularly frustrating.
The middle third of the month was more of a tug of war. High pressure pushing up from the south brought a few drier, sunnier days, but low pressure to the west kept dragging active fronts across the country. Temperatures started to creep up during this period, and for systems that caught the gaps between the fronts, output improved.
From around 20th June, high pressure built more decisively over Ireland and the heat dome that had been developing over western Europe began pushing north. Between 22nd and 26th June, Ireland experienced conditions that haven’t been seen before in June. Athenry in Co Galway hit 32.2°C on the 25th – its highest temperature on record. Six principal stations broke their all-time maximum temperature records, not just their June records. Phoenix Park in Dublin recorded its warmest June since its records began in 1900. Across the country, 13 stations broke their June maximum temperature records and 17 broke their June highest minimum temperature records.
The combination of over 17 hours of daylight and clear high-pressure skies means, for solar generation, this final week of June will have been the standout period of the entire month, and arguably one of the best generation windows of the year. As with the UK heatwave periods, panel efficiency does dip slightly at very high ambient temperatures, but the irradiance gains from cloudless skies at this time of year are so strong that systems will have been producing very well regardless.
Regionally, Casement Aerodrome in Co Dublin led the country at 204.9 hours – 122% of its long-term average – with just one dull day for the entire month. Shannon Airport came in at 169.8 hours, 103% of average. At the other end, Belmullet in Co Mayo recorded just 122.1 hours. The east performed better than the northwest, which spent more time in the path of the Atlantic systems that dominated the first half of the month. So, June performance will vary based on region.
If you’re looking at your monitoring data, expect a slow start through the first two weeks, an improvement in the middle of the month during the drier spells, and then a clear peak in the final third – particularly from around the 22nd to the 26th.
Source: https://www.met.ie/climate-statement-for-june-2026