UK Solar Output by Month: a Commercial Generation Profile
Updated 23 October 2026 · SEO Dons Editorial
What do these monthly figures show?
Each figure is the average energy that 1 kWp of panels delivers in that calendar month, from the European Commission's PVGIS tool (version 5.3, PVcalc, PVGIS-SARAH3 radiation data for 2005 to 2023). Every run used 1 kWp, system losses of 14% (the tool's default allowance for cables, inverters and dirt), fixed mounting and PVGIS's calculated horizon. Two layouts were run:
- South, 35 degrees: modules facing due south on a 35 degree pitch.
- East-west, 10 degrees: the average of an east-facing and a west-facing plane, each at 10 degrees, which is what a flat-roof east-west rack delivers with equal capacity on both sides.
Locations use city-centre coordinates. Figures are modelled averages for an unshaded plane, and rounding can leave a column a kWh or two off its annual total. Annual totals for 13 locations are on the regional yield page and output per panel on the panel output page.
How much does a south-facing 35 degree array make each month?
Between 19 and 36 kWh per kWp in December and between 113 and 138 in the best summer month, depending on the location.
| Month | Plymouth | London | Manchester | Belfast | Glasgow |
|---|---|---|---|---|---|
| January | 41 | 41 | 27 | 30 | 24 |
| February | 59 | 53 | 45 | 47 | 40 |
| March | 95 | 87 | 78 | 81 | 72 |
| April | 129 | 115 | 105 | 108 | 103 |
| May | 138 | 119 | 113 | 122 | 116 |
| June | 138 | 123 | 111 | 116 | 110 |
| July | 136 | 123 | 108 | 110 | 111 |
| August | 125 | 110 | 97 | 101 | 97 |
| September | 104 | 95 | 81 | 81 | 75 |
| October | 71 | 69 | 56 | 58 | 52 |
| November | 49 | 48 | 37 | 38 | 33 |
| December | 36 | 36 | 28 | 26 | 19 |
| Year | 1,122 | 1,019 | 886 | 919 | 853 |
May is the best month at Plymouth, Manchester, Belfast and Glasgow, and July at London, though the summer months sit within a few kWh of each other.
What changes on a flat roof with east-west rows?
Winter output falls far more than summer output. In December the east-west layout makes 34% to 44% of the south figure. In June it makes slightly more than the south layout at all five locations (0.3% to 1.6% more), because the summer sun is high and a low tilt receives it well.
| Month | Plymouth | London | Manchester | Belfast | Glasgow |
|---|---|---|---|---|---|
| January | 20 | 18 | 13 | 12 | 10 |
| February | 36 | 31 | 26 | 26 | 22 |
| March | 71 | 65 | 58 | 59 | 53 |
| April | 111 | 100 | 91 | 93 | 88 |
| May | 134 | 117 | 110 | 118 | 111 |
| June | 140 | 125 | 112 | 117 | 110 |
| July | 135 | 123 | 108 | 110 | 110 |
| August | 115 | 102 | 91 | 93 | 89 |
| September | 82 | 76 | 65 | 65 | 60 |
| October | 47 | 45 | 37 | 37 | 33 |
| November | 25 | 23 | 18 | 17 | 14 |
| December | 16 | 15 | 11 | 9 | 7 |
| Year | 932 | 840 | 741 | 756 | 707 |
It peaks in June at Plymouth, London and Manchester and in May at Belfast and Glasgow. These are per kWp; more kWp on the same roof changes a site's totals, as the sizing guide explains.
What share of a year's output arrives in June and December?
On the south layout June supplies 12.0% to 12.9% of the year and December 2.3% to 3.6%. On the east-west layout June supplies 14.8% to 15.6% and December 0.9% to 1.7%.
| Location | Layout | June share of year | December share of year | June output divided by December |
|---|---|---|---|---|
| Plymouth | South, 35 degrees | 12.3% | 3.2% | 3.8 |
| Plymouth | East-west, 10 degrees | 15.0% | 1.7% | 8.8 |
| London | South, 35 degrees | 12.0% | 3.6% | 3.4 |
| London | East-west, 10 degrees | 14.8% | 1.7% | 8.6 |
| Manchester | South, 35 degrees | 12.5% | 3.2% | 3.9 |
| Manchester | East-west, 10 degrees | 15.2% | 1.4% | 10.6 |
| Belfast | South, 35 degrees | 12.6% | 2.9% | 4.4 |
| Belfast | East-west, 10 degrees | 15.5% | 1.2% | 12.7 |
| Glasgow | South, 35 degrees | 12.9% | 2.3% | 5.7 |
| Glasgow | East-west, 10 degrees | 15.6% | 0.9% | 17.0 |
Further north the winter share shrinks: Glasgow's December on the south layout is 2.3% of the year against 3.6% in London. June output divided by December output runs from 3.4 (London, south) to 17.0 (Glasgow, east-west).
How much does each month vary from year to year?
PVGIS also reports the standard deviation of output from year to year, shown here as a share of the average for the south layout:
| Location (south, 35 degrees) | Whole year | June | December |
|---|---|---|---|
| Plymouth | 2.6% | 11% | 19% |
| London | 4.1% | 10% | 21% |
| Manchester | 3.4% | 12% | 18% |
| Belfast | 3.0% | 12% | 19% |
| Glasgow | 3.1% | 12% | 20% |
One standard deviation is 18% to 21% of an average December, 10% to 12% of an average June and 2.6% to 4.1% of a whole year. One poor winter month says little about a system; a year is far steadier.
What does the monthly shape mean for self-consumption, export and batteries?
Self-consumption and export
It sets a ceiling month by month. If a site uses less in a month than the array makes, some of that output has to be exported, however well the hours line up. If it uses more, export happens only when the array out-produces the building at that moment, such as at a weekend.
The table tests this on a hypothetical site: a 100 kWp array in London facing south at 35 degrees, and an invented flat use of 9,000 kWh every month (108,000 kWh a year). Output is the PVGIS monthly figure times 100.
| Month | Array output (kWh) | Output as % of use |
|---|---|---|
| January | 4,071 | 45% |
| February | 5,319 | 59% |
| March | 8,654 | 96% |
| April | 11,455 | 127% |
| May | 11,945 | 133% |
| June | 12,259 | 136% |
| July | 12,321 | 137% |
| August | 11,037 | 123% |
| September | 9,522 | 106% |
| October | 6,851 | 76% |
| November | 4,818 | 54% |
| December | 3,633 | 40% |
The array out-produces the site's total use from April to September, so export is certain in those months. From November to February it makes 40% to 59% of use, so most of its output goes to the building. If every kWh up to each month's use were consumed on site, about 86% of the year's output would be self-consumed. That is a ceiling from monthly arithmetic; the real figure depends on how output and demand line up across the day and week, which takes half-hourly meter data.
Demand has seasons too. Elexon's profiling page describes a load profile as the pattern of electricity usage by day and by year for the average customer in each of eight profile classes, with five seasons and three day types. Its profile coefficients are data files and are not used here, so the flat month is a deliberate simplification. The load profile page covers the classes.
Battery sizing
A battery can only store output the site is not using at that moment, so its useful size follows the surplus, and the surplus is mostly a summer matter. In London on the south layout the array averages 4.09 kWh per kWp per day in June and 1.17 in December, which is 409 and 117 kWh a day for 100 kWp.
Against the hypothetical site's average use of 300 kWh a day in June (9,000 over 30 days), an average June day leaves up to about 109 kWh above use. In December, with average use of about 290 kWh a day, an average day leaves nothing. Individual days still differ.
So a store sized for the summer surplus has little solar to charge from between November and February, and one sized for winter is too small for summer output. The battery storage guide covers sizing and when a store pays.
How can a buyer use a monthly profile to check a proposal?
- Ask for the proposal's monthly generation, with the location, tilt, azimuth and loss assumptions behind it.
- Divide each month by the array's kWp and compare it with the closest location above. On a south 35 degree plane, a December share above 4% of the year is higher than at any of the five locations here and needs an explanation.
- Lay monthly output against the site's monthly use from half-hourly data and mark the months where output passes use. Those are the export months.
The commercial PV systems guide sets out the components those assumptions refer to. To put a roof forward for this comparison, send an enquiry through the quote form.
Sources
- European Commission Joint Research Centre: PVGIS 5 user manual, checked 22 October 2026.
- European Commission Joint Research Centre: PVGIS 5.3 PVcalc runs (1 kWp, 14% losses, JSON output), checked 22 October 2026:
- Elexon: Profiling, checked 22 October 2026.
Method: one PVcalc request per plane per location in October 2026. East-west figures are the mean of the east and west runs. Percentages, ratios and the hypothetical-site table are illustrative arithmetic, not forecasts for any building.
Common questions
Which month produces the most solar electricity in the UK?
On the south 35 degree layout PVGIS puts May ahead at four of the five locations and July ahead in London, with June close behind. On the flat east-west layout June leads at Plymouth, London and Manchester and May at Belfast and Glasgow. The gap between the best months is small and the gap to December is large.
Do commercial solar panels still work in winter?
Yes, at much lower output. In December the south 35 degree array makes 36 kWh per kWp in London and 19 in Glasgow, 3.6% and 2.3% of each year's output. The east-west layout makes 15 and 7 kWh per kWp in the same month.
Can these figures go straight into a payback calculation?
Use them as a cross-check rather than an input. They assume an unshaded plane, a 14% loss allowance and long-run average weather, while a site model uses the real roof, nearby shading and chosen equipment.