UK Solar Panel Output by Month: Real PVGIS Data

The dataset is PVGIS version 5.2, the photovoltaic geographical information system published by the European Commission's Joint Research Centre. Its PVcalc tool estimates monthly output for any location from the PVGIS-SARAH2 solar radiation database, which is built from long-term satellite observations. The exact query used for each city:

• System size: 0.8 kWp of crystalline silicon panel - chosen because it approximates the 800W per-home cap on UK plug-in solar. Output scales linearly, so a 0.4 kWp panel produces half these figures and a 1.6 kWp array double.
• System loss: 14%, the PVGIS default allowance for cabling, inverter and soiling losses.
• Mounting: fixed, at the tilt PVGIS optimises for the UK (40 degrees from horizontal), facing due south (azimuth 0). This is the model's optimum - a real balcony or fence mounting will usually do worse, and the vertical-mounting section below quantifies how much.
• Locations: London (modelled at 51.51, -0.13), Birmingham (modelled at 52.48, -1.90) and Glasgow (modelled at 55.86, -4.26) - southern England, the Midlands and central Scotland.

One more framing note: PVGIS models a typical year averaged from many years of climate data. Any individual year can come in above or below these figures, and a dull December can halve that month's already small total.

Monthly output in kWh for a 0.8 kWp system at optimal fixed tilt, from PVGIS-SARAH2 (figures rounded to one decimal; annual totals as returned by PVGIS):

Three patterns stand out. First, the summer plateau is broad: in London, every month from April to August clears 87 kWh, and July peaks at 97.7 kWh. Second, the collapse into winter is fast - London loses almost half its monthly output between September (77.7 kWh) and October (55.5 kWh), and nearly half again by December. Third, latitude matters most in winter: Glasgow's annual total is about 17% below London's, but its December figure (16.6 kWh) is nearly half of London's 31.7 kWh. Northern winters are shorter on daylight and cloudier, and both effects stack.

Birmingham tracks London closely all year, sitting roughly 3 to 9% lower each month. For most of England, the London and Birmingham columns bracket what an optimally mounted system would see.

Deep enough that it should anchor every purchase decision. Compare December with each city's best month:

• London: 31.7 kWh in December against 97.7 kWh in July - December delivers about a third of the peak, or roughly 1.0 kWh a day against 3.2 kWh a day.
• Birmingham: 29.0 kWh in December against 93.3 kWh in July - again about a third, or 0.9 kWh a day.
• Glasgow: 16.6 kWh in December against 93.3 kWh in May - less than a fifth of the peak, or about 0.5 kWh a day.

Stretch the window and the imbalance persists. November to January combined contributes 105.9 kWh in London - 12.9% of the year's output in a quarter of the year. In Glasgow the same three months contribute 63.2 kWh, just 9.3% of the annual total. Even taking the whole winter half-year, October to March produces about a third of annual output in London and Birmingham and 29% in Glasgow; the summer half-year produces the other two thirds.

The practical reading: an 800W system in midwinter is a trickle-charger for your home's background load - a router, a fridge, standby devices - not a meaningful dent in heating-season bills. The kWh that make plug-in solar worthwhile are earned between March and September. Our savings guide shows how to turn these monthly figures into money, and why self-consumption decides most of it.

Everything above assumes the model's optimum: panels tilted at 40 degrees, facing due south. Many plug-in systems hang flat against a balcony rail or fence - effectively vertical at 90 degrees. Running the same London query with a vertical, south-facing panel changes the shape of the whole year:

Two things happen at once. Across the year the vertical system produces 597 kWh against 822 kWh - about 27% less. But in December the vertical panel actually wins, 35.7 kWh against 31.7 kWh, because the winter sun sits so low that a vertical surface faces it more squarely, and snow does not settle on it. The cost is summer: June output nearly halves, from 95.8 kWh to 50.5 kWh, because the high summer sun strikes a vertical panel at a shallow angle.

The result is a much flatter curve - the vertical system's best month (April, 61.8 kWh) is only 1.7 times its worst, against 3.1 times for the tilted one. If your mounting is somewhere between the two, say a panel leaned at 60 degrees against a wall, your months will land between these columns. East- or west-facing mountings lose more again; PVGIS lets you model any azimuth for your own address.

Plug-in solar has been legal in the UK since 27 August 2026, when SI 2026/848 came into force - the regulations that created the 800W per-home cap these figures are modelled on, alongside a certified-kit-only rule and a requirement to notify your network operator under G98 within 28 days of plugging in. The rule-change explainer covers what changed and the jargon guide decodes G98 and friends.

Against that backdrop, the monthly curve carries three buying lessons:

• Judge payback on the year, not on June. A seller quoting summer daily output is describing three or four months of the year. Annual figures - roughly 680 to 820 kWh for an optimally mounted 800W system, less for balcony rails - are the honest basis.
• Winter output will not run your heating. At 0.5 to 1 kWh a day in December, the system offsets background load only. If winter evenings are when you use electricity, a battery that time-shifts summer-pattern generation matters far more than an extra panel.
• Location moves the winter floor more than the annual total. Between London and Glasgow the annual gap is 17%, but the December gap is nearly 50%. The further north you are, the more the case rests on March to September.