A 4.5kWp solar system, which the Energy Saving Trust puts at the UK average, produces roughly 3,750 to 5,085 kWh of electricity a year on an unshaded south facing roof in mainland Britain. Where you live decides almost all of that spread: the same panels make about 5,085 kWh a year in Brighton and about 3,748 kWh in Glasgow.
That is not an estimate from a calculator. Every MCS certified installer in the country works out your generation figure from the same published spreadsheet, using one formula with three inputs. Once you know which three, the number on your quote stops being a mystery and becomes something you can check in about two minutes.
Below is what each system size produces in each part of the UK, what the output looks like month by month, and what those kilowatt hours are actually worth on your bill this winter.
Every MCS performance estimate must show the Kk value used and the shade factor applied. Ask for both. If two quotes give different annual outputs for the same roof, one of those two numbers is the reason.
Get My Free Quotes →How much electricity do solar panels produce in the UK?
Between about 736 and 1,130 kilowatt hours per year for every kilowatt peak installed, on an unshaded south facing roof at a typical 35 degree pitch. Multiply that by your system size and you have the annual figure. For the average 4.5kWp home system that is roughly 3,748 kWh in Glasgow, 4,208 kWh in Birmingham and 5,085 kWh in Brighton.
The MCS standard MIS 3002, Issue 6.0 dated 18 March 2026, sets out the calculation verbatim:
Annual AC output (kWh) = kWp x Kk x SF
Three inputs, and that is the lot:
- kWp is your system size, defined by MCS as "the sum of the data plate value (Wp at STC) of all modules installed (the value printed on the module label)".
- Kk is the kilowatt hours per kilowatt peak for your postcode zone, roof pitch and orientation, looked up in a spreadsheet MCS publishes.
- SF is the shade factor. Where there is "an obvious clear horizon and no near or far shading", MCS allows an SF of 1.00. Anything blocking the horizon pulls it below 1 and pulls your output down with it.
Notice what is not in that formula. Panel efficiency is not an input, and neither is panel brand. Two 4.5kWp systems on the same roof get the same estimated output whether the panels are 19 per cent efficient or 23 per cent. Efficiency only decides how much kWp you can fit in the roof space you have, which is covered on our solar panel efficiency page.
Solar panel output by region: the MCS numbers
The table below is read straight out of the MCS Irradiance Datasets spreadsheet, taking the due south column at 35 degrees pitch for each postcode zone. The figures are kilowatt hours per year, before any shading, at SF of 1.00.
| Zone | Kk | 3kWp | 4kWp | 4.5kWp | 6kWp |
|---|---|---|---|---|---|
| Brighton | 1,130 | 3,390 | 4,520 | 5,085 | 6,780 |
| Plymouth | 1,091 | 3,273 | 4,364 | 4,910 | 6,546 |
| London | 984 | 2,952 | 3,936 | 4,428 | 5,904 |
| Norwich | 961 | 2,883 | 3,844 | 4,324 | 5,766 |
| Cardiff | 949 | 2,847 | 3,796 | 4,270 | 5,694 |
| Birmingham | 935 | 2,805 | 3,740 | 4,208 | 5,610 |
| Edinburgh | 902 | 2,706 | 3,608 | 4,059 | 5,412 |
| Sheffield | 892 | 2,676 | 3,568 | 4,014 | 5,352 |
| Aberdeen | 872 | 2,616 | 3,488 | 3,924 | 5,232 |
| Manchester | 865 | 2,595 | 3,460 | 3,892 | 5,190 |
| Belfast | 845 | 2,535 | 3,380 | 3,802 | 5,070 |
| Glasgow | 833 | 2,499 | 3,332 | 3,748 | 4,998 |
| Lerwick | 736 | 2,208 | 2,944 | 3,312 | 4,416 |
Source: the MCS Irradiance Datasets spreadsheet, downloaded and read on 16 September 2026. It holds 25 sheets, one per postcode zone, each covering every degree of pitch from 0 to 90 and every 5 degrees of orientation. Outputs above are Kk multiplied by system size, rounded to the nearest kilowatt hour.
Two things in that table are worth a second look. Brighton produces 54 per cent more than Lerwick from identical hardware, and 36 per cent more than Glasgow. And Edinburgh, at 902, beats Manchester at 865. The rule is not simply "further north is worse". East coast Scotland is drier and sunnier than the north west of England, and the tables say so.
What your solar panels produce month by month
Between 67 and 72 per cent of a UK solar system's annual output arrives in the six months from April to September, and December contributes under 4 per cent of the year everywhere in Britain. The annual figure is real, but it is an average of two very different halves of the year, and the further north you are the more lopsided it gets.
The table below takes the monthly generation profile for London from PVGIS, the European Commission Joint Research Centre tool, for a 4.5kWp array at 35 degrees facing south, and scales it onto the MCS annual figure of 4,428 kWh so everything stays on one basis.
| Month | kWh generated | Average per day | Share of year |
|---|---|---|---|
| January | 175 | 5.6 kWh | 3.9% |
| February | 228 | 8.1 kWh | 5.2% |
| March | 381 | 12.3 kWh | 8.6% |
| April | 497 | 16.6 kWh | 11.2% |
| May | 526 | 17.0 kWh | 11.9% |
| June | 529 | 17.6 kWh | 12.0% |
| July | 539 | 17.4 kWh | 12.2% |
| August | 476 | 15.3 kWh | 10.7% |
| September | 417 | 13.9 kWh | 9.4% |
| October | 292 | 9.4 kWh | 6.6% |
| November | 207 | 6.9 kWh | 4.7% |
| December | 162 | 5.2 kWh | 3.7% |
In London, December returns 30 per cent of what July returns. A system averaging 17.4 kWh a day in July averages 5.2 kWh a day in December, which for most households is roughly the fridge, the lights and the standby load and not much else.
That ratio is not a national constant, and it is the figure that worsens fastest as you go north. On the same PVGIS basis, December output is 27.5 per cent of July output in Plymouth, 26.2 per cent in Manchester and just 17.6 per cent in Glasgow. A Glaswegian roof takes 71.8 per cent of its annual generation between April and September and only 8.8 per cent across November, December and January. If you are sizing a system in Scotland around winter self-sufficiency, that is the number to plan against.
This is the single biggest reason a solar quote's annual figure can feel wrong once you live with it. The system is not underperforming in January. January is just worth 3.9 per cent of the year. Panels do keep working in cold and cloudy weather, which we cover in do solar panels work in winter.
What that output is worth on your bill
Every unit you use yourself is worth 26.32p this winter, so a 4.5kWp system in Birmingham generating 4,208 kWh has a theoretical ceiling of about £1,107 a year. That is the value if every single unit displaced grid electricity at the capped rate and none was exported. Nobody reaches that ceiling, because you cannot use every unit at the moment it is made.
Ofgem set the price cap for 1 October to 31 December 2026 at 26.32 pence per kWh for electricity on a typical Direct Debit tariff, with a standing charge of 54.83 pence a day, a rise of about 4 per cent. Separately, HMRC has applied a temporary zero rate of VAT to domestic electricity in Great Britain from 1 October 2026 to 31 March 2027, down from 5 per cent. The rate of VAT on electricity in Northern Ireland is unchanged, and Northern Ireland sits outside the Ofgem cap entirely under its own regulator.
The split between what you use and what you export is the whole game. MCS makes installers state it: the prescribed performance estimate has a self consumption section with an assumed occupancy archetype of "Home all day", "Home half day" or "Out all day". A household out all day exports far more of its generation than one with someone in it, and exported units earn a Smart Export Guarantee rate instead of displacing a 26.32p import. Those rates are set by each supplier rather than by Ofgem, and the gap between the best and worst is large enough to be worth chasing. See our comparison of Smart Export Guarantee rates.
Does it produce more electricity than your home uses?
In annual terms, usually yes, and by a long way. Ofgem's Typical Domestic Consumption Values, updated on 1 July 2026, put a medium user on a standard single rate meter at 2,500 kWh of electricity a year, with low users at 1,600 kWh and high users at 3,800 kWh.
A 4.5kWp system in Birmingham generates 4,208 kWh. That is 68 per cent more than a medium household gets through in a year, and more than a high user too. Yet almost nobody covers their whole bill with solar, because generation and consumption do not line up in time. The surplus arrives at midday in June. The demand arrives at 6pm in January.
That mismatch is the entire argument for battery storage alongside solar, and it is also why the honest way to size a system is against your roof and your usage pattern rather than your annual kWh total. Our guide on how many solar panels you need works through it.
Why your real output will differ from the quoted figure
The MCS estimate is deliberately conservative, and in one specific way it is conservative by exactly 20 per cent. MIS 3002 states that the Kk data "has been provided by the European Commission, Joint Research Centre. The data is drawn from the Climate-SAF-PVGIS dataset and multiplied by 0.8."
So every MCS quote in Britain already carries a 20 per cent haircut against the underlying irradiance model before shading is even considered. Several things then move the real number in both directions:
- Shading. The biggest single variable. An SF of 0.89 means an 11 per cent loss, and MCS notes its shading method "will yield results within 10 per cent of the actual energy estimate stated for most systems".
- Orientation. The Energy Saving Trust puts an east or west facing system at "around 15-20% less energy than one facing directly south". See which direction solar panels should face.
- Pitch. Worth surprisingly little on a normal roof. Across the 30 to 45 degree band the difference is under 2 per cent, as set out in our guide to the best angle for solar panels.
- Weather in any given year. The Kk tables are long run averages. A dull summer costs you, a bright one pays you back.
- The inverter. The Energy Saving Trust notes panels "should last 25 years or more" but the inverter typically needs replacing after around 12 years. Output over the full life of the system assumes that replacement happens.
How to check the output figure on your own quote
Ask for the MCS performance estimate and read four fields. MIS 3002 requires the estimate in a prescribed table, and it must reach you before you award the contract, so any certified installer already has it.
- Installed capacity in kWp. Multiply the panel wattage by the number of panels. Twelve 375W panels is 4.5kWp.
- Postcode region and the Kk value used. Check it against the table above for your nearest zone. A Kk far above the regional figure needs explaining.
- Shade factor. An SF of 1.00 is a claim that nothing blocks your horizon. If you have a chimney, a neighbouring roof or a mature tree, question it.
- The multiplication. kWp times Kk times SF should equal the annual output stated. If it does not, the figure came from somewhere other than the MCS method.
MCS also requires the estimate to carry the warning that "The performance of solar PV systems is impossible to predict with certainty" and that it "should not be considered as a guarantee of performance". Any installer quoting a generation figure without that caveat, or giving a rival estimate more prominence than the MCS one, is outside the standard.
Payback follows directly from output. The Energy Saving Trust's own figures, based on fuel prices as of July 2026 for England, Scotland and Wales, put payback at 9 years in London across all three occupancy types, 10 to 11 years in Manchester, 9 to 10 in Aberystwyth and 11 to 12 in Stirling. The full cost side is in our solar panel cost guide.
An MCS certified installer will measure your pitch, orientation and shading rather than assume them. Get estimates from more than one and compare the Kk and SF each has used.
Get My Free Quotes →Solar panel output: frequently asked questions
About 10.2 kWh a day averaged over a year in Birmingham, from an annual figure of 3,740 kWh. The daily average is misleading on its own, though. A 4kWp London system averages around 15.5 kWh a day in July and around 4.6 kWh a day in December, because 67 to 72 per cent of UK solar generation lands between April and September, depending how far north you are.
Between about 3,300 and 5,085 kWh depending on where in the UK it is, on an unshaded south facing roof at 35 degrees. Reading the MCS irradiance tables directly: 5,085 kWh in Brighton, 4,910 in Plymouth, 4,428 in London, 4,208 in Birmingham, 3,892 in Manchester, 3,802 in Belfast, 3,748 in Glasgow and 3,312 in Lerwick. The Energy Saving Trust puts 4.5kWp as the average UK domestic system size, using around 12 panels over 20 to 30 square metres.
Roughly 140 to 210 kWh per square metre of roof per year, but this is the wrong way to size a system. The Energy Saving Trust says a 4.5kWp array covers 20 to 30 square metres, which against a Birmingham output of 4,208 kWh gives 140 to 210 kWh per square metre. MCS does not use roof area in its calculation at all: the formula is kWp times Kk times SF, so what matters is how much kWp you fit, not the area it occupies.
Yes, just less of it. Solar cells respond to daylight rather than direct sunlight, and the Energy Saving Trust confirms they "can even work on cloudy days". This is already built into the figures above: the MCS Kk values come from long run measured irradiance data for each UK postcode zone, so British cloud cover is in the number rather than an exception to it.
Because MCS applies a deliberate 20 per cent reduction. MIS 3002 states the Kk data is drawn from the European Commission's Climate-SAF-PVGIS dataset "and multiplied by 0.8". Online calculators often use the raw model output. A shade factor below 1.00 widens the gap further. The MCS figure is the conservative one, and it is the figure your installer is accountable for.
The south coast of England. Across all 25 MCS postcode zones, Brighton has the highest Kk at 1,130 kWh per kWp at 35 degrees facing south, followed by Plymouth at 1,091 and Southampton at 1,021, against 833 for Glasgow and 736 for Lerwick in Shetland. That is a 54 per cent spread for identical hardware. Latitude is not the only factor: Edinburgh, at 902, outperforms Manchester at 865.
Almost certainly not, even though the annual generation figure often exceeds annual usage. Ofgem's Typical Domestic Consumption Values from 1 July 2026 put a medium single rate household at 2,500 kWh a year, and a 4.5kWp Birmingham system generates 4,208 kWh. The problem is timing rather than volume: the surplus arrives at midday in summer and the demand arrives on winter evenings. Battery storage narrows the gap but does not close it.
26.32 pence if you use it yourself, this winter. That is the Ofgem price cap electricity unit rate for a typical Direct Debit customer from 1 October to 31 December 2026, alongside a 54.83 pence daily standing charge. A unit you export instead earns your supplier's Smart Export Guarantee rate, which is set per supplier rather than by Ofgem and is generally well below the import price.
Not for a given system size. The MCS calculation is kWp times Kk times SF, and efficiency is not one of the three inputs. Two 4.5kWp systems on the same roof carry the same estimated output regardless of the panels' efficiency rating. Higher efficiency lets you fit more kWp into a limited roof area, which is where it genuinely matters.
Sources: MCS MIS 3002 Issue 6.0 (18 March 2026) and the MCS Irradiance Datasets spreadsheet, both read on 16 September 2026; Ofgem price cap for 1 October to 31 December 2026; Ofgem Typical Domestic Consumption Values decision of 27 May 2026, implemented 1 July 2026; Energy Saving Trust solar panels advice, last updated 27 August 2026; European Commission Joint Research Centre PVGIS v5.2 for the monthly generation profile. Written by Neil Russell.