How many kWh does a 4 kW solar system produce per day in the UK?

12 kWh a day averaged over the year in London (4 kW × 3.48 × 0.86), 9.9 kWh in Glasgow, 13.4 kWh in Brighton. A June day in London gives about 17.5 kWh and a December day about 5.1 kWh, so the yearly average hides the swing you will see on the inverter's app.

How much does a 4 kW solar system generate per year in the UK?

4,369 kWh in London, 4,897 kWh in Brighton, 3,767 kWh in Manchester, 3,616 kWh in Glasgow, from the PVGIS 2005-2020 irradiation at the optimal tilt with 14% losses. The twelve monthly figures add up to 4,370 kWh in London, within a kWh of the yearly figure, because PVGIS rounds the yearly and each monthly sun-hour figure separately.

Is 4 kW of solar enough to power a house in the UK?

Over the year, more than enough for a medium household: 4,369 kWh against 2,500 kWh (Ofgem medium, 175%), and 115% of a high one (3,800 kWh). By month, no: in December the London system makes 158 kWh against the medium household's 208 kWh a month, and at night it makes nothing, so a grid-tied home still buys electricity and exports the summer surplus. The power-a-house guide sizes the low, medium and high bands in four cities.

What is the difference between kW, kWp and kWh?

kWp (kilowatt peak) is the rated DC size of the array under test conditions; installers and the Energy Saving Trust quote systems in kWp, and a "4 kW system" means 4 kWp. kWh is the energy it delivers over time: kWp × peak sun hours × (1 − losses) per day. So a 4 kWp array in London is 12 kWh a day, not 4 kWh, and never 4 kW for long: the rating is what it would make at midday under a cloudless summer sky.

How much does a 3 kW or 4.5 kW system produce?

Output scales with the size: 3 kW makes 3,277 kWh a year in London and the Energy Saving Trust's typical 4.5 kW makes 4,916 kWh. The first table runs 3 to 6 kWp; the output calculator takes any size and any UK city, with the month-by-month split, and the UK cost guide prices 6 to 16 panels.

Does a 4 kW system make less each year?

Slowly: NREL describes long-term degradation of about 0.5% a year, and the Trina data sheet used for the panel size warrants 0.55% a year. The figures on this page are year-one output; the payback calculator applies the decline to each of its 25 years.

How much electricity does a 4 kW solar system generate in the UK?

A 4 kW (4 kWp) solar system produces about 4,369 kWh of electricity a year in London, 364 kWh in an average month and 12 kWh a day on average: 4 × 3.48 PVGIS sun hours × 0.86 after 14% losses. That is 10 panels of 400 W, and 175% of what a medium Ofgem household uses in a year (2,500 kWh). The year is lopsided: 542 kWh in July, 158 kWh in December. In Brighton the same system makes 4,897 kWh a year, in Manchester 3,767 kWh, in Glasgow 3,616 kWh. The tables below run 3 to 6 kWp in London, 4 kWp in every UK city and the twelve months in three cities.

Open the solar output calculator

How much do 3 to 6 kWp produce in London?

Per day = kWp × 3.48 sun hours × 0.86; per year = per day × 365; the June and December columns use the PVGIS figure for that month (5.08 and 1.48 kWh/m² a day) times the days in it. Sun hours are the daily in-plane irradiation for London at the optimal slope and a south azimuth, averaged over 2005-2020.

3 to 6 kWp in London: kWh a day, a month (average), a year, and the June and December months, 14% losses (NREL PVWatts default)
System size	kWh a day	kWh a month	kWh a year	June	December
3 kW	9 kWh	273 kWh	3,277 kWh	393 kWh	118 kWh
3.5 kW	10.5 kWh	319 kWh	3,823 kWh	459 kWh	138 kWh
4 kW	12 kWh	364 kWh	4,369 kWh	524 kWh	158 kWh
4.5 kW	13.5 kWh	410 kWh	4,916 kWh	590 kWh	178 kWh
5 kW	15 kWh	455 kWh	5,462 kWh	655 kWh	197 kWh
6 kW	18 kWh	546 kWh	6,554 kWh	786 kWh	237 kWh

How much does a 4 kW system generate in each UK city?

The same 4 kW system; only the city’s PVGIS sun hours change. Brighton to Glasgow is a 35% spread over the year, and the December column shows the winter gap is wider than the yearly figure suggests. The output calculator shows all twelve months for any of these cities and any size.

A 4 kW system in every UK city: sun hours, kWh a day and a year, June and December
City	Sun hours	kWh a day	kWh a year	June	December
London	3.48	12 kWh	4,369 kWh	524 kWh	158 kWh
Brighton (South East)	3.9	13.4 kWh	4,897 kWh	612 kWh	166 kWh
Plymouth (South West)	3.7	12.7 kWh	4,646 kWh	568 kWh	152 kWh
Cardiff (Wales)	3.47	11.9 kWh	4,357 kWh	549 kWh	140 kWh
Birmingham (West Midlands)	3.27	11.2 kWh	4,106 kWh	494 kWh	145 kWh
Nottingham (East Midlands)	3.3	11.4 kWh	4,143 kWh	484 kWh	147 kWh
Norwich (East of England)	3.49	12 kWh	4,382 kWh	521 kWh	152 kWh
Manchester (North West)	3	10.3 kWh	3,767 kWh	466 kWh	122 kWh
Leeds (Yorkshire)	3.2	11 kWh	4,018 kWh	469 kWh	141 kWh
Newcastle (North East)	3.18	10.9 kWh	3,993 kWh	462 kWh	130 kWh
Edinburgh (Scotland)	3.07	10.6 kWh	3,855 kWh	459 kWh	103 kWh
Glasgow (Scotland)	2.88	9.9 kWh	3,616 kWh	464 kWh	89 kWh
Aberdeen (Scotland)	2.98	10.3 kWh	3,742 kWh	473 kWh	100 kWh
Belfast (Northern Ireland)	3.09	10.6 kWh	3,880 kWh	487 kWh	117 kWh

What does a 4 kW system make month by month?

Each month = kWp × that month’s PVGIS sun hours × 0.86 × days in the month. London’s best month is July at 542 kWh and its worst December at 158 kWh, a ratio of 3.4 to 1; a medium household uses about 208 kWh every month, which is why the summer is exported and the winter is bought.

A 4 kW system month by month in London, Manchester, Edinburgh, kWh, from the PVGIS monthly profile
Month	London	Manchester	Edinburgh
January	170 kWh	113 kWh	122 kWh
February	221 kWh	193 kWh	207 kWh
March	366 kWh	330 kWh	326 kWh
April	487 kWh	436 kWh	443 kWh
May	516 kWh	483 kWh	511 kWh
June	524 kWh	466 kWh	459 kWh
July	542 kWh	469 kWh	478 kWh
August	479 kWh	412 kWh	431 kWh
September	416 kWh	348 kWh	360 kWh
October	289 kWh	239 kWh	245 kWh
November	203 kWh	162 kWh	168 kWh
December	158 kWh	122 kWh	103 kWh

What the tables leave out

Orientation and tilt: PVGIS figures are for the optimal slope (about 40°) facing south. An east or west roof gives 15-20% less (Energy Saving Trust) and a flat or steep roof less again; raise the losses in the calculator for shade from trees or chimneys.
The kWh you keep: the yearly total is what the array makes, not what you use. Without a battery a home empty in the daytime exports most of the summer output; the Energy Saving Trust puts the Smart Export Guarantee at around 12p a unit, under half the Ofgem cap, and the UK cost guide runs the savings and payback.
Per panel: one 400 W panel is one of the 10 in this system, so divide any cell by 10; the kWh-per-panel guide runs one panel at 3 to 6 sun hours and by month.
The other direction: to go from the kWh you use to the size you need, the power-a-house guide and the panel calculator do that for the Ofgem low, medium and high bands.
Other sizes, with the same city and month tables: 3 kW in the UK and 5 kW in the UK.

Sources

UK sun hours, yearly and by month: European Commission Joint Research Centre, PVGIS 5.2, PVcalc for the city's coordinates at the optimal slope and azimuth. Panel: A 400 W panel is the middle of the Trina Vertex TSM-DE09 range and the common residential class in 2026; Trina Solar, Vertex TSM-DE09 data sheet, product range 390-405 W. Losses: NREL, PVWatts Version 5 Manual, section 11 System Losses, Table 6. Output decline: NREL, PVWatts Version 5 Manual, section 11. Household use: Ofgem, "Review of typical domestic consumption values: decision", Table 1, electricity Profile Class 1, 2026 TDCV. All read 2026-09-20; the full text of each source, with links, is under the calculator when you switch it to UK. A month’s figure is its daily figure times its calendar days (30 in June, 31 in December).

Frequently asked questions

How many kWh does a 4 kW solar system produce per day in the UK?: 12 kWh a day averaged over the year in London (4 kW × 3.48 × 0.86), 9.9 kWh in Glasgow, 13.4 kWh in Brighton. A June day in London gives about 17.5 kWh and a December day about 5.1 kWh, so the yearly average hides the swing you will see on the inverter's app.
How much does a 4 kW solar system generate per year in the UK?: 4,369 kWh in London, 4,897 kWh in Brighton, 3,767 kWh in Manchester, 3,616 kWh in Glasgow, from the PVGIS 2005-2020 irradiation at the optimal tilt with 14% losses. The twelve monthly figures add up to 4,370 kWh in London, within a kWh of the yearly figure, because PVGIS rounds the yearly and each monthly sun-hour figure separately.
Is 4 kW of solar enough to power a house in the UK?: Over the year, more than enough for a medium household: 4,369 kWh against 2,500 kWh (Ofgem medium, 175%), and 115% of a high one (3,800 kWh). By month, no: in December the London system makes 158 kWh against the medium household's 208 kWh a month, and at night it makes nothing, so a grid-tied home still buys electricity and exports the summer surplus. The power-a-house guide sizes the low, medium and high bands in four cities.
What is the difference between kW, kWp and kWh?: kWp (kilowatt peak) is the rated DC size of the array under test conditions; installers and the Energy Saving Trust quote systems in kWp, and a "4 kW system" means 4 kWp. kWh is the energy it delivers over time: kWp × peak sun hours × (1 − losses) per day. So a 4 kWp array in London is 12 kWh a day, not 4 kWh, and never 4 kW for long: the rating is what it would make at midday under a cloudless summer sky.
How much does a 3 kW or 4.5 kW system produce?: Output scales with the size: 3 kW makes 3,277 kWh a year in London and the Energy Saving Trust's typical 4.5 kW makes 4,916 kWh. The first table runs 3 to 6 kWp; the output calculator takes any size and any UK city, with the month-by-month split, and the UK cost guide prices 6 to 16 panels.
Does a 4 kW system make less each year?: Slowly: NREL describes long-term degradation of about 0.5% a year, and the Trina data sheet used for the panel size warrants 0.55% a year. The figures on this page are year-one output; the payback calculator applies the decline to each of its 25 years.

How many kWh does a solar panel produce per day?
One 400 W panel per day, month and year at 3 to 6 sun hours, 1 to 12 kW systems, a panel and a 10 kW system in every US state, UK cities by month.
How much electricity does a 3 kW solar system generate in the UK?
kWh a day, month and year from a 3 kWp system in every UK city, month by month in three cities (PVGIS), and against Ofgem household use.
How much electricity does a 5 kW solar system generate in the UK?
kWh a day, month and year from a 5 kWp system in every UK city, month by month in three cities (PVGIS), and against Ofgem household use.
How many solar panels for 2,000 kWh a month?
2,000 kWh a month is 65.8 kWh a day: 43 panels of 400 W (17.2 kW) at 4.5 sun hours, about $44,720 installed. Every US state and UK city.

Last updated 2026-10-01. Estimates from published averages (NREL, EIA, Ofgem, industry cost surveys), each with its source and date: an installer's site survey and shading analysis replace them. Not financial advice.