How much solar power you get in each region of the United Kingdom

The same solar panel gives very different amounts of energy depending on where it sits and the time of year. This page shows what one 100 watt panel gives on an average day in each month, in the 4 regions our quiz uses, worked out from many years of hourly weather records for one city in each region.

The short version

• A 100 W panel's "100 W" is its output in ideal test light. Over a whole day it gives energy measured in watt-hours (Wh): how much electricity it collects, like water collected in a bucket.
• Across these regions, a 100 W panel gives roughly 40 to 420 Wh on an average day, depending on the place and the month.
• The darkest month matters most for year-round use: in Scotland it gives about 40 Wh a day, in Southern England about 110 Wh.
• Averages hide bad days: in every region, one day in ten in the darkest month gives much less than the average (the figures below show how much).
• That is why our quiz sizes systems by how often you would run short over many real years, not by an average.

How these numbers were worked out

The figures come from PVGIS, the European Commission's free solar calculator, which holds hourly sunshine and temperature records from satellites. For each region we took one city, the weather records for its area (about 5 km across) and every day of the years shown. We assumed one 100 W panel tilted 30 degrees and facing south, standing free so air cools it, and the PVGIS standard allowance of 14 % for losses in wiring, dirt and ageing. The result is the energy that reaches your charge controller (the box that charges the battery), before any battery losses. This is our own calculation from the PVGIS records, with the same method our sizing engine uses (see how we size systems).

A larger panel scales in proportion: a 400 W panel gives about four times these figures, if it is set up the same way. Panels lying flat, shaded, or on a campervan roof give less, especially in winter.

Scotland (Inverness)

• Best month: May, about 370 Wh a day.
• Darkest month: December, about 40 Wh a day; on one day in ten it gives almost nothing.
• Over a year: about 81 kWh (kilowatt-hours, thousands of watt-hours).
• The best month gives about 8.7 times as much as the darkest one.
• Month by month, average Wh a day: Jan 50, Feb 130, Mar 220, Apr 330, May 370, Jun 360, Jul 350, Aug 300, Sep 250, Oct 160, Nov 80, Dec 40.
• Weather records: 2005-2023, PVGIS-SARAH3.

Northern England (Manchester)

• Best month: June, about 380 Wh a day.
• Darkest month: January, about 80 Wh a day; on one day in ten it gives less than 20 Wh.
• Over a year: about 87 kWh (kilowatt-hours, thousands of watt-hours).
• The best month gives about 4.7 times as much as the darkest one.
• Month by month, average Wh a day: Jan 80, Feb 150, Mar 250, Apr 350, May 370, Jun 380, Jul 360, Aug 310, Sep 260, Oct 170, Nov 110, Dec 80.
• Weather records: 2005-2023, PVGIS-SARAH3.

Central England and Wales (Birmingham)

• Best month: June, about 400 Wh a day.
• Darkest month: December, about 100 Wh a day; on one day in ten it gives less than 20 Wh.
• Over a year: about 95 kWh (kilowatt-hours, thousands of watt-hours).
• The best month gives about 4.1 times as much as the darkest one.
• Month by month, average Wh a day: Jan 110, Feb 170, Mar 260, Apr 360, May 380, Jun 400, Jul 390, Aug 340, Sep 290, Oct 190, Nov 130, Dec 100.
• Weather records: 2005-2023, PVGIS-SARAH3.

Southern England (London)

• Best month: June, about 420 Wh a day.
• Darkest month: December, about 110 Wh a day; on one day in ten it gives less than 20 Wh.
• Over a year: about 101 kWh (kilowatt-hours, thousands of watt-hours).
• The best month gives about 4.0 times as much as the darkest one.
• Month by month, average Wh a day: Jan 120, Feb 180, Mar 270, Apr 380, May 390, Jun 420, Jul 410, Aug 360, Sep 310, Oct 210, Nov 150, Dec 110.
• Weather records: 2005-2023, PVGIS-SARAH3.

What this means for your system

If you only use solar in summer, size for the summer months: the figures above show how much less panel power you need than for year-round use. If you need power all year, the darkest month decides the size, and the gap between summer and winter is large everywhere in the UK. Past a point, adding panels for the darkest weeks costs more than it gives back, and a backup source (mains power or a generator) for those weeks can be the sensible choice.

Your own place may differ from the city shown for your region: hills, coast, altitude and local shade all change the figures. Our quiz uses the weather records for your own area, not the regional city.

What can go wrong

• Using the yearly average to size a system for winter: the battery runs flat in the darkest weeks.
• Forgetting shade: a tree or a wall that shades the panel in winter, when the sun is low, can cut the output far below these figures.
• Cold and heat: panels give a little more in cold sunshine and less when hot; the figures include that, but a hot flat roof in summer can still be warmer than assumed.
• Snow: a panel covered by snow gives almost nothing until it slides off; our quiz adds a snow allowance for your area.

Size a system for your place

Tell the quiz where and when you will use solar, and it works out panels and battery from the weather records for your own area, then checks that the parts work together. Terms used here are explained in the glossary.

Our results and guides are estimates and do not replace advice from a qualified electrician.