Is Liverpool too wet for solar panels?

What the Crosby record shows, and what it lacks

The Met Office publishes long-term climate averages for Crosby, on the coast just north of the city. Over 1991–2020 the station averaged 824 mm of rain a year, spread over about 147 days on which at least 1 mm fell (Met Office). By that threshold, roughly 40% of days are wet ones: about two in every five.

The same table has a column for sunshine hours, and for Crosby it is empty. The station does not record sunshine, so this guide prints no sunshine figure for Liverpool rather than borrow one from another station and present it as local. The gap matters less than it looks. Rain measures water, not light. A day can cross the 1 mm line in a ten-minute shower and stay bright either side of it, while a dry day can be grey from morning to dusk.

What a roof needs to know is how much light lands on it over a whole year, cloud included. For that there is a better source than any rain gauge.

What the satellite record says

PVGIS, the solar tool run by the European Commission's Joint Research Centre, estimates output from satellite measurements of the sunlight that actually reached the ground, in this case over 2005–2023 (PVGIS 5.3). Wet summers, grey Novembers and bright springs all sit inside its averages, so Liverpool's weather is already counted. The figures here also allow 14% for losses in the wiring, the inverter and dirt on the glass.

For a south-facing roof pitched at 35° in central Liverpool, PVGIS gives about 965 kWh a year for each kW of panels. Tilting to the best angle for the spot, about 40°, nudges that only to 968. The Energy Saving Trust treats 4.5 kWp as a typical home system (Energy Saving Trust); at that size, the south roof would produce about 4,343 kWh in an average year (our arithmetic). Ofgem's typical figure for a home's electricity use is 2,500 kWh a year (Ofgem).

Those two numbers do not simply cancel out. Panels make most of their power around midday and in summer, and whatever the house is not using at that moment goes to the grid or into a home battery. How much leaves the house, and the rules for being paid for it, are covered in the guide to export payments.

Plenty of Liverpool terraces have room for less than 4.5 kWp. The rooftop estimator works through a smaller array at any direction and pitch, and the page on terraced houses deals with the city's most common house type.

The same figure is a handy check on any quote. An installer's proposal should include an estimate of what the system will generate in a year; divide it by the system's size in kW and set the answer beside the PVGIS figure for your roof's direction. A result far above it deserves a question about the assumptions behind it.

Where the year's output comes from

The calendar matters more than the rain. At the best angle in central Liverpool, each kW of panels makes about 30 kWh in December and 124 kWh in May, 4.1 times as much (PVGIS). The six months from April to September supply 664 kWh of the 969 in the twelve monthly figures added together: 68.5% (our arithmetic). October to March, the darker half, supplies the other 31.5%.

Even December is not a write-off. At 30 kWh per kW, a 4.5 kWp array would still make about 135 kWh that month, against about 558 in May (our arithmetic). The winter months matter most to anyone pairing panels with electric heating, which the guide to solar with a heat pump works through.

Much of the winter dip comes from short days and a low sun, which every British roof shares. Pitch shifts the balance a little. A south roof at 50° makes 33 kWh per kW in December against 28 at 35°, because it faces the low sun more squarely, but 110 in June against 119. Over a full year the steeper roof finishes slightly behind, at 958 against 965.

Single years swing either side of these averages. A wet July shows up as a weak month on the monitoring app and a dry, bright April as a strong one, and neither means anything has gone wrong with the system. The guide to looking after panels explains how to compare your own readings with the expected figures, month by month.

Light through cloud

Panels work from daylight, not only from direct sunshine. On an overcast day the light that gets through is scattered across the whole sky; output falls well below a clear day's, but it does not stop. A grey morning still counts towards the total, which is why the yearly figure for a rainy city is far from zero. Cool air helps slightly, too: panels convert light a little more efficiently when they are not hot.

The PVGIS figures show this indirectly. A panel lying completely flat faces no compass direction and cannot be aimed at the sun, yet in central Liverpool it still makes about 799 kWh per kW a year, 83% of the south-facing 35° figure (our arithmetic). It even beats a panel tilted 35° towards the east or the west. Where the flat panel loses out is winter, when the low sun skims across it: 10 kWh per kW in December, against 28 for the south roof.

Rain also does pitched panels a small favour, rinsing off dust and pollen as it runs down the glass. Panels laid flat shed water and grime less readily, which is another argument for tilting them on a frame if they go on a flat roof.

Why a west roof beats an east one here

Where the choice is between an east slope and a west slope, PVGIS favours the west in Liverpool. At 35° in the city centre, a west roof makes about 766 kWh per kW a year and an east roof 749, a lead of 2.3% (our arithmetic). The order is the same at all 12 points in the table below.

The monthly figures show where the gap opens. East is fractionally ahead in March (62 kWh per kW against 60) and in November, and the two are level through the darkest months. From April to September the west roof pulls ahead, by the widest margin in July: 111 against 106. PVGIS does not say why, and this guide will not guess; the satellite record simply gives the afternoon side a little more light in the long days.

Both sit well behind a south roof. An east roof makes 22% less than a south one at the same spot, so a house with a usable south slope should start there. A house with only east and west slopes can use both, which spreads generation across the day, or begin with the west. In energy terms the west's lead is modest: on a 4.5 kWp array it comes to about 77 kWh a year (our arithmetic).

North of the city against the south

PVGIS was run for 12 points across Liverpool, from Walton and Anfield in the north to Garston, Allerton and Woolton in the south, with West Derby and Croxteth to the east. Several of them fall in the same satellite cell, which is why some report identical figures. For a south roof at 35°, the highest result, 965 kWh per kW, comes at the city centre, Anfield, Walton and Kensington; the lowest, 943, at Toxteth. The whole spread is 2.3% (our arithmetic).

Set that spread beside the 22% gap between a south and an east roof at a single address, and the answer is plain. A house in Garston and a house in Walton with the same roof direction and no shade will make close to the same amount. Direction, pitch and shade decide the output; the district barely does. PVGIS allows for the lie of the land on the horizon, but not for buildings or trees, so the figures here assume an unshaded roof. A neighbour's extension, a tall chimney stack or a street tree can take a share of that, and only a visit to the roof will show how much. If an installer's yield estimate for your roof is far from these figures, ask how it was worked out, and check the firm on the MCS register (MCS).

For the next step, the page on what solar costs in Liverpool sets out what North West homes paid per kW in 2025/26, and the FAQs collect short answers on direction, angle and shade.