The estimator
Rooftop estimator · PVGIS 5.3, central Liverpool
What would your roof make in a year?
3,378 kWh a year
3,378 kWh a year
About 135% of the 2,500 kWh a typical home uses in a year (Ofgem). At the North West average, 3.5 kW comes to about £7,050.
PVGIS 5.3 (European Commission JRC), 14% system losses, pulled 3 November 2026; prices: DESNZ 2025/26 North West means (our arithmetic). Shade from nearby buildings is not included.
Direction and pitch
This table is the grid behind the estimator: kWh a year from 1 kW of panels in central Liverpool, for eight directions and seven pitches, from PVGIS 5.3 with 14% system losses (PVGIS). Read across for pitch, down for direction.
| Faces | 10° | 20° | 30° | 35° | 40° | 45° | 50° |
|---|---|---|---|---|---|---|---|
| South | 871 | 924 | 957 | 965 | 968 | 966 | 958 |
| South-west | 851 | 888 | 908 | 913 | 911 | 906 | 896 |
| South-east | 847 | 880 | 897 | 900 | 898 | 891 | 880 |
| West | 798 | 790 | 776 | 766 | 754 | 739 | 721 |
| East | 792 | 779 | 761 | 749 | 736 | 720 | 702 |
| North-west | 740 | 680 | 623 | 595 | 568 | 541 | 515 |
| North-east | 736 | 672 | 610 | 582 | 554 | 527 | 500 |
| North | 714 | 632 | 551 | 510 | 470 | 431 | 395 |
Two patterns are worth knowing. South-facing roofs gain from being steeper, up to the best angle around 40°, while north, east and west roofs do better the shallower they are, because a shallow roof faces more of the sky. And in Liverpool the west column sits a little above the east one at every pitch, so if you have the choice between an east and a west slope, west is the marginally better bet.
Across the city
We also ran twelve points from Walton and Croxteth in the north to Garston and Woolton in the south. PVGIS uses satellite data in cells a few kilometres across, so neighbouring points often share a cell and return the same figure.
| Point | South | West | East | North | Flat |
|---|---|---|---|---|---|
| City centre | 965 | 766 | 749 | 510 | 799 |
| Anfield | 965 | 766 | 749 | 509 | 799 |
| Walton | 965 | 766 | 749 | 509 | 799 |
| Kensington | 965 | 766 | 749 | 510 | 799 |
| West Derby | 963 | 766 | 751 | 512 | 799 |
| Croxteth | 950 | 758 | 746 | 512 | 791 |
| Wavertree | 949 | 756 | 741 | 506 | 788 |
| Aigburth | 948 | 756 | 741 | 507 | 788 |
| Allerton | 948 | 756 | 740 | 507 | 788 |
| Woolton | 948 | 755 | 745 | 510 | 790 |
| Garston | 948 | 756 | 740 | 507 | 788 |
| Toxteth | 943 | 751 | 734 | 502 | 782 |
The spread, about 2% from top to bottom, is far smaller than the gap between a south and an east roof on the same house. Shade from neighbouring buildings and trees, which PVGIS cannot see, will usually matter more than which district you are in.
Through the year
At the best angle, each kW in central Liverpool makes about 34 kWh in January, 117 in June and 30 in December (PVGIS). The estimator's small chart shows the same shape for whatever roof you choose. Six months from April to September supply about 69% of the year's total, which is why summer surplus, not winter output, drives decisions about batteries and export rates; see batteries and export payments.
Reading your own roof
- Direction. Find your house on an online map with north at the top and read which way each roof slope faces; on a terrace the front and back face opposite ways.
- Pitch. If you do not know it, use 35°; the table shows a few degrees either way changes little.
- Size. Count the usable roof after chimneys, dormers and roof lights. The Energy Saving Trust treats about 4.5 kW as a typical home system (Energy Saving Trust); many terraces have room for less.
- Shade. Note anything that shades the roof between April and September; that is the season that counts.
Then compare the installer's predicted output with the estimator, and the price with the North West averages.
Three Liverpool roofs, worked through
Three cases using PVGIS for the nearest point in the city at 35° (our arithmetic from PVGIS 5.3):
- An Anfield terrace with slopes facing east and west, 1.5 kW on each: about 2,273 kWh a year.
- An Allerton semi with a west-facing back, 3.5 kW: about 2,646 kWh a year.
- A detached house in Woolton with a south roof, 5 kW: about 4,740 kWh a year.
- Panels laid flat on a city-centre roof, 2 kW: about 1,598 kWh a year before any tilt.
Liverpool has its own sources of shade that no satellite model sees: taller blocks beside low terraces in and around the city centre, back offshoots below the rear slope of a terrace, and mature street and garden trees in suburbs such as Allerton and Woolton. These are yardsticks for an installer's estimate, not promises: chimney stacks, offshoots and neighbouring buildings take their share, and only a survey sees them. Put the same size and direction into the estimator above for your own roof, then take the result to the costs page to set the price per kW beside it, and to the terraced houses page if your home is one of the city's many terraces.