The short answer
In the PVGIS runs for this guide, an east roof at 35° in Congleton makes about 81% of the best figure and a west roof about 80%. Splitting 4 kWp across both faces gives roughly 2,925 kWh a year against 3,635 from an all-south array, with output spread from early morning into the evening.
The figures by direction and pitch
We ran the European Commission’s PVGIS 5.3 model for Congleton at eight directions and seven pitches, using PVGIS-SARAH3 sunlight data for 2005-2023 and 14% system losses. The table picks out the five directions that matter for this page.
| Roof faces | 10° | 20° | 30° | 35° | 40° | 45° |
|---|---|---|---|---|---|---|
| East | 765 | 758 | 745 | 736 | 725 | 710 |
| South-east | 812 | 843 | 860 | 863 | 860 | 854 |
| South | 830 | 876 | 903 | 909 | 910 | 906 |
| South-west | 810 | 839 | 854 | 855 | 853 | 845 |
| West | 762 | 752 | 737 | 727 | 715 | 700 |
Two patterns stand out. East and west are almost mirror images, with east a touch ahead. And on those two faces a flatter panel does better, the opposite of a south roof, where output climbs as the pitch steepens towards 40°. A panel lying nearly flat sees the whole sky; tilting it towards the east turns it away from the afternoon sun.
Splitting an array across two faces
A common layout on a north–south ridge puts half the panels on each slope. The table compares 4 kWp split equally between east and west at 35° with 4 kWp on a single south slope at the same pitch.
| Layout | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| East + west | 54 | 110 | 232 | 361 | 426 | 433 | 419 | 359 | 263 | 151 | 74 | 45 |
| South | 110 | 185 | 316 | 435 | 463 | 457 | 448 | 404 | 336 | 228 | 149 | 106 |
Across the year the split array makes about 2,925 kWh against 3,635 for the south roof. The gap is smallest in summer: in June an east panel makes 95% of what a south panel does. In December the figure falls to 43%, because the low winter sun stays in the southern sky. An east and west system is a strong summer performer and a weak winter one.
Morning and evening
PVGIS gives monthly totals, not hour-by-hour figures, but the reasoning is simple. An east slope catches the sun from early morning and loses it after midday; a west slope does the reverse. Split between them, the array produces a flatter curve that starts earlier and runs later than a south array of the same size, with a lower peak around noon.
That shape can suit a household better than the bigger total suggests. Many homes use most electricity at breakfast and from late afternoon into the evening, when a south array is past its best. Units used in the house are generally worth more than units exported, so a system that produces when the kettle, oven and washing machine are running can be worth more than its yearly figure alone implies. Export and self-use follows that through, and batteries covers storing the midday surplus.
Season by season
The monthly table tells a clear story. From April to August the split array keeps close to the south roof, because the summer sun rises in the north-east, climbs high and sets in the north-west, so it spends hours on both faces. From October to February the sun rises south of east and sets south of west, and it never gets far above the horizon. A south slope faces it all day; an east or west slope sees it only at a shallow angle for part of the day.
For most households that matters less than it sounds. Winter output is small on any Congleton roof: even the south array makes only a fraction in December of what it makes in June. What decides value is how much of the spring and summer output the house can use, and there the split array is nearly level with a south roof. If winter generation is a priority, for example to run a heat pump, a south-facing slope or a garden frame angled south is the better place to start.
Shade from long morning and evening shadows
East and west slopes do most of their work when the sun is low, and low sun casts long shadows. A neighbouring house, a tree at the end of the garden or a chimney stack on the ridge can shade an east roof for the first hours of the day and a west roof for the last, even if it seems far away at midday. PVGIS cannot see those obstacles; its figures assume an open sky. A shade reading taken at the roof, or a firm’s shade analysis from photographs, is worth more on an east or west roof than on a south one.
In the runs for this guide, the hills to the east of the town made almost no difference to the yearly figure at the town centre. Local obstacles are the ones to check.
The wiring question
Panels facing different ways produce different currents at any moment. If they are wired into a single string, the weaker face holds back the stronger. The usual answers are an inverter with two independent inputs, each serving one face, or electronics at each panel: micro-inverters or optimisers. The first is the common choice for a simple two-face roof. The second costs more but helps where chimneys, dormers or trees shade parts of a slope at different times of day.
The inverter rating also matters for the grid. An east and west array rarely reaches its full rated output, because the two faces peak at different times, so firms sometimes pair a larger array with a smaller inverter. That can keep the system under the 3.68 kW single-phase limit for the simpler G98 notification. See grid connection, and find the operator for your street with the ENA postcode search.
Batteries and diverters with a split array
Because an east and west system spreads its output across the day, it leaves a smaller midday surplus than a south array of the same size. That can reduce the case for a large battery: more of the output is used as it is made. On the other hand, a battery can still carry the late-afternoon output from the west slope into the evening peak. With mains gas heating most Congleton homes, a hot-water diverter is another way to use summer surplus, sending it to the immersion heater instead of the grid. Size either one on the spring and summer months, when there is something to store.
When one face is enough
Covering both faces is not always the right answer. If the west slope is shaded by a neighbouring house, or broken up by roof lights, putting all the panels on the east may give a cleaner layout and a simpler wiring plan at a small cost in output. If one face fronts the road in a conservation area, that slope still counts as permitted development for an unlisted house, but some owners prefer to keep panels on the rear: conservation areas explains the rules.
Reading a quote for a two-face roof
A good quote shows each face separately: the number of panels, the direction and pitch of each slope, and the expected yearly output of each. Check the figures against the table above rather than against a south-facing assumption, and make sure the estimate uses Congleton’s sunlight data. Firms certified for solar by MCS have to provide a performance estimate; their certification can be confirmed on the MCS search. For a detached house with more slopes to choose from, see detached homes; for the full eight-direction table, output; and to compare prices, costs.