Caterham is folded into the North Downs. The town sits in an upper valley cut into the dip slope of the Downs, running from about 110 m along the railway in Caterham Valley up to 236 m at Gravelly Hill, the seventh-highest point in Surrey. That shape prompts a fair question from people on both sides of town: does it matter for solar whether your house is on the Hill or in the Valley, and which way should the panels face?
Rather than answer from a rule of thumb, we ran the numbers.
How we tested it
We used the European Commission’s PVGIS 5.3 tool, with the same settings throughout: a 4 kWp array, 14% system losses, building-mounted, using PVGIS-SARAH3 radiation data for 2005–2023. We ran it at two points — Caterham Valley (51.2804, −0.0806) and Caterham-on-the-Hill (51.2934, −0.0885) — for five roof directions at a 35° pitch, and for three pitches facing due south. All runs were made on 17 September 2026.
Height: almost no difference
| Location | South-facing 4 kWp at 35° |
|---|---|
| Caterham Valley | about 4,008 kWh a year |
| Caterham-on-the-Hill | about 4,014 kWh a year |
The Hill came out 6 kWh a year ahead, around 0.15%. At the scale of a house, the height of the town makes no practical difference to what panels generate.
Direction: about a fifth between south and east or west
| Roof direction (35° pitch) | Caterham Valley | Caterham-on-the-Hill |
|---|---|---|
| South | about 4,008 kWh | about 4,014 kWh |
| South-east | about 3,791 kWh | about 3,801 kWh |
| South-west | about 3,766 kWh | about 3,774 kWh |
| East | about 3,219 kWh | about 3,229 kWh |
| West | about 3,173 kWh | about 3,184 kWh |
South-east and south-west roofs were roughly 5–6% below south. East and west roofs were roughly 20% below. That matches the Energy Saving Trust’s general guidance that a system facing east or west tends to get around 15–20% less energy than one facing directly south, and its advice against panels on a north-facing roof.
An east- or west-facing roof is not a reason to rule solar out. Morning or late-afternoon output can line up with some households’ usage, and a house with both an east and a west slope can use both. But the annual figure falls by about a fifth while the cost of the installation does not, so the payback has to be worked out for that roof rather than borrowed from a south-facing example.
Pitch: forgiving within the usual range
| Pitch (facing south) | Caterham Valley | Caterham-on-the-Hill |
|---|---|---|
| 20° | about 3,862 kWh | about 3,866 kWh |
| 35° | about 4,008 kWh | about 4,014 kWh |
| 45° | about 3,998 kWh | about 4,006 kWh |
A steep 45° roof lost almost nothing against 35°. A shallow 20° roof, the kind found on some extensions and newer homes, came out about 4% lower. Within the pitches most Caterham houses have, the angle of the roof is a minor factor.
What the model cannot see
PVGIS works from satellite radiation data and the terrain horizon around a point. It does not see the oak at the end of your garden, the house across the road or the way a particular street sits against the valley side. In a town shaped like Caterham, local shade is where two houses with the same roof direction can differ most, and it is the main thing a survey measures on site.
Which homes this applies to
Most of Caterham’s houses have a roof of their own to consider. Census 2021 figures for the Caterham Valley area show 35.3% detached and 21.4% semi-detached homes and 6.2% terraces, alongside 30.5% purpose-built flats, where the roof belongs to the whole block and any system would need the freeholder to commission it. Homes in the CR3 postcode district average an EPC score of 67, band D, so for many older houses insulation and draught-proofing belong in the same conversation as panels.
The electricity network in Caterham is run by UK Power Networks, which receives the G98 notification or G99 application for any new system. And the county’s group-buying scheme, now trading as Switch Together, was inviting registrations on its Tandridge page, without naming round dates, when we checked on 17 September 2026 — a useful benchmark to compare with an independent quote on the same specification.
Our solar panel installation Caterham page carries the town’s planning and housing picture alongside the PVGIS estimate, and the savings calculator lets you set your own bill against it.
Sources: European Commission JRC, PVGIS 5.3 (PVGIS-SARAH3, runs of 17 September 2026 at the coordinates shown); Energy Saving Trust, Solar panels (updated 27 August 2026); Wikipedia, Caterham (geography); ONS Census 2021, TS044, Caterham Valley MSOA via censusdata.uk; EPC.Report, Tandridge council area; UK Power Networks; Switch Together, Tandridge page (read 17 September 2026).