Shading, orientation and tilt: what decides your production
Three things govern how much a roof produces: which way it faces, how steep it is, and what casts shade on it. All three are measured with data, not assumed. Here is how an engineer measures them, and why an electricity bill alone is not enough to size anything.
Orientation: south rules, but east-west is worth more than you think
A south-facing roof yields the maximum per kWp. In Xàtiva, according to PVGIS, a well-oriented south-facing kWp delivers around 1,490 kWh a year with standard losses. An east- or west-facing roof produces between 15 and 18% less. And even so, it is often the right choice.
The reason is timing. A south roof concentrates production in one big midday peak. If nobody is home at those hours, much of it is exported to the grid and paid as surplus, which is worth far less than the kWh you avoid buying. You can see those prices in our surplus tariff comparison.
An east-west roof produces less in total, but it does so in the morning and evening, when most households switch things on. Every kWh produced has a better chance of being used at home instead of being all but given away to the grid. That is why a salesman writes off an east-west roof and an engineer calculates it.
Tilt: your roof's own pitch, almost always
The optimal tilt in Xàtiva is about 36 degrees according to PVGIS. But a typical 20-degree roof facing south loses only around 3% against that ideal tilt. The practical conclusion: panels go flush with the roof, following its pitch.
A raised structure to claw back that 3% makes the installation more expensive, loads the roof more, suffers more wind and complicates the paperwork. It only pays off in specific cases, such as flat roofs, and that too is calculated, not decided on your doorstep.
Shading: what a partial shadow really costs
A partial shadow does not just cost you the panel it covers: in a string installation, panels are wired in series and the whole row performs at the level of the worst one. A chimney shading one panel mid-afternoon can slow the entire series while the shade lasts. The real damage depends on the electronics you choose.
Panels carry bypass diodes that route around the shaded area to limit the damage, but they do not remove it: the series still loses output and the shaded panel works harder. With optimisers or microinverters, each panel works on its own and the loss stays where the shadow falls. Which one suits your case is explained in our comparison of string, optimisers and microinverters.
The key point: shade is not judged on one day at one hour. Your neighbour's aerial, a cypress tree or the hill behind the house cast shadows that shift with the seasons. A proper study simulates the horizon and the shading hour by hour across the whole year, and the electronics are chosen after that calculation, never before.
What a proper study looks like
A proper study crosses two datasets: your roof's radiation according to PVGIS, the European Commission's database, with its real orientation, pitch and horizon, and your hourly consumption curve, the one your smart meter records. From that we calculate how much you will produce every hour of the year and how much you will actually use.
Anyone sizing your installation «from a bill» is working blind. The bill says how much you use per month, but not when, and the when is everything: it decides the system size, whether a battery makes sense, and how much you genuinely save. To understand what that piece of paper hides, start with our guide to understanding your electricity bill.
And the study does not end when you sign it: it becomes the yardstick. The estimated month-by-month production is put in writing, and afterwards we check every day that your system produces what the study promised. A serious calculation is the only thing you can later verify anything against.
Questions about shading and orientation
My roof does not face south. Is solar still worth it?
Almost always, yes. An east-west roof yields less per kWp than a south-facing one, but it spreads production across morning and evening, which is when most households actually use power. The serious answer comes from the study: we simulate your roof in PVGIS and cross it with your hourly consumption.
I only get shade in the morning. Is that a problem?
It depends on the electronics. With a string inverter, one shaded panel can drag down its whole row while the shade lasts. With optimisers or microinverters, the loss stays on the affected panel. That is why shading is measured first and the electronics chosen afterwards.
Where does my hourly consumption curve come from?
From your home's smart meter. Your distribution company records it hour by hour and you can download it from their customer area. If you order the study from us, we walk you through getting it, or download it with you on a short call.
What about the north-facing side of the roof?
On pitched roofs in this area, the north face is ruled out: it receives far less radiation, and that money works harder on the other faces or in a battery. Only on nearly flat roofs does the building's orientation stop mattering.
Find out what your roof can really do
Tell us where your house is and we will study your roof with PVGIS and your hour-by-hour consumption. We will tell you how much it can produce, with which electronics, and whether a battery pays off. With your numbers, not an average customer's.
A Captia Technology company. Chartered, qualified engineers.