South, east or west? Why the best orientation is not the highest-yielding one

Two different questions

"Which orientation is best?" is really two questions. The first: which orientation generates the most kilowatt hours? The answer is unambiguously south at 30 to 35 degrees of tilt. The second: which orientation saves the most money? That is where it gets interesting.

You only save on electricity you consume at the moment it is generated. A kilowatt hour flowing into the grid at midday while nobody is home earns exactly nothing on a plug-in system.

The midday peak is the problem

A south-facing array produces its output in a narrow bell around noon. In a household that is empty during the day, consumption in those hours is the bare base load — fridge, router, standby, together perhaps 120 to 200 watts.

An east-west split, or pure west, shifts the generation. The peak is lower, but output starts earlier and lasts longer. It therefore lands in the morning and evening hours when coffee is actually made, laundry actually run and dinner actually cooked.

What that means in numbers

Take a typical 880 Wp balcony system in Berlin, in a household using 2,500 kWh a year and out during the day. Facing south at 35 degrees it generates about 780 kWh — but only around 45 percent is self-consumed.

The same system facing west generates about 640 kWh, noticeably less. The self-consumption share, however, rises to roughly 55 percent. The difference in actual savings therefore shrinks from an 18 percent yield gap to a few euros.

The calculator on this site reports both figures separately, so you can see which one is really carrying your decision.

The special case of the railing

At 90 degrees of tilt, the high summer sun strikes the module at a very shallow angle. Across the year that costs 25 to 30 percent against an optimally angled mount.

In winter the picture reverses. With the sun 15 degrees above the horizon, it stands almost perpendicular to a vertical module, and snow does not settle. In December, vertical south mounting beats a 35-degree mount. Because consumption is higher and generation scarcer in winter, that share is worth disproportionately more.

Practical recommendation

If you have the choice and are home during the day: south, angled. If you are out at work: south-west or west. If only the railing is available, mount it anyway — a vertical north-facing module does not pay, but a vertical east, south or west one usually does.