East or West? Choosing Panel Orientation When Part of Your Sky Is Blocked

The rule everyone quotes, and why it is only half the story

In the northern hemisphere the sun sits in the southern half of the sky all day. So a fixed panel facing due south, tilted toward the equator, catches the most energy over a year. In Germany the optimum is roughly south-facing at a tilt of about 30 to 35 degrees. That is the textbook answer, and for a single clear roof slope it is correct.

The problem is that the textbook assumes an open sky. Most real spots do not have one. A neighbour's house, a row of conifers, a chimney or a ridge blocks part of the path the sun actually travels. The compass direction that wins on paper can lose to a different direction once you account for what is in the way. That is why orientation should be the second question. The first is: where is my sky blocked, and at what time of day?

It also helps to know how much you really give up by pointing away from south. The answer is less than most people fear.

How much azimuth and tilt actually cost you

Azimuth is just the compass direction a panel faces. Tilt is its angle from horizontal. Both move the yield, but less sharply than you might guess, because a large share of the energy in cloudy climates arrives as diffuse light from the whole sky rather than as a direct beam.

Relative to a south-facing reference at 100 percent, a southeast or southwest roof gives up only about 5 percent. A panel facing due east or due west lands around 80 to 85 percent of the south figure, so a 15 to 20 percent loss. A split system with half the modules east and half west typically loses about 10 to 15 percent of annual energy. A PVGIS simulation of one residential project found the east-west case produced just 12 percent less than a hypothetical south array.

Tilt is even more forgiving. A deviation of up to 10 degrees from the optimum barely moves output. For a 10 kWp system near Hannover, modelled production fell only about 5 percent going from a 30 degree tilt to a steep 50 degree tilt. The lesson: do not lose sleep over a few degrees. Worry about shade and about gross direction instead.

• South: 100 percent (reference)
• Southeast or southwest: about 95 percent
• Due east or due west: about 80-85 percent
• East-west split: about 85-90 percent of a south array
• North: usually not worth it in Germany

Why directional shade flips the decision

Here is the part the calculators miss unless you feed them the truth. Shade is rarely symmetric. A tall building or a stand of trees usually sits on one side of you, blocking either the morning or the afternoon sun, not both equally.

If the heavy obstruction is to the east, your morning sun is already gone. Pointing panels east would aim them straight at the blockage during the only hours they would benefit. A west-facing tilt instead catches the open afternoon sky and wins back far more usable sun. The mirror case is just as real: trees to the west mean an east-facing tilt collects the clear morning hours before the shadow arrives.

This is why a generic map tool can mislead you. Google Project Sunroof, a regional Solarkataster or SunCalc work from rooftop geometry and average horizons. They do not see the specific conifer or gable next door that swallows your 8 a.m. or your 5 p.m. sun. The fix is to measure the real shadow horizon from the exact spot where the panels will sit: the actual altitude, in degrees, of every tree, ridge and wall around you. A phone-based augmented-reality sweep, which is what SunMeasure does, captures that horizon and shows which hours are genuinely clear. Only then does the east-versus-west choice become obvious.

When east-west beats south on purpose

Even with an open sky, plenty of households deliberately choose east-west. The reason is self-consumption. A south array dumps a tall, narrow spike of power around midday, when many homes are half-empty. An east-west layout produces two broader humps: the east modules run from roughly 6 a.m. to noon, the west modules from early afternoon into the evening. That curve lines up with real demand at breakfast, the start of work, cooking and the evening.

The numbers back this up. Without a battery, an east-west split commonly lifts the self-consumption share into the 35 to 60 percent range, against roughly 25 to 30 percent for a pure south system. Because every kilowatt-hour you use yourself is worth about 30 to 35 cents avoided from the grid, while feeding the same unit in earns only around 8 cents under current German tariffs, the higher self-consumption can more than offset the 10 to 20 percent lower total yield.

So the honest framing is: south maximises total kilowatt-hours, east-west maximises the value of those kilowatt-hours if your life happens in the morning and evening. Pick the goal first.

Flat roofs and balconies

On a flat roof you are not stuck with the building's direction, so you mount panels on frames at the tilt you want. Counter-intuitively, an east-west flat-roof layout often produces more total energy than a south one on the same roof. South-tilted rows must be spaced apart so they do not shade each other, which wastes roof area. East-west panels sit back-to-back at a low tilt with almost no gap, so you fit far more modules. Each panel yields a little less, but there are many more of them. For flat roofs the sensible tilt is low, around 10 to 15 degrees, which also cuts wind load. Keep it at 12 degrees or steeper so rain still cleans the glass.

Balcony solar (Balkonkraftwerk) is its own situation, and Germany passed one million registered systems by mid-2025. Here the wall direction is usually fixed for you, and the module often hangs near-vertical on a railing. A vertical panel already gives up yield compared with a tilted one, so the direction it faces matters more, not less. East and west balconies are both fine and favour self-consumption. If you can tilt the panel out from the railing, even a modest 20 to 30 degrees helps. And because a balcony is often boxed in by the building itself, the surrounding shade horizon is frequently the deciding factor, so measure it before you commit.

A simple decision order works for nearly every site: first measure where and when your sky is blocked; then choose the gross direction that faces your clearest hours; then set a tilt within the comfortable 10 to 35 degree band; and only last, decide whether you are chasing maximum kilowatt-hours or maximum self-consumption.

• Open sky, want maximum total energy: south, 30-35 degrees.
• Open sky, want morning and evening cover: east-west, 10-20 degrees.
• Heavy shade on one side: face the opposite, clear side.
• Flat roof, limited area: east-west at 10-15 degrees fits more panels.
• Balcony: direction and the surrounding shade matter most; tilt out from the rail if you can.