Here we are once broadening previous text on PV facades. Even these may be known to some and common it is good to emphasis some advantages on having PV façade vs. regular panels.

If you have a wide space, land or unused flat roof, be free to have efficient array of panels, but keep in mind that you will lock this space to this, and would not be able to use it for other purposes. Surly if you are closer to equator as middle/south Europe countries, you will have more direct sunlight, but you will have more heat as well.

Direct sun means roof panels face the sun most of the day and that is great for light, but not for heat. On hot days, panels can run 20–30 °C above air temperature. Every degree above ~25 °C trims output by about 0.3–0.5%.* So yes, you have tons of sun, but heat quietly eats some of the gain.

As a solution you may look more into vertical ventilated façade that is powered with indirect sunlight. Façade panels don’t stare at the sun all day. East panels work best in the morning; west panels in the afternoon. They also run cooler. The ventilated gap behind the façade moves air and pulls heat away. Lower cell temperature keeps efficiency closer to the sweet spot, which partly offsets the less-than-perfect angle to the sun. Over a full year, though, façades usually make fewer kWh than a good roof.

So what options are there when thinking efficiency. If your goal is maximum annual energy, a well-oriented roof wins. If your roof is small, shaded, or you care a lot about architecture and thermal comfort, a ventilated BIPV façade is a strong option. It uses “dead” wall area, looks clean, cools better in summer, and can even offer useful warm air in winter. As always, the best choice depends on your site, angles, and space.

Besides this if you are constructing in northern countries, where sun is lower in the sky and you don't have peek sunlight, then you could gain more energy just because façade panels have more direct sun through the year, than roof or horizontal panels. With good planning you may maximise this to a perfection.

If you are interested in what solution there are, and how you could benefit from makes sense for you.