Solar energy on roofs | Roofers are not electricians

A matter of opinion: Solar tiles like these are considered a beautiful and high-quality alternative to common photovoltaic systems. Photo: imago/Herrmann Agency Photography Steffen, it's so great, I saw in the Berlin Futurium that there are terracotta-colored solar roof tiles. They look beautifully old-fashioned and yet are ultra-modern. Why aren't they going into series production long ago?

The basic idea is already older; the famous Mr. Musk also tried it, but failed. You can of course coat roof tiles. The so-called beaver tails, which are often found on older houses, are flat. It is probably relatively easy to put an encapsulated semiconductor layer on it and make the appropriate contacting. With solar cells, the total yield is of course directly dependent on the total area. Aside from the fact that you need a lot of roof tiles with solar cells, there is also the problem of color. Bricks with the common shade of red would have a lower yield than the usual solar cells. They're dark blue and almost black.

Crap. The problem of reflection and absorption.

The color that an object has comes from the fact that only this part of the spectrum that we then see is reflected to us as color. Everything that is reflected is absorbed to a much smaller extent.

Dr. Steffen Schmidt, born in 1952, is the editorial team's polymath. He knows an answer to almost every question - and if he doesn't, he answers another one. Ines Wallrodt talked to him about beautiful roof tiles with solar cells.

The exhibit stated that these solar roof tiles have a special surface that mimics the aesthetics of terracotta and is permeable to the sun's rays. And this enables the function of embedded monocrystalline solar cells. No idea what monocrystalline is.

Monocrystalline and polycrystalline are the two predominant types in which semiconductors are used in solar cells. Monocrystalline means that the entire surface consists of a uniform crystal structure, while polycrystalline - which is cheaper - means that individual crystals that are not as large as the total area adjoin one another. The yield of monocrystalline solar cells is higher. The production is again more expensive. I think the core problem, as with many other things that sound nice, is that the effort required for such roof tiles is quite significant.

It is also unclear to me how the stored energy is dissipated. Does every single shingle need a cable?

Exactly, each individual roof tile would have to be connected to the others. This is quite time-consuming, and there are hardly any craftsmen who have this in their program. Roofers have no idea about electricity and electricians have no idea about roof tiles.

Well, that can be solved. A new professional field is developing.

Wait, there's another catch. This is why the Musk project failed: the hotter a solar cell gets, the lower its efficiency becomes. In Musk solar roofs, some contacts actually melted because they became too hot together with the current that was still flowing. Especially in listed buildings, where such roof shingles are supposed to be used, you don't exactly want the Notre Dame effect.

But Notre Dame caught fire in the usual way.

Yes, that was torched with normal welding work. In any case, it's an error-prone story when you put thousands of roof tiles in contact with each other and divert the electricity to where it's needed.

It is probably much more interesting to equip the glazing of these hideous office towers with solar cells. The yield is still significantly worse, but since the surface is there anyway and the things are usually coated in such a way that as little solar heat as possible penetrates inside, it's still worth it.

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