Solar systems on old buildings: possibilities and challenges in retrofitting

Hello,

the topic of solar systems is now on everyone's lips, especially due to the energy crisis and the discussions around sustainable construction. I am particularly interested in: Who has ever dealt with retrofitting a solar system on an old building? I myself am currently facing the decision and am finding that entirely new questions arise, which often do not play a role in new buildings.

What about the statics of old roofs that may not be designed for the additional weight? Does the roof structure need to be reinforced beforehand, or are there lighter systems specifically for older houses? And what about the requirements of [Denkmalschutz] – is it even allowed to simply install solar panels in historic streets? The orientation of roofs is often suboptimal as well. Are there now efficient solutions that allow a good yield even with limited sun exposure?

Another frequently discussed topic is the old electrical wiring in the house. Is the existing electricity sufficient, or does the entire system need to be modernized to make meaningful use of the self-generated electricity? Furthermore, I wonder how expensive such a retrofit really is and which subsidies can currently be applied for.

What experiences have you had? Which providers are reliable? Are there new technical developments (e.g. solar roof tiles) that you can recommend? Which mistakes should definitely be avoided? Perhaps there are also inspiring practical examples from your area – I would be glad if you share your experiences and tips here!

Looking forward to an active exchange!
Theiss

Who has ever dealt with retrofitting a solar system

in 2021.

What about the statics of old roofs that might not be designed for the additional weight?

First, have it checked. Most roofs have no problem with that. Mine from the mid-60s doesn’t either. Same with the neighbors (prefabricated house from the late 60s).

And what about the requirements of the monument protection?

Ask the monument conservator. It ranges from "absolutely not" over the middle ground "full black, definitely not reflective with black covering" to "that’s not a problem." It also depends on the federal state. Here in NRW, monument protection has been practically irrelevant since the end of 2022, because since then you have a legal right to PV even on a monument.

Another topic often discussed is the old electrical wiring in the house. Is the existing electrical system sufficient, or does the whole system need to be modernized in order to use the self-generated power sensibly?

You have to separate the house electrics from PV. They have—except possibly additions in the meter cabinet—nothing to do with each other. The old wiring doesn’t care at all whether the electricity comes from the roof or the energy supplier.

What experiences have you had?

Only good ones.

Which providers are reliable?

Since there are almost 11,000 municipalities in Germany, there are certainly many times more reliable providers. You are in the wrong forum for that.

Are there any new technical developments (e.g. solar roof tiles) that you can recommend?

Only if you have enough money. Otherwise, for a normal system? Nope.

Which mistakes should one definitely avoid?

Ending up with a bad solar installer. Paying too much. Being talked into the wrong things. Storage systems, if they don’t fit your life. Etc.

Maybe there are also inspiring practical examples

What should inspire you with a plain PV system? Modules get slapped onto the roof. Done.

I would first like to clarify what exactly you have planned. The term "solar system" is a general term for all systems that use solar energy, while photovoltaics specifically refers to the conversion of sunlight into electrical power. It is likely that you mean a PV system. has already responded quite comprehensively.

Shadows from tall trees/shrubs on the Pv modules significantly impair the efficiency of the system. A KO criterion is roofing with Eternit and/or shingles