ᐅ Solar Systems on Older Buildings: Opportunities and Challenges of Retrofitting

Hello,

the topic of solar systems has become very popular lately, especially due to the energy crisis and discussions around sustainable building. I am particularly interested in: Who has experience with retrofitting a solar system on an older building? I am currently facing this decision and have noticed that new questions arise that often do not come up with new constructions.

What about the structural integrity of old roofs that may not be designed for the additional weight? Does the roof frame need to be reinforced beforehand, or are there lighter systems specifically for older houses? And what about heritage or historic preservation regulations – is it even allowed to install solar panels in historic streets? The orientation of roofs is often not ideal either. Are there now efficient solutions that provide good yields even with limited sun exposure?

Another common topic is the old electrical wiring in the house. Is the existing electrical system sufficient, or does the entire system need upgrading to effectively use the self-generated power? I am also wondering how expensive such a retrofit really is and which subsidies or incentives are currently available.

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

Looking forward to a lively exchange!
Theiss

DerTheiss schrieb:

Who has experience retrofitting a solar system in 2021?

DerTheiss schrieb:

What about the structural integrity of older roofs that may not be designed to support the additional weight?

First, have it checked. Most roofs handle it without issues. Mine from the mid-60s didn’t have any problem. Same with my neighbors’ prefab house from the late 60s.

DerTheiss schrieb:

And what about heritage preservation requirements?

Ask the heritage authority. It ranges from “absolutely not allowed” through “full black only, definitely no reflective surfaces on black roofing” to “no problem at all.” It also depends on the federal state. Here in NRW, heritage restrictions have been practically irrelevant since the end of 2022, as there is now a legal right to install photovoltaic systems even on protected buildings.

DerTheiss schrieb:

Another often discussed topic is the old electrical wiring in the house. Is the existing electrical system sufficient, or does it need updating to make sensible use of self-generated electricity?

You need to separate the house wiring from the photovoltaic system. Apart from possible additions in the main distribution board, they have nothing to do with each other. Old wiring doesn’t care whether the electricity comes from the roof or the utility company.

DerTheiss schrieb:

What experiences have you had?

Only positive ones.

DerTheiss schrieb:

Which providers are reliable?

There are almost 11,000 municipalities in Germany, so there are definitely many more reliable providers. This is not the right forum for that.

DerTheiss schrieb:

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

Only if you have enough money. Otherwise, for a standard system? No.

DerTheiss schrieb:

What mistakes should you absolutely avoid?

Getting a poor-quality solar installer. Paying too much. Being talked into unnecessary things. Adding storage if it doesn’t fit your lifestyle. Etcetera.

DerTheiss schrieb:

Maybe there are some inspiring practical examples?

What inspiration do you need for plain photovoltaic? Modules get mounted on the roof. Done.

I would first like to clarify exactly what you have in mind.

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 photovoltaic system.

@nordanney has already provided a quite comprehensive answer.

Shading from tall trees or shrubs on the photovoltaic modules significantly reduces the system’s efficiency.
A deal-breaking factor is roofing made of Eternit or shingles.