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Hello, the last few days I have mapped quite a few solar panels in the town where I live (Jülich, Germany). Using JOSM, I have found a workflow for myself with which I think I would be able to gather quite a lot of data from aerial imagery (which is quite good in my area). So far, I've been using the photovoltaic tags


as suggested here:
However, it occurred to me that for future solar panel mapping, even more precise tagging would be possible with regards to PV vs. thermal collectors, as also suggested on above webpage.
My question: Is it possible to differentiate PV/thermal collectors just from aerial imagery? If so, could you provide me with some examples? (I have added some myself below, from mapping done by other users) Or is it preferable to only map PV which you recognize as such, or map everything but stick with more general tags such as


Here are some examples of a nearby German village with some tagging provided by other users; PV left-hand side, thermal collectors right-hand side (I do not know if they are correct, but from the examples, it appears that PV modules have a wider range of different aspect ratios and are usually bigger):

(EDIT: My guess now is that it is quite difficult to differentiate in general, see e.g. this photo of a PV and thermal collector panel which would appear very similar on aerial imagery:
So my question still stands if I should 1. map all panels and use more general tags or 2. map only PV which are clearly recognizable as such)

asked 22 Jan '23, 23:21

HektorSchlegel's gravatar image

accept rate: 0%

edited 22 Jan '23, 23:37

Yes, it is possible to discriminate between the two with a bit of practice. Note that it is not uncommon for houses to have both.

Typical thermal collectors have somewhat larger panels than solar PV (which are usually 1.6 by 1 m), usually only occur as 2-3 panels together, have external pipe work, visible on good quality aerial imagery. Making use of one of the measurement tools available in most editors can often help because of this size difference.

At least in the UK, solar PV is now much commoner than thermal collectors. I suspect the same is true in other European countries.

In Britain we use generator:solar:modules to count the number of visible modules. Adding this count can be useful for a future review as module counts of 3 or under may be either kind of solar panel. If you are really unsure then also add a fieme tag. Also, because of the smaller size of solar collector installations, incorrect identification is relatively unimportant (as long as a module count is available or the installation is mapped as an area).

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answered 23 Jan '23, 21:33

SK53's gravatar image

SK53 ♦
accept rate: 22%

Many of the solar thermo collectors in my area are simple dark rubber or plastic mats with embedded tubing that cover about the same area as a solar photovoltaic. They are often modular with each rectangle about the same size as a photovoltaic panel. Output is warm, not hot, water used for heating swimming pools. Those can be quite hard to tell from photovoltaic as the color is the same, the tubing is about the same diameter as wiring and they cover about the same amount of area. So if the yard associated with the house has a swimming pool, I am much less certain of the type of solar collector.

The domestic hot water solar thermal systems generally can be distinguished from the photovoltaic as you mentioned due to smaller number of panels and, with good imagery, the plumbing being visible.

(23 Jan '23, 21:44) n76

Ahh, yes, I've come across exactly one of these in the UK, but had forgotten that they are much commoner in Germany. I think size will still be a bit odd compared with solar pv, but quite subtle distinction.(Also there's quite a bit of variability in default image quality, which doesn't help)

(24 Jan '23, 13:34) SK53 ♦

On my old house we had solar thermo for water heating. On my current house we have solar photovoltaic.

At least for the part of the world I live in I will have to say, it depends. Some solar thermo have visible tank systems associated with them. And some solar panels have characteristic patterns that can be visible in higher resolution imagery. But there are some that I believe would be quite difficult to tell.

For the roof top solar I have mapped, if I could not tell from the aerial imagery I simply did not map it. In retrospect that probably was not a good way to do things but my general philosophy for OSM is that no data is better than bad data.

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answered 23 Jan '23, 01:10

n76's gravatar image

accept rate: 17%

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question asked: 22 Jan '23, 23:21

question was seen: 713 times

last updated: 24 Jan '23, 13:34

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum