Date offset (France / Winter ?)

[ju44sky]

Hello,

I live in France and since I started using Solcast two months ago, I've noticed a one-hour discrepancy in all the data.

Solcast uses UTC. In Home Assistant, I have the GMT+1 time zone for France.

However, Home Assistant tells me the solar peak is at 1:30 PM every day, whereas in reality it's at 12:30 PM.

I've looked everywhere but haven't found how to adjust for a time zone difference.
Perhaps it's due to our winter time in France?

Thank you for your help :)

[BJReplay]

What are you asking for help with?

If you're going to post screenshots of charts, please, for the love of anything that you venerate, don't cut off the axes or the legends, so we know what you're actually plotting, and make us guess, FFS.

That just shits me.

You want help.

You know what you're looking at.

You'll share some of it.

But not enough.

Let's make the people you're asking for help guess what you're showing, so that they can guess what to tell you the problem is?

Why don't you just ask AI, so it can guess what the solution is?

OK, I'll guess:

• You have a time zone wrong.
• It's in Home Assistant
• Or in the server you're running Home Assistant on.
• Or in your Solcast Configuration.

It's not in this integration because there's no setting for timezone in the integration.

Now, what makes you think that Solcast uses UTC?

I've got other guesses about what is wrong, but you need to do better.

I'll tell you though: your configuration is wrong.

Why don't you try again and post all of the information you have.

Here's a starting point - you've found the discussions, but you haven't found or read the FAQs. Come back after you've read them, and other pinned discussions.

[BJReplay]

autoSteve, I suspect your crystal ball is clear, and you would have pointed to a certain pinned discussion. Which, oddly enough, isn't in the FAQ. But that's because there's a repair for it. Let's wait and see. </rant>

[autoSteve]

My crystal ball is clearing, gradually. After a really big night bringing in 2026 at Bar Selecta...

Through the mist I see... An incorrect azimuth setting. Is it 180 degrees out of phase, @ju44sky?

[BJReplay]

Narrator: And it turned out that the Incorrect Azimuth warning had been ignored.

[autoSteve]

Narrator 2: Yeah, nah. Silent killer in this case.

[BJReplay]

Yeah, interesting; easy to spot (even from truncated screenshots) - the mirroring of the shape is the tell-tale as well as the shift.

[ju44sky]

Hello,

Thank you for your feedback and my apologies for the cropped screenshots. Happy New Year 2026 to you 😁

I provided Claude (IA) with my data for the past month, along with the JSON from the API.

Below you will see my graphs for these 48 hours, comparing actual production and Solcast power.

I find this discrepancy of about an hour surprising.

My GPS position is correct on Solcast. Azimuth is 158.24° according to the coordinates of my terminals on my property (South / Southeast right ?). Tilt is 30° according to the slope of my roof.

However, you are correct, the UTC time returned for the peak is 0:30 PM UTC (example: 2026-01-03T12:30:00Z), which is 1:30 PM in France (my Home Assistant is correctly configured). But in reality, my peak is at 0:30 PM.

The problem might be with the information on Solcast? But I can't figure out what ?

Thnaks very much to you :)

[BJReplay]

Thanks for the proper screen shots.

It is amusing that you used IA instead of AI for Claude; Claude and his illegitimate cousins are all Idiot Assistants rather than Artificial Intelligence; nothing more than semi sophisticated word guessing machines.

Until they have read, enough times, that Solcast uses southern hemisphere based azimuth calculations, and then, be able to derive that from a diagram, they will not be able to tell you, by ingesting json, that you have not realised that Solcast uses different conventions to the native HA Integration.

And, because they don't like training on texts that contain profanity, they won't learn from this comment either.

They are stupid fuckers. Don't use them for anything other than simple autocomplete.

[ju44sky]

Hello,
I know how they operate, and maybe they'll eventually spot this mistake with posts like mine, who knows ? ^^
They are sometimes useful for spotting basic errors, but indeed, he never suggested checking this aspect of the azimuth.

I was completely unaware that the azimuth was calculated this way in the Southern Hemisphere.

Thanks again

[autoSteve]

Solcast generally do not monitor these integration discussions. Billy occasionally drops in.

We are in no way affiliated, nor connected with Solcast apart from consuming their hobbyist account service.

[ju44sky]

Oh dear, I should enter -158.24 and not 158.24 for the Southeast? Why? It doesn't make sense in France to turn the other way ? 🤣

They really need to update the FAQ here to make it clear. For example, in the native Home Assistant integration, it goes from 0 to 360.

[gcoan]

Oh dear, I should enter -158.24 and not 158.24 for the Southeast? Why? It doesn't make sense in France to turn the other way ? 🤣

They really need to update the FAQ here to make it clear. For example, in the native Home Assistant integration, it goes from 0 to 360.

This is extensively covered in the readme https://github.com/BJReplay/ha-solcast-solar?tab=readme-ov-file#solcast-requirements

In particular getting the Azimuth setting correct

If you think it could be made clearer, please do submit a push request with revised text. I am sure it will be welcomed

[ju44sky]

Thanks, no, I think it's clear. I read the FAQ but not this diagram in readme.

I think the information should be directly on Solcast, but that's beside the point here.

Sorry for the trouble, and thank you very much :)

[autoSteve]

🔮 for the win.

The tell-tale here is that the end of the forecast and end of generation finally converge. If it were a time zone thing they would not.

If you didn't have some (guessing) early shading going on then the start of forecast and start of generation would also converge.

As the day progresses to peak the skew gets increasingly worse, then it gets better (so gradually less skewed).

In your case the deviation at peak is extreme because of the +/- config issue.

There is a significant clue when configuring at solcast.com, which often gets overlooked (the "Site is facing" hint), so they try (badly) to let you know whether a setting is silly. In your case that also failed, because both -158.24 and 158.24 will show as being "South". They do not have a South-South-East / South-South-West in that hint, which I think is seriously bad.

An aside, if you're in the northern hemisphere then the general convention with azimuth is to treat South as 0°. The general convention in the southern hemisphere is to treat North as 0°. I think this should be a global standard. (The +/- aspect is globally consistent.) "AI" is particularly bad at misleading folks, thinking that everywhere on the planet is in the northern hemisphere because everything on the planet seems to be measured in "miles from the USA" by AI, but that was not a factor here.

You will not have had a Home Assistant "Repair"/issue raised that you ignored. That test is for whether your North/South is wrong, and not the East/West component. You got North/South correct so it did not get raised to warn you.

I see no way to detect an incorrect East/West setting. Documentation is the only way, and maybe the FAQ needs to do a better job given you read it.

[ju44sky]

It's my fault, I should have reread the readme before posting...
Looking back, it now seems obvious that there was an inversion when I look at the graph. But I was completely unaware that you calculate the azimuth differently, oh well ^^

Ideally, on Solcast, for dummies like me, you'd almost have to draw an arrow indicating the direction of the signs on the aerial view to immediately spot the mistake. But I understand that for Australia this calculation seems normal.

Thanks again, this will help me optimize my solar installation 👍