"Optimal" orientation does always lead to more output

[FabianHofmann]

Version Checks (indicate both or one)

• [ ] I have confirmed this bug exists on the lastest release of Atlite.

• [X] I have confirmed this bug exists on the current master branch of Atlite.

Issue Description

The current CI fails as the total output of optimal orientated pv is not larger than the standard orientation. This only occurs for the ERA5t test, which at the point of writing tests latest summer months (Mai/June). So there might be an issue with the optimal orientation calculation.

See https://github.com/PyPSA/atlite/actions/runs/9887489362/job/27309307583

Reproducible Example

No response

Expected Behavior

The total "optimal" output should always be larger.

Installed Versions

Replace this line.

[fneum]

Optimal orientation might vary if you only look at two months?

[FabianHofmann]

good point! that's probably the reason

[FabianHofmann]

then we can replace the comment here https://github.com/PyPSA/atlite/blob/master/test/test_preparation_and_conversion.py#L672 with an explanation

[euronion]

Yeah... so the latitude optimal orientation we do is based on a simple heuristic from here:

https://www.solarpaneltilt.com/#fixed

The idea is to maximise output for fixed tilted solar PV over the span of a full year. So yes, the orientation is suboptimal if you only consider a few months, especially during central European summer.

NB: the largest output should always results from two-axis tracking.