Fix incorrect power factor device class usage in Fronius

[frenck]

Proposed change

Fixes an case of incorrect device class usage in the Fronius integration.

The power factor sensors have the power_factor device class, but do not provide a valid unit for that device class. The only valid unit is %, but it isn't a percentage that these sensors provide in this integration.

Therefore, I've removed the device class in this PR.

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[home-assistant]

Hey there @nielstron, @farmio, mind taking a look at this pull request as it has been labeled with an integration (fronius) you are listed as a code owner for? Thanks!

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[farmio]

This sensor returns a float 0..1. Should we instead multiply it by 100 and add % as unit?
I think it would be nicer to have unit and device class set.

Afaic power factor is often written as 0..1 without unit (eg. on power supplys).
From Wikipedia I read

Since the units are consistent, the power factor is by definition a dimensionless number between -1 and 1.

https://en.wikipedia.org/wiki/Power_factor

[frenck]

Should we instead multiply it by 100 and add % as unit?

🤷 That was not in my scope; I just spotted this bug.

Afaic power factor is often written as 0..1 without unit (eg. on power supply).

Home Assistant expects a percentage (as documented).

[farmio]

🤷

[epenet]

@farmio I had a quick look at the code and it doesn't seem so easy to adjust the code and multiply by 100.
Do you want to provide a superseeding PR? Or a follow-up PR to reinstate the device class and the multiplication factor.

[farmio]

Yes sure, I can do a follow-up. I'd just add a lambda to the entity descriptions.

@epenet If you ask me, the correct way would be to support dimensionless numbers for power factor in HA. But you are the unit expert here.

[frenck]

If you ask me, the correct way would be to support dimensionless numbers for power factor in HA.

That is an architecture discussion, not a PR discussion.