Is there a website that.....

[IanHx]

... tells you what % of max power you should be generating based on the local weather ?

For example today - bright sunshine through hazy sky - only seeing 66% of max rated value.
Would be great if there was some sort of "sun index" so that we could tell if its just atmospherics affecting everyone locally, or a specific issue with my panels.

[Dave Foster]

Have a look at Solcast.com, it's more of a commercial site but they let you set up as a home user and it gives a pretty accurate assessment of the solar expectations for your system based on the local atmospherics.

https://solcast.com/free-rooftop-solar-forecasting

[IanHx]

Thanks, I'll have a look when I've fished out the relevant technical details !

[IanHx]

Found another one that also seems useful - solar.meteosource.com.