Solar Forcasting

Thanks to the great work by @peter I now have automated control over my powerwall. This lets me top up my battery based on tomorrow’s weather forecast. I currently do this by an IFTTT channel that uses weather underground to turn on a switch if it is forecast to be sunny the next day.
This does have its downsides however, as yesterday was forecast to be windy and rainy, but there was intermittent sunny patches, which actually generated more power than the battery had space (so I didn’t need to top up the battery).

So the question here is: What do people use for more accurate solar forecasting? anyone seen a decent (and free) API that can work with Home Assistant?

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Solcast offers a free API toolkit that is pretty good for solar forecasting. Down the line (and unfortunately this is still a way off) we are keen to integrate this function into our smart meter service and in turn the HEMS - unfortunately no dates for that at the moment, so in the meantime if you are comfortable working with the API Solcast is definitely worth a look!

Make sure to keep us updated with how you get on, I would be interested to hear about your experiences of the accuracy and functionality that you are finding with this!

Looks like someone has created a Solcast → Home assistant integration. Will need editing the backend however - so not something I can do on the HEMS

GitHub - dannerph/homeassistant-solcast for those that can make it work

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Looks like a good start, and a lead for future integration possibilities! Thanks for exploring this and sharing the link!

It’s pretty good actually - accuracy is a bit tricky for me as my panels aren’t all south facing, but it does allow me to know roughly what my generation will be a couple of days in advance, which helps me plan my EV charging!

This post popped up on my LinkedIn this morning and I thought it might be of interest to those who are more IT capable.


Integration between systems is beyond me but I have found

to be interesting. Currently it only supports one array, which covers most domestic installations. Until it was released I would use local weather forecasts to see when to run heavy loads, whereas SolarAid shows generation though cloud cover far more accurately.