forecast: preserve fixed target when solar forecast is unavailable

[filiplajszczak]

FCSolar currently lets network exceptions bypass its existing 12-hour raw-data cache. If no forecast reaches core, the generic error fallback can eventually allow discharge despite a configured fixed grid-charge target.

This change:

• wraps forecast.solar request failures as ProviderError so cached data remains usable;
• uses zero production when no usable forecast remains and fixed min_grid_charge_soc is configured;
• leaves existing fallback behavior unchanged without a fixed target or with the forecast strategy.

[MaStr]

Good catch with the network error!

On making data up with 0.0 production,I am not 100% happy.
Currently, we are following the rule: no data, classic battery mode = allow discharge.

Creating an empty production for non existing forecasts will work for 1-2 hours if outage, but in the long run, that will create wrong behavior on cloudy.

It can result in unnecessary "force charge" events.

Need to think about that.

[Copilot]

Pull request overview

This PR improves resilience of the solar forecast path so that transient Forecast.Solar network failures don’t bypass caching and (when using a fixed grid-charge target) don’t accidentally allow discharge due to generic forecast-error fallback behavior.

Changes:

• Wrap requests.get(...) failures in the Forecast.Solar provider as ProviderError so the baseclass can keep using cached raw data.
• Add a core-level fallback that assumes zero solar production for the current cycle when min_grid_charge_soc is configured and the target strategy is fixed.
• Add regression tests covering both the fixed-target fallback and the provider error wrapping/cached-data retention behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/batcontrol/core.py	Introduces _get_production_forecast(...) to safely fall back to zero production for fixed targets when the solar forecast errors.
src/batcontrol/forecastsolar/fcsolar.py	Wraps requests exceptions as ProviderError so refresh can fall back to cached data.
tests/batcontrol/test_core.py	Adds tests ensuring fixed-target operation uses zero solar forecast on provider errors, and unchanged behavior otherwise.
tests/batcontrol/forecastsolar/test_fcsolar.py	Adds tests verifying request errors are wrapped and cached raw data is preserved across refresh failures.

[filiplajszczak]

Right, Maybe I should remove the zero-production fallback and keep this focused on using cached data after network failures.
I should also sanitize the error message.

[MaStr]

Yes, please remove the 0 padding.
In fact, the cache ttl is pretty long to cover a longer outage period. That is the intention of that complete cache and schedule implementation:

• Have the updates out of the main loop
• Implement a proper way to use existing data beside updates/concurrent usage of the cache
• as long as we got one working set of data, work on this as long as it is possible to overcome network failures.