I warmly appreciate the implementation of solar forecast in VRM. It is a nice feature that allows a better planning of various aspects. Since I was using an own Solcast account before Victron’s implementation, I have the ability to compare.
In the past I observed already that Victron’s numbers were mostly 10% to 30% too optimistic, whereas native Solcast forecast had in most cases a deviation smaller than 5%. This circumstance is not anything to complain. However in current weather condition the VRM forecast shows 350% of Solcast projection. Reality confirms that native Solcast forecast is again quite close.
Solcast shows predicts the low PV production already since more than 36 hours, whereas VRM as of now still predicts 350% of reality.
Since Victron uses the same source (Solcast) for VRM implementation (as I think to remember in relevant announcement), I would appreciate if Victron team could invest some time in improvement measures.
Current screeshot of native Solcast forecast (was nearly identically yesterday afternoon):
Since I was spending yesterday some time in own home automation development and was wondering about next day’s numbers, I logged in into Solcast to get confirmation.
This is something I have been raising for some time. In my case it under-estimates and then tries to correct itself throughout the day, see-sawing as it goes along.
In this chart I compare forecast vs actual, recording the PV that is expected from any moment in time. It is typically off by 30% or more, in poor weather, this delta is much greater, even though the actual irradiance data seems much more accurate, so the issue is the modelling on VRM.
Evening Update:
The Prediction of 34.5 kWh Solar was in Fact a yield of 14.2 kWh.
This needs to be improved, mainly for the Operability of DESS. It has a hard time sticking to a schedule anyway - If the forecast is that far off, the whole schedule may be insufficent as well.
@Barbara : Last 9 days I recorded VRM and native Solcast forecasts and PV results, where I like to share my findings. My post please shall be not considered as criticism, but as collaboration to support.
During first 6 days VRM forecast was steadily predicting essentially lower than native Solcast. Last 3 days it became closer. Since my panels are in a 15° angle only, I would actually expected the oppositive, since VRM does not use more config details for Solcast. Maybe you have an explanation for that issue?
When we look to forecast details (I recorded a 24 hours rolling forecast), I had to observe that VRM showed during 6 out of 9 days a peak, which couldn’t be explained by native Solcast forecast. Mostlikely that peak has major influence on weak forecast quality, since it typically occurs between ~10:00 and ~15:00.
In a few cases the VRM forecast even exceeded the Solcast-max-forecast (90% level). That should be actually not the case.
There a several patterns providing indication that VRM forecast seems to be delayed by 2 hours. Since Solcast delivers in UTC time, maybe the translation in CET is not performed for VRM. Since VRM-API provides time also in UNIX-time, I would expect according to UNIX time definition the same interpretation.
Could you please check and explain?
