KM200 meaning of solarYield value?

Thanks for providing this binding, works great with my buderus stuff. We have warm water solar circuit and the binding provides lots of values about that.
Everything is clear, apart from that solarYield (channel km200:solarCircuit:817200123:sc1:solarYield)

the value right now is zero whereas half an hour ago it was around 300. The heating system itself shows cumulated yield throughout the day, a totally different number.
Checking Buderus Connect website, the value there also does not relate to what I see in the solarYield channel.

Any ideas?