[werk_ag]

So all the arithmetic (wind speed average and so on) is done by the RX unit?

RX unit only does some unit conversion to meet Davis protocol (mph) and to display data in the user selected unit (Km/h, mph or m/s).
Each Wind data packet sent by the TX, includes Wind Gust and Wind Speed which is a rolling average of the last 2.5 minutes. Values are sent in m/s (more precisely m/s * 1000, to be sent as an integer value).

... Actually in most cases that means the power will be supplied by the Solar Cell directly.

Yes, I think that during daylight, the 10W solar panel is enough to feed it and still charge the battery. The TX unit only draws power from the battery at night or on very dark days. I say this because even in days without bright sun, battery voltage stays almost always, between 12.8V to 13.8V