I am convinced that direct sunshine inflates the temperature, even a low sun in winter. I upgraded the VP2 i purchased end Nov 2005, with a daytime aspirated fan, actvated when direct sunshine hits the solar panels but this made little difference in lowering the temps. From around early May to early October a Canadian Maple tree is in full leaf and shades my VP2 and VV for much of the morning. Temperature readings are quite a bit lower than a nearby PWS and even Kenley Airfield, a Meto official site. The reverse is true most afternoons, , at least comparing the Kenley readings, when any sunshine is directly on the VP2 And VV but the Kenley site may be in part/full shade. As it is now home to a gliding club, access is limited so I'm not sure of their setup but a member ther did say it was an AWS. I purchased a new temp/humidity unit in Febrary and this records 0.5c lower than the VP2 most of the time. A sample from yesterday at 10:00 Local PWS 14.8c Kenley 12.9c Vantage Vue 11.8c New kit Temp 11.4c. At 16:00 17.2c, 15.5c, 16.9c and 16.0c. Dont have figures for the 'old' VP2 but as I say, random checks have shown temperaturs to be around 0.5c higher than the new kit. By the way, my Wunderground site is ISURREYC5
Pat, Crawley Down, West Sussex.