A while a go I bought a couple of solar panels from REUK and today I finally got around testing them outdoors (I had previously only tested them indoors with a lamp). These panels are rated at 6V, 250mA which makes them quite perfect for low-power outdoor micro controller applications (sensors for example) if they are combined with a re-chargeable battery (that can be tickled charged).
The size of the panels are about 13×13 cm.
It hovered just at the edge of 6V (~5.5-6V)
The test was done on a day with a clear blue sky. The voltage remained steady around ~6.5V and even peaked at 6.9V at one time.