Plug in Hybrid - mystery charging
 

I drove my charged hybrid for the c. 30 miles and as expected it then switched to petrol. I then parked and visited a shop for about 1 hour. When I returned to the car and switched on, it showed 10% available for electric power, which I was the able to use for 2/3 miles. How did it recharge 10% in this hour - is there some sort of solar charge going on?