With just 6.4 dm² panel area in december (winter in Sweden) I could charge a 2Ah LiFePO4 in less than three hours. The light sensor is just a rough estimate ( It's still uncalibrated ). It is however worth to note that with a drop in temperature the efficiency of the panel increases. As an example a cell that produces 0.6A at 25 °C will produce 0.68A at 0 °C.

( December 22 was the shortest day 2014 )

Plotly from 28 december - sun and clouds