check out this:
www.adamlhumphreys.com/~stuff/ALH_kWh_Logger.zip
I build this on an Arduino / Atmel328mini .... for my 55W Solar panel. I modified the code a little to my needs ... so it logs AH in/out and min/max voltage for each day.
The datalogger can hold this values for the last 86 days (in the atmels eeprom).
I use a ASC712 current circut (more easy) ....
My loogs look like that:
1day 13.1Vmax 12.1Vmin 0.5Amax 1.00AH inn 2.00AH out 18.00WH
A 12V 83mA Solar Panel .... ehm .... much to small! You can't run the arduino on it over time - only when the sun shines good.
A arduino with display will take about 70mA all time!