Thank you for the answers.
One more question is it possible to replace the nissan leaf original small 12v battery with a bigger capacity one from the petrol or diesel car ?
or the car will somehow struggle with the regular car battery ?
You can use a larger 12-volt battery, if you want to find a way to mount it. The car will periodically charge the 12-volt battery from the main battery when it is parked, but the original 12-volt battery may be too small to support your continuous load between charges. The solar panel just provides enough in bright sun to overcome the residual load of various modules in the car--it will not keep the battery charged with accessories on.
I replaced the Nissan original 12-volt battery in my 2011 (when it failed) with an AGM (sealed) deep cycle battery that fit the original tray. The deep cycle was much better for the discharge/charge cycles of the LEAF. When the original battery in my 2015 failed, I also replaced it with a Yellow-top Optima AGM deep cycle battery (group size 51R fits in the tray and has terminals in proper locations).