Hi...

Would anyone tell me about solar panel energy efficiency? And why it still uncommon?

I remember when it was less than 20%:
80% Efficient Solar Panel?! Works at Night?! | EcoGeek - Clean Technology (http://www.ecogeek.org/content/view/1329/)

Hello Fakhri_Achmad

Have a look at the link I provided below for supporting information.
At present solar cells with a maximum efficiency of around 40% are available in the market. Higher efficiencies are mainly based on research data, and promisse higher efficiencies, but these are not (yet) available in the market.

Link to Wikipedia on solar panels and energy efficiency
(http://en.wikipedia.org/wiki/Solar_cell)

When heat energy travels by convection energy is transferred from molecule to molecule?true of false

Hello Meena : please post new and unrelated questions in a new topic.
And yes : in general heat is transferred by collision of molecules.
Convection is heat transfer in a gas medium.
Conduction is heat transfer in a solid medium.
Infrared radiation is heat transfer by photons.