Is solubility of KHCO3 is greater than NaHCO3 ? if yes than reason .

Dear student 

Higher the hydration energy, greater in the solubility.
Higher the lattice energy, difficult to break the lattice and hence the solubility is lesser. 
The actual reason for having higher solubility of potassium bicarbonate over sodium bicarbonate is due to decrease in lattice energy more rapidly over then their hydration energy down the group. 
As hydration energy suppose to be more for smaller cation (Na) but the ultimate solubility of compounds comes from the balance between the hydration and lattice energy.