The molecules of a solid are held closely together.They cannot move freely , therefore. convection is not possible in solids.
Convection is a nonessential heat transfer mechanism in solids because solids do not transport thermal energy via collective, bulk motions of constituent particles across macroscopic length scales.
Convection is a bulk flow of material---the collective, macroscopic motion of uncountably many particles, e.g., a gust of wind or the flow of lava. Specifically, convection occurs when a strong temperature gradient drives bulk flows of a fluid (liquid, gas, or plasma) from regions of higher to lower temperature, thus transporting thermal energy en masse. This is in stark contrast to conduction, the typical microscopic mode of thermal energy transfer.
Conduction is when heat is transferred incrementally from a region of higher temperature to a region of lower temperature due to to the wiggling, jiggling, and collisions of many neighboring atoms and molecules in a material: the kinetic energy at the microscale slowly diffuses outward from the higher-temperature region due to these motions. Whereas in convection both mass and thermal energy were transported away from the source, in conduction only thermal energy is transported---although the particles are jiggling about at the microscale, the collective particle behavior at the macroscale is stationary.
Example: Convection and Conduction in Everyday Life
On a hot summer day, the sun radiatively heats up the outside of your house (solid), which conduct the heat towards the cooler inside. By the afternoon, the air (gas) in the house has conducted an abundance of thermal energy from the walls and is starting to feel very warm. The glass of water (liquid) with ice cubes you left on the counter an hour ago has conducted thermal energy from the air and is now warm as well---no more ice cubes! When it starts to get too hot to stand, you to turn on the air conditioner---this convectively cools the house to a more tolerable temperature.