What is Convection and why Convection can't [simply] happen in solids?

Question Convection can't [simply] happen in solids. Why? Because there are no free molecules. Examples of convection 1.Domestic hot water system Cold water in the tanks is heated by electric element at the bottom. The hot water molecule at the bottom raises up and the cold upper molecules sinks to the bottom. These are also heated and become hot and starts to rise up. The once raised molecules are now cooler and start to sink …

…descends. The circulation continues like that provided the oven is closed. 5.Freezers/Refrigerators The liquid gas is heated by an electric element, it becomes hot and the liquid becomes a gas, which rises to the pipes around the compartments of the freezer or refrigerator. On rising this gas Gets very cooler and therefore while inside the compartments it absorbs heat from them becoming a liquid which is returned to the compressor to be heated again.