This talk aims to explain why classical thermodynamics is insufficient for solids. After a review of classical equilibrium and non-equilibrium thermodynamics, two examples will be considered, grain growth and crystal plasticity, the latter one in more details. The major complication for development of thermodynamic theory for these cases was the lack of understanding of phase flow geometry. Recently, this geometry was described for dynamics of edge dislocations. Based on this finding, thermodynamics of crystal plasticity can be constructed. It includes two new thermodynamic parameters, entropy and temperature of microstructure. They have simple physical meaning: the rate of microstructure entropy coincides with the rate of slip avalanches while microstructure temperature is average energy drop in a slip avalanche. Perhaps, the phase flow geometry and the corresponding thermodynamics are common for many avalanche-type phenomena.