Solar power plant and method and/or system of storing energy in a concentrated solar power plant

A process for storing and retrieving thermal energy using a heat transfer fluid in a heat storage system, the process comprising the steps of:

• (a) providing a flow path in a heat storage tank, said flow path for connection to a source of pressurized gas heat transfer fluid, said flow path having input and output ports for the flow of said heat transfer fluid;
• (b) loading said flow path with a storage medium comprising high temperature high thermal conductivity heat resistant solids having high heat transfer coefficient for interaction with a flow of said heat transfer fluid, said solids being in intimate contact with each other and forming a packed bed, said solids being shaped for low-pressure drop in said fluid flow, and said solids having a contour for reducing contact between said solids wherein the surface area of said solids in said bed is exposed predominantly for direct contact with said fluid flow;
• (c) receiving at one said input port a flow of said pressurized gas heat transfer fluid from said source at or near said high temperature, said heated fluid flow heating at least a selection of said solids to at or near said high temperature as said heated fluid flows in a first flow direction along said flow path in contact with said selection of solids, wherein said heated fluid is flowed at a rate selected to create a sharp front as said flowing heated fluid heats said selection of solids to at or neat said high temperature, wherein the residence time of said flowing heated fluid as it travels from one said input port to one said output port is long compared to the time required for said heating of said selection of solids, for defining said sharp front;
• and
• (d) directing a cooler flow of said heat transfer fluid in a flow direction in said flow path countercurrent to said first flow direction and at a temperature below said high temperature for thermal energy recovery, said heated selection of solids heating said cooler countercurrent flow to at or near said high temperature, said flow path presenting said heated countercurrent flow of fluid at or near said high temperature at one said output port for use in a system needing thermal energy.