A storage heater or heat bank (Australia) is an electrical heater which stores thermal energy during the evening, or at night when electricity is available at lower cost, and releases the heat during the day as required. Alternatively, solar storage heaters are designed to store solar energy as heat, to be released during the night or other periods where it is required, often making it more cost effective than selling surplus electricity to the grid and buying it back at night. Principle of operation Storage heaters are typically composed of clay bricks or other ceramic material (grog), of concrete walls, or of water containers. There are also special materials such as feolite. This material serves as a heat storage medium. There are electrical heating elements embedded in the material which can be switched on to heat the storage medium and thus to store energy. The stored heat is given off continuously (through thermal radiation and convection). To speed up the heat transfer, storage heaters may come equipped with mechanical fans that can move air through the heater; see the section on fan-assisted storage heaters. Types of storage heater High heat retention storage heaters High heat retention storage heaters (HHRSH) are the newest and most advanced storage heaters on the market. Dimplex pioneered this technology with the Quantum, which led to a new category being created in SAP. The UK government approved software which calculates the heating system that can be used in a new building or refurbishment. High heat retention storage heaters are able to retain more heat than traditional storage heaters, with a minimum of 45% heat retention 24 hours after a full charge. This significantly reduces the heat wasted during the day, and is achieved through improved insulation. High heat retention storage heaters also include smart controls and monitor climatic conditions to estimate future heat demand, making them much more responsive to changes in their environment than traditional storage heaters. All high heat retention storage heaters are also Lot 20 compliant, in line with the EcoDesign regulations which came into force on 1 January 2018. Regulations Lot 20 is an EU legislation that was designed to remove inefficient heating technologies from the market and reduce the energy used by products that heat our homes. The goal of the legislation is to achieve the UK's overall carbon reduction targets and has been in place since 1 January 2018. It