Latent heat stores use physical properties, i.e.. high heat and low melting point of some compounds. Cartridges containing salt solutions, Waxes, paraffins or organic acids, are heated by systems using solar energy to a melting point = 30 – 50°C, to then, when the temperature drops, going from liquid to solid state, give off a large charge of heat. The most commonly used hydrated salts include: calcium chloride (Temp. melting ok. 38°C), heat of melting —174,5 kJ/kg, sodium carbonate (Temp. melting ok. 36°C), melting heat — 7950 kJ/kg, sodium thiosulphate (Temp. melting ok. 52,2°C), melting heat — 6750 kJ/kg, sodium sulphate — Glauber salt (Temp. melting ok. 32°C), melting heat — 8100 kJ/kg - most commonly used. Storage tanks containing sufficient heat for a few days for a single-family house weigh from 3 into 10 t. These are containers with plastic or vertically positioned capsules, transversely densely ribbed pipes, in which the salt heating factor and the heat extracting factor are forced.
Apart from substances that change the state of matter on a principle: solid - liquid, in many experiments, substances which change only the form of the crystallization on principle are considered: permanent - permanent (pentaerythritol), or substances that change from a liquid to a gas phase, which is, however, the least convenient.
Phase change heat storage tanks: a powered by a liquid medium, a heat reception by an air stream or vice versa, b) powered and discharged by liquid medium
Chemical warehouses provide the best technical parameters. Photosynthesis is a type of such storage, which has been performed perfectly in nature for thousands of years. Thermo-chemical storage facilities are still in the experimental phase, but surely soon all technical problems will be overcome. In warehouses of this type, the possibility of storing and recovering thermal energy by reversible endo reactions is used- and exothermic.
One of the most interesting and cheap storage devices is a chemical storage tank using calcium oxide, which works on the principle of the following scheme
Chemical storage tanks have the ability to accumulate heat in small devices, which even allows the transport of heat by container method over long distances.
All the methods presented above are methods of accumulating heat briefly- and medium-term.