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Heat Storage Technology

BSR Solar Technologies GmbH, jointly with the Max-Planck-Institut in Mülheim/Ruhr, has developed the thermo-chemical heat storage technology, SOLARSTORAGE^TM. The storage medium is metal hydride, which has a high heat-storage capacity. For instance, 1 kg of magnesium-hydride has the capacity to store 0.8 kWh of medium-temperature heat reversibly and practically without loss.

Storage of heat energy

The heat energy to be stored is supplied to the "high-temperature unit", a closed high-pressure system filled with magnesium hydride (MgH₂). When the system is heated up, the hydrogen is set free and is transferred to the "low-temperature unit", a closed system to store the hydrogen.

The chemical reaction taking place is:

MgH₂ —> Mg + H₂    -75kJ/mol (dissociation reaction)

Release of stored heat:

When the hydrogen is transferred back to the high-temperature unit nearly the same amount of energy stored during the dissociation reaction cycle is released.

Mg + H₂ —> MgH₂    +75kJ/mol (exothermal recombination reaction)

The advantages of the SOLARSTORAGE^TM system are as follows:

	Extremely high conversion factor of solar energy into thermal energy (= 0.8 to 0.9)
	Efficient conversion of heat into electricity via medium-temperature Stirling engine
	Reversible cycle with negligible hysteresis
	High energy density of the storage material
	Long-term heat storage without any leakage or loss
	No environmental hazard: the stored heat is as clean as the incoming solar radiation