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Latent heat-storage units (solar heating)

Latent heat-storage units are storing thermal energy in latent (= hidden, dormant) mode by changing the state of aggregation of the storage medium. Applicable storage media are called "phase change materials" (PCM).

Such PCMs are by way of example paraffin waxes (as used for chandles); during melting they absorb high amounts of thermal energy ("loading" phase), which they emit again during congealing ("unloading" phase). Some salts show a similar behaviour. The temperature of the PCM itself changes during "loading" only a little before reaching the melting point.

Today different types of PCM based on salts or paraffin waxes are available at the market, each designed for specific applications and temperature ranges. Some PCM are used e.g. in building materials to allow automatic temperature regulation: on hot days they alleviate the warming of the outer walls of a building, on colder days they emit the stored warmth again. PCMs permit also mobile utilizing of waste heat by driving the loaded PCM tanks to the point of consumption.

The application of latent heat-storage units to long-term storing of solar heating energy has been discussed for some time now, but hasn't yet reached the mass market. Today available technologies are suitable primarily to large collective systems for settlements, requiring high storage volumes.

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