The main findings of the studies on closed adsorption storage, as reported by EMPA in Switzerland, are the following:

• The heat capacity of the NaOH storage (2 stages) compared to a water storage is about 3 times better for domestic hot water (DHW) and about 6 times better for heating purposes (heating floor). The calculations are made for a building located in central Europe.

• The heat capacity of a one stage (one process unit per storage) system especially for DHW is insufficient. The above specified heat capacity is only given with a second stage.

• The storage is intended to be charged with solar energy with no auxiliary heater. To avoid too big storage volumes, the buildings must be built in low energy standard like “Passive House” or “Minergie” (Swiss standard).

• NaOH — lye as sorbent has a good cost benefit ratio. NaOH is a by-product of the PVC production and costs only about 250€/m3. The estimated volume of NaOH — lye for a passive house is about 5 m3. This figure depends strongly on the climate and the used solar collector area.

• The separation of the process units and the tanks into independent modules, leads to a simple control strategy. In the process unit, there are only small amounts of mass of the chemical process involved. This allows continuous operation.