Capmix (, short for capacitive mixing, is a new technology that – similar to RED – generates electricity from the salinity gradient between two solutions. The process is based on ion-adsorption on porous electrodes. Capmix took shape in the form of a joint project of four universities (based in Italy, Spain, Poland and the Netherlands) and two companies (REDstack in the Netherlands and Mast Carbon International in England). This work was realized in a project funded by the European Union from 2010 to 2014. The aim of the project was to come up with a working prototype and a theoretical analysis of the applicability of the Capmix technology. It was determined that Capmix is a promising alternative to more common salinity gradient power technologies such as RED.

REDstack’s share of this project relates in particular to the design and early technological validation of the Capmix process. REDstack has extensive experience in the design of RED stacks, and was able to use that knowledge to create a fully functioning Capmix stack. Furthermore REDstack has the facilities to test the process with natural feed waters. Initially, this research was completed at the small test facility in Harlingen, the Netherlands, and the final stage was done at the REDstack pilot facility on the Afsluitdijk. Part of the testing included investigating the effects of the used surface water (IJssel Lake) and the necessary water treatment for an operating system.

REDstack made contributions to the Capmix project towards large scale development. To this end, the ten most promising sites in Europe were appointed and an analysis was made of the economic, social and environmental impact of each site. To a large extent, this investigation ran in parallel with the introduction of the RED technology, and the newly acquired knowledge was useful for both Capmix as well as RED. It is not yet clear which of the two technologies will take the lead in the application of SGP, or if they both find their own niche and develop independently.

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