  Blue energy represents a large reservoir of renewable osmotic energy that can
be converted into electricity by reverse electrodialysis (RED). This method is
based on ion-exchange membrane. Before large scale production, these membranes
are compared on very small samples on the basis of the power they enable to
produce per unit area. Through a systematic study of the effect of the membrane
size on the power density, we show experimentally that for classical
measurement cells, the power density strongly varies with the size of the
membrane: the smaller the membrane, the higher the power density. The results
are explained by a theoretical modeling which describes the effect of the
access resistance at the scale of the membrane. Based on this work, a few
recommendations are formulated to perform scalable and meaningful measurements
of membrane resistance and power density.
