Method of Determining the Filling Level of a Solid Ammonia Storage Medium in an Ammonia Storage Container

A method of determining an average degree of saturation with ammonia (X) of a solid ammonia storage medium porous or not and capable of ad- or absorbing and desorbing ammonia reversibly in an storage container having a container volume (Vcon) and essentially free of gases other than gaseous ammonia, wherein a part of the container volume (Vcon) is occupied by said ammonia having a pressure (p) and defines a free volume (Vfree), said container having at least one opening through which ammonia flows out of the container with a flow (f), wherein the free volume (Vfree), the pressure (p) and the flow (f) vary with time (t), the method comprising:

• sampling n pairs ((fi, pi), (Fi, pi)) of flows (fi), or accumulated flows (Fi), and pressures (pi) at a sequence of points of time (ti), i=1 . . . n and n≧2;
• determining an estimate volume value (Vfit) on the basis of the sampled pairs ((fi, pi), (Fi, pi));
• and
• determining the average degree of saturation with ammonia (X) of the ammonia storage medium by applying a predetermined relationship (Rel) between a plurality of estimate volume values (Vfit) and a plurality of values of the average degree of saturation with ammonia (X) of the ammonia storage medium to the determined estimate volume value (Vfit).