At a site that is tight, it may be advantageous to go with the silo shape. The floor area is reasonable for underfloor extraction. The volume is large.But the wall pressure on the silo portion is huge. This dictates extremely large footings or in many locations, pilings to hold the load. This problem grows worse in poorer soil loading, such as along most waterways. The cost per unit stored will be much higher than that of the sphere. This is more traditional in shape. The spherical shape in the past was too hard to form and/or build. With the Monolithic System that is no longer the case. (Larry Byrne)