[imtringued]

One has to consider that the storage capacity of the economy isn't infinite. Charging money for storing something is a very straightforward business model. When your economy is growing the storage capacity appears endless as no storage is actually needed, you can just produce the good in the future with your expanded production capacity. Once the economy stops growing for even a single year, then you will effectively hit the storage capacity of the economy and must pay to store additional goods that are intended to be consumed in the future.