Storage
From OGame Wiki
The storage is the maximum amount of a particular resource you can have on a planet before production stops. It can be increased by leveling up the resource's tank structure.
Note: Despite popular belief, lack of storage silos will not leave you without the rest of the resources if for example your fleet had transported them to the planet, just the production of particular resource will stop. That means that you can store resources on planets without any of the silos.
