Costs of bulk storage

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As a rough rule of thumb, the costs of modern bulk grain storage and handling facilities can be broken down roughly as follows:

Obviously, there are many instances where storage costs are much less than 40% - for instance in high throughput facilities where the 'storage' component is no more than a shortterm buffer to allow optimisation of the use of the handling equipment.

But in true 'storage' situations, where the purpose of the facility is to hold grain for an extended period of time, it is generally the case that the storage structures account for the largest component of the total cost. Thus it is normal practice to develop a design for a grain handling facility around the storage component; in other words to estimate the storage volume required, evaluate the type of store best suited to the requirements, and then to design the conveying and other systems to suit.

The cost of a store depends to such an extent on 'unit size' (i.e. the size of each individual bin or storage unit) and on locality (i.e. cost and availability of labour and materials), that the optimum solution for one given set of circumstances may be quite different to another. However as a rule of thumb, the following points may be helpful (based on 1992 costs):

• Bunker storage is the lowest cost storage available. It is also the quickest to build, and thus provides an ideal solution for emergency storage purposes. The construction cost can be as low as US$2.00 per tonne, depending on topography, drainage requirements etc. Operating costs can be high, and are to a large extent dependent upon the local cost of labour. Plastic covers may cost as much as US$2.00 per tonne or as little as US$0.50 per tonne, depending on material used. Heavy duty PVC covers can be expected to last three or more seasons (depending on the rate of Ultra Violet degradation), while lighter weight polyethylene covers are best replaced each season.
• The larger the size of a storage unit, the lower is its cost per tonne of capacity; current prices for large (greater than 5000 tonne) tank stores in developed countries are in the range of $US25 to $US35 per tonne, excluding handling equipment. Smaller tanks of 1000 or 2000 tonnes capacity may cost $US40 per tonne.
• In terms of cost per tonne, flat bottomed tank storage is generally cheaper than sheds or warehouses, even for stores of 20,000 to 30,000 tonnes capacity. There are few instances where unit volumes larger than this are justified, bearing in mind the difficulties of segregating grain in warehouse type stores.
• Tall hopper-bottom silos are cost justified in high throughput situations, but their cost (per tonne) is likely to be at least twice that of tank storage. Costs of $75 to $100 per tonne (or more in some instances) can be expected.
• The extra costs associated with building sealed storage facilities are negligible if they are properly designed.

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