The production of a consumer product like a loaf of bread; a wind turbine or a photovoltaic cell requires inputs from all the production processes in the host country and, through international trade, from all the production processes in the world. For example a loaf of bread requires:
- Wheat which has to be milled cooked and transported.
- Transport requires fuel and vehicles, for which steel, rubber, copper & fuel for fabrication are necessary.
- Shops and bakeries need bricks, steel, cement, wood and glass; wheat production must have tractors, fertilisers, insecticides etc.
It is clearly impossible to determine the proportion of all the production processes in the world needed to produce a loaf of bread, or any other single product.
Any analysis must be based on a sub-system of the world, a sub-system for which all the inputs and outputs are known. The choice of sub-system is the first crucial step in evaluating a FUEL cost.
Three simple sub-systems of the production of a loaf of bread are shown in Figure 1.
The first is confined to the bakery and the fuel cost per loaf is the fuel delivered to the bakery divided by the number of loaves produced. The second sub-system includes the baker’s shop. The total Fuel cost is:
The third sub-system is the entire diagram and includes eight fuel inputs. As the sub-system is made larger the total fuel cost continues to increase. However, in a finite time it is not possible to take into account all the production processes in the world.
A more feasible objective is to follow each network of inputs back from the final product until it is found that the addition of the next input makes an acceptably small difference to the total fuel cost.
The choice of sub-system is one type of problem in evaluating fuel costs. Another is associated with the types of fuel included in the analysis and how these different fuels are added together.
The production and delivery of fossil fuels involves fuel consumption has to be incorporated into the fuel analysis. Producing secondary fuel supplies, such as gas and coke, wastes some of the fuel available in primary fuels. This uses have to be included too.
Most fuel analyses ignore the fuel input in the form of manpower or the calorific value of food. These difficulties are compounded by the various calorific values of different primary fuels and by the special role played by electric power in many industrial system