To describe the flows of energy and matter in a system, a modeling language, called 'energy system diagram', has been developed. Systems are made up of forces and energy pathways: the former are causal actions, the latter represent how and where these forces are directed. The symbols used in energy diagrams are summarized in Figure 1.
The emergy concept was developed with hierarchical webs in mind (see Figure 2). In these webs, quantity of energy associated with each transformation decreases at each step in the process. Every transformation is accompanied by production of 'dispersed' heat.
In the energy diagram the productive units on the left produce goods and services for those on the right which return materials and control to the left. The different units reinforce each other so that the whole system self-organizes and maximizes power. Energy is transformed from left to right and in each transformation the output has less energy but of higher quality and controls other units of the system. To create quality on the right, a great amount of low-quality energy is necessary. The diagrams show an energy hierarchy with step-wise convergence from left to right. In a food web (see Figure 2), the
Energy sources from outside the system are indicated with a circle. Inside the system we find production processes that transform energy of low quality into of higher quality.
The energy flow produced is consumed by subsystems indicated with a hexagon. There are places where resources are stored, that we call storages.
In real processes, all transformations are accompanied by energy degradation that is indicated by the symbol of the heat sink.
Energy storage tank
Energy storage tank
Consumption subsystem i
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