An energy flow diagram is a type of Sankey diagram that tracks the flow of energy from raw or primary sources of energy all the way till they become the useful service that a consumer needs. Along the way the energy flow diagram identifies all the energy losses and energy wastage that take place, proving a very important tool for energy policy.
Primary sources of energy are raw sources of energy like coal, crude oil, natural gas, wood, water, etc. which has not yet been converted into anything. This primary energy is then converted to secondary energy, or a more usable form of energy, e.g. electricity, diesel, petrol, etc. There are losses during this conversion process.
Secondary energy is then transmitted to consumers to be used. During this transmission, there are transmission and distribution losses
When the consumers receive this energy, in the form of electricity, gas, petrol, etc., it is called final energy. Unfortunately, many countries around the world stop collecting energy usage data at this stage. But what comes after this stage is extremely important to build a complete energy flow diagram and to understand the energy efficiency of a country or the tremendous amount of energy wastage taking place within its borders.
When the consumers receive what is called final energy, that energy is not the final product. The consumers don’t want energy. They actually want a service, like light, cooling, heating, food, entertainment, productivity, mobility, etc. They use the energy to fuel the appliances, machines, cars, etc. that will provide them that service. So there are also conversion losses at this stage based on the energy efficiency of the appliances, vehicles or machines used. And also based on the behaviour of the consumer.
When you track the energy flow of every primary energy consumed inside a country, you can build or compile an energy flow diagram for your country, or even for your office, home, factory or organization. As soon as you compile an energy flow diagram, you can now see all the sources of wastage and energy losses for your country or organization. And once you can see the energy wastage, you can finally do something about it.
As an example, check out the energy flow diagram I compiled for Pakistan some years back. The energy flow diagram showed that Pakistan was wasting at least 83% of the energy supplied to it due to inefficient power generation, inefficient consumer behaviour and appliances and due to transmission & distribution losses in gas and electricity supply.