# Understanding "total primary energy supply"

I am trying to wrap my head around the diagram and explanation here but can not understand completely how it is computed.

https://energyeducation.ca/encyclopedia/Total_primary_energy_supply For electricity it seems to be clear: measure the energy output of the power plant at the point where the power plant touches the grid lines.

But for transportation, there are two options which both sounds reasonable to me:

1. Measure the energy output of the vehicles engines.

2. Measure how much oil barrels are required to produce the gasoline to run the car engines then multiply it by 1,700 KWh (1 BOE).

Is my assumption regarding electricity correct and which of the two options is the correct one for transportation?

• What is the "it" in "For electricity it seems to be clear"? Are you trying to understand how the total primary energy supply of a power plant is measured? Because this is different than what this graphic is explaining, which is at the level of a country. Sep 20 at 19:49
• @LShaver "it" is for a country. I assume that the contribution of electricity to the TPES is the total of all the energy that power plants produce, and the definition of "produce" is what I wrote in that sentence. Sep 20 at 19:56
• I think that's your misunderstanding -- the amount of electricity generated is irrelevant unless it's exported. Otherwise the TPES only cares about the raw fuel used by the power plant, and how much electricity is consumed at the end use. Sep 20 at 19:57

What the diagram is saying in the left part of the TPES is that:

Total primary energy supply is the sum of production and imports, plus or minus stock changes, minus exports and international bunker storage wikipedia

i.e. TPES is the total energy from the mined minerals (coal), and pumped fuel (oil) that is converted to other sources of energy.

The right most part details that during the conversion to

• electricity
• gasoline
• heaters there are losses.

So regarding:

For electricity it seems to be clear: measure the energy output of the power plant at the point where the power plant touches the grid lines.

Fuel is used to run the electrical generators. Approximately 35% to 45% of the energy that is expended (oil, coal or uranium) is converted to electricity. The rest become waste heat on the environment (unless coproduction of heat and power facilities exist which is another matter).

So the total energy supply $$TEPS_{el}$$ for the total electricity $$TE$$ produced assuming an average electricity conversion efficiency of $$\eta_{av}$$ would be equal to:

$$TEPS_{el}= \frac{TE}{\eta_{av}}$$

For transportation the usual method is the second that you describe. I.e. Measure how much oil barrels are required to produce the transportation fuel and convert that to BOE.

(the first option 'Measure the energy output of the engines' is not practically feasible).