Its a strange phenomenon, actually, calculating in ‘primary energy’: You have coal, which as such is not so useful, only if you burn it you can get some energy out. Thats the actual energy that is supplied to you, for instance as electricity for a direct end-use function. But then a strange arguing follows: Theoretically there could have been more energy, in coal, which is what is called primary energy, the actual energy value of the coal. Its not there, but could have been.
What should count in fact is the value which is distributed and comes out of our electricity socket, in a useful way. The rest is pure theory. It only helps fossil fuels give a better image , compared to others. Which are downplayed, as we will see below.
On top of that: since the theoretical potential is higher, a lot of effort is put in innovation to increase the efficiency. Its living by hope: ‘we might continue using them if only we could increase the efficiency’ . The result is also that every other potential energy source is mirrored with the unreachable but theoretical potentials of fossil fuels.
How come? Lets have a look at the definitions of primary energy as given by respected organisations: The Dutch energy research centre, and The Dutch energy grid managing company write: (primary energy is-) energy in the form as is found in the original yielded energy carrier, for instance coal, oil, gas , uranium.
This definitions is limited to fossils only. And as a result everything is recalculated for the theoretical values of fossils. Mostly even not in MJ , but in tonnes oil equivalents…. Which is really a prehistoric approach.
And Wikipedia : “Primary energy is energy found in nature that has not been subjected to any conversion or transformation process. It is energy contained in raw fuels as well as other forms of energy received as input to a system. “
‘ found in nature‘ ? : how nice, look what I found, free energy….! And “ not subject to any conversion process” This is unheard: They just are, pop out without any previous process history?
The weird thing is that if solar energy comes into play in primary energy calculations, say with PV panels, then the output is counted after the conversion process. It would be logical that the original source “found in nature” , namely Solar radiation, should also be used as starting point , being the actual input to the system. Which would raise the ‘ primary energy’ of Solar energy by around a factor 6. Therefore: very inconsistent , the primary energy calculations.
In detailed descriptions with the definitions sometimes renewable energy is mentioned, but always treated as if just another source, while they never make the link to the fact that fossils are a conversion from solar energy as well.  A nice way to hide the truth in a system. Its the same with non-renewable materials: minerals and metals: they just are there, ready for grabbing, and ‘they cant be renewed ‘ is the claim in for instance circular economy. So we can neglect the impact of their depletion….
So where does the term Primary Energy originate from, where and when is that introduced? That was not so easy to find out. The source seems a report by the UN statistical office, which had to find ways to make energy comparisons between fuels and countries.  :
At its nineteenth session, the Statistical Commission proposed the convening of an expert group to consider the preparation of an international classification of energy and the adoption of a common unit of measurement for interfuel comparisons”.
On page 8 we find the recommendations:
Primary energy should be used to designate energy from sources that involve only extraction or capture , with or without separation from contiguous,material, cleaning or grading, before the energy embodied that source can be converted into heat or mechanical work.
Secondary energy should be used to designate energy from all sources of energy that result from transformation of primary sources.
In other words: secondary energy can be the electricity after burning coal or gas .
Another case is the energy captured by solar frames, wind motors and heat pumps by industry, commerce or private citizens. To the extent that such energy displaces energy previously bought on the market, it is a decrement highly relevant to projections of future demands.
Here renewable energy is seen as replacement of fossil fuels, against which they are measured . But this implies referring to a system that has been designed for the imperfections of fossil resources. At least today , where we face a complete transition for renewable energies, it should be turned around: fossil fuels adapted to the ( imperfect) performance of renewables. Not the other way around. Of course there is a lock in, in all calculations as we know today ( like BP statistics etc (.), but if we don’t define the assumptions right, we will never have clear insight. The playing field should be leveled.
Recommendation 16 puts its this way:
The primary energy corresponding to the so-called renewable sources of energy should be defined as follows and applied to the output of the first stage in an energy capturing process that yields a measurable output of heat, electrical or mechanical energy:
Biomass : Heat output of the fermentation, distillation or combustion device
Photovoltaic cell : Electrical energy output
Other collecting device : Heat output of the device
Water and air: Mechanical, heat or electrical output of the device
Geothermal and ocean thermal: Heat output of capturing installation.
In other words: If we stay with the case of PV: the electricity output is the primary energy: so you convert the source, like with a PV panel, and the output is primary. Thats were the problems described in the beginning come from. The question is, why not define fossils the same way: the output ( in electricity for instance) as the primary energy: in that case everything gets simpler and more logical, and you are free from the unreachable theoretical power.
The report in itself is a massive piece of work, and it goes without any saying that the commission already realized that their recommendations were a artificial and finicking approach , as can be read in the following statement: (91 pag 26)
If – and it is at present a big if – complete data were available on useful energy, then this particular
level of accounting would be the most important one for analysing past trends in energy use and for attempting to forecast , or for studying the implications of future patterns of energy consumption.
Here in fact already its stated that its better to calculate in final energy demand.
Its a complex matter, and going through many documents using the Primary energy approach you loose yourself in all kinds of arguing and complex calculations . One example is the guidelines for normalised energy calculation for buildings, as introduced for the recent nZEB approach for NL ( called BENG) Very complex and confusing, how everything as to be brought into one calculation. But ok, its in fact the EU directory called ‘EPBD recast’  that has forced countries to calculate with these old fashioned primary energy approach. (see also the BuildUp platform for a overview how different countries deal with this )
Primary energy approach introduces a lot of inconsistency. Take for instance my laptop: no problem to operate directly on a PV panel, the output is the input, 12 Volt, and no need for two additional conversions with losses via a 220 V grid, plus adaptations for primary energy calculations based on fossil energy. If we do take that route, as we are forced by system and regulation, I would have to install more PV panels. Not that I need them, but to comply with primary energy calculations. Of course there is storage somewhere involved , but accidentally my laptop has built in storage and can function fine through the night without the sun shining or a grid connection. But that is not even relevant in calculations: primary energy calculating has nothing to do with storage, which is just a secondary issue, just like “ location” or ‘availability’ is. ( which is of course relevant for chain analyses, but not for primary energy approaches)
Its now 40 years after the UN report, entering a complete new era, in which renewable sources will take over : Everything is turned upside down: Renewable energy ( streaming energy) will become the norm, and fossil energy will be phased out, or get into a supporting role -at the most-, and should be compared and related to renewable energy, in stead of otherwise. Which will lead to a complete different way of energy calculations, in which primary energy approach only disturbs ad mystifies things. In fact , this gives us only two ways to get lost from the artificial calculation framework from last century:
Firstly: Calculating with end-use , or final- energy. As was already recognized by that same Statistical commission, and which now, 40 years later, seems the right moment to address: the energy that in its final stadium goes into the actual function that is socially wanted, as for instance our laptop.
Or : creating a level playing field by equally calculating with the input source of (nearly) all energy: Solar radiation: This is the input to to fossil fuels as well as PV panels, – and for most secondary forms as wind, waterpower ) . The sun, as the only source that net contributes to our system,without depleting it. Thats what I would prefer, it also overcomes differences in heat and electricity for instance: Therefor Solar radiation : as the real primary energy source for calculations.
 Dept. of International economic and social affairs , Statistical office Studies in methods: Series F No. 29 , “Concepts and methods , in energy statistics, with special reference to energy accounts and balances” A technical report, UN New York 1982
(cartoon: Ron Tandford)