The A to Z of the Energy Transition: P is for Primary (vs Useful Energy )

This edition may sound rather technical and boring but if you want to understand one of the most significant drivers of the energy transition, read on. I've tried to keep it as simple and jargon free as possible.

Going back to your high school science, you will remember that there are many different types of energy: thermal, electrical, mechanical, kinetic, potential, chemical to name just six. And whilst 1 Joule represents the same quantum of energy, regardless of type, there are big differences in what you can do with it, how you store it, how you transport it and therefore how useful it is. There are also significant differences in how energy is transferred from source to end use. 

Most forms of energy are typically transported (or transmitted) processed in some form and often converted from one form of energy to another. At each stage losses are incurred. Some losses are relatively minor, such as electrical losses from high voltage transmission, at around 5%. Other process have much higher losses, a modern combined cycle gas turbine (CCGT) converts around 50-60% of the embedded energy in the gas to useful electrical energy, meaning 40-50% of the energy is wasted largely in the form of heat. And the modern internal combustion engine car converts around only 20-30% of its input into forward motion of a car, meaning a massive 70-80% is wasted.

  
So why does this matter?

First, when measuring energy use it's really important to be clear about definitions. There are complex and very detailed definitions but for the sake of keeping this brief I'm going to just cover this as simple as possible.

The Lawrence Livermore National Laboratory produce some incredibly helpful and informative Sankey diagrams. There's an example of one below.

US Energy Consumption Sankey diagrams - Source: Lawrence Livermore National Laboratory

On the left hand side the charts show all the input energy, accounting for the full energy content of all the coal, oil and gas produced, all of power and heat output of nuclear, plus the electrical generation from renewables. This is typically referred to as 'primary' energy'. Under some definitions, renewable electricity generation is scaled up to reflect the equivalent energy content of gas required for the same quantum of electricity generation. Whilst this scaling puts the proportion of renewables on a more level playing field, it artificially inflates the total measure of primary energy. The Energy Institute Statistical Review of World Energy refreshed its methodology this year to 'total supplied energy', which excludes the scale up for renewable electricity. In 2024 the world used 592 Exa Joules (that's 592 with eighteen zeros!). You can read more here: Statistical Review of World Energy Methodology.

As the chart moves from left to right it shows the various transformation processes, such as the use of coal and gas in power generation, and the associated inefficiencies. Lawrence Livermore National Laboratory define this as 'rejected energy'. I prefer the term 'wasted energy', with the remainder defined as 'energy services', or as the title of this article states, 'useful energy'. There are clearly many nuances within what is defined as wasted energy. For example, the heat from an inefficient lightbulb may be useful energy in helping to heat a home in winter, but quite the opposite in summer. But these nuances are small compared with the big picture.

Second, and far more fundamentally, these charts show the vast inefficiencies of our current energy system. The chart above shows that in 2022, two-thirds of US energy consumption was wasted. The two biggest offenders were transport (predominantly cars and trucks but this also aviation and shipping) and power generation.

  
The big point here is that the US could theoretically heat, cool and light its homes, transport goods and people and run its industries with just a third of its current energy use, if it could avoided the wasted energy.

Implications for the energy transition

Some have described this as the Primary Energy Fallacy. Most reports, be they backward looking, like the Energy Institute Stats Review, or forecasts such as the International Energy Agency (IEA) World Energy Outlook, use a measure of primary energy as their main basis. This makes sense if you want to know how much coal, oil, gas, renewables etc the world is using in a given year, but what it masks is how much less the world could use.

So how do we get to a world that uses a lot less energy to get the same level of useful work? The most significant factor is electrification. Electrification is a super power of the energy transition. Just going back to those losses from transportation in the US, an EV needs around a third of the input energy of an ICE (internal combustion engine) vehicle. Electrification of heating dramatically reduces losses. Although a conventional gas boiler has a relatively high efficiency of 80-90%, compared to a heat pump (see A is for Air source heat pump) with a typical efficiency of 300-400%, there are huge efficiencies to be gained. It also matters how the electrons are generated. Those coming from wind or solar are far more efficient than those require combustion of gas, coal or another fuel.

And beyond electrification, the overall efficiency of every aspect of the energy system helps reduce primary energy input for the same useful energy output. We've seen this in everything from LED lighting to improvements in internal combustion engine efficiency. I covered all of these aspects in far more detail under E is for energy efficiency.

The key point to take away from this topic, is that as the energy transition accelerates we have the opportunity not to replace the current energy system Joule for Joule but to create a far more efficient energy system that delivers the same and more useful energy in terms of heating, cooling, lighting, mobility and industrial processes for a LOT less input or primary energy.

So next time you hear somebody say that the world needs more energy - to power data centres, AI and the massive increase in air conditioning - make sure you ask them which sort of energy we need. Primary energy or useful energy? It really matters!

Further reading

As always, please see some further links for more reading:

What is the primary energy fallacy? by Energy Institute Fellow, Professor Jan Rosenow FEI

Energy efficiency is the key to achieving affordable, secure power in developing nations – World Bank  
Breaking down barriers to industrial energy efficiency