If you follow news about climate change, you’ve probably seen the term “primary energy”.

This phrase refers to the raw energy in fuels and natural resources – the energy content of oil in a barrel, gas in a pipeline, or sunlight hitting a solar panel.

Primary energy is often used to show how much energy humanity uses. The numbers are staggering — billions of tonnes of coal, oil and gas. When graphed, zero-emission options such as renewables and nuclear seem tiny and the sheer bulk of fossil fuels too huge to ever shift. Australia still gets more than 90% of its primary energy from fossil fuels.

But this is misleading. The reason is that truly enormous amounts of energy contained in fossil fuels go to waste. As the world goes electric, it will need much less primary energy for the same result.

From orange to orange juice

To make a glass of orange juice, you start with a whole orange. That’s primary energy. But after peeling, squeezing and straining, the bit we want – the juice – ends up in the glass. This is known as useful energy.

What we actually care about isn’t primary energy – it’s useful energy, the chunk of primary energy that actually powers our appliances, heats our buildings or turns our wheels.

Primary energy and useful energy are often very different. To get energy to our homes, cars or factories, it must first be converted, transported and delivered. Along the way, a surprisingly large fraction is lost – especially from fossil fuels.

Coal power stations burn coal to produce steam to spin turbines to make electricity. Energy is lost every step of the way. As a result, only 35–41% of the energy in coal ends up converted into electricity.

Burning fossil fuels is inherently wasteful. It’s like carrying water in a bucket full of holes — you start with a lot, but by the time it reaches your glass, most has leaked away.

Primary energy has a counting problem

Global energy statistics make renewables look smaller than they really are, not because they produce less electricity, but because of the way primary energy is counted.

Measuring primary energy involves complex assumptions and calculation methods that can lead to unwarranted conclusions.

Take a simple example. Coal, nuclear and solar can all deliver the same 100 units of electricity. But in statistics compiled by the International Energy Agency or European Union, coal and nuclear each show up as 303 units of “primary energy”, while solar shows only 100 units.

This is because the wasted heat from coal and nuclear is counted, but the free fuel of sunlight and wind isn’t.

The result? On paper, renewables look substantially smaller than they really are.

Efficiency, efficiency, efficiency

When we compare energy sources, looking at raw numbers only tells part of the story. For coal, gas, nuclear and biomass power stations, the amount of primary energy used depends on how much potential heat is in the fuel and how efficiently the plant converts this heat into electricity.

When coal is measured on fuel density and conversion, it does well. But by the time coal is dug up, transported, refined, burned and electricity produced and transmitted, much of this potential is lost as waste heat. Older coal power plants are particularly inefficient.

At first glance, solar panels look weak by comparison. They only convert about 20% of sunlight into electricity, while wind turbines seem about as strong as coal, converting about 40% of the energy in wind into electricity.

But solar and wind generate electricity directly. There’s no need to supply fuel, so we avoid the massive conversion losses of thermal power plants or internal combustion engines.

This means that while solar and wind “efficiency” numbers look lower, these energy sources often deliver more usable energy per unit of primary energy than coal does.

In Australia, the economics are now firmly with solar and wind. Even without subsidies, they’re the cheapest way to build new electricity generation, beating coal and gas.

Electrification plugs the leaky bucket

There’s even better news. Across heating, transport and industry, switching from fossil fuels to electric options gives a major boost to energy efficiency, slashing how much energy we need for the same outcome.

Petrol cars convert just 16–25% of the energy in the fuel into actual motion. The rest is wasted — mostly as heat from the engine or as power is transferred to the wheels.

Electric vehicles are much more efficient, using 87–91% of energy supplied by the battery and regenerative braking to move.

Hot water heat pumps are vastly more efficient than gas hot water. For every unit of electricity used, heat pumps deliver 3–5 units of heat. That is, they’re 300–500% efficient. By contrast, gas heaters can have efficiencies between 30% and 80%.

Electricity is a much more efficient way to heat air than gas. Modern gas heaters still waste 10–40% of the heat they generate. Reverse-cycle air conditioners are much more efficient and are the cheapest way to heat a space.

Electricity is also a more efficient way to cook. Induction cooktops transfer 84% of the energy to the pan, compared with 71% for electric coils and just 40% for gas burners.

Going electric is like swapping a leaky bucket for a shiny new one with no holes. Most of the energy you put in is energy you can actually use.

Useful energy, not primary energy

Graphs of primary energy make it seem almost impossible to end our long reliance on fossil fuels.

But primary energy doesn’t really matter. If we focus instead on useful energy, the task ahead is much more doable. Instead of asking how we can replace all of today’s primary energy, the real question is how much useful energy we need, and how clean electricity can provide it more efficiently. Clean, efficient electric options make it possible to double global GDP by 2050 – while using 36% less primary energy.

Renewables, storage and electrification make it possible to deliver energy much more efficiently. This means renewables don’t have to replace every joule of potential fossil fuel energy – just the part we actually use, with far less waste and far fewer emissions.