How primary energy is measured has changed across our charts | Our World in Data

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Some of the most popular charts on Our World in Data are about energy production and consumption: how much energy countries produce, how they compare per person, and what sources this energy mix comes from.<br>But when people talk about “energy”, they’re not always talking about the same thing. There are different ways of measuring energy, from the very top of the chain — for example, coal going into a power plant — to the final link in the chain — the light that eventually comes out of a lightbulb.<br>The differences between the first stage (primary energy) and the last (useful energy) can be very large, so it’s important to be clear about which metric is being referred to when people speak about data on “energy”.<br>In a previous article, I walked through the four different ways of measuring energy. I’ve included the main visualization below.<br>Download

On Our World in Data, we present data on both primary energy and secondary energy in the form of electricity generation . We would like to present final and useful energy too, but international datasets on these metrics are, unfortunately, not openly available.<br>To address this, we have tried for many years to get the International Energy Agency to make all of its data openly available.But even when it comes to primary energy , there are differences in how this is calculated. Recently, the methodology used by our main data source changed. In this article, I want to explain this change and how it affects our charts on this topic.<br>The challenge of comparing energy sources using primary energy<br>The main difference in the calculation of primary energy comes down to how we account for the energy wasted when we burn fossil fuels.<br>If you put coal into a power plant, around two-thirds of its energy value is wasted as heat, and only one-third is converted into electricity. For gas, roughly half is wasted, and half is converted to electricity. So to get 1 kilowatt-hour (kWh) of electricity out, you need to put in the equivalent of 3 kWh of coal and 2 kWh of gas. I’ve sketched this in the diagram below.<br>Download

This is not the case with non-combustible sources, such as solar, wind, and hydropower: they just deliver electricity. We just see 1 kWh of electricity output; there’s no upstream fuel input or waste along the way.<br>That means that 1 kWh of electricity from coal, 1 kWh from gas, and 1 kWh from solar will look very different when measured in primary energy terms. It would be equivalent to 3 kWh of coal, 2 kWh of gas, and 1 kWh of solar. Expressed as a share of primary energy, coal would make up half of our energy mix, gas one-third, and solar one-sixth. Even though the electricity we get out — and can actually use — is split evenly between coal, gas, and solar, each makes up one-third.<br>The old methodology: substitution method<br>Our main data source for primary energy is the Energy Institute’s Statistical Review of World Energy.1<br>It historically presented data on primary energy using the substitution method .<br>This method attempts to account for the inefficiency of fossil fuels by converting renewable and nuclear energy into their “fossil equivalents”. In other words, it asks: if this electricity had been generated from fossil fuels instead, how much fuel would have been used?<br>To get this figure, it divides renewable and nuclear electricity generation by a typical thermal power plant efficiency factor, which is around 38% to 41%. So, if a country generates 100 terawatt-hours (TWh) of electricity from solar, that amount is divided by 40% to get a “fossil equivalent” of 250 TWh.<br>This means renewable energy figures are all inflated by a factor of around 2.5.<br>The net effect of this is that non-fossil fuel sources are measured as the amount of fossil fuel inputs they would have substituted. This has two impacts:<br>Total reported primary energy is higher than reality because we have inflated the true figures for non-fossil sources (the 100 TWh of solar power generated is included in the total as 250 TWh).<br>Fossil fuels make up a smaller share of the primary energy mix than if they were measured directly. Arguably, this share is a better reflection of their contribution to energy demand, because in relative terms, it strips out some of the inefficiencies. This is still not a perfect reflection of energy demand, because it’s not based on final or useful energy.<br>The new methodology: physical energy content<br>The Energy Institute no longer publishes primary energy data based on the substitution method.<br>Instead, it’s based on the physical energy content method, giving a measure of total energy supply . In our charts, we still refer to this as primary energy.<br>The physical energy content method does not make any adjustments to solar photovoltaic (PV), wind, and hydropower generation. 100 TWh of solar electricity generation is included as 100 TWh of primary energy (rather than 250 TWh...