Nathaniel Bullard

The Case for New Green Energy Units

For nearly seven decades, oil major BP has published an annual statistical review of world energy. It includes a wealth of data on what energy the world produces, along with how and where society consumes that energy. The long history of the dataset highlights key inflection points, like the growth of renewable energy. Yet the 2020 review is notable not for the growth of a new type of power but for a seemingly small change in the way energy flows are expressed—one that better reflects the way energy is produced and consumed.

BP has for decades expressed energy consumption in “million tonnes [metric tons] of oil equivalent,” which makes sense for oil, some sense for natural gas and coal, but not very much sense at all for renewable energy. Now, it expresses consumption in exajoules. (One exajoule is the equivalent to 24 million tonnes of oil equivalent and one joule is the energy required to lift an iPhone to your ear.)

Why make this change? I can think of a few reasons. The first is that millions of tons of oil is not a terribly helpful unit in terms of reflecting what energy goes into. While companies produce oil, it isn’t a product in its own right; it’s an input to other processes that produce fuels like gasoline, kerosene, and diesel along with petrochemical products.

The second is that we only consume the final result of an energy source. When driving an internal combustion engine car, we are consuming the end product of a primary energy source (oil) that has gone through a conversion process (refining) to become a fuel that we then burn (gasoline or diesel) that in turn mostly produces waste heat in the process of turning our wheels. We’re only consuming a fraction of the primary energy inherent in oil. That’s why exajoules are important; they’re what we consume.

So, let’s compare the world’s energy not in terms of what gets dug up but in terms of what is ultimately consumed. For fuels, we’ll use exajoules. For renewable energy and hydropower (which use no fuel) and nuclear power (which uses fuel, but doesn’t emit anything), we’ll use terawatt-hours of electricity. Terawatt-hours are a measure of electrical production but importantly, are also final (there’s no further conversion; an electron is an electron).

Here’s where it gets interesting. We consumed just under 500 exajoules of oil, gas, and coal last year, more than three times as much as we did in 1965. For a scale comparison, we also consumed about 88 exajoules of zero-carbon electricity last year.

These are big numbers, but they’re not growing that much. The average growth rate in oil consumption is less than 2% in the last decade; for coal, it’s less than 1%. Coal’s growth—driven by China and to a lesser extent India—looks to be a thing of the past, while oil’s growth is debatable. Gas looks steady, and much of its growth comes at the expense of coal.

Now for zero-carbon electricity, expressed in terawatt-hours: Hydropower is a fairly steady line up; nuclear plateaued but has returned to growth in the past decade, largely thanks to China. Renewables are a line of the sort that shows up in pitch decks: a hockey stick accelerating upwards (and passing nuclear).

Four decades ago, nuclear power was growing at a pace (more than 30% per year) that had total nuclear output doubling in less than three years. It’s only barely above zero now, after some years of shrinking. Hydro, likewise, doesn’t look like it’s growing much but is actually growing at a similar rate to natural gas. Then there is renewable power, which managed quite a feat for most of this century: growing at an increasing rate. At its current 10-year average annual growth rate of 16%, total renewable power generation will double in less than five years.

BP’s choice of units may seem minor, but it has major implications for how we think of energy. Units of consumption, not production, show us what we actually use; the growth rates of consumption show us where the system is dynamic, where it is static, and where it is shrinking. These are new units for a new world, where renewables are not only the fastest-growing new source of energy, but also the single largest contributor to meeting new energy demand.