Category “Energy”

So what’s the potential of renewables, anyway?

Last time I wrote a bit about the outlook for future global oil supplies. Let’s try a similar exercise for renewables.

In 2010, we humans used fossil fuels at an annual rate of 400 EJ (1 exojoule = 10^18 joules), which is equivalent to about 13 TW (1 terawatt = 10^12 watts). In raw thermodynamic terms (ie ignoring the capital costs, and the fact that it takes energy to build and maintain the generating capacity), would renewables be able to replace this? A quick summary of the potential of wind, solar, hydro, wave, tidal, geothermal and biofuel (photosynthesis), based on a recommended book by Vaclav Smil’s:


About 870 TW of solar radiation is transferred to global wind’s kinetic energy (Peixoto & Oort, 1992). A recent study (Marvel, Kravitz & Caldeira, 2013) finds that, in terms of sheer geophysical potential, “wind turbines placed on Earth’s surface could extract kinetic energy at a rate of at least 400 TW, whereas high-altitude wind power could extract more than 1,800 TW.” Although that all sounds like a lot, the accessible energy 80m above ground is estimated to be in the range of 72 TW (Archer & Jacobson, 2005), but we need to bear in mind that turbines need to stand about 5 rotor diameters apart. Computer simulations of a world where accessible areas are covered by 100m tall 2.5 MW turbines with capacity factors of 20% conclude that it’s possible to harnass a maximum of 78 TW (Lu McElroy & Kiviluoma, 2008). So that’s about six times our current fossil fuel use. Hurrah for wind!


About 120 PW (1 pentawatt = 10^15 watts) of solar radiation reaches the biosphere, of which about 25 PW is absorbed by land. If we knock out excluded areas like polar- and steep mountain regions we’re left with a usable flux of about 15 PW. So that’s about a thousand times our current fossil fuel use. Hurrah for sun!


We at SCENE have mixed feelings about hydro. We love the small stuff, though! The total potential of Earth’s runoff is about 10.5 TW, but only about 15% (WEC, 2007) of this is technically exploitable (before even taking the economics into account). Still, hurrah for small-scale hydro!


Wind-driven ocean waves have a kinetic energy of some 60 TW, only 3 TW of which is dissipated along coasts. Well, it’s worth a try!


Tidal energy amounts to about 3 TW, of which only 60 GW is dissipated in coastal zones. Better than nothing, especially if you’re miles away from the nearest electricity grid. Beats running a generator.


Earth’s geothermal flux is on the order of 42 TW (Sclater, Jaupart & Galson, 1980), but mostly (like 80%) in the form of low-temperature diffuse heat on ocean floor which isn’t going to help us out much. Some (Bertani, 2009) reckon that, by using steam, we can tap into 140 GW by 2050. Worth a try if you’re lucky enough to live near a resource – just look at Iceland (cheapest electricity in the world!)

Biofuel (photosynthesis)

Terrestrial (= on land) photosynthesis proceeds at a rate of about 60 TW, about 3 TW of which currently gets used for energy. Hurrah for plants!

Next time, we’ll start thinking about how much of this renewable resource is realistically available to power human lives.

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So What’s The Deal With Unconventional Fuels?

If you’re in any way involved in renewables, it’s becoming increasingly hard to ignore unconventional fuels – oil sands, heavy oil, oil shale, shale oil, coal-to-liquids and gas-to-liquids. It’s becoming evident that a new fault line is opening up between renewables on the one hand, and these high-tech hydrocarbon technologies on the other. Because both require long-term investment and high up-front capital outlays, governments and energy investors alike are increasingly having to make a choice. Because their fate is entwined with that of renewables, I’ve decided to write up a naively short summary of the main unconventional fuels – much of this is based on Kjell Aleklett’s recent and recommended book. Although it’s easy to criticise these technologies on environmental grounds, an equally important question here is, ‘how many millions of barrels of oil a day (Mb/d) can these sources provide?’. Humans currently use about 82 Mb/d, and Kjell’s group argue that global production of conventional oil is dropping by about 4 Mb/d every year. If Kjell’s group is right, then unconventionals will at the very least have to replace that by expanding output by an equivalent amount. If they can’t do that, then the case can be made that remaining liquid hydrocarbon reserves should be used very carefully and strategically to prepare for a low-oil future (by investment in renewables deployment and research, for example), rather than be squandered on consumption goods.

Oil Sands

Also called tar sands. The vast majority of it is mined in Canada’s Alberta province, through old-fashioned strip-mining, as well as cyclic steam stimulation (CSS) and a fancier technique called steam-assisted gravity drainage (SAGD). Both the IEA and Kjell’s group reckon strip-mining and in-situ methods can provide around 3.5 – 5 Mb/d by 2030.

Heavy Oil

Most of this stuff comes from Venezuela’s gigantic Orinoco Belt. Both the IEA and Kjell’s group reckon it’ll account for around 1.5 – 2 Mb/d by 2030.

Oil Shale

A ‘shale’ is a very generic rock type. ‘Oil shale’ is the name given to shale that contains kerogen, which is a catch-all phrase for insoluble hydrocarbon material (astrobiologists find kerogen in meteorites, for example). Unlike oil, kerogen is typically waxy, and needs to be processed into synthetic oil before anyone can truly go around calling it an ‘oil’. Most of it is currently mined in Estonia. The IEA reckons oil shales will contribute up to around 0.3 Mb/d by 2030.

Shale Oil

Shale oil (and shale gas) is what everyone is referring to when they talk about ‘hydraulic fracking’. It’s probably fair to say that this is the most controversial unconventional. The IEA published an estimate of 1 Mb/d by 2035, but opinions differ. Many reckon that shale oil and -gas are the future. Others think it’s a bubble.

Coal-to-Liquids (CTL)

Just what is says. 5.5 Mb/d by 2030, reckon the folks at the US-based National Petroleum Council. Kjell’s group reckon this is way of the mark though, and with the IEA, they put the 2030 forecast closer to 1 Mb/d.

Gas-to-Liquids (GTL)

Just what is says. 0.7 Mb/d by 2030 reckon the IEA, an estimate that Kjell’s group view as hugely optimistic.

Deepwater Oil

It’s probably worth saying a bit about Kjell’s estimates for future deepwater (> 500m depth) oil production as well, as this represents an important flux:

  • Gulf of Mexico: 0.8 Mb/d by 2020
  • Brasil: 3 Mb/d by 2020
  • Angola: 1.64 Mb/d by 2020
  • Nigeria: 1.40 Mb/d by 2020

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Projected global electricity sources in 2035


Source: Vivian Scott, Stuart Gilfillan, Nils Markusson, Hannah Chalmers, R. Stuart Haszeldine (2013) ‘Last chance for carbon capture and storage’, Nature Climate Change, 3, pp. 105 – 111.

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Out, damned plastic! Out, I say!



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Mull on This

Source: David J. C. MacKay

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Apocalypse, Technofix or Back-to-Nature?

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Jevon on Finite Coal

“But the new applications of coal are of an unlimited character. In the command of force, molecular and mechanical, we have the key to all the infinite varieties of change in place or kind of which nature is capable. No chemical or mechanical operation, perhaps, is quite impossible to us, and invention consists in discovering those which are useful and commercially practicable… For once it would seem as if in fuel, as the source of universal power, we had found an unlimited means of multiplying our command over nature. But alas no! The coal is itself limited in quantity; not absolutely, as regards us, but so that each year we gain our supplies with some increase of difficulty.” – Jevons, W.S. (1865), ‘The Coal Question: An Inquiry concerning the Progress of the Nation, and the Probable Exhaustion of our Coal‐Mines’, § 9, §§ 15.

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Energy Inflation & your CPI

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Volatile Meghreb Gas for the EU

Source: Laherrere, Jean (2007) in Mearns, Euan (2010), ‘North African gas supplies to the European gas market’, The Oil Drum.

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The Idiots Guide to the Future of Stuff

The Earth is suspended in a bottom-less Ocean of Oil.  That’s a good thing, since as a result oil will never run out.  People who tell you things like “oil reserves are the result of millions of years of organic matter sequestration” are liars and braggarts, and you should stop hanging out with them.

[1] Oil dominates global energy demand

[2] … most of which is used in the manufacturing sector …

[3] … to make this kind of stuff:

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