Tag Archives: Sustainable Energy Without the Hot Air

Seba’s Solar Revolution Part 2 (I Love Renewables. But I’m also Pro-Arithmetic)

For those interested in climate change and energy issues, the 2009 book “Sustainable Energy – Without the Hot Air” by Cambridge University Professor David MacKay published in 2009 was a revelation (made freely available online as well, and still there). MacKay provided a rigorous but accessible analysis of what it would take to wean the world off fossil fuels.

MacKay was no emotional ‘eco-warrior’ calling the faithful to arms, yet still a strong supporter of renewables. But every renewable or clean energy pathway explored in the book is deconstructed to check the validity of the underlying physics and maths. The book will have you recalling your high school science lessons, but in a fun and entertaining way. Despite it now being 10 years old, I still think “Without the Hot Air” remains a vital desk reference for anyone interested in climate and energy issues.

Tragically, MacKay died of stomach cancer at the far-too-early age of 48. The loss was even more telling as beyond his successful career in academia and his outreach into popular science, MacKay’s influence had extended into public policy sphere, resulting in him being appointed Chief Scientific Advisor to the UK Department of Energy and Climate Change in 2009.

To get an idea of MacKay’s approach to renewables, it is worth listening to his 2014 Ted Talk here. In his words: “I’m absolutely not anti-renewables. I love renewables. But I’m also pro-arithmetic”


With MacKay as my guide, we are now ready to interrogate Seba’s analysis. First thing is to choose our energy unit of measurement. As usual, the flagship energy statistics publications have their favourites, which differ. The International Energy Agency likes to use Mtoe (million tonnes of oil equivalent) while elsewhere we can find Mboe (million barrels of oil equivalent) and MBtu (million British thermal units). Throughout my blog posts on the electric vehicle revolution I focussed on kWh (kilowatt hours). Since MacKay also likes kilowatt hours, this makes life a bit easier. From Mackay’s TedTalk we also learn that the UK consumes an average of 125 kWh of energy per person a day (electricity, heat, transport, etc) and the USA about twice that at 250 kWh per person per day.

To help his audience get an intuitive grasp of what that amount of energy relates to he uses the image of a collection of light bulbs. Unusually, for MacKay, I didn’t think that was a great example since lightbulbs come in all sorts of energy efficiencies these days. But by doing a bit of basic maths backwards, it seems he is talking about 40 watt ones. So the maths goes like this: 40W equals 0.04kW. So if you leave it on for an hour, that’s 0.04kWh and multiply by 24 as its on all day or 0.96 kWh, so basically 1kWh. So 125kWh is equivalent to leaving 125 40W lightbulbs on all day.

Let’s fact check one of those numbers against primary sources just to make sure the daily  numbers are in the right ball park. The International Energy Agency (IEA)‘s publication “Key World Energy Statistics 2018” is one of the most authoritative sources of information in the energy field. On page 34, we find that total primary energy supply (TPES) in the United States in 2016 (latest data) was 6.7 tonnes of oil equivalent per person. That is for the entire year, so we need to change it into kWh and then make it per day. One tonne of oil equivalent is equal to 11,630 kWh (using the conversion tables in the same publication) or 31.9 kWh per day. Multiply, that by 6.7 and we get 213 kWh. That looks a little short, but then we need to adjust for the fact that, despite the fracking revolution, the USA is still a net importer of energy: around 10% is imported (see here). After this correction, we get 237 kWh per day. I think that is sufficiently close to 250 kWh to get a fact check seal of approval.

Now let’s fact check one of Tony Seba’s number using the same IEA report. As referenced in my last post, Tony has existing solar at 1.5% of global total energy production. The IEA report has global photovoltaic energy production at 328 terawatt hours in 2016.

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The same report also gives total primary energy supply (TPES) at 13,761 million tonnes of oil equivalent. Note that the Other category at 1.7% includes not only solar but also wind, tidal and so on. So does solar dominate ‘Other renewables’?

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To answer that question, first let’s check what 13,761 Mtoe in terawatt hours? Again from the IEA‘s conversion charts we get 1 Mtoe equal to 11.63 terawatt hours (TWh). Just as a gentle reminder we go watt, to kilowatt, to megawatt, to gigawatt, to terawatt, with each step change rising by a factor of 1,000.

Accordingly, 13,761 Mtoe equals roughly 160,000 TWh) (for a useful online unit converter see here). Divide that by 328 TWh gives us 0.2%! After this calculation, I decided I needed to fact check my fact checking, so I went away to find different sources. The renewables industry has its own multinational body called the International Renewable Energy Agency (IRENA). They put out at statistical yearbook (here).  From this we get a much more detailed statistical breakdown of the solar industry. But IRENA‘s numbers line up with the IEA. In 2016 according to IRENA, total solar energy production was 329 TWh split between 318 TWh as solar photovoltaic and 11 TWh as concentrated solar.

So Tony’s number for solar within global energy production appear to be out by a factor of five or more. So what could account for this? Some possible mistakes could be:

  • Confusing solar capacity with solar production
  • Mixing up electricity production with total energy production
  • Getting the conversion units wrong; for example, converting millions barrels (Mboe) of oil equivalent into terawatts instead of million tonnes of oil equivalent (Mtoe)
  • Using the overall non-hydro renewables number rather than that just for solar

All of the above would appear highly unlikely given Seba lives and breathes transport and energy economics. So if anyone has any ideas how one can get solar energy production to be 1.5% of the total I would love to hear from you.

At this point you may be wondering whether this is the end of this series of posts. If we are starting at 0.2% solar penetration of total energy production there is no way we will get anywhere near 100% in 2030. True, but if we take Seba’s two-year doubling metric, it only takes 8 years to go from 0.2% to 1.6% so his forecasts are only pushed out to 2038. That is still far more aggressive than any other forecast – and is still world changing. Plus wind power is going to do a significant portion of the heavy lifting in any energy transformation, a renewable source Tony strangely ignores.

And at the heart of Tony’s thesis is a truth: if costs compound down at an exponential rate, then penetration could compound up at an exponential rate. Interestingly, as I dipped back into my well-worn copy of MacKay’s “Sustainable Energy Without the Hot Air” there were certain instances where Tony’s simplistic analysis has been right and MacKay backed the wrong horse.

Before I wrap this post I also want to extract another number from the data we have: average energy production per person across the entire globe. In 2016, the world’s population stood at 7,466 million. From the IEA report above, we also know that energy production in 2016 was 160,000 TWh. Divide one by the other and we get 21,430 kWh. Divide that by 365 and we get 59 kWh per person per day.

With those numbers tucked under our belt, we are ready to look at land mass issues: a subject central to David MacKay’s analysis but one that barely features in Tony Seba’s.