British Energy Demand, and Professor MacKay’s estimate of it: an explanation of the differences

Posted by – 2010/06/29

In “Sustainable Energy Without the Hot Air”, Professor MacKay compares an energy demand of 195 kWh/d with his calculated British renewable resource of 180 kWh/d, and comes to the conclusion that Britain cannot power itself from renewables. But in reality, British energy demand is 155 Mtoe/y. That’s the confirmed 2008 number, from the official Digest of UK Energy Statistics. (pdf, see Table 1.1, Final Consumption minus Non-energy use). That’s less than half the demand figure used in the book, when looking at whether his calculated renewable resource is enough. When we compare the renewable resource with the current demand figure, we see that the resource is more than double current energy demand: and that’s before any energy efficiency measures. And that makes a huge difference: by using the real figure for demand, we see that the UK renewable resource is much higher than current energy demand, so Britain could comfortably power itself from its own renewables.

Here at EnergyNumbers, we emphatically and enthusiastically support Professor MacKay’s aspiration for an informed public discussion about energy: and in that co-operative spirit, let’s take a look at the facts and the numbers.

Perhaps you’re wondering why the official demand figure doesn’t look like the one in the book. Indeed, there are several figures for demand in the book, and that’s not one of them. Let’s look at the differences.

Here we have two bars — the one on the right is our current energy demand of 82 kWh/d; to the left of it is Professor MacKay’s 195 kWh/d figure for energy demand. That 195 kWh/d is presented as the typical demand of an affluent adult: one, it turns out, with an extreme energy consumption. Such an exaggerated demand has mislead the book’s readers into thinking that Britain’s huge renewable resource cannot meet all our energy needs. It’s very misleading to compare an extreme consumption with an average supply. I suppose we could compare the exceptionally high demand of the richest in society, with the very best supply, if we we suspect that think that they might cut themselves off from the National Grid to set up a “grid for the rich” (with gold-plated cables?). That’s silly. Let’s not do that. Let’s compare average demand with average supply, or (amounting to the same thing) total demand and total supply. That 195 kWh/d also includes the energy embodied in imports: energy which is generated and consumed abroad, to make the things we import — for example, the energy involved in mining copper, or making fridges. We don’t supply the energy for that assembly, any more than we provide the copper (not many copper mines in Britain). We may wish to avoid being net importers of electricity or fuel, for strategic security, but that’s completely different to embodied energy. We don’t balance all our imports of embodied energy with matching exports, any more than we do balance imports and exports of embodied copper, embodied water, or embedded anything else.

Let’s look at how our real energy demand of 82 kWh/d compares to the demand figure of 195 kWh/d that Professor MacKay uses to assess whether we have enough renewable resources.

Over-estimate: 73 kWh/d
Cooling towers and other conversion losses: 27 kWh/d
Other supply-side losses: 16 kWh/d
Efficiency savings when making the five plans that add up: 14 kWh/d 82 kWh/d GB Energy Demand
Energy demand used when making the five plans that add up: 68 kWh/d


195 kWh/d is the demand figure Professor MacKay uses when looking at whether we have sufficient renewable resources (p103). But on the very next page, when looking at current energy consumption, he gives a figure of 125 kWh/d (p104). He then takes away some of the losses within the energy industry itself, the conversion losses, which includes the huge amount of heat we waste in cooling towers to give 98 kWh/d (p116). And finally, when building his own scenarios, he uses a figure of 68 kWh/d (p204). Those figures, together with the 82 kWh/d of actual current demand, are shown to the left.

125 kWh/d is indeed the amount of power contained in Britain’s total fuel consumption, so that is at least a real-world figure, albeit one that’s still larger than our real energy demand. It’s larger, because in addition to our energy demand, it contains all the power we waste across the energy industry before it reaches the customer.

The 98 kWh/d number is more representative of current demand. It includes demand, and some waste. After all, some energy will always get used by the power industry itself, however it’s made, and although thermal plant (coal, gas, nuclear, biomass, geothermal) is very inefficient in throwing away much of the energy as waste heat, any energy delivery system will have losses: for example, however we generate electricity, around 7% of it is wasted in the transmission and distribution system. But in that 98 kWh/d there’s a lot of other waste that wouldn’t need to be generated in a decarbonised Britain, such as energy use by oil refineries. So both of those figures reflect the inefficiencies built into the way we currently generate our energy, and neither are representative of demand within our future low-carbon society.

Our current energy demand of 82 kWh/d would be reduced by about 9 kWh/d simply by electrifying cars. That and other modest energy efficiency measures give us us Professor MacKay’s target demand of 68 kWh/d. There are lots of opportunity for other energy efficiencies in there, but also the possibility that rising incomes will cause energy demand to rise.

In conclusion, to assess the potential of Britain’s renewables, as well as to set a figure for building a plan that adds up, anywhere in the range 46 kWh/d to 80 kWh/d would be reasonable — it’s a question of how much money is invested in energy generation, relative to the amount invested in energy efficiency. In contrast, the artificially inflated demand figure of 195 kWh/d is nowhere near our real energy demand, and has mislead people into believing the myth that Britain’s energy demand exceeds its renewable resource, whereas the reverse is true: our renewable resource is much greater than our energy demand.

7 Comments on British Energy Demand, and Professor MacKay’s estimate of it: an explanation of the differences

  1. New:: British Energy Demand, and Professor MacKay’s estimate of it: an explanation of the differences http://j.mp/aqHvpQ

  2. Patrick Stewart says:

    To be fair, that comparison on page 103 is between his two ballpark figures based on back of an envelope estimates. His actual conclusions on what is and isn’t possible are much later in the book (page 203 onwards), but as you seem to half-acknowledge above, on the following pages (104 and 107) he compares both of these estimates to official figures. He finds that he overestimated consumption by about 50% as compared to the same DTI figures you’re using except from 2006 rather than 2008; mostly by including the energy used to make things that isn’t expended in the UK. So pretty much your entire article is already in the book. He uses those corrected figures, with further reductions due to efficiency, in the rest of the book, including in his actual conclusions.
    What you haven’t written about at all is that he also finds that his total renewable energy potential estimates were very optimistic, about 3–10 times higher than similar estimates by several other groups.

    I don’t really know why I’m posting this, you’re clearly already aware of it, it’s in you graphs; I just can’t understand how you can complain about Mackay inflating his figures while also being aware that they’re lower than yours in his conclusions on pg 204. If you actually read the text on page 103 it clearly says “Now we will see if these estimates are correct”, not “so here I have conclusively proved renewables are insufficient”

  3. admin says:

    Hello Patrick,

    I seem to have failed to get the gist of the piece across to you, which is a shame. I’ll try to phrase it differently. Let me know if this helps.

    The numbers in the first third of Professor MacKay’s book all lead to the conclusion on page 103 that even if we used all of our renewable resource to its technical maximum, ignoring economic, social and environmental constraints, then it is not enough to meet our energy demand. And that (as he writes later in the book) this applies to Europe too — he writes: “Europe, like Britain, cannot live off its own renewables”.

    And yet the figures on 103 are wrong — we all agree on that — you, me, David, the official statistics. So any conclusion based on them must be in doubt.

    Indeed, there are plenty of reasons for doubt — because in addition to the inflated demand, the first third of the book also contains economic, social, and environmental constraints on supply, despite the statement to the contrary (I’ll write a bit more about the supply side in a new article, later). So those are not about the physics of the thing at all — they’re opinions. So, we have an inflated demand, and a set of political opinions on supply. That’s not (in Professor MacKay’s words) “what the laws of physics say about the limits of sustainable energy”.

    As it turns out, Britain’s renewable resource is an order of magnitude higher than our energy demand.

    And so Britain, (just like Europe and the whole world) can get 100% of its energy from renewable resources.

    Now, as that’s fundamentally different to Professor MacKay’s conclusion, I think it’s pretty important. Because it means that we have very real choices about the next 40 years. We can choose nuclear or CCS as transition technologies if we want — but we don’t have to have either of them. They are only options, not necessities.

  4. […] claims that the UK’s energy demand figure is 195 kWh/d – but the true demand figure is 82 kWh/d and can be readily reduced with efficiency measures and EVs. Therefore the UK can quite realistically be powered by 100% renewable energy – even using […]

  5. Robert says:

    Good piece Andrew. And please also see:

    Shock: “Food supply could blot out countryside, warns government scientist” > http://bit.ly/rrTZPe

  6. […] of “school boy” errors, both in terms of overestimating the UK’s energy consumption (see here), preposterously suggesting Uranium from seawater as a plausible energy option (debunked by Barti […]

  7. Kevin Graham says:

    Hi,

    The link to ‘Digest of UK Energy Statistics’ is broken — it has been moved to http://webarchive.nationalarchives.gov.uk/20130109092117/http://decc.gov.uk/assets/decc/statistics/publications/dukes/dukes08.pdf — would you be able to update the link?

    Thanks.

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