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David MacKay - Running the Numbers on Reweable Energy

wdolson

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Jul 24, 2015
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I came across a TED talk given by Cambridge Physics professor David MacKay from 2013. Unfortunately he died of cancer in 2016, but he gave a last interview less than two weeks before his death.

He did some interesting analysis on how much energy you get from different types of renewable energy sources and how much energy society really needs. He came up with 125 KWh/person/day for the UK. That isn't just the energy you use at a person's house, but transportation, the energy that went into the goods used, energy used at work, other energy uses like keeping street lights running and delivering water to and taking away sewage from the home, etc.

It's a pretty big demand when you look at all the energy needed to keep modern society running.

He concluded that some places that have low population densities and a lot of energy like Australia, or even Las Vegas, solar might work, but in someplace like the UK which has few hours of sunlight throughout the year and is so far north a lot less solar energy falls on the country even when weather is clear. There is no magic bullet answer.

Just like the scale of what it will take to fully electrify cars, the scale of what it would take to supply just minimal energy needs through renewables only in at least some parts of the world is not feasible.

I find this sort of thing interesting. He felt like I do, that having a mix of renewables is a good thing, but some places are going to have to have something other than wind turbines, biofuels, and solar.

I haven't had a good set of numbers, it's been more of an intuitive thing, but I've felt for a long time that the Earth has too many people to support long term. I suspect a lot of smarter people than I am have come to the same conclusion, but there are no short term answers that aren't horrific so nobody is talking about it.

Longer term we might be able to pare down the population if every country in the world was willing to a plan to encourage birth control and educate their populations that 1 or 0 children is the ideal family size. China tried a draconian one child policy, but the population grew anyway (because it only applied to certain parts of the country). It spawned a lot of ills and the children of that generation are very different from their parents' generation.

The TED talk:
https://www.youtube.com/watch?v=E0W1ZZYIV8o
The last interview:
Idea of renewables powering UK is an 'appalling delusion' – David MacKay
 

TheTalkingMule

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Oct 20, 2012
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Germany has proven you can very easily run the 4th largest economy in the world entirely on renewable energy. Obviously they're not at 100% yet, but it's clear they're 1/4 of the way there with nothing but political will needed to go the rest of the way. Inside of 20 years they'll be at 100% renewables+storage paying a fair bit less than they did in 2010.
 

wdolson

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Jul 24, 2015
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Is that a source energy amount ?

An ICE that gets 33 mpg uses about 1250 Wh of oil per mile
An EV consumes about 250 Wh per mile of wind or PV energy

His book is published online for free. He explains the number in more detail here:
Ch 18 Page 104: Sustainable Energy - without the hot air | David MacKay

It doesn't include the energy that goes into imports which he estimates is another 40 KWH/day. Americans use 250KWH/Day on average.

I don't know where you got the number for the KWH/Gallon of gasoline. The EPA uses 33.7 KWH/Gallon, and other sources vary in the low 30s. In the calculations I did a couple of years ago, I used 33 KWH/Gal for gasoline and had 1.0 KWH/Mi for a 33 MPG car. I used the EPA numbers for EVs, which take into account losses during charging. Most Teslas are in the 300s for Wh/Mi. The most efficient EV at that time was the i3 at 270 WH/Mi.

On average an EV is about 3X more efficient than an average ICE car. That is good, but EVs are barely over 1% of car sales now, they are less than 1% of all the cars on the road. The average car age in the US is around 12 years old. It's going to take more than a decade even when all new cars are EVs to replace all the old ICE.

EV production numbers will grow dramatically over the next decade, but the limiting factor is battery production. Tesla is the only car company today with enough batteries to mass produce EVs. Most European companies are talking about having enough battery supply to mass produce by around 2015 but that's 7 years from now and that doesn't allow them to replace all their production with EVs, just more than a token number (current production numbers). To a large extent the Japanese and American car companies are moving even slower towards mass production.

When we reach a point where EVs are a large percentage of the vehicles on the road, the total energy needed for transportation will drop, but it will still be there and will still be significant. If your driving averages 30 miles a day, that's 10 KWH for transport in an EV, and it is better than 30 KWH/day for a 33 MPG ICE, but that is a small fraction of the 250 KWH/day the average American uses now.

I think Dr MacKay does a very good job of scaling up the problem and looking at the large scale issues with just generating the energy we need moving forward. He points out that all renewable energy sources are good, but the energy production per square meter of space is low compared to other energy sources.

Germany has done a lot of work towards using renewables, but they are still only to 33% usage.
Germany’s energy consumption and power mix in charts
https://www.cleanenergywire.org/factsheets/germanys-energy-consumption-and-power-mix-charts
That doesn't include oil usage for transportation.
 
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SageBrush

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May 7, 2015
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His book is published online for free. He explains the number in more detail here:
Ch 18 Page 104: Sustainable Energy - without the hot air | David MacKay

It doesn't include the energy that goes into imports which he estimates is another 40 KWH/day. Americans use 250KWH/Day on average.

I don't know where you got the number for the KWH/Gallon of gasoline. The EPA uses 33.7 KWH/Gallon, and other sources vary in the low 30s. In the calculations I did a couple of years ago, I used 33 KWH/Gal for gasoline and had 1.0 KWH/Mi for a 33 MPG car. I used the EPA numbers for EVs, which take into account losses during charging. Most Teslas are in the 300s for Wh/Mi. The most efficient EV at that time was the i3 at 270 WH/Mi.
That link clarifies that he is talking about source energies. That leads to ~ 3 - 5x difference when renewables supplant fossil fuels.

There is ~ 33.7 kWh energy in a gallon of petrol but pre-processing it started out as ~ 40 kWh of oil
As for an EV, I used the Model 3 of course ! 126 MPGe = 126 miles per 33.7 kWh of PV = 267 Wh/mile from the meter
 

wdolson

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Jul 24, 2015
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Clark Co, WA
That link clarifies that he is talking about source energies. That leads to ~ 3 - 5x difference when renewables supplant fossil fuels.

There is ~ 33.7 kWh energy in a gallon of petrol but pre-processing it started out as ~ 40 kWh of oil
As for an EV, I used the Model 3 of course ! 126 MPGe = 126 miles per 33.7 kWh of PV = 267 Wh/mile from the meter

It's going to be at least a decade before all major car companies are mass producing at least one BEV and it will be a decade or two beyond that before BEVs become the dominant type of transport. But transport is only about 1/3 of the energy budget and car transport, while being a large part of that, it still only a portion.

At the end of the TED talk he showed how much space would need to be dedicated for producing different energy types in the UK to supply just 16 KWH/day/person, 1/10 the current energy usage (as of 2013). In the book he also said Britons use 40 KWH/day/person that isn't counted in the 125 for imports. The UK is very dependent on imports and fossil fuels are the only viable thing to run cargo ships and fly aircraft right now and that's going to be the case for a while. Electric planes exist as experiments, but batteries are too heavy with too low an energy density to make any kind of useful electric aircraft right now. We don't even have battery tech in the lab that would be useful for aircraft of any range/payload.

Alternative energy sources have a place in the mix, and things like electric cars will be much more efficient. Even if we were able to cut our energy usage in half, there still aren't enough renewables in enough places in the world to fill the need.

MacKay's answer was to build next gen nuclear plants, which are inherently safer designs from what is operating now combined with carbon capture technology to capture as much of the fossil fuel CO2 as possible. He was all in favor of alternatives and conservation, but his whole point was alternatives and energy savings don't cover the entire energy budget in many places once you run the numbers.
 

SageBrush

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May 7, 2015
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But transport is only about 1/3 of the energy budget and car transport, while being a large part of that, it still only a portion.
Agreed, but the electricity sourced from fossil fuels is produced in power plants that have efficiencies in the US that range from 30-50%. So once again for that portion, wind or PV would have 30-50% the energy requirement -- or perhaps less, since the embedded energy is quite a bit less, e.g about 5% for the PV panel manufacture

---------
I know that my use is not typical for the US but my wife and I live a pampered western lifestyle in a 4 season climate from a 3.8 kW PV in the backyard. That works out to ~ 10 kWh a day per capita for our home and cars. I mention this mostly to say that people (and society) have choices. Nuclear is not a necessity unless people make it so.

As for the UK -- biofuels are not the way to go. Off-shore wind is the ticket.
 
Last edited:

TheTalkingMule

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Oct 20, 2012
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The UK(and Ireland) has more offshore wind than they could ever possibly use, all they need is storage.

The idea that it's 2038-2048 before BEVs take over transport is a Chevron level timeline. We should see BEVs comprise more than half of new cars purchased in the US inside of a decade.
 

TheTalkingMule

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Oct 20, 2012
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Philadelphia, PA
Anywhere convenient to the North Sea can pretty much just stop worrying about their energy future and let the tech get cheaper. DO NOT build out any new coal or nuclear and think twice before any new natural gas as a "bridge to renewables".
 

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