Revisiting the work of David MacKay

Fluff, greenwash and claptrap. 

That is how Sir David Mackay, the chief scientific advisor to the UK Dept of Energy and Climate described the climate debate in 2012.

In an unfortunate testament to the success of both green marketers and corporate merchants of doubt, the future of climate change has bogged down in the trenches of social media, leaving the general public confused and apathetic to the long term consequences of inaction.

Or has it?

Mackay’s great insight was to bypass the hyperbole and use a simple back of the envelope calculation to convert numbers to what people understand. Who would have thought, basic math to understand a problem!

And this is what Mackay did in his 2008 book, “Sustainable Energy - Without the Hot Air” and subsequent TEDx talk. He kept it simple and talked in number of light bulbs. Or more to the point a kilowatt hour of light.

 In 2005 each UK resident, used 162 Gigajoules of primary energy per year. This covered mainly oil and gas, a bit of nuclear and some renewables. A gigajoule is 278 kwh and per day it works out to be 123kwh or close enough to 125 lightbulbs running all day and night. 

Then he posed a question. Can you run these 125 lights with green energy?

Replace oil with biofuel?

It was a very simple thought experiment, how much land next to a road do you need to power a car driving on that road? Assuming the car is doing 60 miles/hr, getting 30 miles/gallon and you can get a yield of 1200 litres/hectare for biofuel, how much space do you need next to the road.

Unfortunately, the area required was 5 miles wide or 8km.

Not quite practical but what about with today’s technology? 

A Hyundai Ioniq (petrol) can achieve 55 miles/gallon and if we cheat and use a better crop like sugarbeet instead of canola (rapeseed) then we can produce 5060 litres/hectare.

Will this shrink the land required?

Yes but it would still be 1 km wide. Impressive but still impractical 

So although biofuel is not the answer we can see that engine efficiency partially is. The BP statistical review shows UK oil consumption has dropped 25% since 2005 on a per capita basis and some of this can be attributed to more efficient transport.

And in lightbulb terms, the average UK resident only needs 30 light bulbs instead of 40 for transport purposes.

Can you heat your house better?

All that grey British weather can only mean one thing. It’s cold! This means warming up the houses in winter which takes up 24 kWh, 1 kWh for cooling because global warming hasn’t hit yet and despite what people say about the British, 12 kWh for washing and having hot showers.

Can it be improved in 2020? Yes, but using old technology. A heat pump has a coefficient of performance of around 3 which means it can take 1 kwh of energy and triple the amount of heat from it. In principle, the amount of primary energy required for heating can be reduced to a third.

In the UK, measures like this and others have meant that gas and electricity consumption has dropped by 25% which means we again only need 30 light bulbs in the updated model.

Can renewables replace fossil fuels?

Mackay was pragmatic and believed renewables in 2012 had the potential of only replacing 18 kwh of renewable energy, about 14% of the Britains energy need.

Surprisingly, the UK has achieved this target and in 2019 generated 13.7% of energy from renewables. Not bad for a country with a bumbling prime minister and being distracted with trying to decouple from the rest of the world.

But what of the next 86%?

The reality of covering every inch of land with biofuel plantations, solar and wind farms is not practical and too much to sacrifice. Mackay himself calculated that covering the UK with wind farms would generate 200 kwh/person but it would be unrealistic to get past 10% of the total land which would provide a maximum of 20 out of the 125 light bulbs required.

But technology has improved and where he used wind turbines with a 1 MW nameplate capacity, the larger offshore farms such as Hornsea Project One have 7MW turbines. So while we can’t cover 100% of land, we could make the turbines 10 times bigger and indeed there are 10MW turbines on the horizon.

Pragmatism or Pessimism?

So where are we after all these years?

The good news for the UK is that the amount of primary energy has gone down quite significantly. Per capita consumption has gone from 161 GJ’s to 118 GJ or the equivalent of reducing demand from 125 to 90 lightbulbs.

The bad news is while the western world has improved, up and coming economies have significantly ramped up their energy consumption with China and India up 75% since 2005. And with these two using only a third and a tenth of a typical American consumer respectively, expect this to rise significantly as they catch-up to the west.

Globally, each citizen has gone from using 53 light bulbs in 2005 to 57 in 2019. An extra 4 where only 3 of those are powered by renewable energy. So while improvements have been made, the goalposts have shifted and in 15 years we've effectively gone backwards.

Sadly Sir David Mackay past away in 2016. For those trying to make sense of the energy debate he not only left a valuable body of work but the tools to allow us in his words, "understand the actions that really make a difference, and to focus on ideas that do add up."

His methods and calculations can be found in his book and in addition, keynumbers has converted some of his back of the envelope calculations to online models with links to the latest data on energy consumption and efficiency statistics from a variety of sources including the UK Govt, UN, BP, ICCT and various green vehicle websites. 

Note: Keynumbers is not affiliated with his work but very much appreciative of his legacy.