The other day, I was talking with someone about the wonders (and the satisfaction) of operating a large renewable energy system at our Tasmanian farm, and how I get to charge up my electric motor glider and go flying on sunshine, and how we’ll replace all the farm machinery that burns diesel with electric vehicles as soon as someone will sell that electric farm machinery to me (all of which is true).
One of our children kindly (and accurately) popped that balloon for me with a single sentence, by saying: ‘Yeah, but you also fly a turbojet aircraft’.
The plane we fly is a most wonderful beast called a Pilatus PC12 NGX. The convenience, speed, capability and sheer reach is just fantastic. I also get huge personal satisfaction from flying it. However, ‘satisfaction’ is not a Carbon offset.
This conversation lead me to pose a question to myself:
I decided to work it out.
I don’t claim to be any sort of saint – the idea is just to see if it is possible to achieve something like ‘Carbon Neutrality’ by offsetting the aircraft Carbon emissions with solar array Carbon savings.
I’ve tried to get the numbers right here (and they make sense to me)… but if I’m getting the sums wrong somehow (or misunderstanding the source data), I’d be very keen to find that out. That’s one of the reasons why I’ve posted it all here… to subject these calculations to the light of day.
My annual flying hours in the PC12: 200 (average over the last 3 years)
Average hourly fuel burn for my mission profile: around 250 litres per hour
Carbon Dioxide emitted per litre of Jet-A1 burned: 2.52Kg (source: “COP25: What is the impact of private jets?“)
Solar array size at The Vale: 200 kW
Average energy generated per annum per 1 kW of array size at The Vale: 1340kWh
Thus for a 200kW array we will make about 200 x 1340 = 268,000 kWh annually (Source: LG Solar Output Calculator ; My ‘actuals’ to date are highly consistent with that calculator).
Whether we use it on site for buildings or for electric tractors, or whether we export it, this is all energy that isn’t being generated somewhere else, hence it is net electrical energy we are adding to the total renewable electrical generation of the world.
Our actual export figure right now is above 90%, though that will reduce as we add more electric farm machinery over the coming years – in the process of progressively reducing our diesel burn figure to zero.
Our farm is in Tasmania. This complicates things because the Tasmanian energy grid is already incredibly ‘green’ – see below:
However: Tasmania has one substantial inter-connector to Victoria (Basslink) and there is another big one, MariusLink, on the way. Those interconnections allow Tasmania to sell electricity into the Victorian grid. So we’ll use the Victorian grid as our imputed destination.
The current official figure for Carbon Dioxide emission per kWh generated in Victoria is 1.13Kg per kWh (Source: The Victorian Essential Services Commission).
Now we have all the numbers we need. It is time to start doing some maths.
Annual PC12 Aircraft Carbon Dioxide Emission Created
200 hours x 250 litres per hour x 2.52 Kg per litre = 126,000 Kg
Annual 200kW Solar Array Carbon Dioxide Emission Avoided
268,000 kWh x 1.13 Kg = 302,840 Kg (or 2.4 times the PC12 emissions)
Assuming the energy destination is the Victorian energy grid, we are offsetting the aircraft Carbon footprint more than twice over! This was a (good) surprise to me.
That said, Victoria has a particularly ‘dirty’ grid. Sigh…coal…sigh.
What happens if we make this harder, by using the global average Carbon intensity value for energy grids instead of the value for Victoria?
The global average figure is far lower than Victoria, at around 0.5Kg per kWh generated (source: https://www.iea.org/reports/global-energy-co2-status-report-2019/emissions ).
Taking 126,000Kg and dividing it by 0.5Kg per kWh, we get a clean energy generation target of 252,000kWh.
This is still substantially below the 302,840Kg annualised energy production from the solar array at The Vale. Even on this ‘global average’ Carbon intensity basis, we are (more than) completely offsetting the Carbon footprint of my annual PC12 flying time.
One other thing we can derive from all of this is the ratio between flying-hours-per-year and the needed solar array size (for a solar array in Tasmania, and using the higher bar of 0.5Kg offset per kWh generated):
Dividing 252,000 kWh by 200 hours means 1260 kWh of annual energy production is needed per annual-flying-hour. Given that each kW of array size generates 1340kWh per year (in Tasmania), we need 1260/1340=0.94 kW of solar array size per annual-flying-hour in the aircraft to achieve a full offset of the annual flying time concerned.
To put it another way, we need 94kW of solar array size to offset (on a continuing basis) each 100-hours-per-year of flying time in the aircraft.
Time for a bigger calculation.
How much solar would it take to offset the entire global aviation industry?
According to this source, around 900 million tons of carbon dioxide were emitted annually due to global aviation immediately pre-COVID (assume we wind up ‘back up there’ post COVID… eventually).
So that is 900,000,000t x 1000Kg = 900,000,000,000 Kg of CO2. Yikes.
Dividing by 0.5 means we would need to generate 1,800,000,000,000 kWh of electricity from (new) renewable sources to offset the entire global aviation industry.
We are a small investor in a big project: “Sun Cable” . The first major project for Sun Cable will build around 20 Gigawatts (!) of solar arrays in the wilds of the Northern Territory, and export most of it to Singapore.
Yes, really. If you don’t think big, you don’t get big.
The LG Solar Calculator says one could expect 1940kWh of electricity per kW of solar array in Alice Springs. Multiplying 1940kWh by 20,000,000kW gets us 38,800,000,000 kWh (38,800m kWh) per year.
This is just my back of the envelope approximation, and the real outcome in terms of output energy from Sun Cable could well differ somewhat from that estimation for a whole host of rational technical reasons, including things as obvious as energy loss over long transmission paths, that the project isn’t actually in Alice Springs, etc etc.
So: We’ll de-rate that annual production estimate by an arbitrary 25% to fold in some pessimism and call it a ‘mere’ 29,100,000,000 kWh per annum.
Time for the punchline:
1,800,000,000,000 / 29,100,000,000 = around 60 (these are all huge approximations – so – measure with a micrometer, mark with chalk, cut with an axe)
The punchline (and this was also a surprise to me) is this:
The world could actually do that. If we can make one, we can make sixty.
The Sun Cable web site says that the initial project for the company is an AUD$30+ billion project (US$21bn at the time of writing).
Sixty of those would be a mere US$1260 billion (US$1.3tn). An impossibly large number to consider? Well, the four largest American companies each have a market cap well above this level.
Apple has enough cash on hand (at the time of writing) to build the first 9 of these mega-projects without even taking out a loan. Remember, too, that these will be highly profitable projects, not donations. They won’t merely mitigate carbon – they’ll (literally) power the world.
We have enough sunlight. We have enough land. What we need is enough ambition.
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