ON Saturday Simon Corbell’s office put out a media release (to avoid claims I’ve taken it out of context you can view the entire thing here) which to my eye appeared to invent its own form of mathematics.
Particularly startling was the intro:
Stage one of Canberra’s light rail network will operate on 100% renewable energy, Minister for Capital Metro Simon Corbell announced today.
“Capital Metro is about creating a more sustainable Canberra and we are making sure that environment and sustainability is at the heart of our approach for an integrated public transport network,” Mr Corbell said.
“To ensure the best environmental outcomes are achieved as part of the project, the successful bidder will be required to source, at minimum, 10% of the light rail system’s electricity usage from renewable energy sources such as solar or wind. Combined with the ACT Government achieving its target of 90% renewable energy by 2020 – the time in which stage one light rail will be up and running – this will enable the Capital Metro project to be 100% green energy powered.
Primary school maths on the multiplication of fractions had me thinking that 90% of 90% was going to be a bit shy of 90%.
I raised this concern with one of Mr Corbell’s spokespersons:
My maths is a bit rusty,
But 90% of 90% surely does not add up to 100%?
My maths sees you at around 91% renewable by that measure?
To which they came back with:
Not sure where you are getting that from.
90% of all electricity in the ACT will already be renewable. If Cap Metro buy the additional 10% from additional green sources (wind-solar) then they will be using 100% renewable energy. So the proponent will need to buy 10% of their total electricity use from green power, not just 10% of the remaining 10%.
I wasn’t entirely satisfied with this line of thinking so I turned to the mathematicians of ANU where Dr Barry Croke (Senior Lecturer and Researcher in Computational mathematics, currently in Prague for the International Union of Geodesy and Geophysics meeting) had this to say about the efforts of Minister Corbell’s office:
The question of whether there is a mathematical fallacy depends on what exactly they are trying to say. There are 2 possibilities:
- The company running the light rail system would provide 10% of the power (renewable source), and the ACT government would provide 90% of the power. This would result in 91% of the power sourced from renewable resources.
- The ACT government supplies 100% of the power, and the company pays the premium to make the remaining 10% of the power sourced from renewable resources.
The problem is that the language used suggests the first, but the claim made at the start of the press release suggests the latter. Is this a mathematical fallacy, or just poor use of language? I think it is poor mathematics, particularly given the use of “at minimum” in “… the successful bidder will be required to source, at minimum, 10% of the light rail system’s electricity usage from renewable energy sources …”. Only other option would be the ACT Government having a variable partitioning of the 90% renewable sourcing so other sections have less than 90%.
One hopes that when managing the vast light rail project both the maths and the language will be precise.
UPDATE: Simon Corbell’s office have sent in the following to clear things up:
Unfortunately, Dr Croke and yourself missed a third possibility, that the company responsible for running light rail will purchase 100% of the electricity for light rail. The ACT Government’s 90% renewable energy policy does not require the government to buy renewable energy. Instead, the ACT’s feed-in tariff legislation requires the ACT’s electricity distributor to purchase a certain amount of renewable energy (in 2020 this amount will be large enough to supply 90% of the territory’s electricity needs). Therefore in regards to light rail, it is the successful light rail consortium that will buy 100% of the power for light rail. Because 90% of electricity supplied to the ACT will be from renewable sources then 90% of the electricity used by the company running light rail will be from renewable sources already. If in addition they purchase 10% of their total electricity needs from other renewable sources then 100% of the electricity needed for light rail will be from a renewable energy source.
Nowhere in the media release did it say that the ACT Government would be buying any renewable energy. It simply stated that as a result of the “ACT Government reaching its target of 90% renewable energy by 2020” that 90% of the electricity used for light rail would be from a renewable source already.