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26 June 2009

Does using e10 reduce greenhouse gas emissions?

This is a question that more people are asking Greenfleet, so we thought we'd explain how it works.

As a bit of background about greenhouse gas emissions associated with liquid fuels, there are two types of emission scopes - Scope 1 emissions are those actually contained within and released by the burning of that fuel, and Scope 3 emissions are indirect emissions associated with the production and distribution of the fuel.  Combined, these two scopes are called Full Fuel Cycle emissions.

The factors for greenhouse gas emissions, (expressed as a quantity CO2-e or carbon dioxide equivalent per unit of fuel), are set out by the federal Department of Climate Change in the National Greenhouse Accounts Factors. 

The current edition of that document does not provide a factor for Scope 3 or indirect emissions for ethanol, as "biofuels such as biodiesel and ethanol are highly dependent on individual plant and project characteristics, and therefore have not been estimated.*"  So this makes it somewhat harder to answer the question.

However, earlier versions of the factors did estimate a figure for ethanol, so we'll use that to help shed some light on the issue. The following table shows you how e10 compares with unleaded petrol at a glance.

 

100% Unleaded Petrol

(non-vehicle specific)

100% Ethanol

e10

(10% ethanol /
90% unleaded petrol)

Scope 1 emissions
(t CO2-e / kL)

            2.38*

      0.08 *

            2.15

Scope 3 emissions
(t CO2-e / kL)

            0.18*

      1.3 **

            0.29

Full Fuel Cycle Emissions
(t CO2-e / kL)

            2.56

      1.38

            2.44

% saving vs ULP

            0%

      46%

            5%



Litre for litre, e10 should reduce greenhouse gas emissions by about 5%,
however - ah yes, there's always a 'however' - you will need to compare your fuel efficiency when driving with e10 compared with petrol. 

If your fuel consumption, (L/100km - litres of fuel per 100 kilometres), increases by more than 5% when you use e10, then you will create less greenhouse gas by using unleaded petrol.

 

Sources
 * National Greenhouse Accounts Factors November 2008
** National Greenhouse Accounts Factor January 2008