As Australia’s largest greenhouse gas emitter, which is also taking an industry leading approach to decarbonisation, we take our responsibility to monitor and report on our greenhouse gas emissions seriously. We report every year under section 19 of the National Greenhouse and Energy Reporting Act 2007, as well as in our Sustainability Report. As part of our process we undertake regular analysis and calculations throughout the year.
Let’s have a look at some of the more interesting parts of our calculations.
Our coal-fired power stations are our biggest single sources of emissions and it is the combustion of coal at these facilities that makes up over 98% of their emissions.
There are several ways in which we can determine the emissions from the combustion of coal.
- We can use a standard emissions factor published by the Clean Energy Regulator. We can multiply this by the total tonnes of coal combusted to calculate the tonnes of CO2e emitted from combusting the coal; or
- We can measure the exact amount of energy, moisture and ash in the coal combusted to determine a precise, site-specific emissions factor for the coal. We can then multiply the site-specific factor by the tonnes of coal combusted to arrive at the tonnes of CO2e emitted.
Coal isn’t uniform, it’s made up of many different components, giving the coal different properties depending on where it is from – it varies from mine to mine, and varies within each mine, and even within each volume of coal that is dug up. For this reason, we use the second method to make sure we are calculating our emissions as accurately as possible.
There are many different components we must measure and consider to use this method of calculation, and they must be measured regularly:
- The amount of coal (tonnes) combusted is measured at least every day. This is achieved by using weightometers which sit on the coal conveyors which feed the coal to the generation units at the power stations.
- Coal quality and composition is measured daily. Samples are taken so that they accurately represent the coal combusted that day and then analysed to determine the quality and composition of that coal.
From time to time, much like a car or any other piece of machinery, our monitoring equipment can have faults and must be repaired or serviced. Minor faults happen from time to time, and can usually be rectified very quickly without impacting our emissions calculations, but sometimes we are faced with the situation where we have a prolonged period of incomplete data. In these circumstances, we notify the Clean Energy Regulator about what we’ve done to rectify faulty equipment or procedures, and to propose a way to estimate the incomplete data. We also get our independent auditor involved to go through the numbers with us.
For example, in recent times we have had the following issues:
- Incomplete coal quality data at Liddell Power Station due to a fault in the sampling equipment – to overcome this, we used average values for the month based on the samples that we do have in each month. To make sure our estimates are reasonable we performed some statistical analysis and determined they fall within the 95% confidence interval for the values recorded over the previous seven months.
- Incomplete coal quantity data at Loy Yang Power Station due to a faulty weightometer - to estimate the tonnes of coal which would have gone across the broken weightometer we first looked at the preceding months for which we have data for both measured coal and electricity produced. We took a ratio of coal consumed to electricity produced across that entire period. That factor could then be applied to the electricity generated during the period that the weightometer was broken and a reasonable estimate calculated.
It’s easy to look at the big number which represents AGL’s total annual greenhouse gas emissions and not realise what sits behind that. Hopefully after reading this you can see how seriously we take our reporting responsibilities and, how important it is for us to maintain our accuracy. For more information on AGL’s greenhouse reporting have a look at our Sustainability Report.