NGER criterion AA estimates the quantity of fuel combusted from the amounts delivered during the year, evidenced by invoices, adjusted for the estimated change in the stockpile. It suits facilities that hold material stocks of coal, carbonates or fuel between delivery and use.
Key points
- AA adjusts invoiced deliveries for stockpile change
- Solid fuels use the survey or the error allowance approach
- The error tolerance is not more than 6% of the stockpile
- Bulk density follows ASTM D6347 or auger and coring sampling
- Once used, AA must be used in later years
Two approaches for solid fuel stockpiles
Section 2.15 of the NGER (Measurement) Determination 2008 sets two approaches for estimating the stockpile change. The chosen approach must be used each year unless there has been a material change in how the stockpile is managed that makes it less accurate than the alternative.
| Approach | How it works |
|---|---|
| Survey approach | The stockpile volume is measured by aerial or general survey in accordance with industry practice and multiplied by bulk density. The survey quantity replaces the book quantity, which is then maintained by adding deliveries and deducting consumption. |
| Error allowance approach | The operator sets an error tolerance of not more than 6% of the estimated value of fuel in the stockpile. If the difference between the book quantity and the survey is within tolerance, the book quantity is used. If not, the book quantity is adjusted by the excess. |
Bulk density
Bulk density is measured under ASTM D6347/D6347M-99 or by sampling. The Determination specifies a mechanical auger where the stockpile is not more than 10% of annual combustion, and coring where it is more than 10%.
Book quantity
The Determination defines book quantity as the quantity recorded and maintained by the facility operator as the quantity of solid fuel in the stockpile. Deliveries added to it are evidenced by invoices or by sampling and measurement from equipment calibrated to a measurement requirement.
Other fuels and carbonates
Gaseous fuels (section 2.30), liquid fuels (section 2.51) and carbonates (section 4.36) also allow criterion AA, based on invoiced deliveries adjusted for stockpile change. For carbonates, the stockpile is measured in accordance with industry practice.
The lock-in
If criterion AA is used for a facility in a year, only criterion AA can be used in each following year. Year-end stockpile surveys, density results and reconciliations are therefore part of the evidence an auditor will expect every year.
References & sources
Primary regulatory documents and authoritative references underpinning this answer.