How to Turn Utility Bills into Emissions Data

Utility invoices — electricity, gas, water — are the primary source documents for most organisations’ Scope 1 and Scope 2 emissions calculations. But the path from “invoice in accounts payable” to “verified number in the sustainability report” involves more steps than most teams expect.

Here’s how the process works, and where it typically breaks down.

Step 1: Collect the documents

The first challenge is getting the invoices into one place. Utility invoices typically flow into accounts payable for payment processing, but sustainability teams rarely have visibility into that system in real time.

Common gaps:

• Invoices paid and filed without the sustainability team ever seeing them
• Multiple retailers for the same site type (different electricity providers for different states)
• Tenant vs landlord responsibility confusion — who receives the invoice for occupied premises?
• Estimated reads included on invoices, with an adjustment issued later as a separate document

What to establish:

• A systematic process for forwarding utility invoices to the sustainability team or central repository at time of processing
• A register of expected invoices by site and period so you can identify what’s missing
• A clear policy on who is responsible for invoices at shared or leased premises

Step 2: Extract the right fields

Once you have the invoice, you need to extract:

For electricity:

• NMI (National Meter Identifier) — the unique identifier for the meter
• Billing period (from date and to date)
• Actual consumption in kWh (not estimated — check this on every invoice)
• Tariff type (general business, off-peak, controlled load) — useful for demand analysis but not needed for the basic CO₂e calculation
• Whether the invoice includes any GreenPower component

For gas:

• Meter reference
• Billing period
• Consumption in MJ or GJ (some invoices show cubic metres — you need to convert using the calorific value, which is also on the invoice)
• Gas type (natural gas is the most common; LPG is different and has a different factor)

For diesel/fuel (delivery invoices):

• Site reference
• Delivery date
• Volume in litres
• Fuel type

Watch for estimated reads. An estimated read on an electricity invoice is not actual consumption — it’s a projection the retailer has made because they haven’t accessed the meter. The actual read will come in a subsequent invoice, with an adjustment. If you include estimated reads in your calculation without accounting for the adjustment, you’ll double-count.

Step 3: Attribute to site and period

Each data point needs to be tagged:

• Site: Which physical location does this consumption relate to?
• Project (if applicable): Is this site associated with a specific project?
• Reporting period: Which monthly or quarterly period does this consumption fall in?

The billing period on an invoice often doesn’t align with your reporting periods. An invoice covering 15 May to 14 June needs to be allocated across two reporting months if you report monthly. Decide how to handle this (proration by day, or treat the invoice as belonging to the period in which most of the consumption falls) and apply consistently.

Step 4: Apply the emission factor

With consumption in consistent units and correctly attributed to site and period, apply the NGA Factor:

Electricity (Scope 2, location-based): kWh × NGA grid emission factor for the relevant state (current year) = kg CO₂e

Natural gas (Scope 1): GJ × NGA stationary combustion factor for natural gas = kg CO₂e

Diesel, stationary (Scope 1): Litres × NGA stationary combustion factor for diesel = kg CO₂e

Diesel, mobile (Scope 1): Litres × NGA mobile combustion factor for diesel = kg CO₂e

Note: stationary and mobile combustion have slightly different factors — make sure you’re using the right one.

Divide by 1,000 to convert from kg to tonnes CO₂e.

Record the NGA Factors version and specific table/row reference alongside the calculation.

Step 5: Validate before including

Before a figure enters your emissions total, apply sanity checks:

• Is this consumption higher or lower than the same period last year by more than 20%? If so, investigate before accepting.
• Does the billing period cover the right number of days? An invoice covering 90 days when you expected 30 is a red flag.
• Is this a reasonable absolute number? A 50-person office consuming 500,000 kWh per month is implausible.
• Is there a prior invoice for this same period, or an invoice for an adjacent period that overlaps? Possible duplicate.

Anomalies aren’t always errors — sometimes consumption genuinely spikes due to equipment failure or a seasonal change. The point is to investigate rather than accept blindly.

Step 6: Store the link between number and document

The final step is what makes the calculation auditable: maintaining the link between the reported emissions figure and the source invoice.

This means being able to say: “The 82.2 tonnes CO₂e for Site A in June 2025 is supported by Invoice #123456 from retailer X, covering 87,450 kWh for the period 1–30 June 2025, using the Victorian grid factor of 0.94 kg CO₂e/kWh from NGA Factors FY2025 Table 3.”

Without that link, the number is floating — you know it came from somewhere, but you can’t prove it.

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Ayika automates the extraction, attribution, factor application, and audit linking steps, so your utility invoices become traceable emissions figures without manual calculation. See how invoice ingestion works.