How the calculation works
Energy cost per unit = (electricity cost + fuel cost) ÷ production
Comparing SEC with a baseline gives a quick view of whether the plant is using energy better or worse per unit produced. The energy avoided is the baseline SEC minus the current SEC, multiplied by this period's production.
Worked example
In one quarter a plant uses 1,200,000 kWh of electricity at 0.11 and 800,000 kWh of natural gas at 0.05, and produces 10,000 t. Last year's SEC was 215 kWh/t.
- Total energy: 2,000,000 kWh. SEC: 200 kWh/t.
- Energy cost: 132,000 + 40,000 = 172,000, or 17.20 per tonne. Electricity is 77% of the cost.
- Compared with the baseline, SEC is 7.0% lower, about 150,000 kWh avoided this quarter.
A warning about simple ratios
Most plants have a fixed energy load, such as lighting, compressors idling, HVAC and standby equipment, that does not change with output. So SEC improves automatically when production rises and worsens when it falls, even if nothing has really changed. For ISO 50001 reporting, a regression baseline that separates fixed and variable energy is more reliable. See the EnPI and baseline regression calculator.
- Compare periods with similar production levels when using SEC.
- Track electricity and fuel separately if they serve different processes.
- Convert all fuels to kWh with the same heating value basis (gross or net) every time.
Questions
What is specific energy consumption?
The energy used per unit of output, such as kWh per tonne. It is the simplest energy performance indicator and is widely used for benchmarking and tracking.
Why does my SEC change when production changes?
Because part of your energy use is fixed. When output falls, the fixed energy is spread over fewer units and SEC rises. A regression baseline removes this effect.
How do I convert natural gas to kWh?
Multiply the volume by the calorific value on your gas bill. In normal cubic metres it is roughly 10 to 11 kWh per Nm³, depending on gas quality and whether the gross or net value is used.