Electrical energy cost equations
Operating energy is average input power multiplied by runtime. Cost is energy multiplied by the entered flat tariff.
Pavg = Prated × quantity × load factorE = Pavg × tCost = E × tariffwhere:
- Pavg
- Average electrical input power[kW]
- Prated
- Rated input power per unit[kW]
- E
- Electrical energy consumption[kWh]
- t
- Operating time[h]
The calculation excludes demand charges, time-of-use pricing, reactive-energy penalties, taxes, and fixed fees unless they are added separately.
How to calculate electricity cost
Use electrical input kW, equipment quantity, average load factor, daily runtime, operating days, months, and energy tariff. The calculator first finds average kW, then daily, monthly, and annual kWh and cost.
- Enter rated or measured input power.
- Apply quantity and average load factor.
- Enter the operating calendar.
- Enter the flat energy tariff.
- Add demand and time-of-use charges separately.
Energy cost example
One 7.5 kW load operating at 80% average load for 10 hours uses 60 kWh per day. At 0.12 per kWh, energy cost is 7.20 per operating day before demand charges and fees.
Pavg = 7.5 × 0.8 = 6 kW
Cost = 6 × 10 × 0.12 = 7.20/day
Rated power versus measured power
Nameplate motor output, equipment capacity, and electrical input are different values. Metered average input kW gives a better result than estimating load factor from rated output.
Charges not included
Industrial bills may include peak-demand charges, time-of-use rates, power-factor or reactive-energy penalties, capacity charges, taxes, and fixed fees. Model these separately before using the result for an investment decision.
Assumptions
- Average load factor represents the operating profile
- Tariff is a flat energy charge
- Demand charges, time-of-use pricing, taxes, and fixed fees are excluded
Important Warnings
- Use measured average input power when available; nameplate output power can understate electrical consumption.
- Industrial bills may include peak-demand, reactive-energy, capacity, and time-of-use charges not represented here.