Learn to interpret your results
Standby electricity costs: measure before changing a device
Published on
A device can use electricity while appearing switched off. To assess a change, measure the load, estimate how long that operating mode lasts and apply your variable electricity price. The power printed on its label does not establish its standby consumption.
Choose a meaningful measurement
A compatible meter may display instantaneous power in W or accumulated energy in kWh. One reading can mislead when the load fluctuates. Record energy over a representative interval and divide by elapsed hours to find average power. Check the units and the meter’s accuracy for small loads. A household observation is not a certified laboratory test.
Work through the numbers
Assume a measured average of 2 W for 24 hours each day over a 365-day year. Energy would be 2 / 1,000 × 24 × 365 = 17.52 kWh. At an illustrative price of £0.25/kWh, variable cost is £4.38 per year. These are invented inputs, not typical consumption figures.
An alternative setting measuring 1 W for the same hours uses 8.76 kWh and costs £2.19. Annual savings are £2.19. If the change costs £10, simple payback is 10 / 2.19, approximately 4.57 years. Over five years the cumulative net saving is £0.95, without financial discounting.
Enter the annual figures in Simuily
In the appliance comparison use current annual consumption 17.52, alternative consumption 8.76, electricity price 0.25, investment 10 and a five-year horizon. Set other costs to zero to isolate this effect. Annual consumption already includes operating hours; do not multiply by hours again. Use zero investment if the change is free.
Test the assumptions
The scenario assumes identical behaviour throughout the year. Fewer standby hours reduce the saving, and a different price changes the energy cost. Alter one variable at a time. Fixed charges, other devices and taxes excluded from the price do not vanish when this consumption falls. A bill’s average all-in price is not automatically the marginal price of saved electricity.
Questions before switching off
Check the device instructions and retain necessary functions, including any connectivity, schedules or updates you need. Rated power is not a substitute for measured standby power. If annual savings are zero, a positive investment has no payback through this saving; the calculator should not show a finite recovery time.
Keep the measurement period, hours, price and change cost with your result. Decide using the measured saving and the functionality retained, without applying one device’s estimate to every device in the home.