Phantom Loads, But Real Energy

Tushar Goel
December 5, 2018

Submitted as coursework for PH240, Stanford University, Fall 2018


Fig. 1: Switchable Power Strip. (Source: Wikimedia Commons)

Devices and appliances consistently use energy in our homes when plugged into outlets. Even when they're turned off or on standby, small amounts of current run through the circuits and the electrical energy is converted into wasted heat. This is the concept of Phantom loads; devices, seemingly turned off, using up power and ringing up the power bill. Almost all of us can see something similar to Fig.1 in our homes and offices, unaware of how much energy just 'disappears'. But how significant is this energy sink?

Analysis of the Energy Wasted

To understand the amount of energy wasted, I'll be estimating the amount of energy my desktop computer at home consumes while it is in low-power (sleep) mode. I will estimate the energy use of the CPU and two LCD monitors. A desktop CPU consumes 9W of power on average and an LCD Monitor consumes an average of 2W of power on average. [1]

E = (9 + 2 + 2) W
1000 W/kW
× 22 hours
1 day
× 365 days
1 year
= 104.4 kWh/year

Estimating that I use the computer for ~2 hours per day and it is in sleep mode the rest of the time, we calculate 104.4 kWh of energy wasted by the computer per year. This is equivalent to the energy required to drive 372.8 miles on a freeway (with an efficiency of 0.28 kWh/mi). [2] Given an average of 12 cents paid per kW of electricity, we calculate an approximate of $12.53 per year for energy from which I derive no use. [3]

While this may seem a small amount for me personally, it will result in a significant amount of energy being wasted when summed up to include all the computers in all households across the country.

Reducing Phantom Loads

We can all play our part in reducing this wasted energy by being more mindful of the state of our appliances and devices. We can completely shut down laptops and computers instead of leaving them on sleep. Using switches to turn of power for outlets is a good way of ensuring that no current is allowed to pass into an appliance when turned off - and is common practice in other countries. Alternatively, we could use a power strip with a switch (Fig. 1) for outlets which do not have wall switches installed. Unplugging any chargers when not in use or when the device is done charging is also an easy way to save energy.

© Tushar Goel. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. Roberson et al , "Energy Use and Power Levels in New Monitors and Personal Computers," Lawrence Berkeley National Laboratory, LBNL-48581, July 2002.

[2] X. Wu et al., "Electric Vehicles' Energy Consumption Measurement and Estimation," Transport. Res. D 34, 52 (2015).

[3] J. Jiang, "The Price of Electricity In Your State," NPR, 28 October 2011.