Turn Off Those Lights When You Leave Work Today


The MSP430 Energy Watchdog Tool is a smart plug reference design from Texas Instruments that can be used to measure energy consumption of electrical appliances.  I recently recorded a video of the Energy Watchdog measuring energy consumption of common household electrical appliances like laptops and table lamps.  I also wanted to see how much energy is consumed in an office environment and decided to use the Energy Watchdog Tool for this purpose.

My office has four fluorescent tube lights, a laptop with docking station and monitor, an IP phone and a digital photoframe.  All of these are plugged into power strips which made it easy to insert an Energy Watchdog for power measurement.  With everything turned on, the active power consumption was 194W.  Based on this number, I set up a hypothetical comparison between two employees - one who always turns out lights, monitors, etc. at the end of the work day and another employee who doesn't.

Annual energy cost of energy conscious employee's office:
0.194kW x 8 hours/day x 260 days/year x $0.15/kWh = $61

Annual energy cost of energy hog employee's office:
0.194kW x 24 hours/day x 365 days/year x $0.15/kWh = $255

The estimated annual energy consumption cost of the energy conscious employee is $61, whereas that of the energy hog is more than 4 times as much at $255.  As the number of employees in the office goes up, this excess energy consumption can be a significant (avoidable) cost to businesses.  Many office buildings are outfitted with timers that turn out corridor lights, but usually do not control individual offices as these offices might have critical equipment such as servers that need to stay on all the time.  So it is up to each employee to turn out lights and other unused equipment at the end of the work day.

It is good for the company's wallet and it is certainly good for the planet.

  • Great analysis.  Automation is not yet down to the individual level, so behavior and habits can still have a big impact on energy use.  If we could submeter the energy use of every office and send empooyees their bill directly I suspect behavior would change very fast.  Right now we are benefiting from very low electric rates because of the depressed price of natural gas, but rates will spike back up at some point.

    Also, because these items produce waste heat, for every Watt of energy you use directly, it takes an additional 0.2 Watts to remove the waste heat from the office.  

    A few easy steps:

    1. Turn off task lights unless you need them.  Many people turn them on out of habit.

    2. We should be moving toward centralized printers, but if you have a desktop printer turn it off until you need it.

    3. Make sure your computer is set to sleep when not in use.  Screen savers might save screens, but they use a lot of energy.