Consumer Technology

Published on June 28th, 2012 | by Nicholas Brown


Tablet PCs Save Energy — iPads Cost Only $1.38 Per Year to Charge

June 28th, 2012 by  

Before we get started, I think you should know that this particle story pertains to tablet PCs in general, and their ability to save a considerable amount of electricity, and the iPad is just an example of one. Tablet PCs, in general, consume little power, so it isn’t that the iPad itself is particularly efficient.

Back of Samsung Galaxy Tab

The power consumption of desktop PCs is almost always less than 100 watts. Most of the time, however, cumulative energy usage (total energy used over a period of time) is a sum of the appliance’s time in use and wattage. Time used is just as important as wattage.

You will realize the importance of this in the computer calculations I make below.

In other words, cumulative power consumption/energy usage equals appliance wattage multiplied by time used (more detailed explanation).

Real World Example:

A common but low-power personal desktop computer with a dual core CPU (this is the predecessor of the faster i3 processors) consumes 40 watts on average with normal use and a few programs open, such as the Google Chrome browser, Skype, and a text editor.

If you haven’t already realized, the power consumption (in watts) of such a computer is equal to 40 times the time used. It is common for people to leave their personal computers on all day — in extreme (but still common) cases, computers are left on for 24 hours per day. 40 x 24 = 960 Wh (Watt-hours), or 0.960 kWh, assuming that all power-saving features are turned off. (I made this assumption for the sake of simplicity because people’s computer usage and power saving settings vary widely.)

After a month, this amounts to 28.8 kWh, which costs $2.88 USD, assuming an average electricity cost of $0.10 per kWh. The total annual cost is $34, which is about 25 times more than the tablet PC mentioned above. Despite the fact that tablet PCs have very limited capabilities compared to desktop PCs, and do not provide anywhere near the performance that desktops do for the money, they are portable, convenient, and energy efficient.


I cannot tell you what is best for you. Tablet PCs are not for everyone, so, please think carefully about whether a desktop, laptop, or tablet PC would suit you best.

Another thought about DC-powered tablet PCs: they are easier to power with solar! Solar panels generate DC current by default, which can charge tablet PC batteries, so only a solar panel and voltage regulator is needed to charge a tablet PC, rather than the larger and, hence, more expensive inverter, batteries, voltage regulator, and solar panel that would be required for a desktop PC.

If you do want a tablet PC, good choices are available, such as the Toshiba Thrive product line, as well as that of the Samsung Galaxy Tab, Asus Eee Pad Transformer, and the Blackberry Playbook.

Photo Credit: 3 Sverige

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About the Author

writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is:

  • I don’t know that tablet or PC is a useful comparison. Tablet to laptop, however… Do you have numbers for that?

  • rajesh kumar

    This is very useful blog you have shared with us. Tablet Pc
    become very popular nowadays.Thanks for giving such and informative information.

  • Hope

    I’ve been eyeing a tablet for a while. This is my excuse.

    • me too. this study made my day. seems worth it now. 😀

  • Bob_Wallace

    One of the ways we get fossil fuels off our grid is to make our grid smaller.  Through efficiency.

    “The annual cost to charge an iPad is just $1.36, according to the Electric Power Research Institute, a non-profit research and development group funded by electric utilities.
    By comparison, a 60-watt compact fluorescent bulb costs $1.61, a desktop PC adds up to $28.21 and a refrigerator runs you $65.72 in the U.S.
    But if people are using iPads instead of televisions to play video games, or ditching their desktop computers for iPads, the shift to tablets could mean lower overall power consumption. A desktop computer uses 20 times more power than an iPad. 
    Residential power demand is on track to fall for the third straight year, according to the government. A weak economy is keeping people in smaller houses and shacked up with others. At the same time, efficiency programs are pushing more efficient light bulbs, air conditioners and other devices into homes. Refrigerators use a quarter of the power they used a generation ago, according to EPRI. 

    But there’s an even cheaper way to go than the iPad. EPRI calculated the cost of power needed to fuel an iPhone 4 for year: just 38 cents.” 

    About 11% of our residential electricity goes to lighting.  Moving to more efficient lightbulbs will cut the power used for lighting by a factor of four or more.  

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