What?

A laptop uses about a fifth of the energy used by a full-blown desktop PC. For a desktop, count on using 125 Watt with peeks up to 300 Watt (mainly during games). Laptops are not always suitable for gaming, but they are otherwise perfectly usable. Count on 25 Watt for a laptop.

The most degrading part of a laptop is usually its battry -- it degrades due to constant charging and discharging. At home, you should conside plugging a laptop in the mains supply, possibly without even plugging in the batteries.

Why?

Laptops use less electricity and are therefore better for both the environment and your financial situation. In addition they make more sense to use -- you need no special place to use your laptop, and it even looks nice when it is lying around on the sofa or coffee table. A dedicated computer corner can lead to lively debates in the domestic situation -- considering being together the desktop PC ought to be in the living room, but it does not look very nice. A wireless network makes it possible to locate peripherals such as printers in another room.

Hoe?

We will show in a simple calculation when a laptop is financially a better idea than a desktop. Assume that the desktop costs EUR 600, and compare it to a EUR 750 laptop. We will ignore the lifetime of the hardware, since this depends greatly on usage patterns and demands.

We will calculate how much electricity you must use to win back the price difference. Depending on the number of hours you use your computer each day you can then find out after how many years your laptop earns back its increased cost.

If using your laptop takes 25 W, and a desktop plus monitor uses 125 W, then the energy savings are a staggering 100 W, or 0,1 kWh each hour. At a rate of EUR 0.25/kWh that is EUR 0,025 per hour. The price difference of EUR 150 is therefore earnt back after 6000 hours of computer use.

If you use your computer 4 hours a day, then your annual use is 365 times as much, so 1460 hours. You will then earn back the added price of the laptop in 6000/1460 = little over 4 years.

Modify this calculation to fit your situation. In case a laptop specification does not include its power, you can also look for its battery specs, and determine how long it can run. Batteries are specified as a capacity in mAh and a voltage in V. Multiply those figures to get the number of mWh and divide by 1000 to get the number of Wh. Divide that by the number of hours that a battery lasts, and you have determined the power in W, like the 25 W stated above.

Some stores sell energy meters for the power grid. These are connected in between the computer and the power outlet, and during normal use you can have it score your energy costs. Some meters can even give you a prognosis of your annual energy costs based on a representative measuring period.

Where?

• http://www.eu-energystar.org/fs_select_laptop.html Search Energy Star's laptop database for power usage data.
• http://www.greenpeace.nl/campaigns/giftige-stoffen-2/elektronica/de-ranglijst-van-bedrijven GreenPeace keeps the tabs on large manufacturers of electronics and inhowfar they are responsible with their waste.