# How to compute electric bill for a server netbook

I've taken an old netbook and started using it as a tiny game server. I have removed the screen, wifi card and reproductors, but the rest is there (battery, fan, sata HDD). It runs 24/7 and charger is plugged in at all times.

I wonder whether it is possible to compute a fairly accurate estimate of an electricity bill for this machine in both idle and maximum usage scenario.

The computer is Asus EEE 1201HA and adapter has 19V~2.1A output. Also is the energy consumption affected by having battery plugged in?

• You can put an upper bound on it from the adapter power rating, but you can't really know what it is actually using without measuring - especially as a modern system should adjust to computational load. Sep 9 '17 at 16:30
• If you're going to leave the thing running and plugged in all of the time, remove the battery. It doesn't add anything and Lithium-ion batteries are a bit of a fire hazard at times. Sep 9 '17 at 16:33
• @marcelm Modern lithium ion batteries have some of the best protection circuits built around them in laptops. Lithium ions in a netbook carry very little risk. The benefit from keeping them in is a built-in UPS for when power goes out. The system can stay up and running and won't need restarting. Sep 9 '17 at 16:41
• operating system is ? Sep 9 '17 at 17:47
• 19V 2.1A ... sounds like you could approximate it as 1 unit (1kWh) per 24 hour period. Is it really worth more effort than that? Sep 9 '17 at 17:50

Considering ASUS choose their chargers to both operate the unit and charge a fully drained battery at a slower rate, you may assume it uses <50% of rated output of 19*2.1 = 40 W.

Then since the LCD backlight typically drains 1/2 of the total power at max brightness, you are left with 10W, which is puny compared to running an air conditioner or electric stove.

The battery drains nothing substantial when charged and should be cool if in good shape.

Get a $20 Kill-a-watt and measure the actual wattage during load and idle. Then determine the average amount of time you'll be in each mode and from that you can get a good estimate as to how much power it'll use. At the upper end, you know that it can't use more than 19V*2.1A ~= 40Watts (ignoring powerbrick inefficiencies). 40 Watts * 24 hours * 30 days = 28.8 kW*hrs per month. Lets say electricity costs 0.15 cents per kWHr: the monthly maximum charge from using the netbook is$4.32. If it's idle most of the time, it'll likely be a lot less than this.

• The meters are bit too expensive for my taste, that is why I wanted a rough estimate calculation Sep 9 '17 at 17:08
• @doomista A budget friendly alternative (at the cost of convenience) is: turn off all your circuits on your circuit breaker except for your wall sockets. Unplug all devices except the laptop. Check your electricity meter reading before and after and calculate the cost from that. Sep 9 '17 at 22:51
• The charger can have a maximum power very unrelated to the device (manufacturer can select it by price, compatibility with other models, ...). Moreover, the charger will have enough power to feed the computer and, at same time, load the battery. That means that the real power consumption of the computer will be a very smaller. Thus, as you say, this evaluation is a upper limit but can have more than 50% error. Sep 10 '17 at 11:47
• @pasabaporaqui no doubt. Which is why without actually measuring the power at idle and at load, any estimate is nothing more than a guess. The max upper limit cost was meant to give the idea that it virtually costs nothing. Sep 10 '17 at 16:06

Asus 1201 HA has a 6 cells Li-ion battery, being the expected duration around 7 h (see here). This page is unclear, but we can estimate battery power around 50 Wh (see, by example, this replacement of 62 Wh).

That means that the unit consumes in one hour around 50 Wh / 7 h = 7 W.

7 W * 24 h/day = 170 Wh/day.

At a price of 0.15 e/kWh it means 0.025 e/day.

These numbers can be improved if replaced by the ones of an specific running mode. The method is: first, ask the battery the current power capacity (it decreases with the time), there are software for that; second, fully charge the battery, execute the application/s until discharged and measure the time. These two numbers (capacity and discharge time) must replaced the ones given by the manufacturer.

Moreover there are software that shows power consumption for most of modern operating system. In particular, see here for several options in Debian/Ubuntu/Mint: powertop, powerstat, ... .

• This methodology isn't really valid, as the manufacturer is using some "make us look good" model of live user usage, while the poster is instead operating it as a server - quite likely with a different operating system entirely. Sep 9 '17 at 18:17
• @ChrisStratton: if the number provided by Asus is in doubt, the user can measure runtime easily. Sep 9 '17 at 18:35
• I am running the server with Ubuntu, version 14.04 to be precise Sep 9 '17 at 18:44
• 170W/day is not a meaningful unit. A Watt is a unit of power (J/s). Sep 10 '17 at 5:58
• @doomista. added link to several Ubuntu options. Sep 10 '17 at 11:43

Energy consumption is probably slightly affected by having the battery plugged in, but its a fairly minimal amount. If the battery is bad you might want to leave it out though

The only reliable way to calculate the usage of the device is by connecting one of those home power meters to it, you can get these for around \$10-25 at your local electronics store.