Premise ∆

I run a server from home, utilising old hardware. I want to know how much power this actually consumes, but I have no way to measure it directly.

More specifically, I have used an old laptop for this, but its battery is permanently shot (the device won't power on with the battery connected but works fine without it, drawing power from the charger only). I already have a replacement - an (almost) equally old "multimedia" desktop with a mini-ITX motherboard. I had to replace the "mini" PSU with a normal-sized one. It says 300W on the label (this is not how much power it draws all the time, just the maximum it can provide).

I want to know how much electricity each setup constantly cosumes.

So, both machines are +10 years old, supposed to run as a headless server with at least one SATA 5.4K RPM hard drive (which consumes 7-8W according to 5). The server doesn't really do very much: some modest PHP for my site's CMS, but visitors are few; some personal streaming without transcoding, local network filesystem mounting.

An online PSU calculator helped significantly with the mini-ITX desktop, but not with the laptop. I could not find information on laptop motherboard power consumption, neither generally nor specifically for this model. Therefore any sort of authoritative comparison is impossible (unless I connect a meter to the power outlet). I tried to compile as much information as I could to make an educated guess at least...

Laptop: HP Compaq 530 ∆

Intel Celeron M 420 - TDP: 35W (2)

With 2x1GB of RAM and the aforementioned hard drive, this adds up to ~55W (5) + an unknown (+10W presumably?) for the motherboard itself.

PSU: 65W - according to (1) it runs constantly at ~20% when plugged in? The label says "Efficiency level: IV" - according to (6) this means >=85%. Let's assume 10% of power intake go to the charger itself at all times.

This brings us definitely over 60W altogether, however the actual value is going to be higher because of the motherboard.

Desktop (mini-ITX): ION 330 ∆

Intel Atom 330 - TDP: 8W (3) Mobo: ION 330 - 36W idling according to (4) (this is a measured value and also includes peripherals); according to (5), any mITX motherboard + this Intel CPU weigh in at 40W already.

Assuming a generic mini-ITX mobo, 2x2GB of RAM and the aforementioned hard drive, this adds up to ~68W (5) (the mobo itself weighs in at 32W).

PSU (FSP300-60EP): Intake: 104W max Output: 300W (240W max) Not sure how these numbers add up? It's what was written on the label. Efficiency is 80+ Bronze; that means max. 15% of power intake are blown on the PSU itself.

This brings us to ~78W, however the actual value is likely to be lower because of (4)?

Conclusion ∆

One machine does not appear to be consuming significantly less or more than the other.

The desktop PSU remains cool during operation, the fan blows only slowly. The laptop charger however is hot to the touch, I must assume it runs at close to maximum capacity all the time.

Both consume more than 60W, I presume constantly. That is at least 1.44kWh every day, which is on par with a modern refrigerator.

That's a lot.

Why not a Raspberry Pi instead? ∆

Or a similar SBC? Low power consumption, very affordable. Practically made to run headless - which cannot be said for the two devices above!

The problem is storage. I have a few SATA drives that I want to continue using, ~2TB altogether, and serve their contents; if not continuously, at least on demand. This is where most ARM SBCs fall short. Looking at recent Raspberry Pi models, at the very least you need a larger power supply and an expansion card. Usually this is a SATA-to-USB adapter - not ideal! A real SATA connection requires not only additional cards but also additional power supplies and kernel re-compilation!

A Raspberry Pi only would consume almost no electricity at all, compared to the old systems above. A single spinning drive consumes more. With a setup that integrates those hard drives it would probably still use significantly less - but not orders of magnitude anymore.

I will have to re-think my approach when these spinning drives die.