Goal
Work out:
- how many watts your homelab actually uses
- what that means in £/month
- where the easiest wins are to bring it down
No spreadsheets of shame required (unless you want them).
1. The one tool that makes this easy
Get a smart plug / power meter that can show real-time watt usage.
Examples:
- Cheap inline watt meter with a display
- Smart plug with an app that shows W and kWh
Plug your server or power strip into it, then:
- note idle watts
- note watts under light load (e.g. streaming something)
2. Turning watts into £/month
You mainly care about idle or average load, not the absolute peak.
Let’s say:
- Idle: 18 W
- Light load average over the day: ~25 W
Rough daily kWh:
W / 1000 * 24
25 / 1000 * 24 = 0.6 kWh/day
Monthly (30 days):
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0.6 * 30 = 18 kWh/month
If your kWh price is ~£0.30:
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18 * 0.30 = £5.40/month
So that small box costs you roughly the price of one takeaway side per month to run.
3. Where the power goes
Most of the baseline draw is:
CPU + chipset
RAM
drives (especially 3.5" HDDs)
fans / PSUs
Rough rules:
Spinning HDDs: 3–8 W each when spun up
SSDs / NVMe: usually <1–2 W at idle
Old desktop hardware: often 40–80 W idle
Modern mini PC / low TDP CPU: often 5–20 W idle
If you want low power:
fewer 3.5" HDDs
modern low-TDP platforms
no giant gaming GPU sitting there at 30–50 W idle
4. Quick wins for lower idle
4.1 Kill the zombie gear
Unplug / power off:
old, unused routers / switches
“temporary” extra machines that never got decommissioned
screens / monitors that stay on
Each of these might be 5–15 W of background noise.
4.2 Spin-down policies for HDDs
For bulk media drives, it can be worth setting:
HDD spin-down after X minutes of inactivity
On Linux with hdparm (careful, test first):
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sudo hdparm -S 60 /dev/sdX
60 means 5 minutes in hdparm’s weird units.
Don’t go too aggressive, or you’ll just thrash the drives with spin-up/down cycles.
5. Smarter scheduling
If you run things like:
backup jobs
heavy transcoding / conversions
scrapers
Schedule them for night or specific windows, so the box spends more time at low load.
Example: cron job at 02:30 daily:
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30 2 * * * /usr/local/bin/nightly-backup.sh
6. Compare options with real numbers
If you’re thinking about upgrading hardware, compare like this:
Example A: Old desktop
Idle: 65 W
Cost (30 days, £0.30/kWh):
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0.065 * 24 * 30 * 0.30 ≈ £14.04/month
Example B: Mini PC
Idle: 12 W
Cost:
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0.012 * 24 * 30 * 0.30 ≈ £2.59/month
Difference: ~£11.50/month, or ~£138/year.
Suddenly that cheap used mini PC looks a lot more attractive.
7. Recap: SmallGrid power rule
Measure, don’t guess.
Care about idle / average, not peak.
If a change saves 20–30 W 24/7, it’s probably worth doing.
Your homelab should be fun to tinker with, not a secret second energy bill.