A low energy server is one that idles under about 15 W at the wall, and the pick for most setups is an Intel N100 mini PC, which ServeTheHome measured at 7.4 to 8 W idle. A Raspberry Pi 5 goes lower, around 3 W. A used rack server starts above 50 W before you fill its drive bays.
The idle figure is the one that counts. A home server spends nearly all of its life waiting for a request, so the wall reading at idle sets your power bill far more than the peak number or the CPU’s TDP. Most homelabbers learn this the expensive way: the free rack server from work turns out to cost real money every month just to sit there.
What counts as a low energy server?
There is no formal standard for a home low energy server, so use the number that reaches your bill: wall-socket draw at warm idle, with your services running and nothing actively working. Under 10 W is excellent. Ten to 15 W is fine. Fifteen to 30 W should be buying you something specific, like drive bays. Above that, you are heating a closet.
Idle matters because the math compounds. One watt drawn around the clock is 8.76 kWh a year, about $1.75 at an illustrative $0.20/kWh, so every 10 W of idle costs roughly $17.50 a year for as long as the box runs. Use your own tariff; the N100 power and cost breakdown has the table at other rates.
Ignore TDP when shopping. Intel rates the N100, a four-core chip, at a 6 W TDP. That is a thermal budget for the processor package, not a system figure: RAM, SSD, NIC, fan and power brick all draw on top of it. ServeTheHome’s own reviews show the spread. The CWWK system above idled at 7.4 to 8 W, while a fanless N100 firewall appliance sat at 10.5 to 12 W on the same chip.
How the numbers were compiled
None of the figures here are MiniLabHQ measurements. They come from published reviews and vendor documents:
- ServeTheHome’s CWWK N100 and fanless N100 appliance reviews (linked above), its Project TinyMiniMicro Lenovo M720q feature and its HPE ProLiant MicroServer Gen11 review. All are wall-socket readings.
- CNX Software’s Raspberry Pi 5 review, measured with a wall power meter and the active cooler fitted.
- Synology’s published DS923+ power figures, as listed in StorageReview’s launch coverage. Vendor figure.
- Dell’s SPECpower_ssj2008 result for a PowerEdge R720, a vendor benchmark submission on a deliberately lean configuration.
Different meters, mains voltages and builds mean each row is a band, not a lab constant.
Idle power by hardware class
| Hardware | Published idle | Published load | Tested configuration | Idle cost/yr at $0.20/kWh |
|---|---|---|---|---|
| Raspberry Pi 5 | 3.0 W | 8.8 W (all four cores stressed) | Headless, Wi-Fi only, active cooler | $5.26 |
| N100 mini PC (CWWK) | 7.4–8 W | 20–25 W | Two SATA SSDs attached | $14.02 |
| N100 fanless firewall appliance | 10.5–12 W | 22–23 W | Fanless firewall box | $21.02 |
| Synology DS923+ (4-bay NAS) | 11.52 W, drives hibernating | 35.51 W, drive access | Vendor spec, AMD Ryzen R1600 | $20.18 |
| Lenovo ThinkCentre M720q Tiny | 11–14 W | Never above 50 W | Dual-core unit, 120 V | $24.53 |
| HPE ProLiant MicroServer Gen11 | About 27 W | 71–75 W sustained (87–90 W initially) | Xeon E-2434, one 4 TB drive | $47.30 |
| Dell PowerEdge R720 | 53.8 W (active idle) | 230 W (100% load) | Two Xeon E5-2660, 24 GB, one 200 GB SSD, 750 W PSU | $94.26 |
The cost column uses the top of each idle range and assumes the box idles all year. Real servers do some work, so treat it as a floor.
Two things jump out. The gap between the top and bottom rows is about 18 to 1 at idle. And the middle of the table is crowded: an N100 box, a used business 1L PC and a NAS with sleeping drives all land within a few watts of each other. In the fanless N100 review, ServeTheHome noted that an HP Elite Mini 600 G9, a 35 W TDP 1L PC with a fan, idles under 8 W, which beats that N100 appliance. The hardware class sets the range; the specific board decides where in it you land.
Where each one wins
Raspberry Pi 5: lowest floor, shortest job list. At 3.0 W headless, nothing else here comes close. It suits one or two light services: Pi-hole, a WireGuard endpoint at a relative’s house, a Home Assistant install you never touch. It is ARM, so check every image for linux/arm64 support, and NVMe storage needs an add-on adapter. CNX also measured 1.7 W with the board powered off, a reminder that “off” is not zero.
N100 mini PC: the default. x86, four cores, a dozen containers without strain, and a sub-10 W idle on a decent board. The N100 buying guide covers which specs separate the good units from the 12 W ones.
Used 1L business PC: more slots, a few more watts. ServeTheHome’s dual-core M720q idled at 11 to 14 W, never passed 50 W, and has room for a PCIe network card. Newer 1L units can match an N100 at idle. The M720q vs N100 comparison weighs that trade, and a Wyse 5070 thin client is the cheaper step down.
NAS: low energy only while the disks sleep. Synology lists the DS923+ at 11.52 W with drives hibernating and 35.51 W during access. That 24 W swing is the price of waking the drives and putting them to work, and a NAS that streams media every evening and runs backups overnight doesn’t spend much of its day hibernating.
HPE MicroServer Gen11: a real server in a small cube. About 27 W idle with one 4 TB drive is respectable for a Xeon E-2434 platform, and still more than three times the CWWK N100’s idle. Buy it because you want server hardware, not because it is efficient.
Rack server: skip it unless the point is learning enterprise gear. Dell’s own SPECpower run of an R720 with two Xeon E5-2660s, 24 GB in six DIMMs and a single SSD idled at 53.8 W. That is the lean configuration. A homelab R720 with more DIMMs and a shelf of spinning disks only climbs from there, and rack fans are designed for a datacenter, not a spare bedroom.
What actually sets a server’s idle draw?
Board design, firmware and peripherals set idle draw more than the CPU does, which is why the same N100 reads 7.4 W in one chassis and 12 W in another. Once you’ve picked a hardware class, these levers decide where in its range you land:
- Spinning disks. Often the largest idle load in the box. Keep service machines SSD-only, and read storage options for a mini PC homelab before adding a 3.5-inch drive.
- Displays and peripherals. CNX’s Pi 5 rose from 3.0 W headless to 3.6 W with Ethernet, a keyboard, a mouse and HDMI connected. Run headless.
- Firmware. Deep package C-states and PCIe ASPM are sometimes limited out of the box. The 24/7 BIOS checklist lists the toggles.
- The OS. PowerTOP diagnoses what keeps the hardware awake, and
sudo powertop --auto-tuneapplies its recommended settings in one pass. A single chatty container that wakes the CPU constantly can undo all of it. - Oversized power supplies. The R720’s 53.8 W idle is about 7% of its 750 W PSU’s rating, a load range where a big supply is rarely at its most efficient. A small external brick matched to a small box sidesteps this.
Then verify with a plug-in meter rather than trusting any table, including this one. The method is in measuring mini PC idle wattage.
Which one to pick
Buy an N100 mini PC with SSD storage, spend ten minutes in the BIOS, and expect a single-digit idle on a good board. That covers DNS, a reverse proxy, Home Assistant, a media server and a pile of other containers for about $14 a year at $0.20/kWh. The low-power 24/7 build is the parts list for exactly that.
Pick differently in these cases:
- One tiny job. A Pi 5 does it for about $5 a year, as long as the software ships for arm64.
- Many terabytes. Use a NAS with drive hibernation configured, kept separate from the service box. Budget for Synology’s 35 W-class draw while the drives work; for bulk storage it is still the right tool, and better than bolting 3.5-inch drives onto a mini PC.
- You already own a big server. Meter it before replacing it. Swapping a 53.8 W idle machine for an 8 W one saves 45.8 W, about 401 kWh or $80 a year at $0.20/kWh. Compare that against the replacement’s price, and keep the old box if the payback runs past its useful life.
- You need one public website. A small VPS is a perfectly good answer. The cloud is fine for plenty of things, and it uses none of your electricity.
If you are planning a whole setup rather than one box, the homelab watt budget guide sizes compute, storage and networking against a single target number.
FAQ
what is the most energy efficient home server
A Raspberry Pi 5 has the lowest idle draw of common home server hardware, about 3 W headless in CNX Software’s review, but an N100 mini PC is the better all-rounder. At roughly 7 to 8 W idle on a good board, it runs x86 containers and a dozen services for about $9 a year more at $0.20/kWh.
how many watts does a home server use
A home server uses from about 3 W to well over 50 W at idle, depending on the hardware class. Published figures put a Raspberry Pi 5 near 3 W, N100 mini PCs and 1L business desktops at roughly 7 to 14 W, a compact Xeon MicroServer near 27 W and a lean dual-socket rack server at 53.8 W.
how much does it cost to run a server 24/7
Each watt drawn around the clock uses 8.76 kWh a year, so multiply your server’s average wall draw by 8.76, then by your electricity rate per kWh. At an illustrative $0.20/kWh, an 8 W mini PC costs about $14 a year, a 27 W MicroServer about $47, and a 53.8 W rack server about $94.
do hard drives use a lot of power in a home server
Yes, spinning hard drives are often the largest idle load in a home server. Synology lists its four-bay DS923+ at 11.52 W with drives hibernating and 35.51 W during access, a 24 W swing. Keep service boxes on SSDs and put bulk disks in a NAS configured to spin them down when idle.
is a raspberry pi 5 good enough for a home server
Yes, for one or two light jobs such as Pi-hole, a VPN endpoint or Home Assistant. It idles around 3 W, but it is an ARM board, so x86-only container images will not run, and NVMe storage needs an add-on adapter. Past a handful of containers, an N100 mini PC is the better buy.
