In home server use cases, mini PCs stay idle the vast majority of their runtime. So it's idle power consumption that is the most useful metric to look into. The N100 can have great idle performance in theory, but most data I can find about N100 boxes is them idling in the 12W-15W range. This is something that older enterprise mini desktops have no trouble matching or beating [1]. Especially since roughly the Skylake era (Intel 6th gen), idle power consumption for enterprise PCs has been excellent - but even before then it wasn't bad.
Enterprise vendors like Dell/HP/Lenovo have always optimized for TCO and actually usually use quite high quality power supply circuitry, whereas most N100 mini PCs tend to be built with cheaper components and not as optimized for low power usage for the whole system.
[1]: I recommend reviewing Serve The Home's TinyMiniMicro project, which often finds the smallest enterprise PC form factors to idle at 8 to 13W, even older ones. Newer systems can get below 7W! https://www.servethehome.com/tag/tinyminimicro/
I have a bunch of SFF computers (Dell 7060, HP 600 G4, etc) with i7-8700 or similar CPUs. They all idle around 12 watts.
Most of the mini pcs use the T version of the processors, which are usually 35w TDP.
Power usage will definitely be higher than an N100 (65W TDP vs 6W), but they're a lot more versatile since you're getting more than double the performance, 2-3x the threads, and an iGPU that can do things like transcoding for plex and accelerate ML models for Frigate/Scrypted.
The N100 is definitely powerful enough run a ZFS RAID array. Depending on what all you'd like to run, it might be enough. Check it out with cpubenchmark's compare feature!
I used a Celeron G4900 (also has an iGPU) as a plex server for years, and it's half as powerful as an N100. The celeron is a fairly slow processor, but for plex it was enough since the iGPU did the heavy lifting.
I'd highly recommend joining the serverbuilds dot net discord. They also have a forum with pre-specced NAS build configurations, complete with pricing. People there are very helpful and will give realistic advice.
I think Jellyfin beats Plex on 4k transcoding (tonemapping?) with the iGPU, but fwiw I do not transcode 4k and add subtitles to them just fine. I use an nvidia shield, which direct plays 4k content with the added subtitles. Hearing about transcoding 4k content just to add subtitles is news to me.
In the US electric power might be cheaper. And if it's running only part of the time, you should adjust the calculation.
My desktop/server runs 24/7, so I prefer having a CPU with 65W TDP over one that is 125W TDP. That might run up to 120 Euro per year difference for me (if it would be running at 100% CPU).
I ended up going with a HP EliteDesk 800 G5 Mini I5-9500T (35W) off of Ebay for $100 and it does the stuff I need it to do just fine. According to my current monthly power usage graph, it's averaged 7W which accounts for $0.61 of this month's power bill.
When I did this I was surprised by how much - or how little - it cost to run various devices. It's quite addictive.
It's not always accurate because a lower-power machine doing the same task will often need to work at its full power more often, so the savings may be less. For example, a Raspberry Pi 5 may often be more power effecient than a Pi 4, despite drawing more power at full capacity on paper, because it spends less time at full capacity than the Pi 4 does.
On the other hand, when I upgraded my work PC I found it used less power but I also had to run my office heater more often in winter, as the new PC wasn't as efficient at heating the space.
Just from tweaking my laptop, I’ve noticed that when it is really idle (or I’ve intentionally put it in a low frequency mode), the big power drains are the wireless interfaces (don’t forget bluetooth) and the screen (OLED helps as long as the screen is mostly black). Gotta tweak the whole thing.
So, it goes quite quickly. Savings of 20 watt save you $ 52 a year.
Edit: I should note that there's no fan drawing power because I put it in an Akasa passively cooled case.
The new computer cost me $240 back in late 2022 (with 32GB of RAM and WiFi) so it'll basically pay for itself in electricity savings - and it's 3x faster than what it replaced.
ServeTheHome has some good reviews: https://www.servethehome.com/tag/tinyminimicro/. The tl;dr is just that there's good options from Dell, HP, and Lenovo and the differences are kinda minor, but it's a good source if you care about specific information and teardowns.
It's a great little machine, takes up almost no space, it's almost silent, and it was basically free with the power savings - in fact, once I pass the two year mark, it was cheaper to get the new hardware than to keep running the old.
And you can put Proxmox on it as a hypervisor to run multiple OSs or containers.
Math: 1,000 watts /65 watts/hour = 15.384 hours per kwh. 365.25 days/year * 24 hours/day = 8766 hours/yr <=(accounting for leap days) 8766 hours/yr / 15.384 hours/kwh = 569.81 kwh/yr 569.81 kwh/yr * $0.12/kwh = $68.377/yr
For quick math where accuracy isn't very important, at $0.12/kwh it will cost you ~$1.05/year per watt (65w = $68.38/yr), so every watt you save per year is a dollar in your pocket.
Of course, there are ways to reduce the energy usage of a system, a computer rarely has to run at 100% 24/7/365 unless it is very underspecced for your use case, even things as simple as enabling C states and not utilizing all of the PC resources available will save you many dollars a year.
Looking at the OP, there's a ton of i5-8500s in the same price range as a new n305 on Amazon (not bargain hunting here, I'm sure you can find either option much cheaper anywhere). Compared to an N305, a i5-8500 has less cores/threads (6), has al least 4x the TPD, and has a significantly worse GPU. And many people want to buy new. But the used i5 is more expandable, and particularly affords more max memory.
There isn't one uncontested "best".