If you could point me to a <20W machine with ECC memory that I can buy online like a mere mortal human person, then I'd very interested!
The only thing that comes to mind in that category for me is the PC Engines APU2. The APU2 is a very neat piece of kit, don't get me wrong, but it being the only option is not great either.
The D-1529 can be TDP limited to 20W (at a whopping 1.3GHz), but if you goal is idle power consumption under 20w you are better off with one of the 35w TDP D-1602 since it is only a dual core and has the lowest standby consumption. The D-1518 is also a popular choice, and basically the same as the D-1529 but with a 35W tdp limit so it can turbo to 2.2GHz.
note - the xeon-d series is not socketed, so the motherboard price includes the CPU. Make sure to get board that takes full size DIMMS since there is not a lot of ECC laptop memory on the market.
I'm aware of the Xeon D line, but sadly that was also squarely aimed at the enterprise albeit maybe a smaller scale enterprise. It's not something you can easily go out and buy any more, and when you do it's both very expensive, still PC sized, and not any more power efficient at idle or configured TDP when compared to a new Intel workstation or new AMD setup.
EBay offers a number of Xeon D boards at reasonable prices, many with extensive passive cooling. They have a lot of life left in them, to my mind, with good enough power efficiency for a box with normally very low CPU load. No moving parts, nothing to break. Yes, they are not speed demons, but low TDP presumes that anyway. ECC RAM support is there, though.
I bought it from that page. I wanted fanless silence and I wanted ECC and it took me a long time to find this machine but found it I did and it works. Linux reports seeing the ECC is indeed enabled (edac-utils?). Measured with a Kill-a-Watt meter it does consume more than 20W (maybe 30ish IIRC?). I actually disabled some Linux power management though to get bluetooth mice and keyboards to not lag after being idle for 5 seconds so my system might draw more power than others. Drives a 4K display buttery smooth, can watch all the YouTube and Netflix you want on Linux.
