We tested the peak power consumption of a NAS at the wall during a run of CrystalDiskMark 5.0.2 as this version of the benchmark runs the read and write benchmark suites separately so its easier to monitor what power the device is using during each function.
The W5810 is powered by a CPU with a TDP of just 10 watts and has an SSD (0.35W active typical) holding the OS so with the careful selection of the storage drives, the power demands can be kept reasonably low. The 6TB WD Reds used for testing have an average power rating of 5.3W when actively reading and writing and an idle rating of 2.8W.