HDD vs SSD NAS Running Cost Calculator: What's the Real Electricity Difference?

The Real Power Difference Between HDD and SSD in a NAS

A spinning NAS hard drive (IronWolf, WD Red Plus) draws 5 to 8W under load and 1.5 to 4W at idle. An equivalent-capacity NAS SSD draws 0.5 to 2W at all times. In a 4-drive NAS running 24/7, that difference adds up to 50 to 100 kWh per year. At AU electricity rates of 25 to 40 cents per kWh (depending on state), that is $12 to $40 per year saved by switching to SSDs. For most users, this saving does not justify the $400 to $800 upfront premium of SSDs over HDDs of equal capacity.

The maths changes in specific situations. A 2-bay NAS used purely for backup, running spin-down with infrequent access, sees very little active time and HDDs may actually draw less average power than SSDs (which consume their idle wattage continuously). A 4-bay NAS accessed heavily during business hours but running spin-down overnight shifts the calculation significantly. This calculator lets you model your actual usage pattern: active hours, idle hours, and spin-down hours separately.

When SSDs Make Sense in a NAS

SSDs make sense in a NAS when noise and vibration matter more than cost: SSDs are silent, HDDs vibrate enough to cause resonance in multi-drive enclosures. They also make sense when drive durability over a 3 to 5 year period is the primary concern: enterprise SSDs have predictable, measurable endurance ratings in TBW (terabytes written), while HDD failure is less predictable. For a home NAS under 16 TB capacity storing photos and documents, the break-even between SSD premium and electricity savings is typically 8 to 20 years, making SSDs a preference choice rather than an economic one.

NVMe SSDs in a NAS M.2 slot (cache tier) are a separate consideration entirely: they serve as a read/write cache for HDDs, combining the fast random I/O of SSD with the bulk capacity of HDD. This calculator covers drive-for-drive running cost only.