Caution, some SSDs use almost as much power as some HDDs, ie around 5 Watts. So make sure the SSD you pick is infact low power, ie around 2 -> 3 Watts when ACTIVE. Performance wise a fair -> good SSD (Not just the high end) will out preform the mechanical HDDs. Random 4 K read/writes, 10 -> 40 times better, access time 0.1 or 0.2 mSec vs 10->12 milliseconds for a HDD.
If for a desktop, don't sweat the power difference - insignificant percentage wise. Only a concern for laptops and max run time on battery.