TDP = Thermal Dissipate Power / To Dissipate Power.
TDP does not measure power consumption, it measures the amount of cooling needed to run a certain device.
SSDs emit significantly less heat than your spindle drive does.
And TDP is also ALWAYS rounded up to the nearest "standard cooling device" (and sometimes new standard coolers are made due to marketing demands).
Now, all that being said, if you are asking about power comsumption:
1. It varies by exact model for both SSD and spinde.
2. laptop spindle drives have surprising low power consumption
3. SSDs with high power consumption exist, but are rare.
4. The fact that good SSDs are faster means that the system as a whole will do more work, and can result in a perceived battery life drop. (your computer now runs for 2 hours instead of 2.5 hours, but performs twice the amount of actual work during those 2 hours then it would have in 2 hours before).