Usually an SSD will consume less power. And certainly less than typical HD spin up.
and much less heat. I keep my tablo in a small draw, it has airflow through slots in the bottom of the draw but the tablo gets hot on its own, if you store the hard drive on top, it gets much hotter...
If the SSD supports USB 2.0, it's not suppose to draw more power then the max allowed for the USB 2.0 standard.
But the actual ssd memory maybe be SLC, MLC, or TLC, and that affects the life cycle before cell failure.