You'll want DIPM to be activated, which depends on driver support and also the right SSD controller which doesn't have problems with this technology.
DIPM, or Device-Initiated Power Management, will only activate the SATA link whenever data is to be transferred. This means massive power savings. For example, Intel is rated at 0.6W idle for their X25-M SSD, but with DIPM enabled this drops to a meager 65mW; almost 10 times less idle power. Even during usage the DIPM would show massive power savings unless you're doing massive sequential reads or other workloads that keep the SATA link very busy.