Distributed Power Management (DPM) is a powerful (powerless, really) feature can reduce host power consumption in a DRS cluster. It works in either manual mode or automatic mode only when DRS is enabled. DPM can place idle hosts into standby mode, or awaken them from standby when more resources are needed.
Like most of the features in vSphere, you can manage them with the APIs. A recent question at the open source vSphere Java API forum asks how to get hold of the DpmBehavior data object. This seems easy but