Apple's latest 2011-2012 MacBook Air and 2012 Retina MacBook Pro systems support a new power-saving mode called PowerNap, which allows the systems to perform a number of background tasks when in Sleep mode, thereby maintaining low power but preventing a flurry of synchronization and update activity when the system is woken up.
When activated, the system should go into Sleep mode as usual, but periodically you should see activity with an attached Time Machine drive, and also see received e-mail messages, updated contacts, iCloud content, and also be able to use Apple's Find My Mac remote access features. If these are not working for your system then there may be a few things you can do to correct the problem.
First, even though it is supported on the MacBook Air and Retina MacBook Pro, PowerNap still requires a firmware update to work properly. While moving forward, new systems will have this capability installed at the factory, Apple did not provide this with initial batches of the systems. Therefore if you purchased one recently and PowerNap is not working, then be sure to check Apple's Software Update service (in the Apple menu) and apply any firmware updates that are available.
These updates will only be available for supported models, and even though the requirements for PowerNap are that the system contains flash storage, this does not include those that are capable of accepting conventional hard-disk drives. Therefore, non-Retina MacBook Pro models (even new ones) will not be able to use PowerNap.
If you have updated the system's firmware and PowerNap still does not appear to be working, then try attaching your system's power adapter. Some PowerNap services require the power adapter to be present as an extra precaution against power loss and to provide slightly more power for the service if needed. These services include backing up to Time Machine, indexing the hard drive with Spotlight, and installing system and application updates from the Mac App Store.
In addition to some services needing an active power connection, PowerNap will not work if the battery is low. To ensure the system has ample power for continued function, if the battery charge falls below 30 percent then the system will disable PowerNap. This may be the case before you put the system to sleep, or may happen while the system is in Sleep mode.
If PowerNap is still not working after you have updated the firmware, enabled it in the Energy Saver system preferences, and ensured the system is charged and connected to a working power source, then you can try resetting the system management controller (SMC), which is the component that received the firmware update and which manages the PowerNap feature. The procedure for resetting the SMC on systems that support PowerNap is the following:
- Shut down the system and plug it into a power source
- Press and hold the left Shift, Control, and Option keys on the left side of your system
- Press the power button, and then release all keys at the same time
- Start up your system again
In addition to resetting the SMC, if you have enabled a firmware password on your system for security purposes then you might try disabling it. A firmware password should only affect boot options, but it may help to toggle it off and on. This password can be set and reset by booting to the OS X Recovery HD partition (hold Command-R at startup) and then choosing the Firmware Password Utility from the Utilities menu after you select your language.
Finally, if no other options enable the PowerNap feature, then try reinstalling OS X using the tools on your Recovery HD partition. Doing so will not affect your personal files and settings, and will seamlessly reapply the OS software on your system. This may help kick on the PowerNap feature and allow it to properly work. Ensure you have the latest firmware updates for your MacBook installed before you reinstall the OS.