According to Pocket News, in an article which was translated by Eurogamer, the new PS4 uses 8 memory modules instead of 16 memory modules, both of which give 8GB of RAM. This apparently reduces the overall power consumption, and energy consumption is reduced somewhere between 30 to 50 percent during standby, and around 18 percent while fully turned on.
On top of that, the PS4 is noticeably quieter. It also generates less heat, as it no longer uses up as much energy as it did before. A few other changes were made, such as a smaller motherboard and a slightly different HDMI controller, but it is clear that the real bonus of the new PS4 is that it uses considerably less power.
Currently, it is unknown when this new version will be released outside Japan, although there is a 1TB PS4 set to launch this month in Europe.