No, it's not as energy efficient as the MacBook Air. How could it be? Apple lists the expected (high end) battery life for each of their battery powered devices on their site. If battery life and a large screen are your primary interests, it sounds as though you'd be better off getting an iMac or a Mac Pro, assuming you need the dedicated graphics card. If you don't need the dedicated graphics card, there's always the Mac Mini. These all either come with large screens or can be easily attached to large monitors and their power lasts for as long as you pay your electricity bill. And you won't have to worry about becoming a hunchback from using the least ergonomically designed piece of modern tech, the laptop.