There is number of arguments that can be passed to the open-source Intel Linux DRM kernel driver to reduce power consumption. These enable power-saving features of the Intel Linux graphics driver that aren't enabled by default at this time, commonly because for some hardware configurations they can cause stability problems or other issues.
i915.i915_enable_rc6=1 - RC6 was enabled by default for a while, but then it ended up being too buggy for some hardware configuration so it had to be disabled. For affected systems on the current code-base, enabling RC6 can cause GPU hangs. The Intel RC6 feature allows the GPU to enter a lower power state when the GPU is idling.
i915.i915_enable_fbc=1 - This kernel option enables FBC (frame-buffer compression) for the Intel graphics driver. Frame-buffer compression is not enabled by default since for some systems when frame-buffer compression is active there is a bug where the screen is not being properly repainted when using a compositing window manager. As implied by the name, frame-buffer compression will compress the buffer of what's to be drawn to the screen so that less memory bandwidth is used on screen refreshes, and as a result, less memory being confused.
i915.lvds_downclock=1 - This kernel option will down-clock the LVDS refresh rate, which can increase power savings as a result. However, for systems that do not properly support LVDS down-clocking, the screen can begin to flicker during use.
These options can be added to GRUB boot-loader when booting the system, to the grub.cfg file to be made permanent, or can be passed if manually loading the Intel i915 kernel module.