timelinex_acpi - simple kernel module that disables ATI discrete VGA-card.
make
sudo make install
echo timelinex_acpi | sudo tee -a /etc/modules > /dev/null
Deny Radeon module to start with
echo "blacklist radeon" | sudo tee -a /etc/modprobe.d/blacklist.conf > /dev/null
After reboot your Radeon is deactivated.
see Documentation
Now you can install TLP
sudo add-apt-repository ppa:linrunner/tlp
sudo apt-get update
sudo apt-get install tlp
Start tlp with
sudo tlp bat
sudo tlp start