Streamline

The Streamline mod increases your warframe's Power Efficiency, which decreases the energy cost of abilities. The cost of activating an ability when using the Streamline mod is:
 * Cost = Base Energy Cost divided by (100 + X), where X is the percent power efficiency, and the result is always rounded up.

Power Efficiency
Below are examples of the base energy cost, and reduced energy cost associated with using a max level Streamline mod, which gives a Power Efficiency of 30%.