Power Efficiency linearly affects the energy cost of Warframe abilities. All Warframes have a base Power Efficiency of 100%; Power Efficiency over 100% indicates a reduction of ability cost while Power Efficiency below 100% indicates an increase in ability cost. The Arsenal will not display a Power Efficiency above 175% because abilities cannot consume less than 25% of their base costs.
- Final Ability Cost = Ability Cost × (2 − Power Efficiency)
Channeled abilities drain energy at a specified rate. Power Efficiency affects the energy drained at each tick as expected, but because Power Duration affects the amount of time between these ticks, the formula for effective Power Efficiency for channeled abilities is as follows:
- Final Energy Drain = Energy Drain × ((2 − Power Efficiency) ÷ Power Duration)
An important point worth mentioning is, as seen in the spreadsheet on the right, that the cost of such abilities is minimised at 190% efficiency and 40% duration, which is achievable with just two mods(Streamline and Fleeting Expertise).
The in-game energy bar display is rounded down to the nearest whole number, but the costs of the abilities are not. This results in the discrepancies in the apparent cost of abilities with Power Efficiency mods. For example, an ability with 25 energy base cost will cost 17.5 energy with maxed Streamline (+30%). If this ability is used multiple times in a row, it will appear to cost 18 energy, then 17 energy, then 18 energy, then 17 energy and so on.
Streamline, Fleeting Expertise, Blind Rage and the positive Power Efficiency Arcane Helmets stack additively. Stacking with Meridian Trinity Helmet or Scorpion Ash Helmet does not appear to follow this formula; this suggests stacking is different when you have a helmet that reduces Power Efficiency.
Arcane Helmets also reduce (or increase) ability costs linearly based on the percentage shown on the mod card. The following helmets affect Power Efficiency:
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