Energy Capacity

Energy of a warframe is used mainly to power abilities and melee channeling. All warframes have 4 abilities that at base, cost up to 100 energy to cast. Every warframe has their own energy-pool with varying capacities depending on the types and costs of their various abilities.

Like health and shields, a warframe's energy capacity scales with their rank and through the use of mods or buffs. It is also worth noting that the words "power" and "energy" are often used interchangeably by members of the community

Mods
These are the mods currently available in the game. It is worth noting that Flow and Primed Flow cannot be used in the same build.

Formula For Modded Energy Capacity
These mods increase the energy capacity of a warframe following the following formula:

$$\text{Energy}_{total}=\text{Energy}_{max}+(\text{Energy}_{base}\times \text{Mod Multiplier})$$

So as an example taking Volt Prime with 200 base energy and 300 max energy he will have:
 * With Flow: $$ 300 + (200 \times 1.5)=600$$
 * With Primed Flow: $$300+(200 \times 2.75)=850$$
 * With Primed Flow and Endurance Drift: $$300+(200 \times 2.90)=880$$

Buffs
The only buff currently available to increase energy capacity is Cephalon Suda's Entropy effect. Entropy will release an AoE radial attack 25m around the player, dealing 1000  damage and applying the Magnetic Status Effect to enemies in range reducing their shields. It will also restore 25% of the player's base Energy, and provide a (base) Energy boost of +25% for 30 seconds.

Formula
Upon loading into any mission, each warframe has a fixed amount of energy that they start with. This amount of energy is calculated based off of the warframe's free mod capacity and a base value specific for each warframe (differs even between normal and prime variants). The formula followed is: $$\text{Starting Energy}=\text{Initial Energy}+5(\text{Free Mod Capacity})$$

Table of Initial Energies
The initial energy of the warframes is given from the following table. Do note that this table is currently still under construction and it is still unknown whether these values are calculated off some other attributes or simply fixed parameters for each warframe. This area of research is still very actively pursued.

Casting Effective Capacity
Similarly to how one can define the concept of "effective health" by weighting the number of hit-points with the corresponding damage reduction, one can also define the concept of casting effective energy capacity by weighting the energy capacity using the Ability Efficiency factor: $$\text{Effective Energy Capacity}_{casting}=\frac{\text{Energy Capacity}}{2-\text{Ability Efficiency}}$$

Since casting efficiency is currently capped at 175%, the highest possible upper-bound for the casting effective energy capacity is: $$\text{Effective Energy Capacity}_{casting}\leq 4\times\text{Energy Capacity}$$

Toggle Effective Capacity
Since the efficiency of toggle abilities depends also on the duration, in that case the formula becomes: $$\text{Effective Energy Capacity}_{toggle}=\frac{\text{Energy Capacity}\times\text{Ability Duration}}{2-\text{Ability Efficiency}}$$ For the case where no energy is recovered and a constant rate of energy drain, one can also consider the effective toggle duration as follows: $$\text{Effective Toggle Duration}=\frac{\text{Effective Energy Capacity}_{toggle}}{\text{Base Drain Rate}}$$ $$\text{Effective Toggle Duration}=\frac{\text{Energy Capacity}\times\text{Ability Duration}}{\text{Base Drain Rate}(2-\text{Ability Efficiency})}$$ $$\text{Effective Toggle Duration}=\frac{\text{Energy Capacity}}{\text{Modified Drain Rate}}$$

Due to the definition of the terms, there are many ways in-which the formula for effective toggle duration can be expressed.

Apart from toggle duration, this can be used to work out the effective duration granted per energy pick up.

Examples
Suppose a prowling Ivara has a modded drain of 0.25 energy/sec. An orb of 50 energy would provide:

$$\frac{50}{0.25}=200\text{ seconds}$$

Considering the same Ivara with full energy pool of 744 capacity, she can remain in prowl for:

$$\frac{744}{0.25}=2,976\text{ seconds}\approx 50\text{ minutes}$$

Restoring Energy
In missions, there are various ways to restore energy:
 * Energy can be picked up during a mission from Blue Orbs. Blue Orbs dropped by enemies restore 25 energy while containers drops will restore 50 Energy.
 * Some Arcane Alternate Helmets affect a Warframe's maximum energy.
 * Harrow's Thurible grants players inside its aura a variable amount of energy from kills made by Harrow, depending on how long the ability was charged and whether the enemies were killed by bodyshot or headshot.
 * Trinity's Energy Vampire allows a player to regain energy by standing inside the energy pulses the target releases (target is stunned the entire time).
 * Limbo's Rift Plane slowly restores energy for all players within it. Can stack with Energy Siphon.
 * Octavia's Inspiration passive slowly restores energy over time for all players that were near Octavia when she cast an ability.
 * Team Energy Restores are consumables that grant Energy to nearby teammates in varying amounts, up to 400 total.
 * Weapons triggering an Entropy effect restore 25% of the player's base Energy, and provide a base Energy boost of +25% for 30 seconds.
 * Weapons triggering a Blight effect restore 25% of the player's base Energy, and provide a (base) movement speed boost of +10% for 30 seconds.
 * Zenurik's focus nodes have multiple ways in which a player can regenerate energy.
 * Notable mods that affect energy generation:
 * - Converts damage on health to energy.
 * - Health pickups restore a certain amount of energy alongside health recovery (but only if the Orb is picked up).
 * The Aura slowly restores energy for all players based on its mod rank. Multiple copies of this aura allow for faster energy recovery.
 * - Improves the Warframe's equipped Aura, including.
 * Notable arcanes that affect energy generation:
 * Arcane Energize
 * Exodia Brave

It is important to note that on most occasions, toggle abilities disable energy generation from team abilities, consumables, or passive regeneration methods

Mods
These mods stop lethal damage by allowing hits to drain your energy after your health is depleted in exchange for occasionally staggering the player