Robot Energy Consumption: How to Compare Idle, Task, Charging, and Auxiliary Power

A buyer compares two robots for a production line. Robot A has a rated power of 3 kW. Robot B has a rated power of 5 kW. The buyer assumes Robot A is more energy-efficient. In production, Robot A consumes more energy per part than Robot B, because Robot A's cycle is longer, it idles at a higher power level, and its auxiliary equipment (vacuum pump, conveyor) runs continuously. Robot B completes the same task faster and powers down between cycles. The rated power told the buyer nothing about actual energy consumption. This article explains how to measure and compare robot energy consumption in a way that reflects actual operating conditions, not datasheet numbers.

Rated kW and Actual kWh Answer Different Questions

Rated power (kW) is the maximum electrical power the robot system draws under specified conditions. It is a design parameter used for sizing electrical supply and breakers. It is not a measure of energy consumption.

Energy consumption is measured in kWh (kilowatt-hours) and depends on:

• Power level: How much power the system draws at each moment
• Time: How long it draws each power level
• Duty cycle: What fraction of the time the system is active vs idle vs off

A robot with a 3 kW rated power that runs at 1.5 kW average for 8 hours consumes 12 kWh. A robot with a 5 kW rated power that runs at 1.0 kW average for 6 hours (because it completes the same work faster) consumes 6 kWh. The higher-rated robot uses less energy because it works more efficiently.

The buyer needs kWh per shift or per task, not kW. The rated kW is a starting point for electrical design, not an energy comparison metric.

Define the Measurement Boundary First

Energy measurement depends on what is included in the measurement. Different boundaries produce different results:

• Robot only: The robot arm and controller. Does not include EOAT, safety, vision, or process equipment.
• Robot + EOAT: The robot plus the end-effector and its utilities (vacuum, gripper, sensor).
• Full cell: The robot, EOAT, safety system, vision, conveyor, process equipment (welder, dispenser, spindle), and lighting.
• AMR + battery + charger: For mobile robots, the robot, its battery, and the charging station. The charger's AC input includes charging losses.
• Fleet or site: Multiple robots plus shared infrastructure (compressors, HVAC, lighting).

Robot-only vs full-cell meter

Comparing two robots' energy consumption is only meaningful if the measurement boundary is the same. If Robot A is measured at the robot-only boundary and Robot B at the full-cell boundary, the comparison is invalid. The full-cell measurement will always be higher because it includes more equipment.

The buyer should define the measurement boundary before collecting data and ensure that all comparisons use the same boundary. If the full-cell energy is what matters for the buyer's energy management, the measurement should be at the full-cell boundary, even if the robot manufacturer can only provide robot-only data.

Measured electricity becomes one cost input in a robot fleet TCO, but TCO does not establish the technical meter boundary.

Break Down Idle, Motion, Process, Wait, and Charging

The robot system's power consumption varies throughout the cycle:

• Idle: The robot is powered on but not moving. The controller, drives, and sensors draw standby power. The idle power level varies by robot model, controller generation, and configuration, and should be obtained from the manufacturer's specifications or measured directly.
• Motion: The robot is accelerating, moving, or decelerating. Power consumption peaks during acceleration and may be near zero during deceleration (if the drives regenerate energy).
• Process: The robot is performing a process (welding, dispensing, sanding). The process tool may draw significant power independently of the robot.
• Wait: The robot is holding position while waiting for an external event (part arrival, process completion). Power consumption is similar to idle but may include holding torque.
• Charging (for AMRs): The battery is being charged. The charger's AC input includes charging losses and BMS overhead.

The buyer should measure or estimate the power level and time duration for each state in the production cycle. This produces a power-time profile that shows where the energy is actually going.

Payload, Acceleration, and Robot Path Effects

The motion energy depends on:

• Payload: Heavier payloads require more torque to accelerate, drawing more current
• Center of gravity: Offset CG increases the moment on the wrist joints, increasing energy for wrist motions
• Acceleration: Higher acceleration draws more peak power but for a shorter time. The energy per motion may be similar (energy = force × distance), but the peak power demand affects the electrical supply sizing.
• Path: A path with many direction changes requires more acceleration and deceleration than a smooth path, consuming more energy
• Regeneration: During deceleration, the drives may regenerate energy back into the electrical system or dissipate it as heat (braking resistor). Regenerative systems reduce net energy consumption.

An empty-load test (robot moving without payload) does not represent the production energy consumption. The test must use the actual payload and the actual motion path.

AMR Battery Energy vs Facility-Side Charger Input

For mobile robots, energy measurement has an additional complexity: the battery stores energy, and the measurement point determines what is being measured.

• Battery Wh: The energy stored in and discharged from the battery. This is the energy available for the robot's operation.
• BMS reserves: The battery management system may reserve a portion of the battery capacity (e.g., 20% minimum charge) to protect the battery, reducing the usable energy.
• Charger AC input: The energy drawn from the facility's electrical supply to charge the battery. This includes the charger's conversion losses and any BMS overhead. The actual conversion efficiency varies by charger design, power level, and battery chemistry, and should be obtained from the charger manufacturer's specifications.
• Charger losses: The difference between the AC input energy and the energy delivered to the battery.

Battery discharge is not AC grid consumption

A common error is to equate the battery's Wh rating with the facility's energy consumption. A robot with a 500 Wh battery that runs for 4 hours does not consume 500 Wh from the grid. It consumes 500 Wh from the battery, which was charged from the grid at some efficiency (e.g., 85%). The actual grid consumption to charge that battery is approximately 500/0.85 = 588 Wh, plus any standby losses in the charger.

The buyer should measure energy at the point that matters for their energy management: typically the AC input to the charger or the submeter on the robot's electrical circuit.

mobile robot battery specifications explain Wh, runtime and charge cycles; the present comparison must measure the facility-side energy boundary.

Auxiliary Equipment May Dominate Cell Consumption

In many robot cells, the robot arm is not the largest energy consumer. Auxiliary equipment may draw more power:

• Welding power supply: May draw 10-20 kW during welding, far more than the robot arm
• Vacuum pump: May run continuously at 1-3 kW even when the robot is idle
• Compressor (shared): Provides compressed air for pneumatics; may be a facility-level cost
• Conveyor: Runs continuously regardless of robot activity
• Extraction/dust collection: Runs during process operations
• Oven or UV cure station: May draw significant power for temperature maintenance
• Lighting: Cell lighting is a small but continuous load

If the measurement boundary includes auxiliary equipment, the robot's energy consumption may be a small fraction of the total. The buyer should identify the major energy consumers in the cell and focus energy reduction efforts on the equipment that matters most.

The cobot cell cost breakdown covers peripheral investment, whereas electricity metering must include ongoing loads from those peripherals.

Normalize by Useful Work

Energy consumption is only meaningful when normalized by useful output:

• Wh per part: Energy per completed part (for assembly, machine tending)
• Wh per delivery: Energy per delivery task (for AMRs)
• Wh per move: Energy per motion cycle (for pick-and-place)
• kWh per cleaned area: Energy per unit of surface processed (for sanding, polishing)

Wh per task versus kWh per shift

kWh per shift tells the buyer how much energy was consumed. Wh per task tells the buyer how efficiently the energy was used. Two robots that consume the same kWh per shift but produce different numbers of parts have different energy efficiency. The one that produces more parts per kWh is more efficient.

The normalization must define what counts as a “task” or “part.” Does a failed task (retry, reject) count? Does idle time between tasks count? The buyer should define the denominator clearly so that comparisons are consistent.

Repeatable Energy Measurement Protocol

To compare energy consumption between robots or configurations, the measurement protocol must be consistent:

• Payload: Use the same payload (actual production payload, not a dummy mass)
• Program: Use the same motion program (same path, same speed, same acceleration)
• Ambient conditions: Same temperature, same voltage supply
• Warm-up: Allow the system to reach thermal steady state before measurement
• Meter location: Same measurement point (same boundary)
• Duration: Measure over a representative number of cycles (not one cycle)
• Task count: Record the number of completed tasks during the measurement period
• Downtime: Record any downtime or non-productive time during the measurement
• Multiple runs: Repeat the measurement to verify consistency

A power meter (clamp meter, submeter, or power analyzer) should be installed at the defined measurement boundary. The meter should record power (W) and energy (Wh) over time, with a resolution sufficient to capture the cycle-level power variations.

Energy Data Questions for Supplier Comparison

When comparing suppliers, the buyer should ask:

• Rated power: What is the rated input power? Under what conditions is it specified?
• Idle power: What is the typical power consumption when the robot is powered on but idle?
• Typical operating power: What is the average power during a representative production cycle?
• Peak power: What is the maximum instantaneous power, and how long does it last?
• Charger efficiency (for AMRs): What is the charger's AC-to-DC conversion efficiency? What is the BMS reserve?
• Energy-saving modes: Does the robot have a sleep or low-power mode? How much does it reduce consumption, and what is the wake-up time?
• Auxiliary equipment: What auxiliary equipment is included in the supplier's energy data, and what is excluded?
• Regeneration: Does the drive system regenerate energy during deceleration, and is it returned to the supply or dissipated?

If the supplier cannot provide this data, the buyer should request a measurement test under representative conditions. If a test is not possible, the buyer should plan to measure energy consumption during the pilot or early production phase and use the data to refine the energy model.

IEC 61800-9-2:2023, the standard for adjustable-speed power drive systems (PDS), defines energy efficiency measurement methods and efficiency classes (IE and IES, extended to IES5). The standard's scope is limited to the PDS (the motor and drive system), not the complete robot or production cell. It defines how to measure and classify the efficiency of the power drive system itself. It does not provide a method for calculating the energy consumption of a complete robot system, a robot cell, or a fleet. Referencing the IES class of a robot's drive system provides information about one component's efficiency, not the system's overall energy performance.