Why Voltage × Current Does Not Equal Power
Many people new to energy monitoring assume that multiplying voltage (V) by current (A) gives the actual power consumption. In reality, this method only works for purely resistive loads (like heating elements or incandescent lamps). In most real-world electrical systems, where motors, inverters, or switch-mode power supplies are common, power calculation is far more complex than simply V × A.
The Role of Power Factor (PF)
In AC systems, voltage and current are often out of phase. This phase difference is described by the Power Factor (PF), which ranges from -1 to 1.
Active, Reactive, and Apparent Power
Active Power (kW)
The portion of power that does useful work, such as lighting a bulb or driving a motor.
Reactive Power (kVAR)
The power that oscillates between source and load, used to establish magnetic or electric fields but does not perform real work.
Apparent Power (kVA)
The product of RMS voltage and RMS current (V × A), which includes both active and reactive components.
Relationship Among Them
Active Power (kW) = Voltage × Current × PF
When PF is less than 1, simply multiplying V × A will overestimate the real active power.
Active Energy and Reactive Energy
Power is an instantaneous value, while energy is the accumulation of power over time.
Active Energy (kWh)
The accumulated active power, representing the actual energy consumed to perform work. Household electricity bills are primarily based on kWh.
Reactive Energy (kVARh)
The accumulated reactive power, which helps maintain voltage stability and support equipment operation, but does not directly produce useful work.
Electricity Billing in Different Scenarios
Residential Users
Billing is typically based only on active energy (kWh), without additional charges for reactive energy.
Commercial & Industrial Users
In addition to billing by active energy, utilities may also consider power factor (PF) and reactive energy (kVARh). A low PF can result in penalties or extra demand charges.
Therefore, for commercial and industrial facilities, it is not enough to only monitor active energy. A full understanding of PF and reactive energy is essential.
Advantages of IAMMETER Energy Meters
IAMMETER Wi-Fi energy meters provide comprehensive power and energy monitoring, delivering different insights for different scenarios:
Residential Users
- Voltage, current, frequency
- Active power (kW), active energy (kWh)
- Bidirectional metering for solar PV (supports Net Energy Metering, NEM)
Commercial & Industrial Users
- Reactive power (kVAR)
- Reactive energy (kVARh), including inductive and capacitive kVARh
- Apparent power (kVA)
- Power factor (PF)
Solar PV Users
- Analyze whether inverters are injecting or consuming reactive power
- Gain a more complete understanding of PV system performance
Conclusion
Voltage × Current ≠ Actual Power. True power calculation requires considering the power factor, and energy analysis must distinguish between active and reactive energy. By measuring active, reactive, and apparent power along with their respective energies, IAMMETER meters provide a complete picture of your electrical system, helping you reduce costs and optimize efficiency.
👉 All IAMMETER energy meters, whether single-phase or three-phase, support the measurement of these parameters.
Reference
Reactive Power Parameters Explained: kVAR, kVARh, PF, and More
