Active and Reactive Power: The Intro You Needed

Active and Reactive Power: The Intro You Needed

Active and Reactive Power: The Intro You Needed

Joana Cuenca

Joana Cuenca

May 13, 2024

Have you ever caught yourself in a conversation where 'reactive power' gets thrown around like confetti, and you're just pretending to catch it all? Let’s make sure that the next time it happens, you can confidently tag along or see through some common misconceptions.

In this blog, we aim to flesh out essential concepts in the realm of active and reactive power and explain their significance in the world around us.

Let’s start with the basics

The “adequacy” of electrical power depends on the voltage (amplitude) and the frequency. Disruptions in one or both of these measures impact reliability.


The frequency does not consistently remain at exactly 50 Hertz. The frequency rises if energy supply exceeds demand and vice versa. This delicate balance is important as deviations from established safety thresholds can cause the malfunctioning of household appliances. Your fridge, for example, might simply stop working and break if the frequency were to jump dramatically.

That’s why frequency control is crucial and network operators are assigned the responsibility to keep the frequency in check.


While frequency in the power system is relatively straightforward to manage due to its consistency across the grid, voltage presents a more complex challenge due to its local properties. This complexity stems from the unique properties of transmission lines and the role of reactive power, leading to fluctuations in voltage levels. That's why you can have 230 Volts in your street while the main street of the neighbouring town is at a different voltage. And those different voltages can be detrimental. High voltage means higher currents, and these damage equipment or cause insulation breakdown for installations that are only operating properly to a certain voltage maximum. Low voltage leads to reduced power delivery and, as a result, to underperforming machinery or failing electronic circuits.

Let’s break down the terms:

  • Active Power. Power used and consumed for useful work in electrical circuits, and is measured in watts (W).

  • Reactive Power. Power that, although it doesn't contribute to the performance of the appliance consuming power to operate, is necessary for keeping the voltage at the expected level and facilitating the transfer of active power, measured in volt-ampere reactive (VAR).

  • Apparent Power. Combined total of active and reactive power, representing the actual energy our grids transport. Apparent power can be represented as a vector sum and is measured in volt-amperes (VA).

  • [Extra] Power Factor. The power factor - often also referred to as 'cosinus phi' or 'cos(φ)' - represents the proportion of reactive vs active power in an electrical system and is a number between 0 and 1. A power factor of 1 indicates no reactive power, which is optimal, while values closer to zero signal higher reactive power requirements.

[ADDCAPTION] A visual representation of the maths behind active, reactive and apparent power.

Figure 1. A visual representation of active power, reactive power, apparent power and the relation to power factor

Let’s row in a boat analogy:

Imagine you're rowing a boat. The force you apply to the oars, pushing the boat forward in the direction you want to go into, is like active power – it directly achieves your goal of moving forward. However, to keep the boat on course and account for the current, you must systematically adjust your rowing. These continuous adjustments, while not meant to propel the boat forward, is crucial for a smooth journey. This is similar to reactive power – it doesn’t directly contribute to moving electricity to your home but is essential for ensuring the electrical system operates efficiently and reliably.

Just like the effort that is necessary to compensate for the current of the water in this analogy, the current that induces the reactive power component has two directions, 'upstream’ and ‘downstream’. In electrical systems. reactive power is also induced by two electrical components, ‘capacitive’ and ‘inductive’. And it’s possible to lower the need for reactive power by adding reactive components in the opposite direction (‘capacitive’ power onto ‘inductive’ power and vice versa, just like upstream and downstream currents can cancel each other out).

Reactive power on our grid also needs to be transmitted to guarantee the continuous delivery of sufficient active power. As a result, the reactive power component contributes to losses over the distribution lines and reduces the availability for active power. 

That’s why grid operators are looking for ways to balance out the reactive component as best as they can. Because reactive power is linked to voltage, balancing out the reactive power can be a "local" grid service. In contrast, services like inertia or frequency, affecting the entire system, are considered "global" grid services.

Key Takeaways:

  • Frequency on the grid is influenced by the behaviour of the balance of active power and is managed globally.

  • Voltage is affected by the balance of reactive power, which we rather not transmit, and can be managed locally. 

Stable grids without power control is a fairytale

… and a boring one if you ask me

It’s now safe to say that active and reactive power play a huge role in the stability of our grids. That’s why the parties responsible for operating and maintaining the grids talk about these concepts all the time. For high-voltage grids and frequency control, the so-called Transmission System Operators or TSOs (e.g. Elia for Belgium) are in charge. On the other hand, we have low & medium-voltage grids that are managed by the Distribution System Operators or DSOs  (e.g. Fluvius for Flanders). They are also in the driving seat of local voltage control.

TSOs as well as DSOs are setting up systems to fight net imbalance and congestion of our grids. The TSO, for example, has a set of ancillary services that they activate to maintain stability of the electricity grid. These services activate active and/or reactive energy in flexible ways (also referred to as Demand-side Flexibility or DSF). As you can see in Figure 2 and Figure 3, these ancillary services are often quite lucrative but not everywhere equally accessible.

[ADDCAPTION] Figure 1. Total spend on markets.

Figure 2. Total spend on markets.

[ADDCAPTION] Demand side Flexibility access to those markets.

Figure 3. Demand-side Flexibility (DSF) access to those markets.

But also DSOs are looking to activate such services to leverage DSF for both active and reactive power to lower the burden on their nets during peak moments and fight net congestion. Fluvius, the Flemish DSO, for example, is experimenting with a platform that focuses on activating both active and reactive power to keep the grids healthy. The locations in which flexibility in reactive power currently play a more critical role in Flanders are depicted in Figure 4.

[ADDCAPTION] Figure 3. Key locations for Reactive Energy flexibility in Flanders. source: 12/03/2024 Public Consultations|Fluvius.

Figure 4. Key locations for Reactive Energy flexibility in Flanders. Source.

Elia is doing the same; they are developing a tool to understand and anticipate the grids needs for the foreseeable future. This tool will propose different actions to achieve an optimal voltage plan for the high-voltage grid, which is expected to be operational by the winter of 2024/2025.

Final words, with a touch of Latin

In the intricate dance of electrical grid stability, reactive power is the sine qua non (translation: indispensable or essential condition) for ensuring voltage regulation and the seamless flow of active power.

The balance between active and reactive power is essential for the stability and efficiency of our electrical grids. Active power fuels our daily needs, while reactive power and its control keeps the system balanced and efficient. Managed by TSOs and DSOs through advanced ancillary services, this balance supports the integration of renewable energies and the deployment of demand-side flexibility, crucial for a sustainable energy future.

At Powernaut, we're dedicated to harnessing the versatility of active and reactive energy within households and low-voltage installations to address these issues. Our efforts not only contribute to the stabilisation of voltage and frequency across the grid but also empower consumers to play a pivotal role in the broader energy ecosystem.

Equally excited about the future of energy?

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Equally excited about the future of energy?

Let's do great things together!

Get in touch

Equally excited about the future of energy?

Let's do great things together!

Get in touch