Reactive energy: everything you need to know with clear explanations and tangible benefits

Reactive energy is one of those concepts that often appears on bills, but which is rarely explained clearly. Yet, understanding how it works is essential not only for optimizing consumption but also for avoiding extra costs that, in the case of large plants or energy-intensive companies, can become quite significant. In this article, we will thoroughly analyze what reactive energy is, why it is generated, and how it impacts the electricity grid and rates.

Introduction to Reactive Energy and Plant Efficiency

In recent years, there has been a lot of discussion about energy efficiency, sustainability, and consumption optimization. However, one aspect that is often overlooked is reactive energy, an invisible component that does not produce useful work but influences the stability of the grid and, under certain conditions, also the costs of electricity supply.

Why Reactive Energy Affects Consumption and Rates

Reactive energy does not directly contribute to the operation of a machine or system; it is necessary to power certain physical phenomena present in electrical loads. The problem arises when this component exceeds certain limits: in that case, the energy distributor applies economic penalties.

Active, Apparent, and Reactive Energy: The Differences

To truly understand the phenomenon, it is important to distinguish:

• Active Energy (kWh): the energy that performs useful work.

• Reactive Energy (kVArh): the energy that supports magnetic and electric fields.

• Apparent Energy (kVA): the combination of the two.

These are concepts that travel together, but each plays a very different role.

How Reactive Energy is Measured (and Why It Matters)

Reactive energy is measured in kVArh, and its relationship with active power is interpreted through the cosφ, one of the fundamental indicators for understanding the efficiency of the electrical system.

Fundamentals of Reactive Energy: Inductive and Capacitive Loads

Reactive energy essentially arises from two categories of loads: inductive and capacitive ones. Both require energy to generate magnetic or electric fields, which oscillate continuously and create a phase difference between voltage and current.

Reactive Power: What It Is and Why It Is Generated

Many electrical devices do not absorb all the energy to convert it into work: part of it is used to create and maintain oscillating magnetic or electric fields. It is from this mechanism that reactive power arises.

Inductive Loads

These include very common machinery:

• three-phase electric motors

• transformers

• inverters

• industrial lighting systems
  
  

All produce a phase difference between current and voltage.

Capacitive Loads

These are less common but still present:

• systems with capacitors

• long electric cables

• installations with excessive compensations

This category can also contribute to the generation of reactive energy, albeit in a different way compared to inductive loads.

The Power Triangle

To simplify these concepts, the so-called power triangle is used, which represents the relationship between:

• active power (kW)

• reactive power (kVAr)

• apparent power (kVA)

It is a useful diagram to visualize how "virtuous" or, conversely, how inefficient an installation is from an electrical point of view.

The Power Factor cosφ

The cosφ indicates the ratio between active and apparent power. Low values mean that the system requires a lot of reactive power to function properly.
Generally:

• a value of cosφ > 0.95 is considered optimal;

• lower values indicate possible inefficiencies and, especially, risks of penalties on the bill.

Why Reactive Energy Is Generated and How It Affects the Electrical System

Reactive energy is inevitable for the functioning of devices that generate magnetic and electric fields. However, when the balance between the different components of power is compromised, side effects can arise that may become significant.

Inductive Loads and Phase Shift

The first reason reactive energy arises is the phase shift between current and voltage produced by inductive loads. When this becomes pronounced, the grid must work harder even if the installation is not consuming more active energy.

Capacitive Loads and Overcompensation

In some industrial installations, excessive use of capacitors can cause a production of "excess" reactive energy, with unexpected effects on energy quality.

Harmonics and Non-linear Loads

Harmonics are distortions of the electric waveform. They are typical in installations with:

• charging stations for cars

• photovoltaic inverters

• heat pumps

• servers and electronic equipment

Harmonics complicate the management of reactive power, requiring more advanced solutions.

When Reactive Energy Generates Costs and Penalties

Reactive energy is not always billed. However, when its values exceed certain thresholds, regulations state that the customer must incur additional costs.

How It Appears on the Bill

On the electricity bill, reactive energy is indicated as kVArh billed. Many users do not recognize this item or do not understand its impact, but in companies, it can represent a significant figure, especially when the installation is outdated or poorly optimized.

Impact on Companies and Industrial Plants

Industrial installations with many motors, pumps, compressors, or large refrigeration systems are the most affected by penalties. Hotel chains, supermarkets, and commercial establishments can also feel the effects.

Effects of Reactive Energy on the Grid and Systems

Having too much reactive energy is not only an economic problem: it can also generate inefficiencies in the grid and in installations.

Overloads and Losses

An excess of reactive energy leads to:

• greater current in the lines

• more losses in the cables

• increased stress on transformers

All this translates into a less efficient installation.

Grid Instability

Peaks in reactive energy can cause:

• voltage drops

• overheating

• oscillations in the waveform

It is not surprising, therefore, that many distributors impose penalties.

Impact on the User's Internal Installation

When reactive energy is too high:

• machines wear out faster

• the lifespan of components is reduced

• the risks of sudden failures increase

A well-balanced installation is therefore essential also to reduce machine downtimes and extraordinary maintenance.

In this first part, we have clarified what reactive energy is, why it is generated, how it impacts installations, and in which cases it can become a concrete cost. We have also defined fundamental concepts such as the power triangle, cosφ, and the first effects of reactive energy on the grid and on supplies.