Reactive Energy

Reactive energy consumption is an integral part of an electricity bill for companies and facilities under the Special Low Voltage (BTE), Medium Voltage (MT), High Voltage (AT) and Very High Voltage (MAT) regime. If this consumption is not reduced, it can have a considerable impact on energy bills. Therefore, it is considered important to clarify issues such as, what is reactive energy, why and how is it paid for and how can it be reduced.


To perform the most varied tasks, electrical equipment is used that has several components, of which coils are supplied with alternating current (AC). These coils require magnetic (reactive) current necessary to create a magnetic flux that will operationalize the equipment. This current does not produce useful power and the most common examples of equipment with these characteristics (inductive receivers) are induction motors, compressors, fluorescent or discharge lamps, ferromagnetic ballasts, electronic circuits and / or the transformers themselves used in the Transformation Station (PT). The type of reactive energy that is associated with this type of charge is usually referred to as Inductive Reactive Energy.

When the capacitive reactive power of the capacitor is greater than the inductive reactive power of the equipment, the network is asked for a reactive power, but this time of capacitive origin, that is, Capacitive Reactive Energy, the most common examples being uninterruptible power units (UPS) the low load and capacitors existing in the electronics of the equipment itself.

Why is it paid?

Reactive energy or the injection into the network of inappropriate values ​​are billed to the final consumer according to the rules of the Energy Services Regulatory Entity (ERSE). These rules were created with the main purpose of increasing the efficiency of the electrical system and reducing losses in the transmission and distribution networks.

Reactive energy is billed from the 8th month of the installation’s commissioning, so that the consumer can make a correct dimensioning of reactive energy compensation in the first months.

Components of an invoice with reactive energy

An energy bill with a voltage level MT (with reactive energy) can consist of the following terms, fees and taxes:


  • Active Energy at peak hours – is the energy consumed in the period of delivery of energy at peak hours (from 9:00 am to 10:30 am and from 6:00 pm to 8:30 pm in daily cycle and winter time);
  • Active energy at full hour – represents the energy consumed in the period of flood hours (from 8:00 am to 9:00 am, from 10:30 am to 6:00 pm and from 8:30 pm to 10:00 pm in daily cycle and winter time);
  • Active energy in normal empty hours – represents the energy consumed in the empty period (from 6 am to 8 am and from 10 pm to 2 am in daily cycle and winter time);
  • Active energy in super empy hours – represents the energy consumed in the super empty period (from 2 am to 6 am);
  • Inductive reactive energy – reactive energy consumed in an empty space, can be billed from step 1 or / and up to 3;
  • Capacitive reactive energy – reactive energy supplied to the grid in the period during hours of absence;
  • Contracted power – is a fixed value defined with a daily price when contracting;
  • Peak hours power – is defined by the quotient between the active energy supplied to the customer in peak hours and the number of peak hours in the time interval covered by the invoice;
  • DGEG Fee
    corresponds to the fee for the use and operation of electrical installations that is paid to the state. This fee has a fixed amount and is defined by DGEG;
  • Audiovisual contribution – under the terms of Law no. 30/2003, of 22 August, corresponds to the financing of the public service of radio broadcasting and television, being delivered by the traders to Rádio e Televisão de Portugal SGPS, SA The amount is fixed monthly € 2.85 + IVA (6%), which must be paid 12 times a year to a consumer;
  • Special Consumption Tax – is included in the subcategory of tax on oil and energy producers (ISP), created in 2012 and paid to the state. The fixed fee is € 0.001 per kWh of energy billed.


The energy price should include the tariff for access to the networks.

How is it billed?

The reactive energy consumed is inductive and is only billed during peak hours and full hours (this period is called Out of Void hours (PV), in turn, the reactive energy supplied to the grid is capacitive and is billed during hours of emptiness and super emptiness (this period is called hours of emptiness) .The reactive energy unit is in KVArh.

Reactive energy consumption, one of the variables incorporated in determining the value of the electricity bill, cannot be avoided, can be compensated in order to avoid increased operating costs, as well as to improve the energy quality of the installation and avoid electrical losses distribution (a low power factor can cause overloads in cables and transformers, low regulation of transformers, increased voltage drops and electrical losses).

Reactive energy is measured using the power factor, cos φ, which measures the degree of efficiency of the electrical installation. This factor has values ​​between 0 and 1 that indicate the degree of efficiency. The closer to value 1, the greater the energy efficiency and the greater the use of the electrical system.
To avoid financial penalties on the energy bill, the consumer must install systems that maintain reactive energy with a value of less than 30% of the active energy, that is, the power factor of the installation (cos⁡ φ) must be: cos φ ≥ 0.95 or tg φ ≤ 0.3.

There are currently three levels in force for billing inductive reactive energy that have different multiplicative factors to be applied to the reference price published by ERSE:

How to reduce?

The reduction of reactive energy consumption is possible through the compensation of the power factor. For this purpose, capacitors (capacitor batteries) are used, which can have different configurations depending on the specificity of the installation, as well as the loads to be compensated, and can go through a capacitor solution to equipment with harmonic suppression filters.
The compensation of reactive energy through the installation of capacitor batteries allows the reactive energy necessary for the loads to be supplied together with them, preventing their circulation in the upstream distribution network. In this way, it is possible to reduce active losses in distribution and transformation (that is, in transformers).

NOTE: The design of a reactive energy compensation system must take into account the possible increases in power expected in the installation. It is also important to note that the consumer can install a system that allows the power factor to be corrected for the unit (cos φ = 1), but this option may represent an increase in investment costs, considering that the installation will not suffer any type of change, so in these cases it is sufficient that the system to be dimensioned allows the compensation of the power factor to be higher than 0.95 (cos φ ≥ 1) in order to avoid the penalty in the energy bill.

In order to adequately compensate the power factor and avoid annual costs with reactive energy, the installation of condenser batteries is a measure with a very attractive return period, between 6 months to 1 year in most installations, thus avoiding costs additional costs with the electricity bill, also allowing the optimization of the energy efficiency of the installation and also improving the stabilization of voltage levels and avoiding electrical losses in the distribution.

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