Law 14.300: what is it and how to calculate the simultaneity factor?

Updated October 8, 2025

The entry into force of Law 14.300 brought significant changes to the DG (distributed generation) sector in Brazil, and one of the most important (and least understood) concepts among integrators, technicians and consumers is the simultaneity factor.

After all, it is one of the main determinants of the financial impact of the new Fio B pricing, directly influencing the economic viability of grid-connected photovoltaic projects.

In this article, you will understand:

• What is the Simultaneity Factor?

• What is the relationship with Wire B?

• How to calculate the simultaneity factor in practice?

• Financial impact of concurrency

• Real examples and simulations

• How to reduce negative effects

As reported by Canal Solar, with the entry into force of the Law 14.300 in January 2023 new photovoltaic plant projects are no longer exempt from Fio B. Thread B corresponds to one of the installments that make up the TUSD (Distribution System Usage Fee).

The value of Fio B is responsible for covering the operational costs of distribution and investor remuneration and will be charged for plants smaller than 500 kW in a staggered manner, starting from 15% in 2023 until reaching 90% in 2028.

What will happen after 2029 is still unclear, as the relevant agencies have not yet announced any details. Experts have projected two scenarios as the most likely. In the first, 100% of Fio B would be charged starting in 2029, and in a more unfavorable scenario, the entire TUSD would be charged—which would imply, in addition to Fio B, other charges that make up this rate.

Impact of Wire B on solar energy systems

To simplify for the reader the impact of charging for Fio B on energy bills, we provide a simple explanation for this understanding.

Basically, energy bills for new projects filed after Law 14.300 came into effect have an amount charged for Wire B, which refers to the use of the distribution system.

The owner of the photovoltaic system will pay this fee only on the excess energy that is injected into the grid and subsequently compensated in its own consumer unit or in other units that receive the credits.

With this charge, the return on investments in photovoltaic projects will be directly related to the simultaneity between generation and consumption.

The higher the consumption when generating electrical energy from the photovoltaic system, the lower the injection into the distributor's network and consequently the lower the Wire B rate included in your energy bill.

Simply put, the greater the injection into the grid, the greater the amount charged in the tariff for using surplus energy credits.

Therefore, from now on it is important to know how to calculate the simultaneity factor, as this variable directly impacts the financial return time on the investment.

Greater concurrency represents greater project profitability and shorter return on investment time, while lower concurrency reduces profitability and increases payback time.

Generating units with little injection (little excess energy and high simultaneity between consumption and generation) will not be greatly affected by the new rules. On the other hand, units with low concurrency or remote self-consumption systems will be greatly affected.

Concurrency factor

The simultaneity factor is defined as the ratio between the energy consumed and the energy generated during a given time interval.

Understanding the simultaneity factor requires analyzing the typical daily load curve of the consumer unit, which outlines the customer's consumption profile over a period of one day.

Figure 1 shows a load curve obtained from a simulation with the SOLergo software. The load curve shows the power being consumed by local loads at each moment of the day. The graph area, throughout the day, represents the energy that was consumed in that same period.

The two peaks of the curve in Figure 1 indicate periods in which there is greater energy consumption, which occurs between 6 and 8 am, the period when people are getting ready to work, and between 19 pm and 23 pm, which is the period when people get home and start using showers and appliances.

Simulation of an installation with a low concurrency factor

Knowing the load curve of the residence and using the SOLergo software, it is possible to size a photovoltaic system to meet the energy needs of this consumer.

Figure 2 illustrates the load curve together with the generation curve of the sized photovoltaic system, obtained through simulation in SOLergo. Figure 3 presents the graphs generated by the SOLergo software itself with a summary of the energy generated and consumed annually by the consumer unit, from this database that the curves of the example presented were obtained.

It is possible to make some interesting analyzes regarding the consumption profile of this unit based on Figure 2.

During the period of highest generation (blue curve), low consumption is recorded (red curve), which is the period when residents are at work and few loads are used at home.

This fact means that the simultaneity factor is low, since most of the energy generated will not be used instantly, but injected into the distributor's network.

The energy consumed simultaneously with generation is represented by the area painted in purple in Figure 4, which consists of the lower intersection of the two curves.

This area represents self-consumed energy, that is, the energy generated by the photovoltaic plant and consumed simultaneously by the local loads of the consumer unit.

The green area in Figure 5 represents all the electrical energy generated by the photovoltaic system over a period of one day.

Calculation of the simultaneity factor

To calculate the simultaneity factor, simply divide the amount of self-consumed energy, represented by the purple area in Figure 4, by the total energy amount, represented by the green area in Figure 5.

In order for this division to be understood more clearly, this article will provide a numerical example after explaining the equations that represent the simultaneity factor.

The simultaneity factor is defined as the ratio between the energy consumed in the generation interval (self-consumed) and the total energy generated in the same interval, according to the following equation:

As previously stated, self-consumed energy corresponds to the fraction of the generated energy that is consumed simultaneously by the loads. Ideally, with a simultaneity factor of 100%, all energy generated by the photovoltaic system is consumed on site, with zero energy export. On the other hand, a low simultaneity factor indicates that little energy is consumed on site and most of the photovoltaic generation is exported.

The self-consumed energy in an installation can be calculated by the difference between the total energy generated recorded by the inverter (over a period of one month) and the injected energy that appears on the energy bill, both for the same period.

The equation that represents self-consumed energy is presented below:

Example of a real case

To illustrate, let's calculate the simultaneity factor for a real case, a residence equipped with a photovoltaic microgeneration system.

Firstly, we will calculate the self-consumed energy and to do this we need to collect the injected energy, which is data presented on the energy bill.

This energy corresponds to the surplus (everything that is not self-consumed) of energy injected into the concessionaire's distribution network. Figure 6 presents this data taken from the energy bill of the concessionaire CEMIG, in Minas Gerais.

Once we have the injected energy (446 kWh), we simply take the total generation measured by the inverter to calculate the self-consumed energy.

The reading period for the injected energy was from 18/11/2022 to 20/12/2022, as shown in Figure 6. Therefore, the energy generated in that same period must be taken. To do this, the inverter monitoring is consulted, which presents the daily generation data for this period, as shown in Figure 7.

In the period from 18/11/2022 to 20/12/2022, according to the inverter monitoring system, the photovoltaic system provided 510 kWh of energy. This energy corresponds to the yellow area of ​​the graph in Figure 7.

Knowing the energy generated, measured at the output of the inverter (510 kWh), and the energy injected into the bidirectional meter (446 kWh), taken from the energy bill, the self-consumed energy is calculated, which is:

Self-consumed energy=510-446=64 kWh

Thus, the simultaneity factor of this installation, calculated over a period of one month, is:

Concurrency factor=64 / 510 = 12,55%

Conclusions

For the example residence, the simultaneity factor is 12,55%, which is a low value, meaning that most of its energy (87,45%) is injected into the grid. If this plant were subject to the new law, there would be a higher bill payment due to Fio B, since each injected credit (kWh) that is offset is charged for Fio B (a percentage of Fio B according to the transition rule).

Therefore, projects will have a slower return on investment the lower the simultaneity factor. For consumers such as supermarkets and industries, which have high consumption during generation periods, this factor tends to increase and may reach such high levels that the new rule will barely affect the return on investment time, as long as the simultaneity factor is high enough.

It is important to highlight that the calculations carried out in this article can only be obtained accurately in locations that already have a photovoltaic plant installed, as data such as the total energy generated and the energy injected are required.

However, for new proposals, this data is not available. So, what should we do in these cases? The most reliable way to obtain this simultaneity factor would be to calculate the customer's load curve and compare it with the predicted generation curve (via simulation) of the designed photovoltaic plant. This way, a comparison can be made between these two curves and the simultaneity factor calculated.

As surveying the load curve is a time-consuming process, an alternative is to use simultaneity factor values ​​from plants already installed at customers of the same type.

Thus, to prepare a new proposal, the consumption profile of the customer to be served is compared with the profile of another customer already cataloged and the simultaneity factor is used to calculate the return on investment time.

Another alternative is to use software such as SOLergo, which makes it possible to create the customer's load curve based on knowledge of their installed load. The software also calculates the simultaneity factor and delivers the entire economic analysis considering law 14.300.

References

[1] Badra, Matthew. Simultaneity factor will be key to GD's accelerated growth. Canal Solar. Campinas, January 19, 2022. Available at:https://canalsolar.com.br/fator-de-simultaneidade-sera-peca-chave-para-crescimento-acelerado-da-gd/>. Accessed on: 15/01/2022.

[2] Energês Team. Title: Does simultaneity impact the viability of self-generation?. Energês, March 10, 2022. Available at:https://energes.com.br/simultaneidade/>. Accessed on January 15, 2023.

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