With the collaboration of Mateus Badra
A flow reversal in the electrical energy distribution network occurs when the amount of electrical energy injected, coming from distributed generation, is greater than the demand of consumers connected to that same network, which may cause the operational limits of the network to be exceeded. One of the most common problems is the high level of voltage that may appear at some points in the system.
In this year, energy distributors Operating in states such as São Paulo and Minas Gerais, they began to issue connection budgets with the imposition of energy injection limitations, claiming that this practice would be necessary to overcome the problems that can be caused by the inversion of power flow.
The measure caused fear in the solar energy sector, which started to record losses due to the non-approval of its customers' connection requests.
Recently, associations and entities linked to the solar sector met with one of these concessionaires – Cemig (Companhia Energética de Minas Gerais) – to discuss a technical alignment in order to prevent new failures from occurring.
However, So far, no solution has been reached and customers still continue to receive negative connection quotes due to flow reversal, preventing customers from generating their own energy, as the options presented by concessionaires to overcome this situation, in most cases, are not viable.
To mitigate this problem, professionals in the solar sector explained in the first discussion of this edition of Canal Connect, that storage system installation (batteries) emerges as a solution to overcome rejections of distributed generation projects.
Carlos Brandao, research and development supervisor at Sengi, explains that solar energy with Batteries, for example, can help with the problem in several possible ways.
“In microgeneration, where solar and storage will act with the grid-zero function, it is possible to increase the energy generation capacity in a photovoltaic system, absorb excess energy in the battery and guarantee, with the function of the hybrid systems, not exporting energy to the grid. This way, you don’t have the problem of flow reversal in a solar energy system with a battery,” he explained.
“Speaking of minigeneration, we can see the application of BESS (Battery Energy Storage System) also as a solution, because BESS has the capacity to assist both in controlling the flow of the concessionaire itself and providing ancillary services, from voltage control , frequency and active and reactive power”, he highlighted.
Edmar Moreira, project engineer at Hitachi Energy, also highlighted during the event that he has already there are technologies being studied to resolve the issue of power flow.
“Australia has been researching the possibility of placing automatic control TAPs in distribution networks, because the big problem with inverting power flow is the high voltage profile. So, within the Australian context, research is being done to see if this would pay off economically. From a control point of view, this is a very interesting solution for the consumer to continue having access to the grid without depending on the battery”, he highlighted.
Current overview
Hewerton Martins, president of the MSL (Free Solar Movement), among other issues, brought to the event a general overview about In which regions of Brazil has flow reversal been used by distributors as a justification to deny projects distributed generation.
According to the executive, in addition to problems ed in Cemig's concession area, in Minas Gerais, there are now concessionaires operating in this way in São Paulo, Maranhão and Rio Grande do Sul.
“We had a situation at FL, in São Paulo, that initially improved a little, but we still have rejections. We believe this is just something temporary. In Maranhão it is very complicated, in the Equatorial region, and in RGE, in Rio Grande do Sul.
Necessary improvements
Paulo Freire, owner of Paiol Energia, said, in turn, that the Brazil still has many regulatory issues to be resolved and that go far beyond distributors denying connection requests.
For him, it is necessary to discuss more relevant issues that directly affect the redistribution of energy, such as improvements in transmission networks. “Substations connected and in operation need to have transmission lines to transport the energy generated. We have to better prepare the country's distribution infrastructure so that this energy reaches more consumers,” he said.
Solutions for the market
Adriano Pereira, electrical engineer at PHB Solar, was also present at the event addressing the applications that can be carried out in Brazil. “According to the problems we are having with project failure and the condition of flow reversal, we present three products that control generation in relation to the load. So, I can create a zero grid with such equipment”, he pointed out.
Below are the solutions presented by Pereira in his talk:
- CT-90 (current transformer) – acts on single-phase inverters;
- PHB120T (power limiter) – acts on three-phase inverters of up to 60 kW;
- SEC1000 (intelligent energy controller) – operates on the entire range of three-phase inverters.
Recommendations for zero grid installations
During the speech, Pereira also gave some recommendations for zero grid installations to the sector professionals who were present. “We recommend that the project be carried out with the concessionaire and that the products (CT-90, 120T and SEC1000) be mentioned in the project with the concessionaire”.
“In addition, carry out the study so that they have high local simultaneity (photovoltaic generation/load) and request the mass memory of the energy meter to validate the solution”, he concluded.
Answers of 9
Don't the concessionaires' mega plants affect the reverse flow? Giana plants are often angry with public money! Then Mr José will install 20 s, generating reverse flow! Dona Gema who has a grocery store and will install 60 s will generate reverse flow…. Brazil is the land that sells courses to sell more courses.
Apparently, small photovoltaic sources do not have the capacity to change the voltage of the concessionaire's network, the large ones are previously designed for the installed network, so this inversion of power flow does not fit, unless they have not taken into the system as a whole.
so the computers are being rejected (on grid) for another reason.
We imagine that this is the beginning, but we have already reached a level that is beginning to be significant. Let's study more to have the most viable solutions.
I think the solution will soon be for distributors to define contracted power for homes and small businesses, since they talk so much about increasing energy injection into the grid, as has been the case for a long time in Europe. However, in Europe it is also possible to choose the distributor as well. However, due to these operational problems in the grid with increased surplus, in Europe it is already common to have zero injection with and without storage. Depending on the type of contract with the distributor, it is possible for the consumer to charge the battery via the photovoltaic system or the grid at times when the price of kWh is cheaper and discharge the battery during the period when energy is more expensive.
Two observations that I believe are important: 1) The expression “operating modes” is incorrect and was not used correctly, as it was used in place of the expression “Modus Operantis” (which is in Latin and is best written in “italics”) and cannot be translated into Portuguese in the same way as it is spoken (or heard). I would like to ask the writer of the article to correct the text. 2) It is already common knowledge that the concessionaires want to shift the responsibility for the need to improve the electrical grid to the integrators and, consequently, to the end customers who, in practice, are more victims than customers. The technical effects that arise due to the presence of photovoltaic microgeneration are often caused by the scrapping of the electrical system (which has been the case for decades) which is always delayed from being carried out by the concessionaires, both because they are privatized and because of the lobbying they do with public agencies, politicians, etc. They want solutions, but they don't want to take responsibility for such solutions, much less invest in the improvements they are required to make, improvements that have been necessary since long before the advent of photovoltaic microgeneration became popular in the country, and which also makes it impossible to realize the future (already at the door) of electric vehicles (and God knows what other inventions will come) that will demand ever more robustness and reliability from the electrical system. The country needs a more powerful energy matrix if it wants to grow, win and develop more and more, but the impression I have is that this development is further away and prevented by the "current owners of the machine". Those who agree, breathe!
Hello Raphael, thank you for the .
I worked at an electric power company in Minas Gerais. In the distribution network there were small CGHs that, depending on the time, injected power into the substations. At that time, the protection relays detected reverse flow and the protection setting was changed automatically.
As for the fact that they say that micro generators increase voltage, it doesn't make sense. Inverters are designed to keep up with the frequency and voltage variations of the utility company.
I agree 100%
Geraldo, unfortunately inverters really increase the system voltage. This is because almost all of them work with current injection control, that is, the famous network followers. Furthermore, the flow reversal at the time of generation causes what was previously a voltage drop to become an increase. imagine this throughout the day, it creates a huge variation in tension. That's why there are a lot of complaints about systems that, when activated, the inverter jumps out due to overvoltage. If they were network builders, this tension issue could be different, but then I think the system would be much more complex.
We have to have priorities of use, of the generating sources, daytime use the priorities would be first solar, second wind, third biomass, fourth hydraulic, fifth and last thermoelectric powered by diesel.
And at night, the priorities would be, first wind power, second biomass, third hydraulic, and lastly thermoelectric power powered by diesel.
Another point that needs to be reviewed would be the generation of solar energy by people who do not have their own consumption and set up solar farms to commercialize and obtain profits, a situation that harms the network with excess voltage, and harms people who have consumption and are prevented from setting up their own plant and reducing their own consumption.
Another point that we have to pay attention to is the sale of energy by subscription, which will generate profits for some, but losses for others.