EN 
PT_BR 
With collaboration of Matthew 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 issuing connection budgets with the imposition of energy injection limitations, under the allegation that this practice would be necessary to overcome 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.
Although, 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 panel of this edition of Connect Channel, that storage system installation (batteries) emerges as a solution to overcome rejections of distributed generation projects.
Carlos Brandão, 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 registered 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 CPFL, 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 flow reversal condition, 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.
4 Responses
Don't the concessionaires' mega plants affect the reverse flow? Giana plants are often angry with public money! Then Mr José will install 20 panels and generate reverse flow! Dona Gema who has a grocery store and will install 60 panels 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 account 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 worked at an electricity company in MG. In the distribution network there were small CGH's that, depending on the time of day, injected power into the substations. At that moment, the protection relays detected reverse flow and the protection setting was changed automatically.
As for the fact that they say that micro generators raise the voltage, it doesn't make sense. Inverters are designed to follow the utility's frequency and voltage variation.
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 voltage issue could be different, but then I think the system would be much more complex.