A school managed to install a photovoltaic system even after facing connection restrictions imposed by the distributor, using inverters from Canadian Solar associated with technology that limits power injection.
The solution allowed limiting the maximum power exported to the electricity grid to 60 kW, as required by the energy utility.
The system has approximately 170 photovoltaic modules of 550 Wp, totaling an installed power of approximately 93 kWp. This installed power allows for better utilization of generation throughout the day, especially during periods when the school's internal load can absorb the energy produced.
The inverter has a nominal power rating of approximately 75 kW and was installed about 100 meters from the consumer unit's substation.
The Grid Zero controller was integrated directly into this connection point, which also houses the main circuit breaker and the utility meter.
To enable monitoring of the energy flow, three CTs (current transformers) and three PTs (power transformers) were installed in the substation.
These devices measure the voltage and current at the connection point, allowing Grid Zero to monitor in real time the energy consumed and injected into the consumer unit.
Marcelo Maia, Technical Director of the VA Energia Group and technical manager for the project, explains that the injection limit is not necessarily related to the actual behavior of the unit, but rather to a requirement of the energy concessionaire.
Self-consumption reduces the need for system intervention.
Analysis of the school's consumption profile showed that a large portion of the energy generated is used internally during operating hours, reducing the likelihood of exceeding the authorized limit.
“During weekdays, when activities are underway, the electrical load absorbs most of the photovoltaic production. However, on weekends and holidays, when the institution remains closed and only essential loads remain connected, the surplus generation increases and the limiting system starts to operate more frequently,” explained Maia.
Even during these periods, the restriction occurs mainly during the hours of greatest solar irradiance, usually around midday, when production reaches its peak.
Maia emphasizes that the unit's own demand helps keep exports within the limit.
"During periods of high production, the school may exceed the limit set by the utility company. However, when local demand consumes some of that energy, the net export remains within the permitted value, preventing the limiter from being activated," he added.
Limitation defined by regulatory requirement.
According to Maia, the maximum export value is defined by the distributor and not by the technical design of the system. Grid Zero is programmed to respect this limit regardless of the unit's operating conditions.
The system continuously monitors the power delivery point at the substation and automatically reduces generation whenever the export approaches the value authorized by the power utility. Because the control is based on the values measured at the connection point, the adjustment occurs quickly and accurately.
Despite the limitation, the expert states that the equipment is relatively rarely used throughout the day, occurring mainly during periods of low demand combined with high solar irradiance.
Economic impact is reduced.
Even with the export restrictions, total generation and financial return were minimally impacted. Monthly energy losses are estimated to be between 3% and 5% compared to a conventional system without limitations.
According to Maia, without the need for injection control, the school's payback period will be approximately three to four years.
“Without the need for injection control, the return on investment time would be approximately three to four years. With Grid Zero, this timeframe remains virtually unchanged, since most of the energy continues to be consumed on-site,” he highlighted.
Restrictions imposed by flow reversal drive the use of Grid Zero.
The school case reflects a scenario that is becoming increasingly common in the Brazilian distributed generation market: the rise in connection refusals due to reverse flow issues.
According to Maia, the demand for this type of solution, such as Grid Zero, grew significantly after distributors began claiming grid saturation.
Today, approximately half of the submitted projects face this type of restriction. In these cases, limiting exports becomes the main alternative to make the plant's implementation viable.
"For every ten projects we submit, about five are rejected due to flow inversion. Grid Zero ends up being the solution to prevent the project from being lost," he reported.
Despite its growing importance, Maia believes that Grid Zero is still little known by both integrators and distributors. In many cases, the alternative is only considered after a formal denial of access.
According to him, the concessionaires frequently reject the connection request without explicitly indicating the possibility of installation with export limitations, leaving it up to the integrator to request a project review.
"This lack of standardization and dissemination hinders the adoption of the technology, especially among professionals with less experience," he concluded.
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