Solis Seminar Episode 37 : Key Points of Inverter Selection in BIPV Project

In order to cope with climate change, gradually promote the development of energy saving and emission reduction, and realize the dual-carbon goal as soon as possible, the issue of building carbon emissions will be the focus of the follow-up new energy development.

December 29, 2021. By News Bureau

Background
In order to cope with climate change, gradually promote the development of energy saving and emission reduction, and realize the dual-carbon goal as soon as possible, the issue of building carbon emissions will be the focus of the follow-up new energy development. Therefore, the organic combination of PV system and buildings makes it fashionable and practical to create green buildings.

This Solis seminar will take you to share the characteristics of the BIPV project and the key points of inverter selection.

BIPV project characteristics
In the BIPV project, it is necessary to design the PV system according to the structural characteristics of the building itself. Often the roof area of some buildings is not sufficient. Therefore, in addition to the roof area, other areas of the building need to be used to develop PV curtain walls, daylighting roofs, shading, etc. Many forms.
 

Due to the aesthetic needs of BIPV projects, solar panels are more biased towards power-generating glass, double-glass cells and thin-film cells. Thin-film cells have excellent light transmittance and aesthetics, better low-light conditions, and better scattered light absorption performance. The curtain wall BIPV field occupies the mainstream position. Thin film batteries mainly include copper indium gallium selenium (CIGS), cadmium telluride (CdTe), perovskite (PSC) and other material routes. The PV panels of different material routes lead to different schemes when the system chooses the inverter configuration.

In addition, because the BIPV project has a complex structure and diverse orientations, especially projects that combine multiple application forms, it is necessary to fully consider the project structure, electrical, and safety issues when designing the PV system.

BIPV project inverter selection
Judging from the main features of the BIPV project, there are many architectural application scenarios, such as flat roofs, inclined roofs, curtain walls, transparent roofs, sunshades, etc. In addition, the inclination angle is complex and the selection of materials is diverse, so the following issues must be considered when choosing an inverter.
 
1. BIPV projects give priority to string inverters
The orientation, inclination, and component selection of the BIPV project are complex and diverse, so try to choose a string inverter with multiple MPPTs, so that the PV system has a better maximum power tracking advantage, and effectively copes with the above-mentioned disadvantages. 
 

2. PV panels of different materials need to choose the corresponding inverter configuration scheme
 
In the BIPV project, due to the requirements of aesthetics and maximization of benefits, different building areas will use different PV panels. For example, flat roofs use crystalline silicon panels, light-transmitting areas use photovoltaic power generation glass, and walls use thin-film PV panels.

Therefore, it is necessary to select a suitable inverter for solution configuration according to the selected component materials.

If the component material is a crystalline silicon component or a cadmium telluride thin-film PV panel, you can use a photovoltaic inverter with a Transformerless topology and configure it in accordance with the conventional method.
 

If the PV panel use sathin-film cell that requires negative grounding, since the panel is grounded negatively, the possibility of DC leakage and the potential safety hazards of electric shock for positive person nelarein creased; therefore, it is recommended to use inverter with a high-frequency transformer topology.

Or the system adopts transformerless topology inverter + power frequency transformer solution for configuration.
 
①Configuration using inverter with high frequency transformer topology
 

Advantages: No need to connect an external power frequency transformer, easy to install.

Disadvantages: inverters with high-frequency isolation topology occupies a small market share, making it difficult to purchase;

Secondly, because of its internal isolation transformer power limitation, it is impossible to realize a single high-power product, which may lead to difficulties in the selection and configuration of large-scale projects;


In addition, due to the internal transformer, its inverter efficiency is low;
②transformerless topology inverter + power frequency transformer solution
 

For inverters with Transformerless topology, in the thin-film PV panel solution, a frequency transformer must be processed at the output end; and the primary of the transformer is not grounded; three-phase transformers are recommended to use the "△, Y" connection method, and the end close to the inverter is "△" , The terminal of the distribution box is "Y" type connection, the neutral point can be connected or not (according to the actual situation of the site). The inverter is connected to the protective ground, and there is no electrical grounding; the capacity is recommended to be 1.1 times the rated capacity of the inverter.

Advantages: The inverter products of Transformerless topology are mature, easy to purchase, and the cost is relatively low;
Transformerless topology inverters are widely used, from 700W to 320kW each power section of the single product, the system configuration selection is simple.

Disadvantages: need external processing frequency isolation transformer, large volume.

3. The inverter needs to have a strong leakage current suppression function
Since most BIPV projects use thin-film PV panels, the distance between the battery and the frame is close, so the capacitance to ground is larger, and the leakage current is larger. If the substrate is metal, the surface of the metal foil is large and thin, and the leakage current to the ground will be greater. Even if the negative grounding is used, there will be leakage current problems, which will affect the safety performance of the system.
 

Therefore, the selected inverter products need products with strong leakage current suppression function.

4. The inverter has active safety protection and supporting functions
For PV systems applied to buildings, safety protection is very important, especially for fire hazard functions. Therefore, inverters must have supporting functions such as AFCI and RSD to achieve active system protection and subsequent safe operation and maintenance.
 

5. The inverter has a rich online O&M toolkit
BIPV project is a photovoltaic project designed in combination with architectural characteristics. Therefore, compared with traditional photovoltaic projects, its later operation and maintenance are more difficult and costly. Therefore, choosing inverter products requires a wealth of online operation and maintenance tools to achieve intelligence. ,Convenient operation and maintenance.
 

Conclude
BIPV project products make full use of the area of the building, which can effectively increase the power per unit area by 15-30%; and the development of green buildings is of great significance to society’s energy saving and emission reduction. Therefore, BIPV is undoubtedly the key direction of the later photovoltaic development, and we need to follow Choose a suitable inverter and solution for its own characteristics.
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