AC-coupled BESS in pvDesign

Do you want to add battery storage to your PV plant? Design your hybrid PV + AC-coupled BESS plant in pvDesign.

Introduction 

Now, in pvDesign, you can design an AC-coupled battery energy storage system (BESS). By defining an available area for the storage system in your site, as well as the electrical parameters of the system, you will get the basic engineering of your system and a BESS design report.

How to add batteries to your site

There's two ways that you can add batteries. One would be to do it on google earth and upload the file to pvDesign. And the other would be to create it using the site creator inside the software.

Definition of the storage area in the KML

First, it is essential to define a battery polygon (BA) and an MV placemark within that polygon. 

The size of the user-defined area will determine the space available to install the storage system. The MV point will be the interconnection point between the battery area and the substation. 

Some requirements must be considered so that pvDesign can recognize that area as the battery area: 

• The polygon defining the area of the batteries must be called BA.
• The MV placemark is mandatory, and is placed inside the BA.
• The battery polygon cannot be placed inside any AA polygon.
• The battery polygon has to be located outside the ST polygon. 
• A restricted area (RA) cannot be placed inside the BA.

 

Definition of the storage area inside pvDesign

After getting into the site creator interface (as per the article on how to create a site directly inside pvDesign), you will be able to select the "Polygon" box to draw the BESS area, and then "Placemark" to place the MV point.

How to define the minimum BESS unit?

Once the KML is imported into pvDesign, with the BA defined for the storage system, the "BESS" tab is enabled in the design process. This is where we will design the system.

First, within this tab, the electrical parameters of the unit are defined. The minimum unit or block of the BESS is the set of a PCS and the containers connected to it. 

 

 

• Power Conversion System (PCS): In this first section within the BESS tab, the inverter type and the number of inverters per PCS are selected, thus establishing the power of the PCS or minimum unit of the system.
  
  

In this example, the chosen inverter has a power of 1000 kVA, and the number of inverters per PCS is 2, so the power of the PCS is 2000 kW.

• Battery container: in pvDesign, we assume that the storage solution is modular. As a user, you will set the capacity of a battery container. Alternatively, you can set the capacity of a single battery rack and the number of racks to include per container.

pvDesign will install the necessary number of containers according to the system requirements.

How to achieve your power and capacity requirements?

After having defined the power of the PCS and the capacity of a container, you'll need to define the BESS requirements. This section establishes both the power requirements and the supply hours of the BESS. 

First, choose between maximum capacity or specific capacity.

• Maximum capacity: selecting this option, the maximum possible power will be installed in the area defined for the BESS. 
  
  
  
  
• Specific capacity: In this section, you can configure a specific size for the battery system by defining the number of PCS you want to install. The system power will be the multiple of the PCS power.

You can now define the supply time. The supply cycle duration is calculated as capacity (MWh) divided by rated power (MW). For example, a 2000 kW PCS and a 3000 kWh container, the supply time (time taken for a complete charge or discharge cycle) will be 1.5 hours. If you connect two battery containers (6000 kWh) to the same PCS, you would have a system with 3 hours of supply. 

BESS Layout

In the BESS layout section, you can define the dimensions of both PCS and containers, distances between blocks, and the BESS rotation angle. 

The distance between adjacent blocks and the distance between opposing blocks can be also defined by the user. According to the NFPA 855 standard, the safety distances between containers or between containers and PCS are fixed: 0.9144 m (3 ft) and 1.524 m (5 ft), respectively.

In addition, the user can edit the BESS placement by customizing the orientation angle. The orientation angle plays a role in determining the system's efficiency and space utilization. 

Users are provided with three distinct options to set the BESS orientation according to their specific requirements. 

1. Vertical alignment (90º): This option allows the user to choose a vertical BESS orientation, enabling efficient use of vertical space.
2. Horizontal alignment (0º): By selecting this option, the BESS layout will be aligned horizontally, ensuring maximum efficiency in terms of horizontal space utilization. 
3. Rotated (recommended/user input): For a more personalized approach, users have the flexibility to define a custom orientation angle that aligns with their specific project needs or site characteristics. 

Results

pvDesign provides the following outputs and documents for the design of the BESS.

The top bar of the results screen will provide the installed capacity, the rated power, and the supply duration of the complete system. 

The BESS layout and a system design report are generated as documentation. The rest of the PV plant documents (SLDs, reports) will include references to the BESS system. 

BESS 1.0 

This is the first tool that has been developed for the design of storage systems in pvDesign. We want to keep adding functionalities in this direction, starting with offering DC-coupled BESS design tools. If this is of interest to you and you feel like collaborating, your suggestions are more than welcome.

Energy Yield Results 

 

The "Battery Energy" tab was added to all the Energy Yield Results excel sheets when the AC-coupled BESS option was launched. Even if no BESS is added to the design, we'll find:

• Column A- represents the inverter power limit energy loss: the DC system produces more power than the inverter can process, therefore part of the power is lost (inverter clipping). If a DC-coupled BESS was in place, that's the amount of energy that would be available to store.
• Column B- represents the delivery active power limit loss. If you have set a curtailment, any power that exceeds that value at the delivery point is discarded (clipping at delivery point). If a AC-coupled BESS was in place, that's the amount of energy that would be available to store.

For now, pvDesign does not calculate any energy storage flows. Charge or discharge dispatch strategies of these systems are out of scope at the moment. The only information we provide are the columns mentioned above, which are the excess energy that are lost if no battery energy storage system uses it.

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