The customizable nature of Nor-Cal’s SCADA offerings presents flexible designs for solar sites and can be used to build cost-effective and innovative solutions for both PV production and battery energy storage systems (BESS), particularly for sites that contain both.
A Growing Industry
Combined PV and BESS sites are becoming increasingly popular as an effective tandem to help ensure grid stability during periods when solar produces little or no power. Many sites around the country are being built exclusively for storage, and some previously PV-only sites are adding BESS. Meanwhile, many new sites are being designed with both power generation and energy storage in mind. Nor-Cal can provide SCADA options for any of these designs, but adding BESS to a site may not require as much equipment as one would expect.
Types of BESS Generation
To properly consider the options when including BESS in a site, it is important to understand the different types of BESS generation. BESS can be built independently of a PV controls system, but whether it is co-located with a PV site or not, the BESS will be one of three types: DC-coupled with flexible charging, DC-coupled with PV-only charging, or AC-coupled. In a flexible DC-coupled setup, the batteries can charge either from PV modules or from the grid by way of a shared inverter, while in PV-only DC-coupled sites, the batteries are only able to charge from the PV modules. AC-coupled systems use a separate inverter to charge from the PV system. This can make AC-coupled systems popular when augmenting an existing PV system because it is easy to simply add new inverters, and the BESS can act independently from the PV system. Since field communications are located at each inverter skid or medium-voltage transformer, the field communications will be determined based on the type of BESS site.
Understanding Power Generation vs. BESS
SCADA systems are vitally important in solar plants for both monitoring and control. They can be used in many different PV applications and will communicate with solar modules, trackers, inverters, power meters, MET stations, and other plant equipment to act as the central control hub for the solar energy generation at the point of interconnection (POI) as well as to provide trending, report on site issues, and help guarantee the POI power output capacity is being met.
A BESS SCADA will be used to make sure the plant is meeting the power output for a set time. It will primarily communicate with the batteries but will also interface with inverters, converters, and auxiliary meters as well as ensure that the batteries are charging and the energy storage system is meeting site requirements. Additionally, the BESS SCADA can be used to monitor the state of charge (SOC) of the BESS.
A Centralized SCADA
There are several components that are common to both PV and BESS sites as well as some that are unique to BESS. Because BESS is often viewed as separate from the PV portion of the plant and has its own control demands, owners will commonly plan on purchasing a separate BESS SCADA. However, this is seldom necessary. By understanding each component, one can appreciate the advantages of condensing them into a single SCADA.
A Master or Main Plant Controller (MPC) is used primarily to manage the real and reactive power and the voltage stability of the plant. It is the overarching controller that will communicate with the BESS controller and the plant controller and act as the central point of control for the entire site.
The Power Plant Controller (PPC) is used to control and regulate the inverters and other PV plant equipment to meet the plant’s required setpoints. It can also be used to complete automated plant maintenance.
The Battery Management System (BMS) is a system that is built into the BESS to maintain the health of the batteries. This system regulates the charging and discharging of the system based on the input it receives from the SCADA or EMS. Based on factors such as the state of charge, the BMS is used to manage the batteries on an individual level to avoid any damage to them.
The Energy Management System (EMS) is used to monitor grid demand and determine when to transfer energy to the BESS through control logic. This is most often the system that provides input to the BMS and will ultimately work to determine the charging and discharging schedule of the batteries. The SCADA will communicate with and control the devices throughout the PV plant. The EMS can be supplied along with the SCADA, along with the batteries and BMS, or by a subcontractor that specializes in EMS.
While an EMS specialist will have a high level of experience with the EMS, they generally only have expertise in that singular area and will not have a strong level of proficiency with the full scope of a combined site. Therefore, they may struggle with balancing the full plant with regards to components such as the PV generation, the transformer, and the overall output across the whole site.
All these systems are ultimately designed to work in concert to run a plant efficiently and maintain the required power and storage output. In some cases, the EMS, PPC, and MPC can utilize a single programmable logic controller (PLC) to supply control, but this is rarely a prudent choice. The MPC is the control device most likely to need a dedicated PLC, as determined by the size of the plant and the number of devices that are integrated back through the SCADA system. Trying to use the same PLC for both master plant and PV/BESS control can also create a single point of failure that is often not acceptable in the control system. If the plant is large enough, it may not even be possible to use a single device. In instances like this, utilizing separate devices is the recommended solution to most effectively manage the plant.
Unlike the MPC, a single PLC can generally be used for PV plant control and BESS control. Cases that may require separate devices would be co-located sites that require individual controllers for each site or sites where the BESS was added subsequently to when the PV was initially installed. It is also prudent to have a separate BESS controller if EMS logic is added to the controls. Furthermore, large sites with a high number of control points may work better with dedicated devices for BESS and PV. It should also be noted that individual PLCs can offer other advantages, such as the ability to perform maintenance on one device without having to take more of the plant offline.
Using multiple PLCs does not necessitate using multiple SCADA racks. SCADA racks also use other equipment that does not require duplicating when the PLC quantity in the rack is increased. Firewalls, servers, switches, KVMs, backup batteries, data concentrators, and other equipment can all be used for a single SCADA rack with multiple PLCs. Even the HMI can be shared and the display customized to delineate the sites and information as needed. This can create a more economical system with logic designed to run the entire plant efficiently.
The Benefits
Using a single SCADA can create a more efficient system with logic designed to run the entire plant – and even co-located plants – as economically as possible. The shared equipment of a single rack can reduce resources in the design and construction of a plant, requiring less equipment to install and commission and saving on space and labor.
While there are many technical advantages to a single PV+BESS SCADA system, one of the greatest is the cost savings. Dividing the two into separate systems can nearly double the costs of the controls at the site.
Nor-Cal’s customizable SCADA racks offer seamless PV+BESS designs with the ability to add to the controls if a plant expands in the future. Additionally, with our new fully integrated BESS solution in partnership with International Energy Storage, Nor-Cal can now provide an all-in-one solution for BESS SCADA with EMS. Connect with Nor-Cal to discuss your next project.
