PLCs, Data Concentration, and Commissioning in the Real World
Nor-Cal Controls believes that informed customers are empowered customers. That’s why we frequently engage with questions from the field – whether they come from experienced asset owners, EPCs, or engineers delving into new renewable energy projects. We’ve heard some excellent questions from our customers touching upon fundamental aspects of SCADA and site operations. Let’s break them down and share some insights.
1. Can PLCs Communicate via Modbus? How Do You Set It Up?
The Short Answer: Absolutely, yes! PLCs (Programmable Logic Controllers) are the workhorses of industrial automation, and Modbus is one of the most ubiquitous and enduring communication protocols in the world of industrial control. Its simplicity and open nature make it a common language for devices from different manufacturers to “talk” to each other.
Why Modbus?
Modbus provides a standardized way for a “master” device (often your PLC or SCADA system) to request information from or send commands to “slave” devices (like inverters, meters, sensors, or other PLCs). It’s widely adopted because it’s:
- Simple and Robust: Easy to implement and relatively forgiving in industrial environments.
- Open and Royalty-Free: No licensing fees, fostering broad adoption.
- Versatile: Supports both serial (Modbus RTU over RS-485/232) and Ethernet (Modbus TCP/IP) networks, offering flexibility for different site layouts and distances.
How Do You Set It Up? (A Simplified Overview)
Setting up Modbus communication with a PLC generally involves a few key steps, often managed within the PLC’s programming software (like Emerson Machine Edition for Emerson PLC PLCs, which Nor-Cal commonly uses):
- Hardware Connection:
- Modbus RTU (Serial): This typically involves an RS-485 connection. You’ll wire two (or four) twisted-pair wires between your PLC and the Modbus slave devices. Ensure proper termination resistors are used to prevent signal reflections.
- Modbus TCP/IP (Ethernet): This uses standard Ethernet cabling. Both the PLC and the Modbus TCP/IP slave devices need to be connected to the same network (or accessible via network routing) and have unique IP addresses.
- PLC Configuration:
- Protocol Selection: Within the PLC programming environment, you’ll enable and configure the Modbus communication port or module (e.g., an Ethernet port for Modbus TCP/IP, or a serial port for Modbus RTU).
- Master/Slave Role: Define whether your PLC will act as a Modbus Master (initiating communication requests) or a Slave (responding to requests from another master). In a typical SCADA setup for a renewable plant, the Power Plant Controller (PPC – often a PLC) acts as a Modbus Master, polling data from inverters, meters, and other field devices.
- Communication Parameters: For Modbus RTU, you’ll set parameters like baud rate (e.g., 9600, 19200), parity (none, even, odd), and stop bits – these must match the slave device’s settings. For Modbus TCP/IP, you’ll configure IP addresses and port numbers.
- Device Addresses (Unit IDs): Each Modbus slave device on a serial network (RTU) needs a unique Unit ID. For Modbus TCP/IP, the IP address is typically the primary identifier, though a Unit ID can still be used.
- Data Mapping (Registers):
- This is the core. Modbus uses “registers” to hold data (e.g., coil status, input status, input registers, holding registers). You’ll need the Modbus register map (or communication protocol document) from each slave device. This map tells you which register address corresponds to which data point (e.g., inverter active power, battery state of charge, meter kWh).
- In the PLC program, you’ll write logic to read from or write to these specific Modbus registers on the slave devices and then map that data to internal PLC tags for use in control logic, calculations, and sending to the SCADA system.
Nor-Cal regularly implements Modbus communication as a foundational element of our SCADA and PPC solutions, ensuring seamless data flow across diverse equipment in utility-scale solar and BESS plants.
2. Can We Use SCADA as a Data Concentrator?
Yes, the SCADA system inherently acts as a powerful data concentrator. In fact, it’s one of its primary functions.
What is a Data Concentrator?
At its simplest, a data concentrator is a device or system that collects data from multiple sources, processes it (if necessary), and then makes it available to other systems or applications. Think of it as a central hub gathering information from various spokes.
How SCADA Fulfills This Role:
A (SCADA) system is designed precisely for this purpose. Here’s how it acts as a data concentrator for your renewable energy assets:
- Polling Diverse Field Devices: The SCADA system (often through its PLC-based Power Plant Controller and communications gateways) actively polls data from hundreds or thousands of field devices across a plant: inverters, Battery Management Systems (BMS), meters, meteorological stations, trackers, substation IEDs, and more.
- Protocol Translation: These devices might communicate using a variety of protocols (Modbus, DNP3, IEC 61850, OPC UA). The SCADA system (and its underlying architecture like Kepware or custom drivers) acts as a translator, normalizing this diverse data into a unified format.
- Centralized Database (Historian): All collected data is funneled into a centralized, high-speed database – often referred to as a “historian” (like ETAPro Historian which Nor-Cal utilizes). This historian timestamps and archives every data point, creating a rich, searchable record of plant performance.
- Real-time & Historical Access: From this concentrated data, operators gain real-time visibility into plant operations via the Human-Machine Interface (HMI) screens (e.g., built with Inductive Automation’s Ignition). Additionally, historical data allows for trend analysis, performance reporting, troubleshooting, and long-term optimization studies.
- Integration with Enterprise Systems: As a data concentrator, the SCADA system can then serve this consolidated data to higher-level enterprise systems (e.g., ERP, asset management, O&M analytics platforms) through various APIs and integration tools. This seamless data flow supports everything from billing and maintenance scheduling to long-term strategic planning.
By centralizing data acquisition, processing, and storage, Nor-Cals’ SCADA systems provide a single source of truth for your entire renewable energy fleet, transforming raw data into actionable intelligence.
3. Can We Commission the Site in Non-Ideal Weather Conditions?
This is a critical operational question, and the answer is: It depends, but often careful planning and specific precautions are necessary. While some elements of commissioning can proceed, others absolutely require optimal conditions for accuracy, safety, and proper validation.
What “Non-Ideal” Means:
Non-ideal weather can include:
- Rain/Snow/Ice: Direct moisture can compromise electrical connections, create safety hazards, and impact sensitive electronic equipment. Ice can prevent mechanical components (like trackers) from moving.
- Extreme Cold/Heat: Temperatures outside of equipment operating ranges can lead to false readings, equipment failure, or safety risks for personnel.
- High Winds: Can be dangerous for personnel working at heights or with large equipment and can impact the stability of certain tests.
- Overcast Skies/Low Irradiance: Crucial for solar PV sites, as performance tests rely on sufficient and stable sunlight.
- Dust/Sandstorms: Can damage sensitive equipment, especially rotating parts or cooling systems.
Impact on Commissioning Phases:
- Mechanical & Electrical Checks (Pre-Energization): Many visual inspections, torque checks, cable routing verification, and continuity tests can proceed in light non-ideal conditions, provided safety measures are strictly followed (e.g., proper PPE, waterproof tools). However, pouring rain or heavy snow would halt most outdoor electrical work.
- Insulation Resistance Testing & Grounding Tests: These are highly susceptible to moisture and extreme temperatures. Accurate results often require dry conditions. For example, grounding resistance measurements can be significantly impacted by soil moisture.
- Functional Testing of Components: Individual inverter energization, communications checks (Modbus, etc.), and basic device functionality can often be tested in varying conditions, as long as equipment operating ranges are respected.
- Performance and Power Plant Controller (PPC) Testing: This is where weather becomes paramount, especially for solar PV.
- Solar Performance Tests (PPA Tests): These absolutely require clear, stable irradiance for accurate measurement of power output, efficiency, and degradation. Attempting these in cloudy or fluctuating conditions will yield unreliable results and may invalidate warranties or contractual obligations.
- PPC Controls Tuning & Validation: While basic control loops can be tested, fine-tuning complex active power curtailment, ramp rate control, and voltage/reactive power responses often requires stable environmental conditions to observe predictable plant behavior and validate against grid requirements.
- Safety Protocols: Non-ideal weather significantly increases safety risks (slips, falls, electrocution). Strict adherence to site-specific safety plans and weather-related work stoppages is essential.
Nor-Cals’ Approach:
At Nor-Cal, our commissioning teams prioritize safety, accuracy, and compliance. While we strive to meet project schedules, we advocate for:
- Phased Commissioning: Breaking down the commissioning process into distinct phases allows for progress on certain tasks even if others are weather-dependent.
- Strategic Scheduling: Working closely with clients and EPCs to schedule critical, weather-sensitive tests (like performance guarantees) during periods with the highest probability of ideal conditions.
- Robust Pre-Commissioning: Thorough Factory Acceptance Testing (FAT) and rigorous internal checks reduce the reliance on perfect site conditions for basic functionality.
- Communication: Clear communication with all stakeholders regarding weather impacts and adjustments to the commissioning schedule is vital to manage expectations and ensure project success.
Ultimately, while some progress can be made, successful and accurate commissioning, especially for power performance and grid compliance, often hinges on the cooperation of Mother Nature. Planning for potential weather delays is a key component of realistic project management in renewable energy.
Have more questions about optimizing your renewable energy project’s controls and data?
Nor-Cal specializes in delivering robust, open-architecture SCADA and Power Plant Controller (PPC) solutions for utility-scale solar and BESS projects. From seamless Modbus integration to comprehensive data concentration and expert commissioning support, we’re here to help you navigate the complexities of modern energy systems.
Contact us today to discuss your project needs or explore our range of solutions and training programs. Let Nor-Cal be your partner in powering a more efficient and reliable renewable energy future.
Inspired by our FAQ video series, this post was shaped by the expertise of our SCADA Subject Matter Expert, Roshen Borkar. Thanks to him for his collaboration and for the technical review.