Use-Case: Commercial Facility Microgrid System - 1MW Solar + 3.34MWh Energy Storage

Table of Contents

Project Overview

The Challenge

Why this project came to be.

  • High operational energy costs from peak demand charges

  • Need for reliable backup power for critical operations

  • Desire for energy independence and sustainability goals

  • Complex facility power requirements (elevators, HVAC, lighting, equipment)

Solution Summary

  • System Type: AC-Coupled Microgrid Architecture

  • Total Capacity: 1MW solar generation + 3.34MWh energy storage

  • Configuration: Eight AES CAB 426 battery cabinets with six 100kW solar inverters

  • Applications: Peak shaving, backup power, energy independence, grid services

  • Key Benefits: 99.9% power reliability, significant cost savings, environmental impact reduction

System Diagram (Single-Line Drawing)

Microgrid System Overview 1MW3.34MWh AC Coupled Architecture

AC Couple PV Distribution

Overview

The system accommodates up to 1MW of AC-coupled photovoltaic (PV) input, forming the primary energy generation source within the microgrid. The configuration includes six Solis S5 100kW three-phase string inverters, each operating at 480VAC with nominal 120A output per unit.
Microgrid System AC couple PV 1MW3.34MWh AC Coupled Architecture

Inverter Specification

  • Model: Solis S5 100kW three-phase string inverters
  • AC Output: 480VAC, 3-phase, 120A nominal per unit
  • DC Input: Ten independent MPPT inputs per inverter
  • MPPT Voltage Range: 180-1000V with up to 1000VDC and 50A Isc per channel
  • PV String Flexibility: Designed for high granularity and precise optimization

Electrical Integration

  • AC Bus Configuration: All six inverters paralleled on dedicated AC bus
  • Safety Compliance: Each unit connected to PV breaker cabinet via dedicated breaker
  • Breaker Cabinet Functions: Houses individual disconnects for each inverter
  • Motor-Based Control: Supports both manual lockout/tagout and automated control

Controls and Communication

  • Communication Protocol: Modbus TCP/IP with direct interfacing to site MGC
  • Active Power Control: Real-time export limiting, PV smoothing, and dynamic derating
  • Grid Integration: Seamless operation alongside battery PCS units and utility connection
  • Monitoring Capabilities: Real-time balancing and performance optimization

Learn about Discover Energy Systems' C&I controls

Expandability & Design Considerations

  • Future Integration: Additional AC-coupled PV inverters can be installed on load side branch circuits
  • Capacity Limitations: Expansion must consider feeder capacity, voltage drop/rise tolerances
  • System Coordination: Protective coordination with existing system required
  • Hybrid Compatibility: Seamless operation alongside battery PCS units and generator input

Energy Storage Subsystem Distribution

Overview

The energy storage system is designed specifically for off-grid or grid-independent operation. The BESS provides the backbone of energy stability for the microgrid, ensuring seamless operation during periods of insufficient PV generation. Grid or co-generation sources are only utilized as backup during sustained PV generation deficits.

Microgrid System Energy Storage Subsystem 1MW3.34MWh AC Coupled Architecture

Capacity and Architecture

  • Total Installed Capacity: 3.34 MWh usable energy (3.41 MWh rated)
  • Configuration: Eight AES CAB 426 battery cabinets, each with 418 kWh capacity
  • Design Considerations: Fully modular for easy scaling to match site growth
  • Redundancy: Multiple levels ensuring any single cabinet can be taken offline without disabling the system
  • Maintenance: Allows selective maintenance or service with no interruption to site power

Learn about Discover Energy Systems' AES CAB product

Power Conversion System (PCS)

  • Inverter Pairing: Each battery cabinet directly paired with Sinexcel PWS1-160M-H-NA battery inverter
  • Power Rating: 160 kW AC derated output, 125 kW continuous across all eight PCS units
  • Electrical Protection: Each PCS protected and isolated via individual breaker within BESS breaker cabinet
  • System Synchronization: All PCS units synchronized and paralleled on common AC bus

Electrical Integration

  • Bus Configuration: Multi-branch modularity to facilitate segmented operation
  • Service Isolation: Thermal coordination and operational reliability through centralized switchgear
  • Distribution Integration: Centralized point for interconnection to switchgear or distribution nodes

Communication and Control

  • EMS Integration: Micro-Grid Control System (MGC) interfaces with all PCS units via Modbus TCP/IP
  • Real-Time Dispatch: Logic implemented for battery charge/discharge control
  • Load Response: Dynamic response to load profiles and PV production variability
  • Safety Management: Operational safety limits, temperature monitoring, and fault conditions
  • Autonomous Operation: PCS adheres to MGC commands autonomously

Learn about Discover Energy Systems' C&I controls

Operational Role

  • Primary Function: Main buffer and dispatchable energy reserve within the microgrid
  • Load Support: Smooths out fluctuations in PV generation and supports loads during night/low-irradiance periods
  • Grid Independence: Maintains system operation when both PV and external grid are unavailable
  • Backup Integration: Coordinated through MGC when both PV and storage are unable to meet critical load demands

MGC, Load Distribution, and Interconnect Subsystem

Overview

The Microgrid Control (MGC), load distribution, and interconnect subsystem manages power flow, load prioritization, and grid interface for the entire facility. This subsystem ensures reliable power delivery to critical loads while maintaining safe operation and grid compliance.

Learn about Discover Energy Systems' microgrid controls

Microgrid System MGC Load Distribution and Interconnect Subsystem 1MW3.34MWh AC Coupled Architecture

Load Cabinet

Configuration and Expandability

  • Initial Buildout: Six dedicated branch circuits with individual protection
  • Scalability: Supports up to twelve individually protected load circuits
  • Breaker Ratings: Each branch circuit can accommodate breakers rated up to 250A
  • Load Profiles: Suitable for range of commercial and industrial load profiles
  • Power Distribution: Delivers conditioned power from shared AC bus (fed by PV and BESS)

Functional Role

  • Primary Distribution Point: Delivers conditioned power from shared AC bus to site loads
  • DER Accommodation: Allows for connection of additional distributed energy resources
  • Load Management: Fully compatible with site-level load shedding strategies
  • Circuit Control: MGC can open non-critical load circuits during undergeneration, islanding events, or grid recovery transitions
  • Maintenance Support: Selective circuit isolation for maintenance or fault events without full system interruption

Grid/Generator Interface (Microgrid Interconnect Device | MID)

Interface and Breaker Design

  • Breaker Rating: Motor-actuated 200A breaker for utility interconnection
  • External Sources: Interfaces microgrid with external AC sources (utility grid and/or generators)
  • Design Intent: Used for supplemental power only when internal generation (PV + BESS) cannot meet load demand
  • Grid Integration: Supports import operation with utility up to ~160kW
  • Generator Support: Supports parallel genset operation managed via CANbus under MGC control

Supported Operational Modes

  • Grid-Connected Mode: Allows import operation with utility up to ~160kW
  • Grid-Independent Mode: Engaging only when PV and BESS are depleted or insufficient
  • Generator Support Mode: Supports parallel operation with one or more generators integrated via CANbus
  • Staged Genset Operation: Enables staged genset ramp-up, synchronization, and safe breaker closure
  • Co-Generation: Multiple generation assets can operate simultaneously with proper synchronization
  • Economic Dispatch: Flexible dispatching of generation assets based on demand, availability, and cost optimization

Protection and Sequencing

  • Logic Control: Breaker sequencing and interlock conditions driven by Microgrid Controller (MGC)
  • Anti-Backfeed: Prevents unintentional export during grid outages or maintenance
  • Grid Synchronization: Monitors phase, voltage, and frequency to ensure safe parallel operation
  • Transfer Commands: Provides open/close commands to prevent overlapping supply conditions
  • Fault Protection: Upon detecting grid loss or instability, MGC isolates MID and transitions to standalone mode
  • Reconnection Safety: Grid parameters validated before MID closure after outage recovery