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PlantPredict models AC-coupled battery energy storage systems (BESS) integrated with solar PV plants. The ESS model calculates charge/discharge scheduling, battery state of charge, degradation effects, and system losses to determine the combined PV+storage output at the point of interconnection.

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Node Positions

Single Line Diagram of AC-Coupled Energy Storage System

Single Line Diagram of AC-Coupled Energy Storage System (with Nodes 1-6 Identified)

The energy storage model tracks power flow at seven node positions through the system. These nodes represent measurement points where power values are calculated:
  1. Battery DC terminals — DC power at the battery cell/module level
  2. Storage inverter AC output — AC power after DC-AC conversion
  3. Storage MV transformer output — Power after storage-side MV transformer
  4. PV MV transformer output — Power from PV system before combining with storage
  5. Combined PV+ESS at MV — Combined power from PV and storage systems
  6. HV equipment output — Power after HV transformers and transmission lines
  7. Point of interconnection (POI) — Final grid delivery point
The models in this section calculate power and losses at each of these nodes.

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Models in This Section

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Dispatch Algorithms

Determines when the battery charges and discharges based on three algorithm options:
  • LGIA Excess: Charges when PV output exceeds interconnect capacity
  • Energy Available: Charges when PV energy is available and not in discharge period
  • Custom Dispatch: User-defined charge/discharge schedule with inverter capacity percentage

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Battery State of Charge

Tracks battery energy content over time, accounting for:
  • Charge and discharge power flows
  • Round-trip DC efficiency losses
  • Maximum capacity constraints
  • Time interval scaling (Version 12)

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Battery Degradation

Models capacity and efficiency decline over time:
  • Cycle Degradation: Based on cumulative discharge energy
  • Calendar Degradation: Based on system age

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ESS Losses

Calculates power losses in the storage system:
  • DC round-trip efficiency losses
  • Inverter efficiency losses (charge and discharge)
  • MV transformer losses (including no-load losses when idle)
  • HVAC losses (heating/cooling)

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PV+Storage Integration

Combines PV and storage power flows:
  • Adjusts PV output for battery charging
  • Adds battery discharge to PV output
  • Applies HV equipment losses to combined output
  • Enforces LGIA capacity limits

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Calculation Sequence

  1. Determine charge/discharge state from dispatch algorithm
  2. Calculate available capacity for charge and discharge
  3. Update battery state of charge
  4. Calculate battery DC and AC power
  5. Apply storage MV transformer losses
  6. Combine with PV output
  7. Flow through HV equipment to grid