Battery State of Charge

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Summary

Battery State of Charge (SOC) tracks the energy content of the battery over time. PlantPredict calculates SOC by integrating charge and discharge power flows, accounting for round-trip DC efficiency during charging and maximum capacity constraints. The SOC calculation includes proper time interval scaling in Version 12 for accurate energy accounting.

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Inputs

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Outputs

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Detailed Description

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Initial Conditions

At the first timestep, the battery is initialized to full charge: $$SOC_1 = E_{max,year1}$$ $$\eta_{RTE,1} = \eta_{RTE,year1}$$

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SOC Calculation

Charging (Version 12): $$SOC = \min\left( SOC_{prev} + P_{charge} \times \frac{\Delta t}{60} \times \eta_{RTE}, E_{max} \right)$$ Charging (Versions 3-11): $$SOC = \min\left( SOC_{prev} + P_{charge} \times \eta_{RTE}, E_{max} \right)$$ Discharging (Version 12): $$SOC = \max\left( SOC_{prev} - P_{discharge} \times \frac{\Delta t}{60}, 0 \right)$$ Discharging (Versions 3-11): $$SOC = \max\left( SOC_{prev} - P_{discharge}, 0 \right)$$ Idle: $$SOC = SOC_{prev}$$

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Battery DC Power

Charging (SOC increased, Version 12): $$P_{DC} = \frac{(SOC - SOC_{prev}) / \eta_{RTE}}{\Delta t / 60}$$ Charging (Versions 3-11): $$P_{DC} = \frac{SOC - SOC_{prev}}{\eta_{RTE}}$$ Discharging (SOC decreased, Version 12): $$P_{DC} = \frac{SOC - SOC_{prev}}{\Delta t / 60}$$ Discharging (Versions 3-11): $$P_{DC} = SOC - SOC_{prev}$$

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Battery AC Power

AC Discharge (when ): $$P_{AC,discharge} = -P_{DC} \times \eta_{inv}$$ AC Charge (when ): $$P_{AC,charge} = \frac{P_{DC}}{\eta_{inv}}$$

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Efficiency Losses

DC Round-Trip Efficiency Loss (charging only): $$L_{RTE} = (1 - \eta_{RTE}) \times |P_{DC}|$$ Inverter Efficiency Loss: $$L_{inv} = (1 - \eta_{inv}) \times |P_{DC}|$$

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