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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

NameSymbolUnitsDescription
Previous SOCSOCprevSOC_{prev}WhState of charge from previous timestep
Charge Flag—booleanTrue if battery is charging
Discharge Flag—booleanTrue if battery is discharging
Available Capacity to ChargePchargeP_{charge}WPower available for charging
Available Capacity to DischargePdischargeP_{discharge}WPower available for discharging
Round-Trip DC EfficiencyηRTE\eta_{RTE}—Battery DC round-trip efficiency
Maximum CapacityEmaxE_{max}WhCurrent usable energy capacity
Time IntervalΔt\Delta tminutesWeather data time interval

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Outputs

NameSymbolUnitsDescription
State of ChargeSOCSOCWhCurrent battery energy content
Battery DC PowerPDCP_{DC}WDC power flow (positive=charge, negative=discharge)
Battery AC ChargePAC,chargeP_{AC,charge}WAC power into battery
Battery AC DischargePAC,dischargeP_{AC,discharge}WAC power out of battery

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Detailed Description

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Initial Conditions

At the first timestep, the battery is initialized to full charge: SOC1=Emax,year1SOC_1 = E_{max,year1} ηRTE,1=ηRTE,year1\eta_{RTE,1} = \eta_{RTE,year1}

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SOC Calculation

Charging (Version 12): SOC=min⁡(SOCprev+Pcharge×Δt60×ηRTE,Emax)SOC = \min\left( SOC_{prev} + P_{charge} \times \frac{\Delta t}{60} \times \eta_{RTE}, E_{max} \right) Charging (Versions 3-11): SOC=min⁡(SOCprev+Pcharge×ηRTE,Emax)SOC = \min\left( SOC_{prev} + P_{charge} \times \eta_{RTE}, E_{max} \right) Discharging (Version 12): SOC=max⁡(SOCprev−Pdischarge×Δt60,0)SOC = \max\left( SOC_{prev} - P_{discharge} \times \frac{\Delta t}{60}, 0 \right) Discharging (Versions 3-11): SOC=max⁡(SOCprev−Pdischarge,0)SOC = \max\left( SOC_{prev} - P_{discharge}, 0 \right) Idle: SOC=SOCprevSOC = SOC_{prev}

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Battery DC Power

Charging (SOC increased, Version 12): PDC=(SOC−SOCprev)/ηRTEΔt/60P_{DC} = \frac{(SOC - SOC_{prev}) / \eta_{RTE}}{\Delta t / 60} Charging (Versions 3-11): PDC=SOC−SOCprevηRTEP_{DC} = \frac{SOC - SOC_{prev}}{\eta_{RTE}} Discharging (SOC decreased, Version 12): PDC=SOC−SOCprevΔt/60P_{DC} = \frac{SOC - SOC_{prev}}{\Delta t / 60} Discharging (Versions 3-11): PDC=SOC−SOCprevP_{DC} = SOC - SOC_{prev}

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Battery AC Power

AC Discharge (when ): PAC,discharge=−PDC×ηinvP_{AC,discharge} = -P_{DC} \times \eta_{inv} AC Charge (when ): PAC,charge=PDCηinvP_{AC,charge} = \frac{P_{DC}}{\eta_{inv}}

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Efficiency Losses

DC Round-Trip Efficiency Loss (charging only): LRTE=(1−ηRTE)×∣PDC∣L_{RTE} = (1 - \eta_{RTE}) \times |P_{DC}| Inverter Efficiency Loss: Linv=(1−ηinv)×∣PDC∣L_{inv} = (1 - \eta_{inv}) \times |P_{DC}|