Skip to main content

​
Summary

ESS Losses calculates power dissipation in the battery energy storage system, including DC round-trip efficiency, inverter conversion, MV transformer, and HVAC thermal management. These losses are applied to the battery power flow before combining with PV output. The storage system uses the same transformer loss model as the PV system.

​
Inputs

NameSymbolUnitsDescription
Battery DC PowerPDCP_{DC}WDC power at battery terminals
Battery AC DischargePAC,dischargeP_{AC,discharge}WAC power from inverter (discharge)
Battery AC ChargePAC,chargeP_{AC,charge}WAC power to inverter (charge)
Round-Trip DC EfficiencyηRTE\eta_{RTE}—Battery DC round-trip efficiency
Inverter Efficiencyηinv\eta_{inv}—Storage inverter efficiency
MV Transformer CapacitySMVS_{MV}kVAStorage MV transformer rating
MV No-Load LossLNLL_{NL}—MV transformer no-load loss fraction
MV Full-Load LossLFLL_{FL}—MV transformer full-load loss fraction
HVAC No-Load LossLHVAC,NLL_{HVAC,NL}—HVAC no-load loss fraction
HVAC Full-Load LossLHVAC,FLL_{HVAC,FL}—HVAC full-load loss fraction
Nameplate Energy CapacityEnomE_{nom}kWhBattery nameplate capacity

​
Outputs

NameSymbolUnitsDescription
DC RTE LossLRTEL_{RTE}WRound-trip efficiency loss
Inverter LossLinvL_{inv}WInverter conversion loss
MV Transformer LossLMVL_{MV}WMV transformer loss
HVAC LossLHVACL_{HVAC}WThermal management loss
AC Discharge at MVPdischarge,MVP_{discharge,MV}WDischarge power after MV transformer
AC Charge at MVPcharge,MVP_{charge,MV}WCharge power including MV transformer loss

​
Detailed Description

​
DC Round-Trip Efficiency Loss

Round-trip efficiency losses represent energy dissipated within the battery during charging and discharging cycles. In PlantPredict, this loss is applied entirely during charging (when PDC>0P_{DC} > 0). The loss is calculated as the inefficiency fraction multiplied by the absolute DC power: LRTE=(1−ηRTE)×∣PDC∣L_{RTE} = (1 - \eta_{RTE}) \times |P_{DC}| When the battery is discharging or idle, no RTE loss is applied.

​
Inverter Efficiency Loss

Linv=(1−ηinv)×∣PDC∣L_{inv} = (1 - \eta_{inv}) \times |P_{DC}|

​
MV Transformer Loss

The storage MV transformer uses the same quadratic loss model as PV transformers. See Transformer Loss Model for the detailed equations. The transformer loss consists of two components:
  • No-Load Loss: Power dissipated in the transformer core regardless of load (constant when energized)
  • Full-Load Loss: Additional resistive losses that scale with the square of the power flow
Discharge direction: During discharge, the transformer loss reduces the power delivered to the grid: Pdischarge,MV=PAC,discharge−LMV,dischargeP_{discharge,MV} = P_{AC,discharge} - L_{MV,discharge} Charge direction: During charging, the transformer loss increases the power drawn from the grid: Pcharge,MV=PAC,charge+LMV,chargeP_{charge,MV} = P_{AC,charge} + L_{MV,charge}

​
MV Transformer No-Load Loss (Idle)

When the battery is idle (neither charging nor discharging), the transformer still draws power from the grid to maintain core magnetization: LMV,idle=LNL×SMVL_{MV,idle} = L_{NL} \times S_{MV} Pdischarge,MV=−LMV,idleP_{discharge,MV} = -L_{MV,idle} The negative value indicates power drawn from the grid rather than delivered to it.

​
HVAC Loss

Thermal management losses include no-load and load-dependent components: LHVAC=(LHVAC,NL×Enom×1000)+(LHVAC,FL×∣PDC∣×1000)L_{HVAC} = (L_{HVAC,NL} \times E_{nom} \times 1000) + (L_{HVAC,FL} \times |P_{DC}| \times 1000)

​
Loss Application Sequence

  1. DC RTE loss (during charging)
  2. Inverter efficiency loss
  3. MV transformer loss
  4. HVAC loss (reported separately)