Battery Energy Storage (BatteryBESS)¶

Class: BatteryBESS | Module: energysim.models.storage | Validation benchmarks | Units

Overview¶

Lithium-ion Battery Energy Storage System (BESS), Rint equivalent circuit.

The pack is a Rint model: an open-circuit voltage source Voc(SoC) in series with an internal resistance Rin(SoC) (no RC / Thevenin polarisation branches). Models:

OCV curve Voc(SoC) and internal resistance Rin(SoC)
inverter efficiency eta(P/P_rated)
SoC integrates the stored chemical power VocI, so joule heat I^2Rin is accounted for: P_dc = VocI + I^2Rin (energy in = stored + heat)
1-state thermal balance: C_th * dT/dt = I^2 * Rin - (T - T_amb) / R_th
calendar fade (Arrhenius-scaled) and cyclic fade (full equivalent cycles)

Parameters¶

Parameter	Type	Default	Unit	Description
`name`	`str`	`'BESS'`	-	-
`capacity_mwh`	`float`	`1.0`	MWh	Nominal energy capacity in MWh.
`p_max_mw`	`float`	`0.5`	MW	Maximum charge/discharge power in MW (AC side).
`soc_init`	`float`	`0.5`	1	Initial state of charge [0.0, 1.0].
`soc_min`	`float`	`0.05`	1	Operating SoC window; requests are scaled so SoC never leaves it.
`soc_max`	`float`	`0.95`	1	Operating SoC window; requests are scaled so SoC never leaves it.
`nominal_voltage_v`	`float`	`800.0`	V	Pack nominal DC voltage in Volts.
`c_th_kj_k`	`float`	`50000.0`	kJ/K	Lumped thermal capacitance of pack in kJ/K.
`r_th_k_w`	`float`	`0.002`	K/W	Thermal resistance to ambient in K/W.
`t_init_c`	`float`	`25.0`	degC	Initial battery temperature in degrees C.
`ocv_curve`	`Optional[Curve1D]`	`None`	-	-
`rin_curve`	`Optional[Curve1D]`	`None`	-	-
`inverter_curve`	`Optional[Curve1D]`	`None`	-	-
`step_size`	`float`	`1.0`	s	-
`calendar_fade_pct_per_year_25c`	`float`	`2.0`	%/year	Calendar capacity fade per year at 25 C (Arrhenius scaled, Ea = 25 kJ/mol).
`cycle_life_to_eol`	`float`	`4000.0`	-	Full equivalent cycles (2 x nominal capacity of DC throughput) to reach `eol_fade`.
`eol_fade`	`float`	`0.2`	-	Cyclic capacity fade at `cycle_life_to_eol` (0.20 -> 80 % SOH).

Inputs¶

Variable	Unit	Description
`P_cmd`	MW	Active power setpoint (positive = charge, negative = discharge)
`T_amb`	degC	Ambient surrounding temperature for convective cooling

Outputs¶

Variable	Unit	Description
`P_actual`	MW	Actual active power delivered to or absorbed from the grid
`SoC`	1	Current battery state of charge fraction
`T_batt`	degC	Internal lumped battery pack temperature
`SOH`	1	Remaining battery state of health capacity fraction
`V_terminal`	V	DC bus terminal voltage across the cell string
`I_current`	A	DC battery current (positive = charging)
`Q_heat_kW`	kW	Ohmic joule heat dissipation generated inside the pack

Validity and notes¶

Validity: meaningful for roughly 0-45 C pack temperature, SoC between ~5 and 95 %, and |P| <= p_max_mw. SOH is floored at 0.5. Q_heat_kW is DC joule heat only (inverter losses are not included).

Usage example¶

from energysim import world
from energysim.models import BatteryBESS

sim = world(start_time=0, stop_time=3600, t_macro=900)
sim.add_model('batterybess', model=BatteryBESS(), outputs=['P_actual', 'SoC', 'T_batt'], step_size=60)
res = sim.simulate()
print(res['batterybess'].tail(2))