Containerized BESS Efficiency & Auxiliary Power Consumption

Containerized Energy Storage System — Single Charge-Discharge Cycle Energy Link and Auxiliary Power Consumption Analysis Report

This report analyzes the energy link for a complete SOC 0% → 95% → 0% cycle of the D-Ocean-5016D containerized energy storage system (12 clusters × 418 kWh, Hihtium 314 Ah cells 1P416S). The system uses the Envicool EMW600HCNC3E air-cooled chiller (CE-certified / C5-M anti-corrosion), and the auxiliary equipment draws power directly from the main circuit + UPS + distribution box (DC 24 V/48 V).

• Core RTE (25°C ideal conditions) = 88.48% (including step-up transformer 0.99² × PCS 0.98² × battery DC RTE 0.94)
• Electrical auxiliary system (14 items per the project's actual electrical design; see Section 1.1 for details): 7.25 kW fixed continuous operation, consuming 13.0 – 14.7 kWh per cycle
• System net RTE range at 0.5P full-power operation: 85.88% – 87.97% (maximum power to liquid cooling shutdown)
• Liquid cooling self-circulation 0.74 kW consumes about 1.5 kWh per cycle; rated cooling 27.8 kW consumes about 57.5 kWh per cycle
• 88.5% net RTE is unachievable in this model (maximum is 87.97%); 87% net RTE control target: cooling duty cycle ≤ 48.3%
• Container continuous auxiliary total power 7.25 kW, peak (including maximum liquid cooling power) 37.25 kW

1. System Parameters

1.1 Electrical Auxiliary System Architecture

D-Ocean-5016D project actual electrical design load list (from engineering distribution diagram):

Architecture notes:

• The high-voltage box SMPS outputs 24 V DC to power the whole-cluster contactors/control/heating, etc.; the AC-DC 350 W is the main power supply, and the DC-DC 200 W is only switched in when AC fails.
• The distribution box SMPS supplies the container-level 24 V/48 V bus (not UPS-backed), powering the main circuit loads.
• Six AC dehumidifiers GCH-8120S (130 W actual power) are powered from the main circuit, continuous operation.
• 12 cluster BMS power supplies (60 W/cluster) are UPS-backed, ensuring the BMS continues to operate and report alarms during power loss.
• Fire host 200 W is UPS-backed (continuous monitoring); explosion-proof exhaust fan 240 W is only started by UPS backup on alarm (transient about 3 seconds).
• Maintenance socket and spare socket are rated at 1 kW peak reservation, not counted in RTE continuous auxiliary.
• The electrical auxiliary system above does not include the emergency water firefighting main circuit (fire pumps, sprinklers, etc.). Actual projects equipped with an emergency water system must supplement per EN 12845 (typically 5 – 10 kW including fire pumps), and the container main breaker margin must be verified.

2. Wiring and Terminals

This section does not involve external wiring; it focuses on energy metering points, suggested as follows:

• Grid-side metering: bidirectional meter at the outlet end of the grid-connection switch, as the statistical source for $E_{\text{grid\_in}}$ / $E_{\text{grid\_out}}$.
• PCS AC-side metering: bidirectional meter for verifying the PCS's own efficiency.
• Battery DC-side: BMS DC bus sampling for calculating battery DC round-trip efficiency.
• Auxiliary branch: liquid cooling unit, BMS/EMS, and dehumidifier supply circuits should be metered separately to facilitate auxiliary power consumption traceability.

3. Liquid Cooling Unit Specifications (EMW600HCNC3E)

3.1 Working Mode Control Logic (BMS active, reference Envicool platform general control)

Note: The EMW600HCNC3E specification sheet does not disclose a detailed control logic table. The temperature thresholds above are general reference values for the Envicool platform; actual projects must follow the D-Ocean-5016D BMS integration specifications.

3.2 BMS Power-loss Protection Logic (BMS inactive)

3.3 Mode Priority

Cooling > Heating > Self-circulation; forced protection conditions (3.2) can override the above priority and directly enter self-circulation.

4. Communication

This report does not cover external communication protocols, but it is recommended to unify the following interfaces and data points during on-site data acquisition to facilitate EMS upper-level RTE calculation:

• BMS → EMS: 12 clusters DC voltage/current, SOC, SOH, cell maximum/minimum temperature.
• PCS → EMS: AC-side voltage/current/power, charge/discharge state, fault word, efficiency curve.
• Liquid cooling unit → EMS: outlet liquid temperature, compressor/pump/fan start-stop, current mode (cooling/heating/self-circulation), fault word.
• Auxiliary branch meter → EMS: main circuit auxiliary branch total meter (for calculating total auxiliary consumption), UPS output itemized meter, BMS/EMS DC side, dehumidifier branch.

5. Operating Steps and Calculation Basis

5.1 Baseline Link Energy

• Battery DC round-trip efficiency 94%, symmetrically split as 96.96% × 96.96%
• PCS charge/discharge efficiency both 98.0%
• Step-up transformer efficiency (step-up + step-down) 0.99 × 0.99 = 0.9801 (two-way)
• DoD = 95%

$$E_{\text{usable}} = 5016 \times 95\% = 4765.2 \text{ kWh}$$

$$E_{\text{grid\_in\_basic}} = \frac{E_{\text{usable}}}{\eta_{\text{TR}} \times \eta_{\text{PCS}} \times \eta_{\text{DC\_ch}}} = \frac{4765.2}{0.99 \times 0.98 \times 0.9696} = 5065.7 \text{ kWh}$$

$$E_{\text{AC\_gross}} = E_{\text{usable}} \times \eta_{\text{DC\_dis}} \times \eta_{\text{PCS}} \times \eta_{\text{TR}} = 4765.2 \times 0.9696 \times 0.98 \times 0.99 = 4482.0 \text{ kWh}$$

System theoretical efficiency excluding liquid cooling and fixed auxiliary consumption (core of PCS + battery + step-up transformer, 25°C ideal conditions):

$$\eta_{\text{core}} = \eta_{\text{TR}} \times \eta_{\text{PCS}} \times \eta_{\text{DC\_RT}} \times \eta_{\text{PCS}} \times \eta_{\text{TR}} = 0.99 \times 0.98 \times 0.94 \times 0.98 \times 0.99 = 88.48\%$$

5.2 Single-Cycle Energy Link

• Charging path: grid → step-up transformer (×99.0%) → PCS (×98.0%) → battery DC (×96.96%) → stored 4765.2 kWh.
• Discharging path: battery DC (×96.96%) → PCS (×98.0%) → step-up transformer (×99.0%) → AC gross output 4482.0 kWh.
• Liquid cooling and auxiliary consumption are presented as floating branches: charging side adds auxiliary consumption; discharging side deducts auxiliary consumption from PCS gross output.

5.3 General Formulas

Let cooling duty cycle $\delta$ (self-circulation duty cycle $1-\delta$), based on 0.5P continuous operating power $P_{\text{rated}} = 2500 \text{ kW}$:

• Charging time $T_{\text{ch}} = E_{\text{grid\_in\_basic}} / P_{\text{rated}} = 5065.7 / 2500 \approx 2.026 \text{ h}$
• Discharging time $T_{\text{dis}} = E_{\text{AC\_gross}} / P_{\text{rated}} = 4482.0 / 2500 \approx 1.793 \text{ h}$

Fixed auxiliary power $P_{\text{aux\_fixed}} = 7.25 \text{ kW}$ (project actual electrical design list, see Section 1.1 for details).

$$P_{\text{liq\_avg}} = P_{\text{liq,idle}} + (P_{\text{liq,cool}} - P_{\text{liq,idle}}) \cdot \delta = 0.74 + 27.06\,\delta \quad \text{(kW)}$$

$$E_{\text{grid\_in}} = E_{\text{grid\_in\_basic}} + T_{\text{ch}} \cdot \left( P_{\text{liq\_avg}} + P_{\text{aux\_fixed}} \right) = 5065.7 + 2.026 \cdot \left( P_{\text{liq\_avg}} + 7.25 \right) \quad \text{(kWh)}$$

$$E_{\text{grid\_out}} = E_{\text{AC\_gross}} - T_{\text{dis}} \cdot \left( P_{\text{liq\_avg}} + P_{\text{aux\_fixed}} \right) = 4482.0 - 1.793 \cdot \left( P_{\text{liq\_avg}} + 7.25 \right) \quad \text{(kWh)}$$

$$\eta_{\text{RTE\_net}} = \frac{E_{\text{grid\_out}}}{E_{\text{grid\_in}}}$$

Closed-form after substitution (eliminating the $P_{\text{liq\_avg}}$ intermediate variable):

$$E_{\text{grid\_in}}(\delta) = 5065.7 + 2.026 \cdot (0.74 + 27.06\,\delta + 7.25) = 5081.89 + 54.82\,\delta \quad \text{(kWh)}$$

$$E_{\text{grid\_out}}(\delta) = 4482.0 - 1.793 \cdot (0.74 + 27.06\,\delta + 7.25) = 4467.67 - 48.51\,\delta \quad \text{(kWh)}$$

$$\eta_{\text{RTE\_net}}(\delta) = \frac{4467.67 - 48.51\,\delta}{5081.89 + 54.82\,\delta}$$

5.4 Auxiliary Power Consumption Scenarios

Fixed auxiliary consumption per Section 1.1 actual electrical design: 12 cluster high-voltage boxes 4.2 kW + distribution box 0.6 kW + 6 dehumidifiers 0.78 kW + industrial air conditioner 0.24 kW + emergency lighting/cooling/HMI screen 0.15 kW + 12 cluster BMS power supplies 0.72 kW + fire host 0.20 kW + video surveillance 0.24 kW + 24 V auxiliary 0.12 kW, totaling $P_{\text{aux\_fixed}} = 7.25 \text{ kW}$. Liquid cooling unit modeled in 8 typical states:

Note: In the scenario table, the $P_{\text{liq}}$ for 25%/50%/75% cooling is linearly interpolated based on the rated cooling power of 27.8 kW (excluding the self-circulation floor of 0.74 kW), which slightly differs from the Section 5.3 formula $P_{\text{liq\_avg}} = 0.74 + 27.06 \cdot \delta$; for strict consistency, it is recommended to use the Section 5.3 formula + explicit duty cycle as input.

AC failure boundary case: When all 12 cluster high-voltage boxes switch to DC-DC 200 W backup, fixed auxiliary becomes $12 \times 200 + 0.6 + 0.78 + 0.24 + 0.15 + 0.72 + 0.20 + 0.24 + 0.12 = 5.25 \text{ kW}$, corresponding RTE slightly higher than this table (about 88.7% when liquid cooling is off); however, this is an emergency condition, and normal RTE protocols are based on AC mode.

Fire alarm transient: When H₂ detector or smoke/heat sensor triggers, the fire host enters alarm state, the explosion-proof exhaust fan (240 W) starts, and transient auxiliary power jumps up by ~240 W (about 3 seconds); the impact on RTE statistics is negligible.

5.5 Conclusions and Recommendations

• Core RTE (25°C most ideal conditions) = 88.48% (step-up transformer 0.99² × PCS 0.98² × battery DC RTE 0.94). This value is the theoretical upper limit, corresponding to ambient temperature 25°C, battery optimal working temperature, no auxiliary consumption, no standby, SoH=100% extreme ideal conditions.
• After including 7.25 kW fixed auxiliary (project actual electrical design list), net RTE is 87.97% with liquid cooling off; 87.89% with liquid cooling self-circulation; 86.99% at 50% cooling duty cycle; 86.04% at rated cooling.
• 88.5% net RTE is unachievable in this model: even with liquid cooling completely off + 25°C ideal conditions + 7.25 kW fixed auxiliary, net RTE can only reach 87.97%; the theoretical core upper limit of 88.48% requires simultaneously eliminating all auxiliary consumption (infeasible).
• 87% net RTE control target: From $\eta_{\text{RTE\_net}} \geq 0.87$:

  $$\frac{4467.67 - 48.51\,\delta}{5081.89 + 54.82\,\delta} \geq 0.87$$

  $$4467.67 - 48.51\,\delta \geq 4421.24 + 47.69\,\delta \;\Rightarrow\; 46.43 \geq 96.20\,\delta \;\Rightarrow\; \delta \leq 0.483$$

i.e., cooling duty cycle must be ≤ 48.3% (approximately corresponding to the lower edge of the 50% cooling scenario), liquid cooling single-cycle average power must be ≤ 13.81 kW.

• Typical operating range (25°C ideal): net RTE 86.5% – 88.0% (covering 25% – 75% cooling), single-cycle AC-side output 4432 – 4457 kWh. Actual field RTE is usually below this range due to ambient temperature, battery temperature rise, auxiliary fluctuation, and other factors.
• Electrical auxiliary system total power 7.25 kW is one of the main RTE burdens: single-cycle fixed consumption 13.0 – 14.7 kWh, already exceeding self-circulation liquid cooling (1.5 kWh) by an order of magnitude. Optimizing 12 cluster high-voltage box SMPS efficiency (350 W → 280 W) can recover about 0.4 percentage points RTE.
• Liquid cooling remains the dominant RTE term: single-cycle liquid cooling consumption 1.5 kWh (self-circulation) – 57.5 kWh (rated cooling); fixed auxiliary about 13 kWh, liquid cooling + fixed auxiliary RTE loss contribution ratio is approximately 75% / 25%.
• Six dehumidifiers consume significant power: 0.78 kW accounts for 10.8% of total auxiliary, single-cycle consumption 1.58 kWh. It is recommended to evaluate dehumidification necessity (decide start/stop based on ambient humidity sensor data); on-demand operation can recover about 0.2 percentage points RTE.
• Technical protocol recommendations: clarify RTE measurement point (recommend grid-side bidirectional meter), whether to include liquid cooling/fire protection/standby/sockets, test temperature range (baseline 25°C), SOC window (0-95%), auxiliary metering method (recommend SMPS branch + fire host + 12 cluster BMS separately metered, facilitating traceability per Section 1.1 architecture).

5.6 Container Main Breaker Load Verification

Based on the continuous/peak total power statistics from the Section 1.1 table:

6. Notes

1. The energy link in this report is based on the symmetric charge-discharge efficiency assumption under 0.5P conditions. If the actual PCS efficiency deviates significantly across different SOC/power segments, segmented re-fitting should be performed.
2. Core RTE 88.48% is the theoretical upper limit under 25°C most ideal conditions, corresponding to the series efficiency of step-up transformer 0.99², battery DC RT 0.94, and PCS 0.98². Actual on-site RTE will degrade item by item due to battery temperature rise (>25°C), line losses, SoH degradation (<100%), etc.
3. Liquid cooling unit cooling/heating duty cycles differ significantly at different ambient temperatures; RTE should be calculated within the protocol temperature range.
4. DC round-trip efficiency decreases with battery aging; RTE calculation should simultaneously introduce an SOH correction factor.
5. If dehumidifiers are started/stopped on demand rather than continuously running at 120 W, the fixed term in the formula should be replaced with the actual duty cycle.
6. All power/energy values are single-cycle statistical values and cannot be directly extrapolated to daily/monthly data.
7. Container @25°C 0.5P measured liquid cooling power (about 23 kW) + fixed 7.25 kW ≈ 30.5 kW total power.
8. Fire protection system includes fire host 200 W continuous monitoring power; explosion-proof exhaust fan 240 W starts only on alarm and is not included in RTE statistics; emergency water firefighting main circuit (fire pumps, sprinklers, etc.) is not included; actual projects equipped with such must supplement (typically 5 – 10 kW), and the main breaker D100A total load capacity must be verified or an independent branch added.
9. Six AC dehumidifiers (780 W) run continuously, accounting for 10.8% of total auxiliary. It is recommended to decide start/stop based on ambient humidity sensor data; on-demand operation can recover about 0.2 percentage points RTE.
10. Maintenance socket and spare socket (each 1 kW) are peak reservations, not included in the RTE continuous auxiliary model; however, on-site use should be metered separately to avoid affecting RTE protocol reconciliation.

Appendix A Symbol Definitions

A.1 System Parameters

A.2 Efficiency and Baseline Energy

A.3 Time and Auxiliary Power

A.4 Liquid Cooling Unit

A.5 Energy and System-level RTE

A.6 Symbol Naming Conventions

• Subscript in / out indicates energy flowing into/out of the grid.
• Subscript ch / dis indicates charging/discharging process.
• Subscript aux indicates auxiliary system; subscript liq indicates liquid cooling.
• Subscript idle / cool / heat / max indicates liquid cooling operating gear.
• Subscript max / min (bare subscripts) indicates cell maximum/minimum temperature (not power gear).
• Greek letter $\eta$ denotes efficiency, $\delta$ denotes duty cycle (note distinction from DoD), $\Delta$ denotes difference.