Overview
To support TWAICE’s Digital Commissioning analysis, we recommend running specific test profiles designed to key performance metrics such as energy capacity, round-trip efficiency (RTE), and DC resistance (DCR). These metrics establish a quantitative baseline for the system prior to the start of commercial operation.
In most cases, each test profile is executed while TWAICE maintains a continuous data connection to your BESS. This enables rapid processing of the test results in the TWAICE platform, where any anomalies, inhomogeneities, or signs of underperformance are flagged.
These test profiles include:
Test Profile 1: Charge-Discharge Cycle
Test Profile 2: DC Resistance (DCR) Determination
📘 For information on how these profiles fit into the commissioning workflow, refer to the Digital Commissioning Process article.
Profile 1: Charge-Discharge Cycle
This profile is used to evaluate several key performance metrics:
Energy Capacity: Determined using the discharge portion of the cycle
DC-DC Round-Trip Efficiency (RTE): Calculated over one complete discharge–charge cycle
Voltage Spreads: Calculated during the entire cycle
Temperature Spreads: Calculated during the entire cycle
To ensure reliable results, the cycle should be performed only after the manufacturer’s initial checks have been completed.
Prerequisites
Before executing this test profile, please ensure:
The BESS is in a balanced and stable initial state
The ambient temperature is around 23 °C ± 5 °C.
Test Profile Description
Since capacity and RTE depend on the charge and discharge rates, the ideal test setup mirrors your storage’s typical operating regimes. For most energy storage applications, a constant power (CP)-phase profile is most appropriate:
For a 4-hour system, use a CP-rate of 0.25
For a 2-hour system, use a CP-rate of 0.5.
Other CP-rates can also be used, as long as the same rate is applied to both the charge and discharge steps to ensure an accurate RTE calculation.
Procedure
Charge the system to full SoC before performing the discharge part of the test.
Rest for 15 minutes.
Fully discharge the battery at constant power.
In some systems, this is limited by a cutoff voltage, in others the BMS SoC limits discharge. Where possible, aim for the largest possible depth of discharge-ideally close to 100%, though CP-phase testing may prevent reaching 100%.
Rest for 15 minutes.
Fully charge the battery at constant power. The goal is to reach the maximum achievable SoC.
Rest for 15 minutes.
Example test procedure for a 0.5 CP system. For systems with a different power ratings, the charging and discharging times can be proportionally increased or decreased to ensure the cycle reaches the maximum and minimum SoC levels.
Profile 2: DC Resistance (DCR) Determination
This profile is used to evaluate the DC resistance (DCR) of each string in the system.
Prerequisites
Before performing the DCR profile, please ensure:
The BESS is charged to 50% ± 3% SoC.
High CP-rates are avoided during charging to reduce overpotentials.
The BESS rests for at least 60 minutes prior to the test.
Test Profile Description
Accurate DCR calculation requires a sharp current pulse. The key requirement is that the current transitions from 0 to full current within ~1 second. A slower ramp reduces accuracy by introducing time-dependent electrical effects. If system limitations prevent a fast ramp, use the quickest possible transition and inform the TWAICE team.
The maximum CP-rate of the pulse is flexible. If the system cannot reach 0.5 CP, please use the highest achievable power rate.
If constant-power control is not possible for short pulses, a constant-current pulse is also acceptable. For a 1-minute pulse, the difference in results is typically negligible.
To ensure high-quality measurements, the pulse duration must be at least five times the longest sampling interval of the voltage or current sensors. For example:
If both voltage and current are sampled every 2 seconds, the pulse must last ≥10 seconds
If voltage is sampled every 10 seconds and current every 60 seconds, the pulse must last ≥5 minutes
If grid constraints prevent running the profile across the entire BESS, different portions of the BESS may be operated in opposite directions such that the energy from discharging racks is used to charge other racks, resulting in no net grid impact. An inverted pulse profile yields equivalent results.
Procedure
Charge or discharge the system to 50% SoC.
Rest for 1 hour.
Charge at the maximum rated power for 1 minute, ensuring that the maximum current is reached within 1 second.
Rest for 14 minutes.
Discharge at the maximum rated power for 1 minute, ensuring that the maximum current is reached within 1 second.
Rest for 14 minutes.
Repeat steps 3-6 two additional times, for a total of 3 charge pulses and 3 discharge pulses.
Example DCR test procedure for a 0.5 CP system. For a system with a different power rating, apply a pulse at maximum power.
Time | CP-Rate |
12:00:00 | 0 |
13:00:00 | 0 |
13:00:01 | 0.5 |
13:01:00 | 0.5 |
13:01:01 | 0 |
13:15:00 | 0 |
13:15:01 | -0.5 |
13:16:00 | -0.5 |
13:16:01 | 0 |
13:30:00 | 0 |
13:30:01 | 0.5 |
13:31:00 | 0.5 |
13:31:01 | 0 |
13:45:00 | 0 |
13:45:01 | -0.5 |
13:46:00 | -0.5 |
13:46:01 | 0 |
14:00:00 | 0 |
14:00:01 | 0.5 |
14:01:00 | 0.5 |
14:01:01 | 0 |
14:15:00 | 0 |
14:15:01 | -0.5 |
14:16:00 | -0.5 |
14:16:01 | 0 |
14:30:00 | 0 |
Example test profile for a 0.5C-rate system starting at 12:00. The initial resting period lasts 1 hour and the test procedure itself a further 90 minutes. For a system with a different power rating, apply a pulse at maximum power.
Data Requirements
TWAICE Digital Commissioning can be performed for any data resolution and quality. However, the accuracy and comparability of the calculated results may vary depending on the sampling rate and data resolution provided, as well as the test profile that was run.
📘 For details regarding BESS data model components, expected sensor requirements, sensor data resolution, data logging methods, please refer to the TWAICE Help Center article: BESS Sensor Requirements & Model Components.
To support proper interpretation and benchmarking, the following additional meta information is needed:
Date of first operation
System topology and/or electrical hierarchy
Battery specifications, including cell chemistry, including nominal capacity (Ah) and energy (Wh), format, and manufacturer
👉🏻 Reach out to us for any question or further details: support@twaice.com.