In continuation to part 6 of the series (Understanding BESS), published in July 2024, part 7 focuses on implementation planning of BESS projects.
Project implementation planning begins with finalization of the following components:
Capacity of each BESS container
Number of BESS containers
Capacity of each PCS (bi-directional inverter)
Efficiency of PCS – larger PCS have higher efficiency.
Number of PCS (depending on the power:energy ratio)
Capacity of MV (medium voltage) transformer and MV switchgears.
If the energy measuring point is after the MV transformer, higher-efficiency transformers must be used to allow for higher RTE (round-trip efficiency) at measuring points. Some projects incentivize higher RTE.
Number of MV transformers and MV switchgears
Configuration of EMS for each site (in case of multiple sites), including local data storage or cloud monitoring, if applicable.
Number of EMS (multiple used in case of very large projects)
Auxiliary power can be provided separately from the grid or from the battery system. Off-grid BESS projects and peak shaving BESS projects cannot use auxiliary power separately from the grid, so the battery needs to be oversized, and another inverter needs to be added to power the auxiliary from the battery during discharge and idle time.
Cables such as DC cable, LV cable, MV cable, communication cable and other accessories need to be sourced accordingly to ensure the project is completed on time.
Understanding BESS Operation Characteristics
The degradation of BESS capacity must be considered until the project is commissioned from the date of production. Unexpected delays can occur, such as clearances and synchronization between BESS and other components on the site. Oversizing of the battery capacity needs to be considered accordingly.
The first- and second-year degradation of BESS is on the higher side, and oversizing the battery capacity needs to be considered accordingly.
DC side round trip efficiency (DC-DC RTE) reduces with time (calendar aging and cyclic aging), and additional losses need to be considered for annual degradation because they will impact the depth of discharge (DoD) to get the desired energy output.
For projects over 10 years, state-of-power (SoP) plays a vital role since the battery’s C rating capability reduces, which can lead to higher heat generation, lower RTE, and lower cycle life. Battery derating (lower C rate operation) needs to be considered, and long-term contracts must incorporate such conditions.
For higher DoD operations, there is a higher necessity for system balancing, which includes a lot of operation protocols, and it can lead to a disturbance in the commitments as per the contracts. Additionally, capacity augmentation is necessary when the DoD is close to 100%. There could be many reasons for the DoD to reach maximum levels, and this leads to higher battery degradation than expected, and a chain of events follows. The best solution for this situation is to implement capacity augmentation (adding more battery systems).
There must be a good understanding of the temperature at which the active cooling system activates and at what temperature it gets deactivated. If activated at a lower temperature, the auxiliary power consumption goes up, and if activated at a higher temperature, the battery cycle life goes down. There must be a balance ensuring not very high energy bills for auxiliary power and at the same time not reducing the cycle life by too much. This balance varies based on the project location’s operating conditions.
BESS degradation varies based on the operating temperature. A heating system is needed on very cold days; otherwise, the output will drop, and the cycle life of the BESS will reduce faster than expected.
Replacement planning for non-battery components such as PCS, transformer, and EMS needs to be well planned to reduce project downtime and achieve higher BESS availability.
Operation and Maintenance (O&M)
It is a very common question if battery containers need maintenance. The answer is yes and no.
No immediate maintenance is required after installation.
An air-cooling system needs maintenance because it has air conditioners, which need maintenance like any other air conditioners. This leads to downtime and lower BESS availability.
Regular monitoring of faults and issues shown at the BESS project control centre is required.
Check non-battery components in the battery containers, such as the fire protection system and the liquid cooling unit. The liquid cooling unit’s liquid levels may go down after some use and need a top-up. Fire protection systems have an expiry time and need replacement, especially for long-term projects.
System balancing may be required when the SoC levels of various clusters for the whole project are not at the same level.
Some components in the future may have different specifications, so it is necessary to communicate with suppliers to keep updated about model changes and stock them if they are going out of trend, if the new model is not compatible with the existing system, or if it’s larger than required. For example, if PCS capacity gets bigger than today’s existing model.
Regular monitoring of battery system health is required to ensure replacement of battery components, reduce downtime, and achieve higher BESS availability.
Construction/Civil Planning for Project
It starts with the need for land leveling and then implementing civil structures to hold the battery containers and other components. The civil structure must be strong enough to hold containers that weigh up to 43 tons (5MWh in 20 feet container). There should be a provision for the cables to be laid below the containers, hence the containers are kept at a higher level.
The battery cooling units (placed on one side of the battery containers in case of a liquid cooling system) must have free space for exhaust.
MV skids (PCS + Transformer integrated solution) are used for projects requiring low footprints.
Cables must have extra insulation to ensure safety and withstand wear and tear for the long-term project duration.
About the author:
Rahul Bollini is an R&D expert in Lithium-ion cells with 10 years of experience. He founded Bollini Energy to assist in deep understanding of the characteristics of Lithium-ion cells to EV, BESS, BMS and battery data analytics companies across the globe. Rahul can be reached at +91-7204957389 and bollinienergy@gmail.com.
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