BESS Plant Setup – Part 2

Understanding Customer Requirement

This article is a follow-up to ‘BESS Plant Setup – Part 1’, published in our June 2025 edition by Rahul Bollini. Part 1 focused on understanding customers’ requirements and key considerations for executing ESS in commercial and industrial applications. Part 2 focuses on understanding the customer requirement for larger BESS for grid-connected projects.

Understanding Large size Grid-connected BESS Projects

The number of grid-connected BESS tender projects in India is one of the fastest-growing in the world, and it is showing signs of multi-fold growth with solid VGF (viability gap funding) support.

Grid-connected projects have their energy measured at the point of common coupling (PCC).

The following points are to be considered while sizing the BESS of the project:

• Energy losses from BESS discharge energy until the energy measuring point.

• LFP cells have a flat voltage, and their SoC estimation is challenging; hence, 100% DoD usage is not recommended.

• With time, the SoH (state-of-health) of clusters vary. When there are weaker cells in the overall system, they can experience overvoltage and undervoltage cutoffs more quickly, preventing the complete discharge of energy from the system.

• BESS lose capacity (SoH) due to cycling and calendar ageing, and hence, the dischargeable energy also varies.

• Particularly, the first two years have very high degradation (LFP battery behaviour), and the BESS sizing must be oversized to compensate for it.

• There is SoH loss from FAT (factory acceptance test) to SAT (site acceptance test) because of calendar ageing, and it is exposed to high temperatures with no active cooling system running. This SoH loss must be accounted for when oversizing the BESS capacity, especially if the project is delayed.

Additional points to consider during project execution:

• Ensure high-efficiency components are installed between the BESS and the energy measurement point.

• Components must operate at an optimal capacity to deliver maximum efficiency.

• Component ratings must be well-sized and derated according to the actual operating temperature of the project’s environment.

• Grid-connected projects have strict RTE rules, and BESS RTE reduces every year due to its increasing IR. This will shift from a positive RTE (above 85%) to a negative RTE (below 85%) during the project’s duration.

Hence, BESS manufacturers must not commit to a flat RTE of the battery system for the complete project duration.

• The timeline of the RTE shift depends on the initial RTE, which in turn depends on the measuring point, whether it is 33kV (MV) or 132kV/220kV (HV), as well as the number of cycles operating per day.

• If planning capacity augmentation, a domestic BESS manufacturer has the advantage of quick delivery of BESS when the project is nearing capacity shortfall and immediate capacity augmentation can be done to cater to the required capacity availability to avoid liquidated damages.

It is important to document the customer’s requirement in a questionnaire, and a reference questionnaire is below the questionnaire to understand the project well.

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Battery Energy Storage System (BESS) Requirement Checklist

• Discharge Energy Required at the energy measuring point – (kWh or MWh)
• Provide AC side SLD (Single-Line Diagram) of the project
• Indicate the Energy Measuring Point in SLD for energy-delivery calculation
• Discharge Power Rating and Discharging/Backup Hours
• Charging Hours
• Is it an On-grid or Off-grid solution?
• Mode of Charging – Grid, Solar and/or Wind
• Operating Temperature (average, min, max)
• Altitude of the Project Location and Distance from Sea or Salt Water Body
• Minimum Battery Degradation Level Accepted at the end of the Project Tenure
• Allowed Annual Degradation Every Year
• No. of Years of Warranty Required on BESS
• Number of Cycles Used per Day
• Number of Cycles Used per Year
• No. of Days Operation per Year
• No. of Years of Operation
• Required System Availability and how is it measured – Monthly or Annually?
• If buying only BESS from us, share losses of transmission on the SLD of project
• If you have your own PCS supplier, what is the DC operating voltage?

Do you require PCS, EMS, MV/LV Transformer, HV/MV Transformer, etc.? Share Project Details

In part 3 of this series, I will write about understanding the equipment requirement for BESS manufacturing.

About the author

Rahul Bollini, Bollini Energy

Rahul 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. Contact | +91-7204957389; bollinienergy@gmail.com.

This article was first published in EVreporter July 2025 magazine.

Also read: BESS Plant Setup – Part 1