Simplified BESS Specifications in Bids/RFPs

Introduction

Battery Energy Storage Systems (BESS) are vital for renewable energy projects, ensuring a steady power supply. This blog examines the technical specifications from an old NTPC Renewables Invitation for Bid (IFB) for BESS. By explaining complex terms in simple language, the blog aims to help readers grasp these specifications and their relevance in the BESS setup. The qualifying requirements, both technical and financial, are not covered in this post.

About the Invitation for Bid (IFB)

The Invitation for Bid (IFB) document we will be discussing is no longer active as it dates back to 2023. It was issued by NTPC Renewable Energy Limited (a wholly owned subsidiary of NTPC Limited) which invited bids for a Battery Energy Storage System (BESS) to support solar PV-based construction power at NTPC REL's Khavda RE Park in the Rann of Kutch, Gujarat.

Overview of Technical Specifications

The requirements below are copied as-is from the Scope of Work mentioned in the IFB. If you're new to this field, this list of technical requirements might read like encrypted text—full of jargon that could make your head spin.

• Design, engineering, manufacturing, supply, packing and forwarding, transportation, unloading storage, installation, testing and commissioning of Battery Energy Storage System for Solar PV Based Construction Power for standalone application at NTPC REL's Khavda RE Park.
• Battery storage of minimum capacity 250KW, 1200 kWh till the end of 3rd year.
• PCS (with total capacity of at least 250 KW) with black start facility for bidirectional inversion/charging of Batteries and providing voltage reference for solar inverters. Coupling with Solar PV System shall be at AC output bus (ACDB which will be provided by the Owner) and the entire system shall be capable of standalone operation (off-grid) delivering power to variable loads including motors without interruption.
• Containerized storage for BESS for protection of equipment from environmental factors.
• Battery Management System (BMS) for monitoring healthiness and optimized charging of batteries and Energy Management System (EMS) for Load management, Control of PCS and Solar Inverter based on load. Remote operation of Incomer feeder of Solar PV System as well as outgoing load feeders in the 415V ACDB shall also be possible from BESS.
• Associated Electrical system, AC and DC Wiring, earthing, lightning protection for BESS up to owner's 415 V AC bus.
• Comprehensive Operation & Maintenance of Battery Energy Storage System for a period of Three years from the date of commissioning of full Project capacity.

Explanation of Technical Requirements

Requirements on Battery Storage Capacity

• Installed battery energy storage system must be able to deliver at least 250 kilowatts (kW) of power output and have a usable energy storage capacity of at least 1,200 kilowatt-hours (kWh), enough to supply 250 kW for about 4.8 hours (= 1200kWh/250kW).
• The system must maintain this minimum capacity (i.e., the batteries should not degrade below this level) for at least 3 years from the date of commissioning.

Requirements on the PCS and related terms

• The Power Conversion System (PCS) serves as the key interface between batteries and the grid or loads, facilitating efficient energy flow. It converts DC power from the batteries to AC for use in grids or devices, and reverses the process to charge batteries from AC inputs. The PCS also maintains proper voltage and frequency levels for compatibility with grids or local systems. Moreover, it supports smooth switches among charging, discharging, and standby states, allowing the BESS to supply or draw power amid grid fluctuations. Overall, the PCS is crucial for the dependable and stable performance of energy storage setups.
• Its capacity, measured in kilowatts (kW), indicates the maximum power the PCS can transfer between the batteries and the grid or connected loads at any given instant.

Why Is PCS Capacity Important to Specify?

• Defines Maximum Instantaneous Output/Input
  • Specifying the PCS capacity (e.g., 250 kW) sets the upper limit on how much power can be delivered to the grid or load, or absorbed while charging, at any moment.
  • This ensures the BESS can meet the application's operational requirements, such as supporting critical loads, grid stabilization, or peak-power demands.
• Design & Performance Guarantee
  • Including PCS capacity in documents establishes minimum performance criteria for bidders and suppliers.
  • It allows for clear, enforceable guarantees about system capability, supporting technical due diligence and quality control.
• System Sizing and Compatibility
  • Other system components—such as transformers, cabling, circuit breakers, inverters, and protection equipment—must be properly rated to handle the specified power.
  • It ensures that the battery and PCS are optimally matched so the system can discharge or charge at the expected power rate.
• Grid Compliance and Safety
  • Power grid operators and regulations often require specific limits on how much power a system can export to or import from the grid.
  • Stating the PCS capacity up-front is essential for grid interconnection studies, safety inspections, and compliance with local codes.
• Financial and Commercial Operations
  • The size of the PCS affects commercial aspects like project economics, return on investment, and tariff calculations.
  • It defines the value proposition for applications like frequency regulation, demand response, or time-of-use optimization, where power capability directly impacts revenue.

Coupling with Solar PV System

This line means that the Battery Energy Storage System (BESS) must connect to the solar photovoltaic (PV) system at the point where the solar power has already been converted from direct current (DC) to alternating current (AC). The "AC output bus" refers to a central electrical panel or distribution point (often called an AC Distribution Board or ACDB) where AC power from the solar inverters is collected and ready for use or distribution. Instead of linking directly to the solar panels (which produce DC), the connection happens after the solar inverters have transformed the power, allowing the BESS to integrate smoothly without needing extra conversions.

This is relevant because it ensures efficient and compatible operation in a standalone (off-grid) setup, like for construction power. By coupling at the AC bus, the BESS can easily charge from excess solar AC power, provide backup during low sunlight, or stabilize voltage for loads like motors. It simplifies design, reduces costs by using existing AC infrastructure provided by the owner, and supports reliable power delivery without interruptions, which is critical for renewable projects where solar output varies.

Monitoring Systems

Battery Management System (BMS)

The Battery Management System (BMS) is the brain of the battery, focusing on monitoring, protecting, and optimizing battery performance.

• It continuously tracks essential parameters like voltage, current, temperature, and state of charge (SOC), ensuring the batteries operate within safe limits.
• The BMS also protects against issues such as overcharging, over-discharging, overheating, or short circuits by isolating faulty cells to prevent further damage.
• Furthermore, it balances the charge among individual battery cells, preventing imbalances that could degrade battery performance or shorten its lifespan.

By acting as the guardian of the battery, the BMS ensures both safety and longevity while providing real-time data to other system components for coordinated operation.

Energy Management System (EMS)

The Energy Management System (EMS) oversees the entire BESS, acting as the operational brain.

• The EMS optimizes energy flow by deciding when to charge or discharge the battery based on energy prices, grid conditions, or renewable energy availability.
• It coordinates the interaction between the BESS, the power grid, and renewable energy sources like solar panels or wind turbines, ensuring that energy is used as efficiently as possible.
• Additionally, the EMS plays a crucial role in providing grid stabilization services such as frequency regulation, peak shaving, and voltage support.

By analyzing energy usage patterns and predicting future demand, the EMS helps minimize costs and maximize the benefits of the BESS.

Remote Operation of Incoming and Outgoing Feeder

This line means that the Battery Energy Storage System (BESS) must enable remote control of the two main electrical connections:

• the incoming power line (incomer feeder) from the solar PV system, and
• the outgoing lines (load feeders) that distribute power to devices or equipment.

This control happens through the 415V AC Distribution Board (ACDB), a central panel that manages AC power at 415 volts. The remote operation is made available using the BESS' Energy Management System (EMS).

The EMS has communication protocols such as Modbus RTU/TCP, DNP3, or IEC 61850, which enables it to send commands over wired or wireless networks to circuit breakers or contactors in the ACDB, allowing remote switching of the incomer feeder (from solar PV) and outgoing load feeders.