Grid-Scale ESS

EG Solar Energy Storage System(BESS) is designed based on high performance Lithium Iron Phosphate (LFP) battery rack, and it has also integrated with EG Solar Battery Management System, Thermal Management System, Alarming System, etc.

What is grid-scale battery storage? Battery storage is a technology that enables power system operators and utilities to store energy for later use. A battery energy storage system (BESS) is an electrochemical device that charges (or collects energy) from the grid or a power plant and then discharges that energy at a later time to provide electricity or other grid services when needed. Several battery chemistries are available or under investigation for grid-scale applications, including lithium-ion, lead-acid, redox flow, and molten salt (including sodium-based chemistries).1 Battery chemistries differ in key technical characteristics (see What are key characteristics of battery storage systems?), and each battery has unique advantages and disadvantages. The current market for grid-scale battery storage in the United States and globally is dominated by lithium-ion chemistries (Figure 1). Due to technological innovations and improved manufacturing capacity, lithium-ion chemistries have experienced a steep price decline of over 70% from 2010-2016, and prices are projected to decline further.

The key characteristics of battery storage systems.

Rated power capacity is the total possible instantaneous discharge capability (in kilowatts [kW] or megawatts [MW]) of the BESS, or the maximum rate of discharge that the BESS can achieve, starting from a fully charged state.

• Energy capacity is the maximum amount of stored energy (in kilowatt-hours [kWh] or megawatt-hours [MWh])
• Storage duration is the amount of time storage can discharge at its power capacity before depleting its energy capacity. For example, a battery with 1 MW of power capacity and 4 MWh of usable energy capacity will have a storage duration of four hours.
• Cycle life/lifetime is the amount of time or cycles a battery storage system can provide regular charging and discharging before failure or significant degradation.
• Self-discharge occurs when the stored charge (or energy) of the battery is reduced through internal chemical reactions, or without being discharged to perform work for the grid or a customer. Self-discharge, expressed as a percentage of charge lost over a certain period, reduces the amount of energy available for discharge and is an important parameter to consider in batteries intended for longer-duration applications.
• State of charge SOC, expressed as a percentage, represents the battery’s present level of charge and ranges from completely discharged to fully charged. The state of charge influences a battery’s ability to provide energy or ancillary services to the grid at any given time.
• Round-trip efficiency, measured as a percentage, is a ratio of the energy charged to the battery to the energy discharged from the battery. It can represent the total DC-DC or AC-AC efficiency of the battery system, including losses from self-discharge and other electrical losses. Although battery manufacturers often refer to the DC-DC efficiency, AC-AC efficiency is typically more important to utilities, as they only see the battery’s charging and discharging from the point of interconnection to the power system, which uses AC (Denholm 2019).

Lithium-ion batteries Technology

Li-ion batteries get their name from the transfer of lithium ions between the electrodes, both when energy is injected for storage purposes and when it is extracted. Instead of metallic lithium, Li-ion batteries use lithiated metal oxides as the cathode (the negatively charged electrode by which electrons enter a device), and carbon typically serves as the anode (the positively charged electrode by which electrons leave a device). Unlike other batteries with electrodes that change by charging and discharging, Li-ion batteries offer better efficiency because the ion movements leave electrode structures intact.

Within the lithium family there are a variety of different chemistries and designs from numerous suppliers. Innovation and manufacturing volume have continued to yield improvements in cost, energy density, and cycle life.

For storage durations of 30 minutes to three hours, lithium batteries are currently the most cost-effective solution, and have the best energy density compared to the alternatives. For longer durations, lithium may or may not be the most cost-effective choice depending on the application, particularly when considering lifetime costs. Lithium batteries are also highly configurable into a variety of string sizes and battery racks to create a wide range of voltages, power ratings, or energy increments. This allows for application-specific designs that can range from a few kilowatts with a few minutes of storage, up to multi-megawatt solutions with hours of storage that may be used at a utility substation or a wind farm.

Lithium ion LFP battery is the best solution based on currently market. Picking an ideal battery application and designing the best system and operating strategy can make or break the economics of an energy storage project. Learning about the benefits and challenges of the different commercially available battery technologies is key to making the right choice.