Technology basics
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Source: NREL 2020
Each technology, whether mechanical systems like pumped hydroelectric storage or electrochemical systems like lithium-ion batteries, will have set characteristics and unique advantages and disadvantages that affect the degree to which they are suitable for different grid system applications. The definitions of several of these characteristics are provided below.
Definitions of Key Battery Technical Characteristics
Technical Characteristic |
Definition |
Rated power capacity |
Total possible instantaneous discharge capability (in kilowatts [kW] or megawatts [MW]) of the battery energy storage system (BESS), or the maximum rate of discharge that the BESS can achieve, starting from a fully charged state |
Energy capacity |
Maximum amount of stored energy (in kilowatt-hours [kWh] or megawatt-hours [MWh]) a battery can hold |
Energy/power density |
Measure of the energy or power capacity of a battery relative to its volume (kW/L, kWh/L) |
Specific energy/power |
Measure of the energy or power capacity of a battery relative to its weight (kW/g, kWh/g) |
Storage duration |
Amount of time storage can discharge at its power capacity before depleting its energy capacity |
Cycle life/lifetime |
Amount of time or number of cycles a battery storage system can provide regular charging and discharging before failure or significant degradation |
Round-trip efficiency |
Ratio of the energy charged to the battery to the energy discharged from the battery |
Self-discharge |
Reduction of stored energy of the battery (percentage of charge/time) through internal chemical reactions, rather than through discharging to perform work |
Dispatch |
The way that the battery is operated, including the times at which it is charged and discharged, and the depth of charge or discharge |
Degradation |
The decrease in the battery’s capacity over time and through use |
State of charge |
The battery capacity as a percentage of its maximum capacity at a given time |
Depth of charge |
The battery capacity that has been discharged as a percentage of its maximum capacity |
Reading List and Case Studies
Handbook on Battery Energy Storage System
Asian Development Bank, 2018
This handbook serves as a guide to deploying battery energy storage technologies, specifically for distributed energy resources and flexibility resources.
DOE/EPRI 2013 Electricity Storage in Collaboration with NRECA
Sandia National Laboratories, Electric Power Research Institute, National Rural Electric Cooperative Association, AECOM Technical Services, Inc, 2013
The Electricity Storage Handbook (Handbook) is a how-to guide for utility and rural cooperative engineers, planners, and decision makers to plan and implement energy storage projects. The Handbook also serves as an information resource for investors and venture capitalists and provides the latest developments in technologies and tools to guide their evaluations of energy storage opportunities.