NABCEP ESIP key terms

The amount of energy currently stored in a battery, expressed as a percentage of its rated usable capacity. It is the primary value used to control charging and discharging and to verify system performance.

The portion of a battery's capacity that has been withdrawn, expressed as a percentage of rated capacity. Designers limit maximum DOD to preserve cycle life and to guarantee the energy available during outages.

A measure of how much capacity and power a battery can still deliver compared with when it was new. It is typically reported as a percentage and used to schedule replacement or warranty action.

The current at which a battery is charged or discharged relative to its capacity; 1C means a full charge or discharge in one hour. Designers use it to size conductors, inverters, and thermal systems.

The energy a battery system can actually deliver under specified conditions after accounting for depth-of-discharge limits, inverter losses, and end-of-life degradation. It is smaller than the nameplate or gross capacity.

The percentage of energy put into a storage system that can be recovered on discharge, including conversion and auxiliary losses. It drives sizing decisions and the economics of arbitrage or backup operation.

The number of charge and discharge cycles a battery can complete before its capacity falls to a defined end-of-life threshold, often 70 or 80 percent. It depends strongly on depth of discharge, temperature, and rate.

The gradual loss of a battery's ability to hold charge over time and use. It is caused by calendar aging and cycling stress and is tracked to predict when replacement is needed.

Electronic controls that monitor cell voltage, current, and temperature and balance cells while enforcing safe operating limits. The BMS communicates with the inverter and protects the battery from overcharge, overdischarge, and overheating.

The process of equalizing charge among series-connected cells so that no cell is driven outside its safe voltage window. Passive balancing dissipates excess energy as heat; active balancing moves energy between cells.

A power conversion device that changes direct current from the battery to alternating current for loads or the grid, and reverses the flow to charge. It coordinates with the BMS and controls grid interaction.

A single inverter that manages both a battery and a photovoltaic array, often with backup output capability. It reduces equipment count but requires careful design of power ratings and backup circuits.

A distribution panel fed through a backup path so that selected circuits keep operating during a grid outage. Its load total and starting currents determine the required backup power rating.

The condition in which a storage system continues to energize local circuits while the utility grid is de-energized. Intentional islanding supports backup loads; unintentional islanding is hazardous and must be prevented.

A protective function that detects loss of grid voltage and stops or disconnects the inverter within a required time. It protects utility workers and is verified during commissioning and periodic testing.

A device that disconnects loads from one source and connects them to another, such as grid to storage. It may be automatic or manual and must be rated for the load and for the available fault current.

The contract and technical terms under which a storage system connects to the utility distribution system. It defines protection settings, metering, export limits, and required documentation.

The specific location where the storage system's wiring ties into the utility service or distribution circuit. It sets the point at which utility protection and metering requirements apply.

The switch or breaker that severs the electrical service from the utility supply. It provides a visible means to de-energize the system for maintenance and emergency response.

A disconnecting means that safely separates equipment from all energy sources, including the battery, photovoltaic array, and grid. It must be lockable and clearly labeled for service personnel.

A formal procedure for de-energizing, isolating, and marking equipment so it cannot be re-energized during work. It is required before servicing batteries, inverters, or associated circuits.

A dangerous release of energy caused by an electrical fault through air, producing intense heat, light, and pressure. Storage systems have high available fault current, so arc-flash boundaries and labeling are required.

Specialized clothing and gear such as arc-rated clothing, face shields, insulating gloves, and eye protection worn to reduce injury from electrical and thermal hazards. Selection follows an arc-flash risk assessment.

The maximum short-circuit current a source can deliver into a fault at a given point. Battery systems can supply high currents, so equipment ratings and arc-flash calculations depend on this value.

The maximum fault current a component or assembly can safely withstand without damage or hazard. Equipment must be selected so its rating meets or exceeds the calculated available fault current.

A fuse or circuit breaker that interrupts current above a set threshold to protect conductors and equipment. Correct sizing coordinates with battery output, conductor ampacity, and equipment ratings.

The maximum continuous current a conductor can carry under stated conditions without exceeding its temperature rating. It depends on material, size, insulation, ambient temperature, and how the conductor is installed.

The reduction in voltage along a circuit caused by conductor resistance and reactance. Excessive drop wastes energy and can cause inverters to trip, so it is calculated for battery and feeder runs.

An integrated assembly of battery modules, thermal management, power conversion, and controls that stores and delivers electrical energy. It is designed, installed, and commissioned as a coordinated system rather than as separate parts.

The supervisory controls that decide when the storage system charges or discharges based on tariffs, load, solar production, or grid signals. It also logs data and enforces operating constraints.

A utility charge based on the highest average power drawn during a billing period. Storage can reduce it by discharging during peak intervals, which is a common design objective.

Discharging storage to reduce the site's maximum power draw from the grid. It lowers demand charges and relieves constrained service equipment, and it drives power-rating and duration choices.

A self-accelerating temperature rise inside a battery cell that can lead to fire or explosion. It is triggered by abuse, internal defects, or overheating and is managed through spacing, detection, and suppression.

Equipment and controls intended to detect and control a battery fire or prevent its spread. Design considers chemistry, enclosure layout, ventilation, detection, and emergency responder access.

Energy consumed by the storage system's own auxiliary equipment, such as thermal management, controls, and communications. It reduces round-trip efficiency and must be accounted for in performance estimates.

The heating, cooling, and ventilation equipment that keeps battery cells within their safe temperature range. Proper operation extends life and reduces the risk of thermal runaway.

A documented series of checks and measurements performed after installation to confirm that the system operates as designed and safely. Results are recorded and compared with design and manufacturer criteria.

A test that exercises the storage system through realistic operating sequences, such as charge, discharge, backup transfer, and alarm response. It verifies integrated behavior rather than individual components alone.

A written record of incomplete or deficient items found during inspection and testing that must be corrected before final acceptance. Closing the list is a condition of substantial completion.

Project drawings updated to show the system as actually installed, including routing, device locations, and ratings. They are essential for future maintenance, troubleshooting, and permit records.

The embedded software that runs inverters, battery management systems, and controllers. Version compatibility between components must be verified during commissioning and updated under a controlled procedure.

Scheduled inspections, cleaning, torque checks, and testing performed to keep the storage system reliable and within warranty terms. Intervals are set by the manufacturer and by site conditions.

Site-specific procedures describing how to respond to fire, gas release, electrical hazard, or other incidents at a storage installation. It includes shutdown steps, contacts, and information for first responders.