How do battery energy storage systems work?

Energy from the power grid or from renewable energy sources is delivered via a bi-directional inverter, which converts the energy from alternating current (AC) into direct current (DC). Today's batteries can only store DC. This energy goes into an array of batteries that is typically housed within a battery container or a building structure.

When the energy is needed on the power system, the inverters are then used again, but this time to convert the DC from the batteries into AC. Once the power has been transformed, it is stepped up in voltage and subsequently sent to an on-site substation or directly to a distribution or transmission line.

A Battery Management System monitors the individual cells and controls the voltage, temperature and current for safe, reliable transfer of energy. The system automatically shuts off if the batteries are operating outside of predefined parameters.

The electricity is then distributed to homes, schools, businesses and other consumers.

What are the components that make up a battery energy storage system?

A storage system consists of:

• Individual battery cells (the size of an iPad)
• These cells are put into battery modules and stacked on racks
• The racks fill containers, similar to a storage container you'd see on a ship or truck
• The containers are paired with inverters to convert DC-AC electricity
• The system includes HVAC to maintain temperature control
• Can be paired with a renewable energy asset (solar, wind) or stand alone

What is the value of energy storage for both a utility and its customers?

Battery storage helps optimize the way the power grid delivers electricity to customers with a wide variety of use cases, including: 

• Smoothing out fluctuations in frequency and voltage
• Replacing traditional peaking generation units
• Reducing energy losses and waste
• Avoiding the need for some system upgrades, including big transmission projects
• Extending the hours a renewable energy project can operate, i.e., even after the sun goes down or the wind stops blowing
• Allowing customers to enjoy more renewable energy, more hours of the day

Energy storage systems are highly flexible and fast responding. They can instantly scale to full capacity for both charging and discharging. Energy storage projects are scalable for any location, whether co-located with power plants, transmission lines or customer sites. They can seamlessly provide services across wholesale markets, distribution grids and directly to end users.

What type of batteries will the storage system employ?

Most battery energy storage systems employ lithium ion batteries.

• Lithium ion is the dominant technology because it benefits from more than $100 billion in R&D from the electric vehicle industry
• This is also the prevalent battery technology found in laptop computers, iPads, and other electronics
• NextEra Energy Resources has its own battery testing facility to measure battery performance and degradation, as well as testing alternative technologies

What's the risk of a battery energy storage system catching fire?

• While batteries contain organic material that may be flammable, NextEra Energy Resources storage facilities include both on-site and off-site monitoring systems as well as fire suppression systems
• NextEra Energy Resources has a control center in Florida that is staffed 24 hours a day, 7 days a week, that monitors and can control the operation of all our assets remotely
• The company works with local first responders and fire officials to educate them about the technology and coordinate any response, in the unlikely event of a fire
• NextEra Energy Resources storage systems comply with all local, state, and federal regulations in terms of operations, fire protection, and disposal of waste from storage options