What is Battery Energy Storage? Inside The System Structure of a BESS

What is Battery Energy Storage System?

Battery Energy Storage System is a fundamental technology in the renewable energy industry. The system consists of a giant enclosure containing many batteries that are intended to store electricity that can be used at a later time. The battery of choice may vary; but industry standard uses Lithium-Iron Phosphate (LiFePo4) batteries. We dedicated a specific blog comparing the top two most used batteries in a BESS.

Battery Energy Storage Systems (BESSs) are a subset of Energy Storage Systems (ESSs). Examples of other subsets include hydro, air storage, and flywheels. Each system has their own pros and cons, however, energy storage is by far the most popular sub-set due to its many advantages.

Advantages of a Battery Energy Storage System

Battery Energy Storage Systems are by far the most widely used subset of energy storage, and for good reason. They offer multiple advantages in terms of capacity, charge and discharge rate, energy density, safety and overall cost.

Cost

In the last 20 years, lithium-ion battery technology has steadily decreased making BESS a more viable option compared to previous years. In addition to the influx of government initiatives and rebates, the payback period for BESS has made it affordable for residential and commercial businesses to invest in. 

Capacity & Density

Lithium-Iron Phosphate batteries are the best chemistry for BESS due to its high energy capacity and small space. Paired with TROES’ proprietary battery technology, this allows us to develop highly modular systems with long lifecycles in a small form factor enclosure.

Charge & Discharge Rate

Another advantage of LFP technology is the charge and discharge rate, meaning it can charge and discharge faster or slower compared to other chemistries. This makes it ideal for projects that require large amounts of energy at one time.

Applications That Take Advantage of Battery Energy Storage

Battery Energy Storage System plays an important role in the smart grid and Internet of Things (IoT). It is widely used in a variety of applications including:

  • Power generation
  • Solar & wind farm
  • Virtual power plant for remote communities
  • Peak shaving
  • Load shifting
  • Demand management
  • Critical load back-up
  • Power quality improvement 
  • Reducing global adjustment charges
  • And more

For additional details on exactly what these applications provide and their benefits, we wrote a separate blog. The continuous progress of energy storage technology will drive the rapid development of the entire power industry chain and create huge economic value and social benefits.

The System Structure of a Battery Energy Storage System

A Battery Energy Storage System is made up of different integral parts. Each part plays a crucial role in effectively keeping the batteries and the BESS cool, safe & efficient. Below is an image of how these parts are connected in the BESS.

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Fig 1. Battery Energy Storage System Structure

Monitors & Control

Battery Management System (BMS)

The storage device is controlled by the Monitors & Control module, also referred to as BMS (Battery Management System). It is a real-time monitoring system which consists of electronic circuit apparatus that will monitor the state of the battery. It also manages the process of charging and discharging, alarm and protect the battery, and optimise the operation of battery cells and modules to guarantee their safety, reliability, and stability. TROES’ proprietary BMS has three layers of design which includes cell supervision circuit, sub battery management unit and master battery management.

Local Microgrid Controller

The microgrid controller is provided as an optional component according to the project requirement. The microgrid controller performs the monitoring, dispatching and management of distributed energy storage systems. It also displays information to users in real-time including operating status, operating parameters, anomalies and is a useful tool for operating costs and revenue analysis of the energy storage system.

Temperature Control

Environment Sensor & Control System

The environmental sensor detects any abnormal surrounding conditions of the BESS and if found, sends a signal to the environment control module. This includes door sensors, flooding sensors, smoke sensors and more. The environment control module is mainly composed of a precision air conditioner, air cooling duct and automatic control system, which provides an ideal temperature and humidity environment for batteries during charging and discharging.

Fire Suppression System

The fire suppression system guarantees the safe operation of the energy storage system and is designed in accordance with the potential risk characteristics of the battery charging/discharging process, to prevent electrical fire inside the container. TROES provides two options for the fire suppression system with low to zero carbon emission.

Power Conversion System (PCS)

The Power Conversion System (PCS) is an electrical or electro-mechanical device for converting electrical energy DC to AC and vice versa. Most loads use AC but batteries and solar panels have a DC output. This could be as simple as a transformer to change the voltage of AC power, but also includes far more complex systems. An energy storage using PCS is bi-directional inverter/charger, compared with a PV inverter.

Breaker, Switch & Transformer

For additional protection, there is a DC switch between PCS and storage device and an AC breaker between PCS and AC transformer. The solar energy DC input or DC output load can be connected to the system after the DC switch. The transformer is a major external component that ensures the output of the BESS fits the client requirements on AC voltage. 

Enclosure

Customers have the option of choosing an indoor cabinet or an outdoor cabinet or container. Enclosures come in various default sizes, but can also be customized to fit the project’s space limitations and requirements. All Battery Energy Storage System components except the transformer are integrated into a container or cabinet.

Storage

For a Battery Energy Storage System, the storage device is the core component.  The storage device is used to store the energy charged from grid or renewable energy. Below is the structure of our storage device with a breakdown of what each part does and how they come together.

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Fig 2. Storage Device Structure
Mono-Cell & Cells

The mono-cell is the most basic unit, which is a single aluminium sealed battery unit of LiFePO4 technology. These mono-cells are packaged together and turned into the cell. A cell refers to a single anode and cathode separated by electrolyte used to produce a voltage and current. A battery can be made up of one or more cells. Battery cells are then connected in series or in parallel to compose a battery module.

Module

The module is a combination of several single battery cells which are electrically connected and housed in a shell forming the module. These modules are then packaged and connected together into our proprietary battery packs.

Battery Pack

A battery pack is a set of any number of identical battery modules or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density.

Battery System

The battery system is a multitude of battery packs that are connected in a series to make it a string. There is a limitation on the number of battery packs in a rack based on the limitation of certification and DC voltage. One or more of these strings of batteries become the battery system.

Putting It All Together

The BESS enclosure, batteries and all components are shipped out of our manufacturing facility and built at TROES’ main office in Markham, Canada. Once the system has been built, its then shipped to the customer for commissioning and final testing. Prescott Hartshorne, Director of Distributed Energy and Renewables for National Grid Ventures, says: “The next decade will be big for energy storage in general and for batteries in particular. It will be an important proving time for batteries and for other technologies.”

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