What is a Battery?
Several battery chemistries are now available for grid-scale applications, but we will focus on the most common one – lithium-ion batteries.
A battery is a device that stores electric charges and generates current through the conversion of what is called electrochemical energy into electrical energy.
All batteries have positive and negative terminals to create and supply electricity to a device – like your smartphone.
Electrons, which are negatively charged, create the electricity that flows from the negative terminal through the phone and then ends up at the positive terminal.
So where does this flow of electrons come from?
In 1991, Sony engineers discovered that lithium atoms are the ideal material for a battery, because they have the highest tendency of any element to lose electrons.
Engineering and material improvements have now made lithium-ion batteries very popular for large industrial applications.
Not only are they used in grid-scale battery farms—the topic of this module—but also in the Tesla and other electric vehicles, or EVs.
Large amounts of R&D expenditure are being committed to battery storage, so the picture could change over time.
Meanwhile, let’s take a Tesla cell out of its battery pack and break it down.
At the negative terminal, the lithium is stored in layers of graphite, similar to the lead in a pencil.
Graphite functions as a stable storage space for the lithium atoms.
At the positive terminal, there is cobalt oxide, which loses electrons when it comes in contact with the air.
In our example, the lithium and graphite are layered onto aluminum foil, and the cobalt oxide is coated onto copper foil. These foils act as current collectors and allow the positive and negative tabs to be easily attached.
However, if the two sides touched, an uncontrollable chemical reaction could occur, causing a fire. Thus a nonconductive, but permeable, separator is added. This layer can contain what is called an “electrolyte” that enables the electrochemical reaction that produces the battery’s power.
We now have a complete circuit. The electrons flow from the lithium (that seeks to give up electrons) through the device and back to the cobalt (that seeks to gain electrons).
All the sheets—graphite-lithium, the electrolyte separator, and cobalt-oxide—are wound around a central steel core to make the cell more compact.
A standard Tesla cell has a voltage ranging from 3 to 4.2 volts.
Many lithium-ion cells are connected in series and parallel fashion to form a module and battery pack.
For example, a Tesla Model 3 battery pack is made of about 3,000 individual cells, and generates 50 kWh.
How do Grid-Scale Batteries Work?
A similar battery pack design is used in grid-scale applications, with a much larger number of modules, as you would expect.
The industry term used for this application at grid scale is a Battery Energy Storage System, or BESS.
A BESS system collects spare energy from a wind or solar farm, or power plant, and then discharges the electricity as required at a later time. Small-cell modules make up most BESS designs.
Lithium-ion cells and other grid battery devices produce significant heat as they operate, and the high temperatures will degrade the cell performance.
So in small-cell applications, a cooling technology must be used. A common method is circulating glycol, similar to the coolant system in a fuel-powered vehicle.
There are a number of common components in any BESS facility, including:
● The battery modules which generate direct current or DC power
● An inverter to convert DC power to alternating current, or AC, which remains at a low voltage, and
● A step-up transformer is needed to meet the voltage requirements of the grid
The Battery Management System monitors the condition of such a huge number of cells.
It adjusts coolant flow rates to maintain optimum battery temperature.
The entire BESS distribution system is managed with a remote console operator, similar to a renewable wind or solar farm.
Voltage protection is another crucial job of the Battery Management System. This is called cell-balancing, where the charging and discharging activity is divided equally among thousands of cells to protect them from damage.
Increasingly, BESS storage installations are acting like traditional power plants. But instead of producing energy, they are purchasing, storing and selling electricity.
A Vehicle-to-Grid Innovation
One power storage innovation that is getting wide interest is called Vehicle-to-Grid, or V2G energy storage.
This means your electric vehicle can communicate with the power grid using bi-directional inverter equipment.
A V2G installation can enable EVs to store electricity generated from distributed renewable energy sources such as solar and wind.
In effect, the car batteries are mobile distributed energy storage units. They can then sell their capacity by returning electricity to the grid when plugged in.
We next discuss the challenges associated with any grid-scale battery installation.
009 Challenges of Grid-Scale Batteries Words 190
Picking the ideal battery application and designing the best operating strategy can make or break the economics of an ESM project.
Here are some of the operational and environmental challenges that must be considered in any project.
Costs have been declining so quickly that project managers have difficulty selecting the most cost-effective long-term option. What is cost-effective today could turn out to be expensive and outdated as the technologies on the drawing boards rapidly improve.
Participants in this early-stage market face a range of technical standards, as well as varied processing options. Lack of standardization can be a roadblock to project deployment.
It is like deciding whether the best software exists in the Windows or iOS environment.
Local regulations need to be updated for both the wholesale market and retail markets, especially as residential, commercial, and industrial installations grow and have the ability to sell power back to the grid.
A key environmental concern is disposal of batteries once they have exceeded their cycle lifetime. A recycling industry is being developed to recover the high-cost metals like cobalt and lithium, and to carefully dispose of the other battery components.
Summary: ESM and Grid-Scale Batteries
What have we learned in this section of the Energy Storage Management module?
- Grid-scale storage is designed to supply reactive power to the grid at peak times.
- Engineering and material improvements have now made lithium-ion batteries very popular for large industrial applications.
- A BESS facility gets charged when spare power is available, and then it is discharged later when electricity is needed.
- The Battery Management System is used to control the temperature, provide voltage protection, and monitor the condition of the cells in the battery system modules.
- The lithium-ion design is currently the most popular cell used in grid-scale batteries, but the picture could change over time as more research is completed.
- Regulatory policy is lagging behind energy storage advances, especially regarding the sale of surplus power back to the grid.
- Interesting applications like vehicle-to-grid are being initiated as numerous retail and industrial batteries have spare capacity to support the grid, especially during emergencies.
- There are environmental challenges with recycling used batteries and their chemical components.