Needs of BESS
Now, all over the world, fossil fuels are becoming limited. To reduce fossil fuel consumption, we are increasingly moving towards renewable energy sources. Among renewable energy sources, the two main ones are wind and solar. But both wind and solar energy generate highly variable power.
For example, wind energy generation happens only when the wind is blowing. Solar energy works very efficiently during the daytime when there is strong sunlight. However, we see that during the evening, the load demand becomes the highest in most places. At that time, solar energy cannot generate any power because there is no sunlight. And wind energy is also very uncertain. Because of this, the energy generated during the daytime cannot be fully utilized. This is because the load demand during the day is not as high as in the evening.
So, to overcome this problem, an energy storage system becomes necessary. The most common form of energy storage system is the battery. We know this already.
How does a BESS work?
The system is very simple. Solar energy plants or wind energy plants inject power into the grid. In the same grid, we connect the battery energy storage systems. Along with that, conventional energy also flows in the grid.
During the daytime, when solar energy is at its peak or when wind energy is at its peak, excess energy can be generated on the grid. However, the grid-connected battery storage system uses this excess power to charge the battery. However, during the evening peak time, this battery can inject its stored energy into the grid to fulfill the lack of energy and to sustain the excess load demand.
Overview of a BESS
Now we will take an overall idea about the battery energy storage system.
Battery Bank or Battery Pack
The basic component of the battery energy storage system, or BESS, is obviously the battery bank or battery pack. Three types of batteries are used here. One is the lithium-ion battery, the second is the lead-acid battery, and the third is the flow battery. Among these, lithium-ion batteries are the most popular till now.
Battery Management System
But only having a battery is not enough. When the battery will charge, when it will discharge, means when the battery will receive power from the grid and charge itself, and when it will inject power into the grid, all these must be controlled by a management system. The battery management system does the task. This component always monitors the battery bank voltage, current, and temperature. Depending on the battery condition, this battery management system decides whether the battery should charge or discharge. This battery management system cuts off charging at the right time or starts discharging at the right time, and keeps the battery in a safe zone between overcharging and deep discharging.
Power Conversion System
The next vital system is the power conversion system. Now, another question may come to mind: the grid operates on AC power, but the battery works on DC power. It charges with DC power and also discharges DC power. So there must be a converter in between the battery circuit and the grid. We call this system the power conversion system.
What it does is it converts the DC power of the battery into AC power using an inverter circuit and injects it into the grid. Additionally, when the battery needs charging, it takes AC power from the grid and converts it into DC using a rectifier circuit, and charges the battery. So the main components of the power conversion system are an inverter and a rectifier circuit.
Energy Management System
Next is the energy management system. It controls the overall operation of the battery system. The battery management system controls charging and discharging, based on demand, pricing, and grid conditions.
All these components together form the complete battery energy storage system. We call this an AC-coupled system.
DC Coupled System
Till now, we have discussed the grid-connected battery storage system. However, there is another type of battery storage system, which we call the DC-coupled system. The previous one was an AC-coupled system, because the grid is AC and the battery feeds the grid. If this battery storage system is connected individually with a solar plant, then the power coming from the solar panel is DC, and the battery is also DC.
We also use this type of system. Additionally, this system is more efficient than the previous system, because it directly works on DC. Here, the solar output directly goes to the battery in DC form. So there is no need for DC to AC conversion at that stage. Because of this, energy loss is less, and efficiency is higher. But the problem is that for each plant, a separate battery storage system is required. Obviously, it is not always economical.
Benefits of Battery Energy Storage Systems
Now, the benefits of the battery energy storage system are mainly four.
- First is, it balances supply and demand. Obviously, it maintains balance between generation and load.
- Second is, integration of renewable energy. When renewable energy is connected to the grid, battery storage helps to utilize it properly.
- Third is, it can work as backup power. If the grid or any part of the grid becomes totally blackout, then the system can take power from the battery and continue operation. So if a battery storage system is connected with the grid, then the chance of total blackout becomes very less.
- Lastly, since the battery is always connected to the grid, the grid stability also increases. Voltage fluctuation reduces. So whenever a battery is connected to any system, it always improves the stability of that system.