Renewable Energy Needs Efficient BESS

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A clean and sustainable method for supplying the world’s energy needs has arisen, utilizing renewable energy sources like wind and solar energy. However, renewable energy sources face unique difficulties in supplying a steady and reliable power supply, as they are prone to fluctuation. As a result, energy storage devices that can store excess energy produced during times of high generation and release it when demand is high are now a necessity.

Battery energy storage systems (BESSes) have become very popular in recent years. In fact, they can solve renewables’ intermittency issue by storing vast amounts of energy and releasing it as needed. Typically, a BESS solution is made up of battery banks coupled to renewable energy sources like solar and wind farms. These batteries retain extra energy produced during times of high generation and discharge it during times of high demand. When renewable energy sources are not producing enough electricity, homes, businesses and industries can be powered by the energy stored in these batteries.

Benefits of BESSes

Scalability is one of the major benefits of BESS technologies. BESSes are perfect for both small and large energy projects, as they can be scaled up or down based on the user’s energy requirements. BESS technologies also offer a reliable and sustainable source of energy in remote locations with restricted grid connectivity.

Additionally, environmentally friendly BESS solutions are available. They help to mitigate climate change by reducing the demand for fossil-fuel–based power plants, which are a source of greenhouse gas emissions.

The potential of BESS solutions to ensure grid stability is another benefit. Due to their intermittent nature, renewable energy sources like wind and solar energy can make the system unstable. Yet BESS solutions can assist in overcoming this difficulty by offering a reliable source of energy when renewable sources are unable to produce enough of it.

In recent years, the cost of batteries has been decreasing, making BESSes more affordable and accessible. This has led to an increase in the use of BESSes for renewable energy applications, and they are expected to play a critical role in the transition to a more sustainable energy future.

BESS block diagram

The internal structure of a BESS is shown in Figure 1. The renewable energy source, such as solar panels or wind turbines, provides the DC power input to the BESS. The DC power is then processed by the power electronics block, consisting of an inverter, a charger, a DC/DC converter and a battery management system (BMS).

The inverter converts the DC power into AC power, which can then be directly used by the load or injected into the grid, while the charger charges the battery when excess energy is available. The DC/DC converter is used to adjust (step up or step down) the voltage of the DC power input to match the requirements of the battery or inverter.

The BMS is responsible for monitoring the state of the battery, including its state of charge, temperature and state of health. It also manages the charging and discharging of the battery to ensure optimal performance and safety.

The energy management system is responsible for managing the overall operation of the BESS, including the control of the power electronics and auxiliary equipment, such as cooling systems and other control systems.

The internal structure of a BESS is designed to store and release energy from renewable sources, maximizing efficiency while ensuring optimal performance and safety.

BESSes suitable for renewables

There are several types of BESSes that are suitable for renewables. The choice of BESS depends on various factors, such as the application, size of the system, energy storage capacity and cost. Here are the main classes of BESSes suitable for renewables:

• Lithium-ion (Li-ion) batteries: Li-ion batteries are the most used BESSes for renewable energy applications. They are lightweight and compact and have a high energy density, making them ideal for small to medium-sized applications. Li-ion batteries also have a high round-trip efficiency, meaning they can efficiently store and release energy. They are commonly used in residential and commercial applications, as well as in electric vehicles.
• Flow batteries: Flow batteries are a type of BESS that uses two tanks of liquid electrolytes to store energy. The liquid electrolyte that “flows” through the battery system gives flow batteries its name; each category has a different method. Like Li-ion batteries, flow batteries feature a variety of chemistries within and between each category, including the most popular vanadium and less popular zinc-bromine, polysulfide-bromine, iron-chromium and iron-iron. They are known for their long lifespan, high energy density and scalability. Flow batteries can also be used for large-scale renewable energy applications, such as grid-scale storage, thanks to their high storage capacity and scalability.
• Sodium-sulfur batteries: Sodium-sulfur batteries are another type of BESS suitable for renewable energy applications. They have a high energy density and can store large amounts of energy, making them ideal for grid-scale applications. Sodium-sulfur batteries also have a long lifespan and can withstand extreme temperatures, making them suitable for use in remote areas.
• Lead-acid batteries: Lead-acid batteries are a more traditional form of BESS that have been in use for several decades. They are relatively inexpensive and have a high cycle life, making them suitable for small to medium-sized renewable energy applications. Lead-acid batteries do, however, have a low energy density, and their performance can degrade over time.
• Nickel-cadmium batteries: Nickel-cadmium batteries have been in use for several decades. They are known for their high cycle life, reliability and resistance to extreme temperatures. Like lead-acid batteries, however, nickel-cadmium batteries have a low energy density and are not as efficient as newer BESS technologies.

Ultimately, Li-ion batteries are the commonly used BESSes for small to medium-sized applications, while flow batteries and sodium-sulfur batteries are suitable for large-scale grid applications.

Challenges of BESSes in renewable applications

While BESSes offer several advantages in renewable energy applications, there are also some challenges that need to be addressed. Here are some of the main challenges of BESSes in renewable applications:

• Cost: One of the biggest challenges of BESSes is their cost. While the cost of batteries has been decreasing in recent years, they are still relatively expensive compared with other forms of energy storage. This can make it difficult to justify the investment in BESSes, particularly for large-scale renewable energy projects.
• Safety: BESSes can pose a safety risk if they are not designed and installed properly. Batteries can catch fire or explode if they are damaged or overcharged. This risk can be mitigated through proper design, installation and maintenance, but it is still a challenge that needs to be addressed.
• Efficiency: The efficiency of BESSes can vary depending on the type of battery used and the operating conditions. Some batteries are more efficient than others, and the efficiency can be impacted by several factors, such as temperature, charge/discharge rate and cycle life. Improving the efficiency of BESSes can help reduce costs and improve their performance.
• Durability: BESSes must be durable and able to withstand a range of environmental conditions. Batteries can degrade over time, particularly if they are subjected to extreme temperatures or high levels of use. Improving the durability of BESSes can help reduce maintenance costs and extend their lifespan.
• Integration with the electrical grid: BESSes must be integrated with the electrical grid to be effective. This can be a challenge, particularly for large-scale renewable energy projects. The integration process needs to be carefully planned and managed to ensure that the BESS operates effectively and does not disrupt the grid.

High–efficiency BESS

The efficiency of BESSes can vary depending on several factors, such as the type of battery used, the operating conditions and the specific application.

Generally, Li-ion batteries are considered to be the most efficient type of battery for BESS applications. This is due to the following key factors:

• Li-ion batteries have a high round-trip efficiency, which means that the amount of energy that can be discharged from the battery is almost equal to the amount of energy that was stored in the battery during charging. This is because Li-ion batteries have a low internal resistance, which allows them to discharge energy quickly and efficiently.
• Li-ion batteries have a high energy density, which means they can store a large amount of energy in a relatively small space. This makes them well-suited for BESS applications in which space is often a constraint.
• Li-ion batteries can operate at high voltages, thus reducing the power loss during charging and discharging. This is because the power loss is proportional to the square of the current (I²R), so higher voltages can reduce the amount of current needed to deliver a given amount of power.

It is important to underline, however, that the efficiency of a BESS is not only dependent on the battery technology but on the design and operation of the entire system.

The role of WBG materials in BESSes

Wide-bandgap (WBG) materials play an essential role in BESSes, as they improve the efficiency and performance of the power electronics used in the system.

Power electronics are used to control the flow of energy between the battery and the electrical grid, converting the DC power from the battery into AC power, which can then be used by the grid. These power electronics consist of several components, such as power transistors, diodes and capacitors, typically made from silicon-based semiconductors.

However, silicon-based semiconductors have a limitation in terms of their ability to operate at high temperatures and high frequencies. This can lead to inefficiencies and limitations in the performance of the power electronics, thereby reducing the overall efficiency and reliability of the BESS.

WBG materials, such as silicon carbide (SiC) and gallium nitride (GaN), offer several advantages over traditional silicon-based semiconductors. These materials have a wider bandgap, which allows them to operate at higher temperatures and higher frequencies with lower losses.

This leads to several benefits in BESS applications, including higher efficiency, improved power density and higher switching frequencies. This can help reduce the size, weight and cost of the power electronics while improving their reliability and performance. By enabling power electronics to operate at higher temperatures and higher frequencies with lower losses, WBG materials help improve the overall efficiency and reliability of BESSes, making them a more viable solution for renewable energy applications.