What`s PCS and BMS and EMS used in HESS?

Author：TT UpdateTime：2023-11-04 Clicks：

The expansion of renewables and a global tendency towards efficient energy consumption have boosted interest in energy storage solutions and, particularly, battery energy storage systems. Reading this article will help in understanding what these systems are about and the benefits of using them.

A BESS: what stands behind it?

A battery energy storage system (BESS) is a complex solution that makes use of rechargeable batteries to store energy and release it at a later time. BESS types correlate with electrochemistry or the battery they employ—the systems can be based on lithium-ion, lead-acid, nickel-cadmium, sodium-sulfur, and flow batteries. An energy storage system (ESS) is a broader term and it may rest on a variety of technologies other than batteries, for example, hydropower, flywheels, compressed air, and others.

To understand what a BESS is and how it works, it will help to look at its structure and core elements as showed in Figure1.

BATTERY

Electrical energy supplied from different sources, such as solar, wind, or power stations, converts to chemical energy during the battery charging process. The energy released from the battery during discharging can power homes, vehicles, commercial buildings, and grids. Batteries are made up of cells and can be arranged in modules, packs, and containers.

BATTERY MANAGEMENT SYSTEM (BMS)

A BMS provides for the safe and correct operation of the battery. Every battery type has certain charging and discharging conditions. A BMS makes sure the battery stays within the required current, voltage, and temperature range. By monitoring the parameters and estimating the state-of-charge (SOC) and state-of-health (SOH) of the battery, a BMS ensures its reliable and long-lasting performance.

POWER CONVERSION SYSTEM (PCS)

Through the use of a power conversion system, a BESS converts direct current (DC) into alternating current (AC) and vice versa. AC flows from a power source and converts to DC during battery charging. When the battery is discharged, it produces DC, which is converted back to the AC necessary to power BESS applications.

ENERGY MANAGEMENT SYSTEM (EMS)

An EMS is a control unit of a battery energy storage system. It manages the power available in a BESS—namely, when, why, and in which amounts to accumulate or release the energy. An EMS puts the elements of a BESS together and optimizes its overall performance.

SAFETY SYSTEMS

There can be an array of safety systems, each responsible for a specific task. For example, an HVAC system enables a BESS to maintain the desired temperature and humidity through heating, ventilation, and air conditioning. A fire protection system can detect smoke and prevent fire incidents.

Figure 1: A typical BESS structure. (Image source: Integra Sources LLC)

What can a BESS do?

Every year, battery energy storage systems supply power to thousands of homes, businesses, plants, and communities worldwide. They vary in scale and storage capacity.

For example, having 13.5 kWh of usable capacity, the Tesla Powerwall is a compact device that can serve as a source of uninterrupted power for a single household. While with its total capacity of 1,600 MWh, the Vistra Moss Landing Energy Storage Facility—the world’s largest BESS—can provide energy to 300,000 homes.

However, despite the difference in size and capacity, BESS can fulfill similar functions and address similar problems. Let’s consider the cases when battery energy storage can come into play.

Renewable energy integration

BESS can utilize solar and wind power efficiently at all times and in all weathers. Rechargeable batteries can store excess energy generated by intermittent renewables. Later, this energy can be dispatched according to the users’ needs.

When integrated with battery storage solutions, renewable energy sources can replace fossil fuels, offering cheap and clean energy to a diversity of applications. Renewable integration is widely adopted in:

solar and wind farms
off-grid and isolated communities (islands and hard-to-reach areas)
home energy storage devices coupled with solar panels (such as Powerwall)

Apart from off-grid systems, a BESS can significantly support on-grid and hybrid solutions for residential, commercial, and industrial use.

Figure 2: Battery energy storage systems are widely used in solar and wind farms. (Image source: Integra Sources LLC)

Energy arbitrage

There is a positive correlation between the demand for electricity and its cost. The energy price increases during peak demand periods and decreases when the demand drops. Energy arbitrage, alias time-shifting, is what consumers can apply using a battery storage system.

By charging the battery at off-peak times, consumers can buy cheap energy and store it with their BESS. Then, they can wait until the electricity price rises and discharge the battery to either use low-cost energy or sell it to the grid.

Thus, households and businesses can effectively manage energy resources, cutting down on their costs.

Load management

Energy is consumed differently throughout the day and based on the season—there are on-peak and off-peak times. A BESS allows users to navigate between these periods, adjust energy consumption, and save on electricity costs.

Peak shaving is one of the most popular BESS use cases in load management. This is about reducing power consumption during peak periods. Along with that, consumers can cut their expenses just like with energy arbitrage.

A battery storage solution can help avoid peak loads on an electricity grid and, consequently, blackouts and other emergencies. By discharging the stored energy, a BESS takes the load off the grid and supplies power without interruption.

Black start

A BESS can help power stations and electricity grids restore quickly after power outages. Instead of using a diesel generator, consumers can take to a battery storage system—a cheaper and greener black start solution. A BESS can work independently of the grid’s transmission line and supply energy for the time required—from minutes to hours.

Power backup

A BESS can provide energy to homes, businesses, and other facilities, ensuring their continuous operation. This is of vital importance for healthcare institutions and other organizations that deliver services connected with people’s health and safety. Depending on the storage capacity, a BESS can supply backup power as long as it takes, even in the case of a severe grid failure.

Frequency and Voltage Control

Frequency and voltage can go outside their operating limits if the power supply is out of sync with its actual demand. This may lead to the loss of power and blackouts. A BESS can ensure the stability of an electricity grid or power system through voltage and frequency regulation. Because of its fast response time, a battery energy storage system becomes an efficient grid balancing solution.

Microgrids

These are small electric grids that can supply electricity to commercial buildings, manufacturing plants, or neighborhoods when connected to a larger grid. Autonomous microgrids can power remote areas and communities, such as islands. When combined with a BESS and integrated with renewable energy, a microgrid can act as a resilient power system for multiple users.

Transmission and distribution deferral

Transmission and distribution (T&D) lines are prone to aging and depreciation because of peak loads and congestions. A battery storage solution can solve this problem by taking on the role of T&D assets. A BESS can offer additional storage capacity and balance loads, thus deferring the upgrade of the existing T&D lines and construction of new infrastructure. This means saving heaps of money.

Where can a BESS be used best?

BESSs rely on affordable technologies, for example, the price for lithium-ion batteries has fallen by nearly 90% over the past 10 years and is going to drop further. Battery storage solutions have a broad range of configurations, including storage capacity and size, so they can fit many industries and applications.

These applications can be divided into front-of-the-meter (FTM) or utility-scale systems (the energy consumed is measured by an electric meter) and behind-the-meter (BTM) or on-site solutions (the energy consumed cannot be connected to a grid and thus measured by an electric meter). Here’s a list of FTM and BTM BESS applications (which is definitely not complete).

Front-of-the-meter applications

Battery energy storage systems can contribute heavily to the operation and maintenance of utility-scale facilities and equipment. A BESS can offer reserve capacity and black-start services, provide voltage and frequency stability, and save money through deferred maintenance. FTM BESS applications include:

Utility grids
Substations
Transmission and distribution lines
Power stations

Behind-the-meter applications

BTM systems can supply power to consumers, bypassing an electricity grid. Along with green energy sources, a BESS can ceaselessly support standalone power systems or microgrids. Manufacturers can use battery storage for power backup to avoid downtime at production facilities. By using BESSs, companies and families can significantly reduce electricity tariffs with energy time-shifting. BTM battery energy storage systems can be found in: