BATTERY STORAGE MWh battery energy storage: Redefining modern power infrastructure

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Non-industrial, household, and EV-related energy storage systems involve a few kilowatts. Whenever megawatts come into play, applications shift from a small household to an entire city. Megawatt-hour (MWh) represents a unit of utility-scale energy storage, a large amount of energy on which the renewable industry thrives.

Before exploring large-scale storage systems in detail, it helps to review the fundamentals of how electrical quantities are defined.

MW vs MWh

The terms “megawatt-hour” and “megawatt” are two different things. Watt(s) is an SI unit of electrical power that measures the instantaneous rate of energy transfer. In actual terms, watts are equal to joules per second. Simply put, watts represent the rate of power generated or consumed.

Kilowatts equal 1000 Watts or 1000 Joules per second. KW is a common amount of power consumed in our day-to-day lives. Home appliances, such as water heaters, dryers, air conditioners, ovens, and various others, are rated in milliwatts or a few kilowatts. In a practical sense, kilowatts represent a household-level quantity.

Megawatts equal 1 million watts or 1 million joules per second, a large power corresponding to small to medium power plants and most commonly renewable energy installations. To understand MWh, “hour” is as important as Watts. Combining hours with watts helps understand time periods.

1 MWh equals 3.6 billion joules! MWh describes the amount of power produced from a generating system or consumed by all the users over a time period. Simply put, MWh defines the amount of energy produced when 1 Megawatt of power is sustained for an hour.

DOSSIER ENERGY STORAGE

Stationary energy storage systems

MWh battery energy storage systems

In the context of renewable energy, megawatt-hour battery energy storage systems, or simply MWh BESS, are independent large-scale units that store energy from solar panels or wind farms. MWh BESS are rechargeable and dispatchable sources of power for grids.

The main function of MWh BESS is to empower a large number of homes, commercial spaces, and industrial sites. MWh can charge and discharge as demand and generation needs vary. Two BESS systems, both 5 MWh, could have different meanings based on ratings.

• 5MW/5MWh — 5 MW continuously for 1 hour

• 1MW/5MWh — 1 MW continuously for 5 hours

• 0.5MW/5MWh — 0.5 continuously MW for 5 hours

The total stored energy is the same, but at different power levels for different grid applications. Contrary to popular belief, MWh BESS is not a huge battery visible to Google Earth.

MWh BESS are containerized energy storage systems, typically in 20 ft or 40 ft units. The size increases with an increase in MWh ratings. MWh BESS consists of a large number of lithium-ion, lead-acid, or flow batteries, with power conversion systems, battery management systems, and other auxiliary systems.

Batteries: Modern MWh BESS, in fact, 98% of BESS, use lithium-ion batteries due to high energy density and performance. Some legacy BESS use lead-acid batteries for cost-effectiveness. Emerging MWh BESSs also use Vanadium-based flow batteries and lithium-ion phosphate batteries.

Power conversion systems (PCS): PCS use bidirectional power conversion units. Inverters are applicable during the discharge process to convert DC to AC. DC from the battery is converted to AC to support the grid, which in turn powers home appliances and commercial systems. The system contains transformers to step up or step down the power.

MWh BESS can charge through DC-DC converters from solar/wind sources or grids with the help of AC to DC converters. Power electronic converters in MWh BESS must have high conversion efficiency, an appropriate power factor, and a faster response to changing conditions.

Battery management systems (BMS): BMS is an electronic system that monitors the state and performance of a battery pack to prevent any failure. When it comes to BESS, especially large power MWh BESS, a fully functional BMS can monitor the state of batteries through sensors and transducers.

BMS systems consist of controllers that use sensor data to monitor charging and discharging processes, protect against overcharging and undercharging. Communication modules in such systems ensure integration with other internal systems and regular updates to staff. BMS systems function like an energy management system (EMS) in accordance with pricing signals and economic values.

The other auxiliary components include enclosures for fire suppression systems and surge protectors for overvoltage/undervoltage. For effective thermal management, MWh BESS implements cooling systems, including liquid cooling solutions, air cooling, and sometimes large heat sinks. All this auxiliary equipment must be present to protect against potential hazardous events.

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Applications of MWh BESS

On a general note, the term “Wh” is an important factor in billing, economics, energy planning, and battery storage. All electricity bills are based on Watt-hour readings. In residential areas, kWh (kilowatt-hour) is a common term. However, utility companies may plan the energy consumption of cities in several MWh.

Residential areas: MWh BESS effectively integrates renewable energy systems into residential grids. MWh BESS can store excess energy during peak sunlight hours or windy days. Users can take advantage of grid services, such as frequency regulation, peak shaving, load shifting, voltage support, virtual power plant, and many more.

Commercial power supply: MWh BESS can support grids in factories, large warehouses, retail complexes, hotels, stadiums, and most importantly, data centers. MWh BESS can help these commercial spaces to lower electricity bills, improve energy efficiency, and provide much-needed power backup. In some cases, MWh BESS systems can support multiple EV charging stations.

Microgrids: A microgrid is a localized group of interconnected loads over various locations operating in an island mode. MWh BESS can support small-scale microgrids over commercial and industrial areas. During power outages, islanding grids can be backed by MWh BESS. Most islands, mining areas, remote areas, mountainous regions, and camps rely on such systems.

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Road to GWh

Gigswatts (GW) is another big term in the power electronics industry. Gigawatts equal 1000 megawatts or 1 billion watts! Any energy storage system, whether a large battery energy storage system, in GWh, covers an entire region or nation. GWh BESS supplies multiple MWh to various places.

Some existing projects, such as Edwards & Sanborn, in CA, USA, are known to house 3.28 GWh battery storage capacity. The UAE has planned one of the largest energy storage projects, which is expected to house 19 GWh of energy by 2027.