A battery energy storage system (BESS) captures energy from renewable and non-renewable sources and stores it in rechargeable batteries (storage devices) for later use.

A battery is a Direct Current (DC) device and when needed, the electrochemical energy is discharged from the battery to meet electrical demand to reduce any imbalance between energy demand and energy generation.

The batteries discharge to release energy when necessary, such as during peak demands, power outages, or grid balancing. In addition to the batteries, BESS requires additional components that allow the system to be connected to an electrical network.

A power conversion system (PCS) is the main device that converts power between the DC battery terminals and the AC line voltage and allows for power to flow both ways to charge and discharge the battery. The other primary element of a BESS is an energy management system (EMS) to coordinate the control and operation of all components in the system.

For a battery energy storage system to be intelligently designed, both power in megawatt (MW) or kilowatt (kW) and energy in megawatt-hour (MWh) or kilowatt-hour (kWh) ratings need to be specified.

Example:
If a Battery Energy Storage System is rated at 100 MW / 400 MWh, it means:

• Power (MW): The system can discharge up to 100 megawatts at once, this is the “strength” or maximum output at any given moment.

• Energy (MWh): The system can provide that output for 4 hours, since 100 MW × 4 hours = 400 MWh total storage.

So if the same system were instead sized at 100 MW / 200 MWh, it could still discharge 100 MW, but only for 2 hours before the stored energy runs out.

Battery System or Battery modules – containing individual low voltage battery cells arranged in racks within either a module or container enclosure. The battery cell converts chemical energy into electrical energy. The batteries are connected in series and parallel for the required capacity.

Storage enclosure - a containerized solution along with thermal management.

Battery Management System (BMS) – which ensures the battery cell's safe working operation, ensuring it operates within the correct charging and discharging parameters. In doing so, the BMS monitors the battery cell's current, voltage, and temperature and estimates its state of charge (SoC) and State-of-Health (SoH) to prevent safety risks and ensure reliable operation and performance.

Inverter or a Power Conversion System (PCS) – the battery cell produces direct current (DC), which the PCS converts into alternating current (AC) used for the power grid, commercial or industrial applications. Bidirectional inverters allow for the charging and discharging of the battery cell.

Energy Management System (EMS) – controls and monitors the energy flow of the BESS and systems. The EMS coordinates the BMS, inverters and other components of the battery energy system by collecting and analysing data used to manage and optimise the overall system performance.

Safety Systems – subject to system functionality and operating conditions, a BESS will include fire suppression, smoke detection, a temperature control system, and cooling, heating, and air conditioning systems. A dedicated monitoring and control system will ensure the safe operation of the BESS and the prevention of fire and hazardous incidents. The BESS will also be housed within a secure restricted access area and include CCTV monitoring.

Balancing Supply and Demand
Electricity use goes up and down throughout the day, peaking in the evenings when people get home, cook, and plug in devices. Energy storage charges when demand is low (or when renewable generation is high) and discharges when demand is high, keeping the grid balanced.

Supporting Renewable Energy
Wind and solar don’t always produce electricity at the same time people need it. Storage captures that clean energy and makes it available later, reducing reliance on gas plants and improving grid reliability.

Improving Reliability
Storage acts like a backup shock absorber for the grid. If a power plant trips offline or demand suddenly spikes, storage can instantly provide electricity, preventing blackouts.

Cost Savings for Everyone
Traditionally, Ontario has relied on expensive “peaker plants,” gas plants that only run during the highest-demand hours. Storage can replace much of that role, which keeps costs down. It also delays the need for costly upgrades to transmission lines. Over time, this helps stabilize electricity bills for households and businesses.

Future-Proofing Ontario’s Grid
With nuclear refurbishments, electrification of vehicles and industries, and rising population, Ontario’s electricity needs are changing quickly. Storage ensures we have the flexibility to meet those needs into the 2030s and beyond. So instead of building new power plants, storage ensures supply is available when it’s needed