Energy Storage System Technologies

Energy storage systems store electricity and deliver power when needed to proactively manage peak loads and balance supply-demand fluctuations. They’re all-in-one, turnkey systems with built-in inverters and computerized control components.

Battery, pumped hydroelectric, compressed air, and flywheel energy storage are the most common types of grid-scale storage technologies. Read on to learn more about how each works.

1. Battery Storage

Energy storage technologies play a critical role in speeding up the replacement of fossil fuels with renewable energy. These systems enable energy from renewables to be stored and then released when customers need power most. By adding capacity and resiliency to the grid at key times, battery storage systems help avoid the need to build new transmission and distribution lines – an expensive and challenging endeavor.

ESS technologies can also help reduce high demand, which drives up electricity prices on hot summer days when air conditioners are running and at nightfall as families turn on lights and appliances. This capability is called peak shaving.

Similar to the batteries in your phone or the uninterruptible power supply under your desk, best-in-class commercial- and industrial-scale battery energy storage systems have multiple, swappable battery modules with onboard sensors that keep cells at their optimal temperature for longevity and safety. They can be DC or AC coupled, with integrated inverters for easier installation and more capabilities.

2. Supercapacitor Storage

A relatively new energy storage technology, supercapacitors bridge the gap between batteries and conventional capacitors. They have high power throughput, can deliver short bursts of energy at very high speeds, and can provide hundreds, if not thousands, of amperes.

They are also safer than chemical batteries, which can degrade over time and cause thermal runaway. They can be charged and discharged thousands Energy storage system of times without losing their voltage rating or cycling life.

They operate by storing static electricity through the separation of negative and positive charge. The simplest supercapacitor is made with Nafion foil soaked in an electrolyte. More complex supercapacitors use porous carbon electrodes to store the charge. These can be combined with hybrid electrodes that include double-layer (electrostatic) capacitance and pseudocapacitance.

3. Superconducting Magnetic Energy Storage (SMES)

SMES stores energy in a coil of superconducting wire that generates both magnetic and electric fields. The stored current is not lost as with many other storage technologies and can be quickly discharged. Several micro-SMES units that store 3 MJ of power and deliver it in one second have been built for use on electric grids to damp power swings.

SME plants must operate at temperatures near the boiling point of liquid helium – about 4.2 K (-269degC or -452degF). Since this is very cold, large SMES plants require a substantial mechanical structure to contain the Lorentz forces generated by the coils.

Regardless of size, SMES systems consist of three stationary components – a superconducting coil, a refrigerator and a power conversion/conditioning system. The coil is cryogenically cooled to maintain the superconducting state. When the superconducting coil is charged, a positive voltage is applied to it by the power conditioning system and the current increases. The current Energy storage system is reversed when the coil is discharging and a negative voltage is applied to it.

4. Lithium-ion Battery Storage

Lithium-ion batteries are the dominant energy storage technology, used in rechargeable electronics like mobile phones and electric vehicles (EVs), and increasingly in large scale plants to help electricity grids respond quickly to changing power demands. They also play an important role in solar systems, enabling excess energy to be stored for later use.

A lithium-ion battery system is an electrochemical device consisting of an anode, cathode and a flammable electrolyte between them. During discharge, lithium atoms in the anode are ionized and separated from their electrons to move to the cathode through the electrolyte, where they recombine with the electrons in the cathode to produce electrical energy.

Since each individual cell in a battery has different characteristics, a power management system is required to monitor their voltages and currents for safety and performance reasons. More sophisticated power management systems can also operate thermal control systems and communicate with external monitoring systems.

5. Compressed Air Energy Storage (CAES)

CAES plants use electricity to compress air under pressure in underground reservoirs, such as salt caverns. They then recover the energy by expanding the air through a turbine, powering a generator to produce electricity. CAES systems are currently limited by their inefficiencies; the compression process loses energy as heat, and the expansion process is not adiabatic, so round-trip storage efficiency is only around 40-52%.

The first commercial CAES plant is the Huntorf power plant in Germany, which uses two salt domes as storage caverns and operates a daily cycle with 8 h of compressed air charging and 2 h of operation at rated power. A more advanced adiabatic CAES plant, known as ADELE (Adiabatic Compressed Air Energy Storage for Electricity Supply), is under construction at the Pollegio-Loderio Tunnel in Switzerland using an abandoned tunnel as the storage cavern and a packed bed of rock thermal energy storage to capture the waste heat.

6. Flywheel Storage

Flywheel storage utilizes a massive spinning mass called a rotor that stores energy. The work done to spin the mass, also known as kinetic energy, is converted into electrical power when the rotor is discharged.

Flywheels have a long history of use in mechanical systems. Pottery wheels used a similar design that enabled craftsmen to perform repetitive tasks with ease using only their feet. The technology was later adapted for electric railways where the system allowed trains to operate between stations without stopping.

Modern flywheel systems use carbon-fiber composite rotors on magnetic bearings to reduce friction and increase efficiency. They are typically encased in a vacuum to diminish air resistance.

Flywheel energy storage systems are being implemented to provide short-term spinning reserve for power grids to balance supply and demand. They are also being employed as uninterruptible power supplies (UPS) to provide emergency backup for data centers.

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