Energy Storage System

Energy storage systems can smooth out electricity supply from renewables, particularly wind and solar. They can replace fossil fuel peaker plants at times of high demand, and they also benefit lower-income communities and neighborhoods overburdened by pollution and climate change impacts.

Energy storage systems are crucial to speeding up the replacement of fossil fuels with green power. They can store electricity at the grid-scale or even in residential battery storage.

Battery

Battery energy storage systems (BESS) are key to overcoming the intermittency limitations of renewable power sources like solar and wind. They allow grid operators to smooth the output of these intermittent power sources by storing and then discharging the electricity as needed. They are available in both DC and AC versions, each with different power and energy densities.

A BESS consists of several electrochemical cells, each one consisting of anodes and cathodes. Electrolyte solutions flow through the cells to charge and discharge them, storing the energy in them. When the battery is almost flat, the anode re-injects the positive ions back into the electrolyte and returns the electrons to the cathode, completing a full charge cycle.

The battery can be arranged in series or parallel. In series, the cells are connected in parallel with each other, and the total current is the sum of the individual cell currents. This design offers simplifications in fabrication, ruggedness and safety. However, a short circuit in one cell can lead to overheating and possibly explosion.

A BESS can be used in many ways, from providing power to buildings during peak demand to reducing transmission losses. It Energy storage system can also provide flexibility for customers to adapt their energy consumption. It can be combined with software that enables advanced management of energy use, including artificial intelligence and machine learning.

Flywheel

A flywheel stores energy by converting electrical energy into rotational kinetic energy stored in a spinning mass. These systems are capable of absorbing and releasing high power for short periods of time; typically, they respond to control signals adjusted every few seconds. They can do many tasks, including smoothing out fast fluctuations in electricity supply and demand, regulating the frequency of alternating current as generators may briefly operate out of sync with the grid, recapture braking energy from electric trains in some installations, and provide ride-through power until backup generation is restored during a grid outage.

A modern flywheel system consists of a heavy cylinder, known as a rotor, enclosed in a vacuum chamber to eliminate air friction. The rotor is made from new materials that can withstand high speeds better than traditional metals. A motor accelerates the rotor to very high speeds and converts the stored energy back into electricity. The rotor can rotate at rates up to 10,000 revolutions per minute, with the latest systems using magnetic levitation to further reduce friction.

Flywheels are quick to ‘charge’, can release large amounts of energy very quickly, and are expected to have longer life expectancies than chemical batteries. A 30 kWh facility can provide the equivalent of the electricity demand of a typical single-family house, and it takes up very little space.

Compressed air

Air has long been a popular medium for energy storage. From breathing gas in diving cylinders to air-powered elevators at hotels, the technology has a wide range of uses. It can be stored at high pressure for use when demand is low and then quickly decompressed for generating power. Using compressed air also cuts costs compared to hydrogen storage.

Large-scale CAES plants compress air and store it underground in a cavern, then recover the energy by expanding (or Energy storage system decompressing) the air to drive a turbine and run a generator. The energy produced is fed back into the grid during peak usage. CAES is an inexpensive method for large-scale energy storage, but it’s less efficient than other methods such as pumped hydropower and chemical batteries. The loss of energy during compression and expansion is because the air heats up while being compressed, then cools down when it’s released. This requires re-heating the air, which is often done with natural gas. New technologies like adiabatic storage systems are attempting to address this issue, but none have reached commercial or utility scale so far.

Currently, most CAES plants utilize salt caverns, but companies are researching alternative storage vessels for the future. For example, researchers are working on storing CAES energy in huge bags deep underwater, which could be a cheap way to store renewables’ intermittent power.

Mechanical gravity

The world’s grids need energy storage. But while technology advances are making batteries better and cheaper, a lack of storage capacity has held back renewables. That may be about to change with a new type of gravity battery.

The principle is simple. When you raise a mass through a height, it stores energy as gravitational potential energy (mass times vertical acceleration). When you lower the mass, the energy is recovered by electric motor/generators that generate electricity. This is similar to pumped hydro storage, which accounts for 90% of current grid-scale energy storage capacity.

Edinburgh-based green engineering start-up Gravitricity recently tested a prototype gravity battery. The 15-meter steel tower suspends a 50-tonne iron weight, and electric motors power a generator as it is raised inch-by-inch. The system can produce 250kW of instantaneous power and can also store energy over time.

Other companies are experimenting with similar designs. Switzerland-based Energy Vault, for example, uses concrete blocks stacked up and down like the Tower of Babel. When it’s needed, a multiarmed crane with motors/generators lifts the bricks, which stores and releases energy through a sequence of lifting and lowering cycles. This can deliver a long duration of storage, and the bricks are made from waste materials that would otherwise end up in landfills. The company is aiming for large-scale commercialization of this technology, which is already in use at some community energy projects.