Energy Storage Technologies

This energy is released during a chemical reaction or combustion.

Fossil fuels are a form of chemical energy storage. Millions of years ago, organisms took in solar energy for photosynthesis. This energy remained locked into fossil fuels.

Food is also a form of chemical energy storage. When we digest food, enzymes in our body break down food molecules, releasing energy stored in the bonds.

Batteries are another form of chemical energy storage, storing electrical energy until it is needed.

Fuel Cells

Fuel cells use the chemical energy of hydrogen to produce electricity.

A fuel cell consists of two electrodes:

• A negative electrode (known as an anode)

• A positive electrode (known as a cathode)

These electrodes are placed into an electrolyte, usually a potassium hydroxide solution.

Hydrogen fuel is fed to the anode, and air is fed to the cathode.

A catalyst at the anode splits hydrogen molecules into protons and electrons.

The electrons travel through an external circuit, creating a flow of electricity. Meanwhile, the protons travel through the electrolyte to reach the cathode. They unite with oxygen (from the air) and the electrons to produce water and heat.

2H₂ + O₂ → 2H₂O

The Most Efficient Energy Storage

Earlier, we mentioned batteries as a form of energy storage. Did you know that lithium-ion batteries have an efficiency of 99%, making them the most efficient form of energy storage?

Lithium-ion batteries are rechargeable batteries that use lithium ions to store energy.

Like hydrogen fuel cells, lithium-ion batteries use two electrodes:

• A cathode made of lithium

• An anode made of graphite or silicon-carbon

Charging and discharging of the batteries allows energy to be accumulated and restored.

Electrical Energy Storage

The electric power grid balances generation and consumer use (a.k.a. supply and demand). To balance fluctuations in supply and demand, it's possible to store electrical energy during periods of high generation and low demand, then release it back to the grid during periods of lower generation and greater demand.

The following energy storage technologies store electricity until periods of high demand. They help the grid operate more efficiently, reduce the likelihood of brownouts, and allow for more Renewable Resources to be incorporated into the electricity system.

Pumped Storage Hydropower (PSH)

Pumped storage hydropower plants use power to pump water uphill into a reservoir. When the demand for energy is high, the water in the reservoir is released. It flows downhill, travelling through a turbine that powers a generator, converting the kinetic energy into electricity. PSH systems act like a giant battery, storing power and releasing it when needed.

Pumped storage hydropower systems are associated with peak shaving.

Compressed Air

In compressed air storage systems, a gas is compressed and stored under pressure in an underground cavern or container. When the demand for electricity is high, the pressurised air is heated in an expansion turbine, which drives an electrical generator.

Flywheels

Flywheel energy storage systems accelerate a rotor to a very high speed, maintaining the energy as rotational energy. The flywheel floats on magnetic bearings inside a heavy cylinder to minimise air resistance and energy loss. As long as the flywheel is rotating, it stores the energy used for acceleration. When demand for energy is high, the rotational energy is converted back into electricity.

Vehicle to Grid Systems (V2G)

Vehicle-to-grid technology is a bidirectional charging technology that allows car batteries to give back to the power grid. Specially designed charging stations can push and pull energy to and from connected vehicles, based on the demand for electricity.

The extra energy can be used to power anything connected to the grid: homes, shops, or schools!

Renewable energy storage

These technologies focus on storing renewable energy in a different form.

Power to Gas Systems (P2G)

Power-to-gas systems convert renewable energy into hydrogen gas. The systems use electrolysis techniques to split water into hydrogen and oxygen. The newly formed hydrogen can displace natural gas, reducing greenhouse gas emissions and reliance on fossil fuels.

Alternatively, P2G systems can be used to produce methane by combining the newly generated hydrogen with carbon dioxide gas.

The gas products can be used directly for heating, or converted to electricity using fuel cells when the demand is high.

Thermal Energy Storage

A material gains energy when its temperature increases, and loses that energy when it cools. Thermal energy storage makes use of this to store energy in the form of heat. When demand is high, the stored thermal energy can be used for heating and cooling, or power generation. Thermal energy storage is typically used in buildings and industrial processes.

Like pumped storage hydropower, thermal energy storage systems are associated with peak shaving strategies.

Evaluating Energy Storage Technologies

No energy storage technology is perfect. They all have advantages and disadvantages.

Hydrogen is a low-carbon energy source. Producing only water vapour when burned, it will not contribute to climate change or Environmental Pollution. Most hydrogen is currently sourced from fossil fuels. Less than 5% of hydrogen fuel is sourced by electrolysis of water, but this will likely change as new technology becomes available. A highly efficient, carbon-free energy resource made from seawater could change society forever.

I hope that this article has clarified energy storage technologies for you. Energy storage systems allow the capture of heat or electricity when readily available, and storing it for later use. The capacity of energy storage will accelerate renewable energy systems.

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