Energy storage

We can save power for later.

This is called energy storage. We save power when we have extra. Then we use it when we need it.

Some ways use water.

Large dams hold water high up. When we need power, the water falls down. This makes electricity.

Other ways use air. Some machines squeeze air tight. This stores the power in the air.

We also use spinning parts. A heavy wheel can spin very fast. This spinning keeps the energy ready.

Batteries are very common too. They help our phones work. They help cars move. Storing power helps us every day.

We can save power for later. This is called energy storage.

We save power when we have extra. Then we use it when we need it. This helps when the sun is not out. It also helps when the wind stops blowing.

Many big systems use water.

This is called pumped-storage hydroelectricity. It uses two pools of water. One pool is high up. One pool is low down. When we have extra power, we pump water up. When we need power, the water falls down. It turns a turbine to make electricity.

Some systems use air. They squeeze air into a tight space. This is called compressed-air energy storage. The air is kept in a big tank.

When we need power, the air is let out. This can even power small trains.

Other ways use spinning parts. A heavy wheel spins very fast. This is called a flywheel.

It stores energy as it spins. We can use that spin to make electricity later.

Energy storage is the way we capture energy to use later.

This helps balance how much energy we make with how much we need. Sometimes we make too much energy at once. Other times, we need more than we are making. We use devices called accumulators or batteries to hold that extra energy. Energy can be kept in many forms. These include things like heat, electricity, or even the position of an object.

Storing energy is important for a steady power supply.

Many systems work by changing one kind of energy into another.

In pumped-storage hydroelectricity, we use water and gravity. When there is extra electricity, a pump moves water to a high reservoir. This gives the water gravitational potential energy. When people need power, the water flows down through a turbine. This movement turns the turbine to create electricity. Another way is using a flywheel.

A flywheel uses electricity to spin a heavy rotor at very high speeds. This stores energy as rotational motion. When we need power, the spinning wheel helps generate electricity.

People have used mechanical energy storage for many centuries. Large hydroelectric dams have served as energy storage sites for over one hundred years. In the 20th century, most power came from burning fossil fuels. When people needed less power, they simply burned less fuel. Today, things are changing because of new energy sources. Wind and solar power are very helpful but can be unpredictable. The wind may not blow when we need it most. The sun does not shine at night. This makes storing renewable energy a very important goal for the future.

There are many big facts about how we store power today.

Pumped-storage hydroelectricity is the largest way we store bulk energy for the grid. As of March 2012, it made up over 99% of the world's bulk storage. This is about 127,000 MW of capacity. These systems are very efficient, often between 70% and 87%. We also see growth in other areas. BloombergNEF says energy storage deployments could grow by 27 percent each year through 2030. Even small things like the batteries in your phone use these same ideas.

Energy storage connects to almost everything in your daily life. You likely use a rechargeable battery every day to power a mobile phone.

Even cars are changing as electric vehicles replace engines that burn fuel. Some buildings even use ice storage tanks to stay cool. They freeze ice at night when energy is cheap. Then, they use that ice to provide cooling during the hot day. Whether it is a tiny battery or a huge dam, these systems keep our world running smoothly.

Energy storage is the process of capturing energy produced at one time for use at a later time. This practice helps reduce imbalances between energy demand and energy production.

A device that stores energy is often called an accumulator or a battery. Energy exists in many different forms. These include radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat, and kinetic energy. To store it, we must convert energy from forms that are difficult to keep into forms that are more convenient or economical to store.

One common method is pumped-storage hydroelectricity, or PSH. This is a mechanical way to store energy using water and gravity.

During times of low electrical demand, excess generation capacity is used to pump water from a lower source into a higher reservoir. This process gives the water gravitational potential energy. When demand grows, the water is released back down through a turbine to generate electricity. Most facilities use the height difference between two water bodies to do this. Reversible turbine-generator assemblies, which are usually Francis turbine designs, act as both a pump and a turbine.

Another mechanical method is compressed-air energy storage, known as CAES. This system uses surplus energy to compress air for later use. The compressed air is stored in an underground reservoir, such as a salt dome.

When electricity is needed, the air is released to generate power. Compressing air creates heat, which makes the air warmer. If this heat is stored and used during the expansion phase, the efficiency of the system improves. CAES plants can help bridge the gap between the volatile production of renewable sources and the needs of consumers.

Flywheel energy storage, or FES, uses rotational motion to hold energy.

A system accelerates a rotor, called a flywheel, to a very high speed. This converts electrical energy into kinetic energy. Most FES systems use electricity to accelerate or decelerate the rotor. These rotors are often made of high-strength carbon-fiber composites. They are frequently suspended by magnetic bearings and spin inside a vacuum enclosure. These flywheels can spin at speeds between 20,000 and over 50,000 revolutions per minute.

We can also store energy using solid masses and gravity. By changing the altitude of heavy weights, we can store or release energy.

An elevating system driven by an electric motor/generator can winch weights up to a higher location. This creates potential energy. When the weights are allowed a controlled descent, that energy is released. Some studies suggest this method can release energy with only a one-second warning. This makes it a useful tool to balance sudden surges in the electricity grid. Efficiency for these systems can be as high as 85%.

Thermal energy storage, or TES, involves the temporary storage or removal of heat. This can include sensible heat, which takes advantage of the heat within a material.

There is also seasonal thermal energy storage, or STES. This allows heat or cold to be used months after it was collected. Other thermal methods include ice storage tanks. These tanks freeze ice using cheaper energy at night. The ice is then used to meet peak daytime demand for cooling. This is a practical way to manage energy costs and demand.

Historically, the 20th-century electrical grid relied heavily on burning fossil fuels. When less power was needed, less fuel was burned. However, the rise of renewable energy like wind and solar has changed things. Wind power is uncontrolled, and solar power varies with cloud cover or daylight hours. This creates a need for better storage to handle intermittent sources. As of March 2012, pumped-storage hydroelectricity was the largest-capacity form of active grid storage. It accounted for more than 99% of bulk storage capacity worldwide, totaling around 127,000 MW. BloombergNEF forecast that total energy storage deployments could grow at a rate of 27 percent annually through 2030.

Energy storage connects to almost every part of modern life. We use rechargeable batteries to store chemical energy for mobile phones.

We are also seeing the growth of electric vehicles that replace combustion engines. Even in rural settings, solar panels and portable devices are becoming common. Whether it is a massive dam or a small battery, these technologies ensure that energy is available exactly when we need it.