Thermal battery facts for kids

A thermal energy battery is like a special container. It is used to store heat energy and release it later. Think of it as a way to save energy when you have extra. Then you can use it when you need it.

These batteries work by adding or taking away energy from a material. This changes the material's temperature. Some thermal batteries can store even more energy. They do this by changing from a solid to a liquid, or from a liquid to a gas. This is called a "phase change."

History of Thermal Batteries

Thermal batteries have been around for a long time. You might even have one at home, like a hot water bottle.

People in the past used simple thermal batteries too. They used stone and mud cook stoves. They also heated rocks in fires to keep warm or cook food. Kilns, which are ovens for baking pottery, also store heat for a long time. These early examples show how people have always found ways to save and use heat.

Types of Thermal Batteries

Thermal batteries come in different forms. They are all used to store and get back heat energy. They also store heat in different ways and amounts. Here are the main types:

Phase Change Thermal Batteries

These batteries use special materials called "phase change materials." These materials can store and release a lot of heat. They do this when they change from one state to another, like from a solid to a liquid.

Scientists choose these materials for specific uses. This is because different materials change phase at different temperatures. Some common materials include special salts and waxes. Water is also a phase change material. When ice melts into water, it absorbs a lot of heat. This happens at 0 degrees Celsius (32 degrees Fahrenheit).

• Cold Storage: Sometimes, water or ice is used to store "cold." Ice can melt to cool down a room.
• Heat Storage: Water can also be frozen to store cold. Then it can be melted to warm up a cold place.

The great thing about phase change batteries is they can hold a lot of energy. They do this without their temperature changing much. This means they can be lighter. They can also store more energy without getting too hot inside.

Encapsulated Thermal Batteries

An encapsulated thermal battery holds a material inside a container. This material is heated or cooled to store energy. Unlike phase change batteries, the material's temperature changes without it changing its state. This means many more materials can be used.

A key feature of these batteries is how much heat they can hold per volume. Common materials include water, concrete, and wet sand.

A good example is a home water heater. It slowly heats water over time. Then, you can use that hot water quickly for a shower. Power companies sometimes use water heaters to store extra energy. This happens when there is a lot of renewable energy, like from solar or wind. This can save money for everyone.

Scientists in Finland are even using sand to store heat. They built a "sand battery" to save solar and wind power as heat. This heat can then be used to warm buildings in a city.

Unencapsulated Thermal Batteries

Ground Heat Exchanger (GHEX) Batteries

A ground heat exchanger (GHEX) uses the earth itself as a giant thermal battery. Pipes are placed in the ground to move heat in or out. It's called "unencapsulated" because the ground area is not sealed off.

You can add energy to the GHEX by sending warm liquid through the pipes. This warms up the ground around the pipes. You can also take energy out by sending cooler liquid through the pipes.

GHEX batteries are often used in two ways:

• Horizontal GHEX: Pipes are buried in trenches, usually in a closed loop.
• Drilled GHEX: Pipes are put into deep holes drilled into the ground. These are also called "borehole thermal energy storage systems."

These batteries are often used for seasonal energy storage. In summer, heat is taken from a building to cool it down. This heat is then stored in the ground. In winter, that stored heat is taken from the ground to warm the building. This cycle repeats every year. It's a type of renewable energy because the sun's heat in summer is saved for winter.

Other Thermal Batteries

Some special batteries are also called "thermal batteries." For example, in the defense industry, there are non-rechargeable electrical batteries. They use melted salts as a key part. These batteries can last for up to 50 years when the salts are solid. When they are activated, the salts melt, and they produce a lot of power. They are used in things like guided missiles.

Other items also use the name "thermal battery." Skiers use heat packs to keep their hands warm. These packs contain iron powder that rusts quickly when exposed to air, releasing heat. There are also instant cold packs. These absorb heat when certain chemicals mix, making things cold.

The main difference with these "other" thermal batteries is that their reactions are not reversible. This means you can't use them to store and get back heat energy over and over again.

See also

• Thermal energy storage
• Seasonal thermal energy storage
• Ground-coupled heat exchanger
• Geothermal heat pump
• International Ground Source Heat Pump Association
• Steam accumulator