Thermopower and the Body Heat-Powered Flashlight

Imagine this. You’re at home. There’s a blackout. You can’t see a thing. You try every flashlight in the house. But all of them have dead batteries! Wouldn't it be great if you had a flashlight that could generate electricity from the heat of your hand? 

Sound impossible? It isn’t! In 2013, a Canadian scientist named Ann Makosinski invented a flashlight that could do exactly this. She was 15 years old at the time! 

Body heat is a convenient energy source. So why don’t we power everything that way? After all, heat is one of the most abundant forms of energy. Unfortunately, it’s also a form of energy that’s very hard to put to work.

What is heat energy?

Heat is a form of energy that is associated with the motion of atoms, molecules and other particles. Everything above absolute zero (-273 degrees Celsius) has some heat energy. That is pretty much everything around you! As temperature increases, the molecules move faster and faster. This results in heat energy.

Do humans give off heat energy?

Humans radiate (give off) about 350 000 joules of heat energy every hour. This energy is a waste product of our body using the food we eat. 1 W (watt) is equal to 1 J/s. That means you give off close to enough heat energy to power a 100 W light bulb all of the time! 

Normally, we do not do much with the heat energy we give off. It just radiates out into our environment. But imagine if we could capture that heat energy and use it in some way. This is what Ann Makosinski did when she designed and built a body heat-powered flashlight. 

How is heat transferred?

In short, heat is a way for energy to be exchanged between a system and its surroundings. Heat can be transferred in three ways:

What is conduction?

One way that heat can be transferred is through conduction. Conduction involves the transfer of heat (heat flow) within and between materials and objects that are in direct contact with each other. 

When a warmer object comes into contact with a cooler one, the cooler object will get warmer. Eventually, the temperatures between the two objects will become equal. The flow of heat energy is always in the direction from a warmer body to the cooler body.

How does this happen? When molecules get warmer, they vibrate (move back and forth) faster. This means that molecules at the warmer end of an object will vibrate faster than molecules at the colder end of an object. The faster molecules will collide with the slower molecules. This makes the slower molecules vibrate faster and get warmer.

Have you ever seen a blacksmith at work? If so, you may have seen them heat a metal rod in a fire. Thanks to conduction, energy from the hot end of that rod will transfer to the colder end. This will continue until the temperature of the entire rod is the same. That’s why it is important for blacksmiths to wear gloves when they’re handling rods!   

Did you know?

Wooden spoons are a favourite of chefs because they are not good conductors of heat energy. This means the spoons won't heat up too quickly and burn their hands. 

What is thermopower?

Thermopower is an object’s ability to generate electricity from heat flow. Electric current flows when electrons move in one direction through a conductor. Most metals make good conductors. When a conductor heats up, its electrons begin to move quicker and spread out. They bump into the slower moving electrons in the cold part of the conductor. This causes these electrons to heat up and move more quickly. So, if one end of a conductor is heated, the electrons will eventually transfer their energy through the entire conductor, from the hot end to the cool end. This produces an electric current. 

Did you know?

The thermopower effect was discovered in 1821. However, electrons weren't discovered until 1897, and the effect wasn't fully understood until the mid 20th century.

How did Ann Makosinski make a body-powered flashlight?

A cleverly-designed circuit will keep the electrons moving for as long as there is heat flow. For her flashlight, Makosinski used a device called a Peltier tile to convert heat flow into electricity. A Peltier tile uses the Peltier effect.

A Peltier tile is made up of two ceramic tiles placed on top of each other. In between, the tiles small pieces of conductor are arranged. Think of a sandwich. The ceramic tiles are like the two pieces of bread. The conductor is like the meat in the middle. When one side of the Peltier tile is heated and the other is cooled, an electric current is generated.

Did you know?

Most water coolers contain Peltier tiles.  

Makosinski also used a transformer to increase the voltage. She also used very efficient LED lights to make the most of what little electricity she could generate with the Peltier tiles.

Can you use your body heat to power your devices?

The amount of electricity you can produce by harnessing the flow of heat from your body to the air around you may not be very large. But it could be enough to charge cell phones and various types of wearable devices. Who wouldn’t want to live in a future where you never have to plug in your phone?

Did you know?

Makosinski’s latest invention is called the eDrink. It’s a mug that stores excess heat energy from your hot beverage. Later, you can use that heat energy to charge your cell phone!