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4 March 2025
Thermal energy: what it is, how it works, and what it’s used for
Thermal energy is one of the most essential forms of energy in today’s world. It plays a key role in our daily lives and is crucial in industries such as transportation and household consumption. Here’s everything you need to know to become an expert in this type of energy.
What is thermal energy?
Did you know that the human body generates as much thermal energy as a conventional light bulb wastes in the form of heat? But what exactly is thermal energy?
Thermal energy, also known as heat energy, is responsible for the warmth we experience every day.
From a more technical perspective, it is the energy stored in an object's particles. It is determined by two factors: their constant movement (as they vibrate, rotate, or move), and how they are arranged, whether closely packed in a solid or more spread out in a liquid or gas.
How is thermal energy calculated?
Thermal energy is calculated using a formula that takes into account the object's mass, its heat capacity, and the change in temperature:
Q = m · c · ΔT
- Q represents thermal energy → measured in joules, J
- m is the object's mass → measured in kilograms, kg.
- c is the material's specific heat capacity → measured in J/kg·K
- ΔT is the change in temperature → measured in Kelvin, K, or degrees Celsius, °C.
How does thermal energy work?
Thermal energy works by transferring heat from a warmer to a cooler object until both reach the same temperature. This process occurs naturally whenever there is a temperature difference.
How is heat transferred? Heat transfer occurs in three ways: through conduction, when heat moves between objects in direct contact. Through convection, when heat is transferred by liquids or gases. And through radiation, when heat travels in the form of waves, such as sunlight.
Everyday examples of heat transfer
- Conduction: conduction occurs when a metal pan heats up on the stove and the heat transfers from the base to the rest of the pan, spreading through the solid material. Another example is the warmth we feel when we touch a hot coffee mug. The heat transfers from the liquid to the mug’s surface and then to our hands.
- Convection: convection commonly occurs when cooking food in boiling water. Heat transfers from the bottom of the pot to the water, causing hot water to rise while cooler water sinks, creating convection currents. This same principle is used in heating radiators.
- Radiation: an everyday example is the warmth we feel when sunbathing. In this case, solar radiation transfers thermal energy to our skin without the intervention of a physical medium. We also experience radiation when standing near a fireplace or an electric heater.
Understanding these mechanisms is essential to optimise thermal energy use in both technological and household applications. Is thermal energy related to the electricity sector? More closely than you might think!
The relationship between thermal energy and the electricity sector
Thermal energy plays a crucial role in electricity generation. Thermal power plants convert heat from fossil fuels, biomass, or nuclear reactions into electricity using turbines and generators.
Likewise, combined-cycle power plants maximise efficiency by utilising both thermal energy and exhaust gases.
Sustainable alternatives, such as solar thermal and geothermal energy, are also worth noting in this context, as they help reduce reliance on fossil fuels.
Combined-cycle power plant. Source: Endesa Foundation.
In domestic settings, solar thermal panels harness the sun’s heat to provide hot water and heating, reducing conventional energy consumption.
Types of thermal energy and their origins
Thermal energy is classified based on its origin, and there are three main types depending on its characteristics and method of generation.
Solar thermal energy harnesses the sun's heat using solar panels designed to capture and convert solar radiation into thermal energy. This form of energy is used for applications such as water heating or climate control, as it utilises a renewable and inexhaustible source.
Geothermal energy, on the other hand, is based on the heat stored within the Earth. This renewable, constant source is harnessed through systems that extract heat from deep within the Earth and use it to generate electricity or provide direct heat for homes and businesses.
Finally, combustion-based energy is generated by burning fuels such as coal, natural gas, or biomass. While this is one of the most common ways to generate thermal energy, its environmental impact varies depending on the type of fuel used. For example, biomass, being organic and renewable, offers a more sustainable alternative to fossil fuels.
Benefits of thermal energy and its future
Thermal energy offers a wide range of benefits. It can be generated from both renewable and non-renewable sources, is easy to store, and plays a vital role in both industrial and domestic processes. Its versatility makes it a key component of the energy system.
In the future, technological advancements will allow for better utilisation of thermal energy. Technologies such as efficient heat storage and the integration of renewable sources promise to reduce greenhouse gas emissions, ensuring a cleaner and more reliable energy supply.