The energy demand has become crazy high recently. We’ve got all these gadgets that run on electricity – from wall or batteries. The fact is also true that we kind of take it for granted how that power gets in our wall. Let’s see how the generation of energy actually happens.

Types of Energy

Energy is the ability to do work. Power is energy over time. Energy comes in many forms:

  • Chemical – primary
  • Nuclear – primary
  • Heat – primary
  • Renewable – primary
  • Gravitational – secondary
  • Electric – secondary
  • Kinetic – secondary

Primary Energy Sources: Harnessed directly from nature

Secondary Energy Sources: Resources that have previously been converted or stored


Fuel is a material that can react with other substances and release energy in form of heat or work. For example, gas reacts with oxygen. It burns and releases heat.

Humanity’s main source of fuel is from fossils. Fossil Fuel is essentially made from buried, dead organisms. It is also important to mention that it takes millions of years for these materials to produce.

Types of Fuel

Below you can see a table with a list of materials. These contain energy that we release and use. Note the difference in energy released between nuclear energy and batteries.

Material Energy Type Energy Released Use
Deuterium-Tritium Fusion Nuclear 340,000,000 MJ/Kg Power Plant
Petrol Chemical 123 MJ/Kg Cars
Fat Chemical 37 MJ/Kg Nutrition
Coal Chemical 25 MJ/Kg Power Plants/Heating
Wood Chemical 16.2 MJ/Kg Heating
Alkaline Battery Electro-chemical 0.5 MJ/Kg Portable Electronic Devices
Lithium Battery Electro-chemical 1.8 MJ/Kg Portable Electronic Devices
Lithium-ion Battery (rechargeable) Electro-chemical 0.35 MJ/Kg Portable Electronic Devices
Lead-Acid Battery (rechargeable) Electro-chemical 0.17 MJ/Kg Car ignition
Super-capacitor Electrical 0.018 MJ/Kg Electronic Circuits

Batteries are dividided in two groups:

  • Primary cells – non rechargeable
  • Secondary cells – rechargeable

Deuterium & Tritium

Just to mention as some of you might not be familiar of these terms. Let’s recap the following terms as they might be confusing:

  • Atom: contains protons and neutrons in the nucleus and electron around it. The periodic table contains elements. All elements are made of atoms.
  • Hydrogen element: Contains a single proton in the nucleus and an electron around it.
  • Hydrogen molecule: H2 – the most common form of hydrogen in nature. It is a gas. Contains two hydrogen elements that are held together by electrostatic force.
  • Hydrogen ion:
    • Cation: when a Hydrogen atom loses its electron. Becomes positively charged.
    • Anion: Gains an extra electron. Becomes negatively charged.
  • Hydrogen isotope:
    • Referred to when we talk about the neutron numbers in the nucleus.
    • Each isotope has the same number of protons & electrons but different number of neutrons.
    • With different number of neutrons each isotope have different masses.
    • Hydrogen has 3 naturally occurring isotopes:
      • Protium – stable.
      • Deuterium – stable.
      • Tritium – unstable – means it decays over time and will turn into another isotope or element. We refer to unstable isotopes as radioactive.
    • In power plants they fuse Deuterium with the unstable Tritium to generate energy.
Structure of Hydrogen Isotopes. Deuterium and Tritium used fro Energy Generation

The image above describes the structure of the hydrogen isotopes. The difference is in the neutron number.

There are two important numbers next to the hydrogen symbol:

  • Bottom left – Atomic number – the amount of protons.
  • Top left – Atomic mass – the sum of protons and neutrons. Electrons have such a small mass number that it can be negligible.

How Energy is Measured

Energy is measured in 3 different units:

  • Joule (J)
    • it is an SI unit.
    • 1 joule is the energy transferred when a force of 1 Newton moves an object 1 metre.
    • 1 Newton is the force needed to accelerate a 1kg object by 1m/s. So, an increase in velocity by 1m/s every second.
  • Kilowatt Hour (kWh)
    • Used at measuring the consumed electricity at home
    • Watt is power.
    • Power = Energy transferred per unit time. P = dE/dt
    • 1 kWh = 1000 W x 3600s = 3.6 MJ
    • so: 1000 W = 3.6 MJ/3600s
    • so: 1W = 3600J/3600s
    • 1W = 1J/s
  • Calories (Cal)
    • Used in nutrition
    • 1 Calorie is the energy required to heat 1 g water by 1°C.
    • 1 Calorie = 4.184 joules

Energy Generation Sources

The diagram below speaks for itself. It shows the World’s biggest Energy Generation sources:

  • Coal
  • Nuclear
  • Combined Cycle Gas Turbine
  • Oil
  • Renewables
Pi Chart: Energy Generation Source

Looking at it, we see that even though the coal is not efficient at all (from our table above) we still use it! But it is being reduced and renewables are growing.

The Demand/Supply Balance

Some of the energy sources can’t just be turned off at once when there is no need for it. It can involve a complex process.

With renewables, more specifically with solar panels, energy pants are facing an issue. People tent to install solars on their roof to save energy. This means when the sun is out the demand for energy from the wall is low.

The graph below shows how the demand for energy varies by time from the grid.

Diagram: The Duck Effect. When solar panels are in use during the day, the required energy from the grid is low.

These requirements have to be met by joined forces:

  • Nuclear Power Statins
  • supplies base load
  • can’t respond to short-term changes
  • Combined Cycle Gas Turbines
    • responds very quickly to changes
    • steam and gas turbines are primemovers
      • primemovers produce mechanical rotation of a shaft
    • simple cycle turbines – older types
    • combined cycle turbines – consists of 2 cascaded turbines where the exhaust heat from the first one is recycled in the second one.
  • Coal-fired Power Stations

    • Can respond to changes but not quickly.

Thermal Power Plant Operation

We can break down thermal power plants into 3 stages:

  • Heat source
    • fossil fuel
  • Heat engine
    • converts heat energy to mechanical energy (rotational)
  • Electric generator
    • driven by the turbine
    • this is a 3-phase synchronous machine
    • generates electricity
Block Diagram: Thermal Power Plant Basic Operation
In the diagram below we break down the thermal power plant in a little more detail.
  • The fuel combines with air and burns.
  • This heats up water in a pipe that turns to steam (gas).
  • The steam rotates the propellers in the turbine, thus, generating rotational energy.
  • The rotating shaft rotates the rotor in the 3-phase synchronous machine, thus, generating electricity.
Block Diagram: Thermal Power Plant Detailed Operation
A good video that explains this functionality of Gas Turbines: click here