1.2.2 Energy basics

Helpful prior knowledge and learning objectives

Helpful prior learning:

Learning objectives:

All life on Earth requires energy, and humans are no exception. Everything we do needs energy - breathing, working, playing, driving, watching Tik Tok videos - all of it! But what is energy, and how have we come to be so dependent on it?

What is energy?

Energy is the ability to do work or cause change. Energy makes things happen, like moving objects or producing heat and light. Energy is essential for all life and comes in different forms.

Kinetic energy: energy of motion

Radiant energy

Energy from electromagnetic waves.

Electrical energy

Energy produced by the movement of electrons; powers electronic devices.

Thermal energy

Energy related to heat; it increases as things get hotter.

Potential energy: stored energy

Nuclear energy

Energy released from the nucleus of atoms.

Chemical energy

Energy stored in the bonds of chemical compounds and released during chemical reactions

Gravitational energy

Energy stored in an object's position or height

Elastic energy

Energy stored in objects when they are stretched or compressed

The First Law of Thermodynamics says that energy cannot be created or destroyed in the universe. The Earth is a closed system, which means that no new matter enters Earth’s systems, but radiant energy of the sun can enter. Earth is constantly bathed in solar radiation, which has an impact on most other energy sources, as you will see later in this text.

How do we measure energy?

Energy is measured in different units: Joules (J), kilowatts (kW), and kilowatt-hours (kWh). 

For example, using a 100-watt light bulb for 1 hour consumes 100 watt-hours or 0.1 kilowatt-hour (kWh) of energy. Using a 100-watt light bulb for 10 hours consumes 1 kilowatt-hour (kWh) of energy.

For comparison, 1 litre of petrol (gasoline) contains about 32,000,000 Joules or roughly (a little under) 10 kWh. That is a lot of energy! To understand this in human terms, a healthy adult male labourer can perform manual work (Figure 1) such as moving and laying bricks in an eight-hour work day equal to about 0.5 kWh. So, to match the energy in 1 litre of petrol, a person would have to  work for 8 hours per day for 20 days. These numbers are approximate, but give you an idea of the energy associated with fossil fuels relative to human labour.

Men moving and laying bricks to build a wall

Figure 1. Even hard manual labour like moving and laying bricks is only the equivalent of 0.5 kWh for an 8-hour workday, far less than the energy from 1 litre of petrol

(Credit: M Mahbub A Alahi, CC0)

You may hear people complain about how expensive petrol is. But considering the amount of energy petrol contains and the work it does for us, it is incredibly inexpensive. This is especially true considering rises in incomes that have made fuel more affordable and the improvements in machine efficiency that enable us to do more with less fuel. 

Because we pay so little for energy, the products we produce and buy are also much less expensive. These low energy costs and low product prices contribute to the high consumption of both energy and material resources, which is discussed in Section 1.2.3 and  Section 1.2.4.

What sources of energy do we have?

Most of the energy on Earth comes from the sun. The sun is the source of:

Windmills of Nashtifan, Iran

Figure 2a. Windmills of Nashtifan, Iran are used for milling grain. Wind has been used for centuries as an energy source.

(Credit: Hasanahmadifard CC BY-SA 4.0)

Windmills in Denmark

Figure 2b. Windmills in Denmark are used for electricity.

(Credit: Dirk Goldhahn CC BY-SA 2.5)

Other sources of energy include geothermal and tidal. Geothermal energy comes from the Earth's internal heat. Below the surface, the Earth is very hot. Pipes deep in the ground bring up hot water or steam, which is then used to generate power. Geothermal energy is used around the world, but is a particularly large source of energy in Kenya, El Salvadore, Iceland, New Zealand, Nicaragua, and Costa Rica.  

Tidal energy, which comes from changing tides along coastlines, is caused by the gravitational pull of the moon and the sun on the Earth’s oceans. Tides move enormous amounts of water, particularly in places where there is a big difference between high and low tide. So in some places, we use this water movement to generate power.

What is the difference between renewable and nonrenewable energy sources?

Renewable energy comes from sources that are continuously available or regenerate quickly. For example, solar, wind, geothermal and tidal energy are always flowing from their sources and will not run out. On the other hand, biomass, like wood or crops that can be burned for energy, regenerates as plants grow back. Renewable energy sources are sustainable only if we use them at slower rates than they replenish and if their surrounding ecosystems remain healthy. 

Figure 2 shows a stock and flow diagram (Section S.x) for a stock of wood biomass in a forest. If inflows from tree growth and outflows from tree death and human harvesting are in balance, then one of the conditions for biomass to be renewable is met.

Stock and flow diagram of wood biomass

Figure 2. Stock and flow diagram for biomass, a renewable energy resource if inflows and outflows are in balance

Figure 3 shows the share of electricity production from renewable energy by country. Which countries use more renewable energy? What could explain that?

Nonrenewable energy comes from sources that do not replenish quickly or are finite. This includes coal, oil, natural gas, and uranium for nuclear power. These materials took millions of years to form and, once used, cannot be replaced within a human lifetime. 

Figure 4 shows a stock and flow diagram (Section S.x), where coal stocks have a mining outflow, but no inflow.

Stock and flow diagram for coal

Figure 4. Stock and flow diagram for coal, a non-renewable energy source with outflows, but no inflows

Today, we use a wide mix of energy sources including non-renewable coal, oil, gas, nuclear power, and renewable hydropower, solar, wind, and biomass. Until the mid-1800s, most of the world's energy came from burning biomass such as wood, crop waste or charcoal. Coal then became a major energy source in the Industrial Revolution. By the early 1900s, coal provided about half of all energy, with biomass providing the other half (Figure 5).

During the 1900s, we began using more energy types. Oil and gas came first, followed by hydropower and then nuclear energy starting in the 1950s. Looking at the last 200 years, changing from one dominant energy source to another has been slow, often taking decades. But this transition can happen more rapidly. In the UK, the share of electricity powered by coal declined  from nearly two-thirds in 1990 to about one-third by 2010, and then to around 1% in the following decade.

Renewable energy production, especially for electricity, is increasing very rapidly. However, while some countries have been able to replace fossil fuels with renewable energy sources, globally we still use fossil fuels for about 80% of our energy. It is difficult to lower that percentage because our economies and the demand for energy are growing so quickly that in many places renewable energy is simply being added to fossil fuel energy sources, rather than replacing them. This will be discussed more in the next Section 1.2.3.

This optional short video below is a nice summary of energy information from this section.

Activity 1.2.2

Concept: Systems

Skills: Research skills (information literacy)

Time: varies (see below)

Type: Individual, pairs or group (option-dependent)

Option 1 - Comparing energy use of various devices

30 minutes

Select some common electrical devices in your school, or at home and figure out how many watts they use. If you have them on hand, you may be able to find the information on the device. If not, do some quick research on the internet to find some rough estimates.

Make a table to compare the items, listing the item, the kilowatts, and a guess of the amount of time the device is used each day. 

Note: electrical devices that are connected to the internet use more energy than what is listed on the energy label. This is because of the computing power and networks needed to store data and connect devices. You may find it interesting to learn more about how much energy our use of computers, cloud storage and streaming uses - it’s a lot!

Device / machine Kilowatts Time used per day (hours)

Option 2 - Using an energy calculator to determine the cost of electricity for various devices

30 minutes

There are many energy calculators online that can help you estimate how much it costs per month or per year to use various devices. See if you can find such a calculator for your country. If not, you can choose one for another country, but the assumptions in the calculator may be different from your region. You may need to find the cost of electricity per kWh to input into the calculator.

Select various devices and compare the cost of the energy used. You could add a column for this in the table from Option 1.

Option 3 - Understanding your home or school energy use

40 minutes for initial research if energy bills are ready for analysis, longer if a plan for energy reduction is developed

Option 4 - Calculating the difference between human labour and petrol

20 minutes

Ideas for longer activities, deeper engagement, and projects are listed in Subtopic 1.5 Taking action

Checking for understanding

Further exploration


Blain, C., Jancovici, J. (2021). Welt Ohne Ende. Berlin: Reprodukt.

Daly, H., Farley, J. (2011). Ecological Economics (2nd ed.). Washington, D.C.: Island Press.

Ritchie, H. et al. (2023). Energy. Our World in Data. https://ourworldindata.org/energy.

Sneideman, J. (n.d.). A guide to the energy of the Earth. TED-Ed. https://ed.ted.com/lessons/a-guide-to-the-energy-of-the-earth-joshua-m-sneideman.

Terminology (in order of appearance)

Link to Quizlet interactive flashcards and terminology games for Section 1.2.2 Energy basics

energy: the ability to do work or cause change

kinetic energy: energy of motion

radiant energy: energy from electromagnetic waves

electrical energy: energy produced by the movement of electrons; powers electronic devices

thermal energy: energy related to heat; it increases as things get hotter

potential energy: stored energy

nuclear energy: energy released from the nucleus of atoms.

chemical energy: energy stored in the bonds of chemical compounds and released during chemical reactions

gravitational energy: energy stored in an object's position or height

elastic energy: energy stored in objects when they are stretched or compressed

First Law of Thermodynamics: energy cannot be created or destroyed in the universe

joule (J): a measure of the amount of work done or energy transferred

watt (W): a unit of energy transfer equal to 1 Joule/second

kilowatt (kW): 1000 watts, where each watt is a unit of energy transfer equal to 1 Joule/second

kilowatt-hour (kWh): a measure of how much energy is used or produced over time.

food chain: a series of organisms, each one dependent on the one before it as food; shows the transfer and transformation of energy and matter through living organisms in an ecosystem

hydropower: a renewable energy source that uses falling or running water

fossil fuel: a non renewable energy source including coal, oil, and natural gas, formed over millions of years in the Earth's crust from decomposed plants and animals

geothermal energy: a renewable energy source that uses the heat produced inside the Earth's crust

tidal energy: a renewable energy source that uses the movement of water from changing tides

renewable energy: energy from sources that are continuously available or regenerate quickly

biomass: organic matter that is burned for energy

stock and flow diagram: a diagram showing the accumulations of energy, matter, information or other things (stocks) and the movement (flow) of those things

nonrenewable energy: energy from sources that cannot be regenerated in a human timescale, such as coal, natural gas and oil