Sustainable Energy Explained

What is sustainable energy? How is it connected to the environment? How does it differ from renewable energy? What are the different types? What are the three principles of sustainability? What is energy security? What does social equity have to do with a sustainable energy system? We answer all these questions and more.
Solar Power Tower, Andalusia Spain
Solar power is the perfect sustainable energy. Photo: © Koza1983 (CC BY 3.0)

Why Do We Need Sustainable Energy?

The generation of sustainable energy is fast becoming a critical goal and it’s easy to see why. Planet Earth is being slow-cooked by increasing levels of greenhouse gases from fossil fuels like coal, oil and gas.

In fact, global warming is the greatest danger to the planet since the “Palaeocene-Eocene Thermal Maximum” (PETM) about 55 million years ago, when Earth’s temperature rose by 5-8 degrees Celsius due to a massive release of seabed methane. 1

With global temperature projections now showing a likely rise of 3-5°C by the end of the century, which itself could trigger several climate tipping points leading to even higher temperatures, a rapid switch to sustainable, clean energy is our only hope of averting disaster. Examples of sustainable energy include solar power and offshore/onshore wind-power.

What is Sustainable Energy?

Sustainable energy can be defined as: energy which is generated and used in such a manner that it meets the needs of the present without compromising the ability of future generations to meet their own needs. 2

Note that this definition is not just about the energy source involved. It’s about how the energy is generated and used, and how this use affects succeeding generations.

This is because sustainable energy comes under the umbrella of environmental sustainability, which is the responsibility we have to conserve natural resources and protect the global biosphere, in order to support the wellbeing of present and future generations.

Don’t forget, human wellbeing is directly linked to the environment. For example, according to the World Health Organization (WHO), 24 percent of all deaths around the world can be traced back to environmental problems. 3

At a minimum, people need clean air to breathe, fresh water to drink, access to food and a safe place to live. They also need the resources to look after themselves and their families. Any environmental, social or energy system that fails to provide these things, is not sustainable.

Other important environmental threats include:

• The dangers of global warming, notably sea level rise and extreme weather events, as well as the spread of diseases like malaria.

• Hazardous ambient air pollution, such as smog in urban areas, and indoor air pollution from cooking appliances, especially in Africa.

Deforestation due to farming, mining and dam construction, especially in the Amazon Rainforest, the Congo Rainforest and throughout Southeast Asia. Unfortunately, the break-up of wildlife habitats leads to serious loss of biodiversity and encourages illegal hunting. 4

So, a better description of sustainable energy might go something like this:

Sustainable energy is any economically viable energy resource that is not, in its life-cycle, a net contributor to climate change and does not have a particularly negative environmental or social impact.” 5

That said, no definition of sustainable energy should be taken too literally, or too seriously. Sustainability is a concept not a measurement, and its scope can vary according to one’s perspective. In practice, a sustainable energy system requires a balance of energy security, environmental protection, and social equity. Thus, while the vast majority of sustainable energy will come from renewables, we shouldn’t rule out the efficient use of conventional energy sources to ensure energy security.


For more about the specific dangers of climate change, check out these articles:

Effects of Global Warming on Humans.
Effects of Climate Change on Animals.

Types of Sustainable Energy

Sustainable energies include most renewables, such as wind and solar power, underground geothermal energy, some biomass, and most hydropower. Other sustainables are tidal power and wave power, although both are in the early stages of development, as well as hydrogen energy (also in its infancy) and nuclear fusion (still futuristic).

In general, no source of energy is automatically sustainable, as the situation is always open to change. For example, if companies started building solar panels using non-renewable resources buried deep in the rainforest, or if medical studies showed that wind turbines caused ill-health to local inhabitants, environmentalists would be quick to re-evaluate the energy source’s sustainability.

What’s the Difference Between Sustainable and Renewable Energy?

A renewable energy source will not be sustainable if it is depleted or if it has a significantly negative effect on the environment (including climate) or society. Here are two examples.


First, an energy source may be renewable but if it is used faster than it regenerates, it can become unsustainable. This is sometimes seen occasionally in geothermal energy systems, where the underground heat is not renewed fast enough by the hot rocks and the temperature decreases below the point that produces steam. Wood burning is another example. Trees are renewable if you plant replacement saplings. But if you burn too many trees, too quickly, all you’ll have left is a plantation of saplings. (See also: Does Tree Planting Stop Global Warming?)

What’s more, it takes a replacement tree at least 60 years to offset the global warming caused by cutting down and burning its predecessor for fuel. Unfortunately, most tree plantations are harvested at 20–30-year intervals – far too soon to repair the damage. 6

Easter Island is a perfect example of overuse of an energy resource. Large parts of the island have never recovered from rapid deforestation during the period 1600-1800. The loss of the soil surface led to ecological disaster, mass starvation and the complete collapse of the Easter Island civilization. 7

Environmental Impacts

Second, an energy source may be renewable and generate endless power but its adverse effects on the environment or society may exceed its energy-related benefits. Take palm oil, for example. This is a major constituent of biodiesel, but is typically grown on plantations carved out of the rainforest. And the ecological effects of deforestation can be similar or worse than those caused by burning fossil fuels. So, although biofuels that contain large amounts of palm oil may be renewable, they are not sustainable.

Furthermore, biofuel crops that are grown specially for climate change mitigation purposes have attracted controversy for several reasons. First, they use up lots of water; second, they increase pollution in the air and soil from fertilizer use; and thirdly, they divert land resources away from food production.

For example, according to Dr. Larigauderie, executive secretary of the IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services), most IPCC projections predict a major increase in the amount of land needed to grow biocrops like maize (corn), in order to reduce the speed of warming by 2050. Land area of up to 724 million hectares in total might be needed – an area about the size of Australia. Conservationists say the current land area devoted to biocrops lies somewhere between 15 and 30 million hectares. 8

Nuclear power is another case in point. Proponents say the 4 billion tonnes of uranium in seawater (enough to power the planet for thousands of years) makes nuclear energy a sustainable source of power. Except that no nuclear power plant has yet been fully decommissioned – because there is still no universally accepted mode of waste disposal, or even an official disposal site for non-military nuclear waste. Critics also point to the astronomical costs of planning, building and decommissioning a nuclear power plant, as well as the ongoing safety and contamination issues surrounding both the Chernobyl and Fukushima nuclear disasters.

But Nuclear Fusion (not fission), which involves the fusion of two isotopes of hydrogen, may yet prove to be sustainable.

What about hydroelectricity? Is hydropower sustainable? The answer is, it depends. It depends on the environmental impact of the dam construction and infrastructure on the local ecosystem, including the rivers, forests and fields submerged by the man-made reservoir. The displacement of local communities is another factor.

Also, its impact on climate change is by no means insignificant. Cement is a major ingredient in concrete, which most dams are made of, and cement emissions are a significant contributor to global warming. Steel is another high emission material used in dam construction.

Ecological threats derive from the creation of a large static pool of water (the reservoir), and the ecological changes made to the river bed downstream. Bottom line: while hydropower is low in emissions, compared to fossil fuels, it is not always sustainable, due to its environmental impacts. However, sustainable or not, hydropower is a much more reliable source of energy than either solar or wind, and thus it remains an essential element in the low-carbon energy mix.

Wind power in Costa Rica. Wind is an excellent source of sustainable energy.
In 2019, more than 99 percent of Costa Rica’s energy came from renewable sources. Most (67.5 percent), is generated from hydropower. About 17 percent comes from wind power, 13.5 percent from geothermal energy, and 1 percent from biomass and solar panels. Image: National Center for Energy Control, Costa Rica.

Creating a Sustainable Energy System

Sustainable energy systems require a series of new techniques and procedures, such as whole life-cycle analysis, energy modelling, carbon foot printing, carbon budgets, energy audits, energy efficiency and conservation.

This is because the amount and type of energy we use, and how efficiently we use it, is a major element in determining the sustainability of our cities, institutions, corporations, businesses, transport and homes, as well as the energy systems that power them.

Let’s not forget, sustainability has been around since the World Commission on Environment and Development produced its report “Our Common Future”, also known as the Brundtland Report, in October 1987. But it has only been since the Intergovernmental Panel on Climate Change identified human actions as the unmistakable cause of our climate crisis (Third and Fourth Assessment Reports 2001 and 2007), that renewable energies and sustainability have properly taken hold.

In any event, it won’t be long before any business that adds significantly to global warming through its use of fossil fuels will face public pressure to improve its environmental performance. Likewise, a company which damages the environment by growing crops on deforested land, or who profits through the use of child labor.

Of course, this type of public censure is already happening, and even powerful oil companies are wary of it – witness the lack of interest in Alaska’s recent auction (December 2020) of oil rights in the state’s Arctic National Wildlife Refuge. But standards will get stricter. For more, see: Environmental Effects of Fossil Fuels.

Three Principles of Sustainability

A sustainable energy system ideally contains a balance of environmental protection, energy security, and social equity.

Only Environmentally-Friendly Energy Can Save Us

At the heart of any sustainable system is a reliable supply of clean, environmentally-friendly energy. Unfortunately, as the following charts show, the world is still heavily dependent on high-carbon fossil fuels such as coal, its precursor peat, all types of petroleum and natural gas. It is the combustion of these fuels for heating, cooling, transportation and electricity, that produces the greenhouse gas emissions which are overwhelming our climate system and polluting the planet. Hence the drive to decarbonize our energy system.

Primary Energy by Fuel Type 2020
Source: BP Statistical Review of World Energy 2020
Electricity Generation by Fuel Type
Electricity generation by fuel type in 2019. Source: Electricity – BP Statistical Review of World Energy 2020

In view of our massive addiction to fossil fuels, the decarbonization of the global energy system will be one of the greatest challenges facing humanity in the 21st century. Already, experts are saying that our climate plan can’t cope and should be junked, although no one seems to know what to put in its place.

What is clear, is that the so-called Anthropocene Epoch has given rise to the world’s greatest predator – Homo sapiens – who must be reined in before he causes extinction-level damage to the planet and to all of Earth’s creatures, including humanity.

Global warming is unquestionably the greatest menace, especially when we realize that 93 percent of all of its heat has been absorbed by the oceans. Unfortunately, this hidden 93 percent will eventually emerge from the water is some form. Already the Antarctic ice sheet is feeling the effects of ocean warming, as is the Greenland Ice Sheet.

Let us hope that UN Climate Talks at COP26 in Glasgow (November 2021) can produce a new global consensus on climate action which might ramp up the adoption of renewable energies and inspire nations to make serious climate commitments.

Energy Security

Deng Xiaoping famously once said that it made no difference whether a cat was black or white, as long as it was able to catch mice. Similarly, we can say that no energy source can be described as sustainable if it can’t keep the lights on. Energy security is all-important.

One mitigation technique which is neither sustainable nor renewable, but which can help to reduce carbon dioxide emissions and keep the lights burning, is co-firing in conventional fossil fuel power plants.

Co-firing is the co-incineration of biomass-based substitutes (e.g. industrial wood pellets) together with fossil fuels, usually coal. By diluting the carbon content of the total material being incinerated, the rate of emissions can be significantly reduced while still meeting base load demands.

If a majority of coal-fired power plants and boilers operating around the world were to adopt co-firing systems, the total reduction in CO2 emissions would be substantial. 9

Today, co-firing is widely regarded as a highly cost-effective, albeit short-term, method of reducing CO2 emissions in the electricity sector. One recent study which evaluated the effectiveness of co-firing in the German electricity sector, found that widespread implementation of the technique would have led on average to a 21 percent reduction in CO2 emissions.

If nothing else, co-firing can help reduce emissions while emerging renewable energy technologies are developed, and established renewables are integrated into national power grids. Like Deng’s cat, co-firing may not appeal to the purists but if it provides energy security and reduces emissions, it will do fine.

Social Equity

What has social equity got to do with sustainable energy? Answer: Social equity is an important criterion for energy access – that is, ensuring that renewable energy is made available at affordable prices to those currently suffering from energy poverty. The point is, renewables tend to be more expensive to access (purchase prices of electric vehicles are far higher than those of diesel cars), while carbon taxes raise the price of fossil fuels like diesel and coal.

Social equity is also a touchstone to ensure that poorer countries are allowed to increase their energy consumption in order to develop their economies, pending their transition to more sustainable energy systems. At the same time, wealthier countries should reduce their energy consumption to facilitate this equitable arrangement. For more on this, see: The Ethics of Climate Change.

The point is, most of the world’s population live in the developing world, where energy usage is low. If these people feel they are being denied fair access to energy – by pricing, availability or any other imposed factor – they will simply boost their consumption of cheaper fossil fuels. This will be bad for everyone and solve nothing. So a global approach to sustainable energy, based on social equity, is essential if we are to resolve our climate crisis.


  1. “A perturbation of carbon cycle, climate, and biosphere with implications for the future”. McInherney, F.A., et al; (2011). Annual Review of Earth and Planetary Sciences. 39: 489–516. []
  2. “Principles of sustainable energy systems.” Kutscher, Charles F., Milford, Jana B., Kreith, Frank (2019) (Third ed.) Boca Raton, FL: CRC Press. Chapter 1. ISBN 978-0-429-48558-9. []
  3. “Public health and environment.” World Health Organization (WHO). []
  4. “Sustainability criteria for energy resources and technologies”. Hammond, Geoffrey P.; Jones, Craig I. (2011). In “Handbook of Sustainable Energy.” Galarraga, Ibon; González-Eguino, Mikel; Markandya, Anil (eds.). Cheltenham, UK: Edward Elgar. pp. 21–47. ISBN 978-1-84980-115-7. []
  5. “The Politics of Investing in Sustainable Energy Systems.” Alan Owen, Leuserina Garniati, in “Storing Energy: With Special Reference to Renewable Energy Sources,” 2016. Edited by Trevor M. Letcher. Chapter 25. Pages 529-538. ISBN 978-0-12-803440-8 []
  6. “Correcting a fundamental error in greenhouse gas accounting related to bioenergy.” Helmut Haberl, et al; Energy Policy. Volume 45, June 2012, Pages 18-23. []
  7. “Islands in time”. Dirt: The Erosion of Civilizations (1st ed.). David Montgomery (October 2, 2008). University of California Press. []
  8. “Biofuel land grab will slash nature’s space.” []
  9. “Biomass co-firing options on the emission reduction and electricity generation costs in coal-fired power plants.” Prabir Basu et al. 2011. Renewable Energy. Volume 36, Issue 1, January 2011, Pages 282-288. []
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