Module 6. Green Energy Definition: Which Renewable Energy Is Reliably Green?

Climate change is an energy problem. In this module, you’ll learn about the cleaner alternatives to burning oil, coal and oil. You’ll clarify that for energies to be green, they have to be both renewable and sustainable. You’ll run through some low carbon energies to develop a sense of which offer the most potential for a clean future. You’ll discover the conditions under which burning biomass mimics the carbon cycle. By the end of this module, you’ll understand the benefits of combining energy sources, and you’ll have discovered why everything labelled as green isn’t necessarily healthy.

What You’ll Learn In This Module

What is the definition of green energy?

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Green energy is energy that comes from renewable and sustainable sources.

Renewable means from a natural source that is continuously replenished through natural processes.

Sustainable means meeting the needs of present generations without compromising those of future generations.

Examples of green energy include wind, solar, biomass, wave, tidal, hydro, geothermal and hydrogen. Controversially, Nuclear energy is also sometimes included in this group (for more about this, read below).

Since green energy doesn’t release greenhouse gases into the environment, it offers a clean and increasingly cheap alternative to energy from fossil fuels. Both for industries and also for heating and lighting in households.

But since it’s still quite difficult to store electricity, the amount of electricity produced at any moment needs to be almost the same as the amount being used by businesses and households.

What are variable renewable energies?

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Variable renewable energies are available only some of the time because they depend on the weather.

For example, wind electricity is available only when the wind is blowing. Solar energy is available only during the day and when the sun is shining. Tidal electricity is generated when the tides are coming in and out and wave electricity is produced when the waves are crashing.

These energies are the cheapest source of clean electricity when they are available.

Other renewable sources, such as geothermal, hydro or nuclear power, are available all of the time – their supply is fairly constant.

Constant supply can bring the costs of production down for a producer, but it means that there isn’t the flexibility to increase or decrease the amount of electricity being produced.

Finally, sources such as biomass and hydrogen can be made available when we need them. But their production can be more complicated and costlier.

Also, with biomass, there are many methods to produce it, some good for the climate and others bad (for more on this, read below).

What is the best green energy?

How best to heat and power light using renewable resources will depend on where you live.

The variability in some green energies, along with variation in when we use electricity, means that a combination of renewable energy sources is likely to ensure a supply of electricity exactly when you need it.

Plus, you may also need a method of storing electricity, such as in batteries.

The first integrated renewable energy grid in the world was built on the Island of Egg, in the Hebrides, UK. It uses a mixture of hydro, wind and solar to ensure electricity supply on an island with a lot of wet and windy weather.

Light is the most abundant source on earth.

In many regions of the world, solar is replacing electricity from coal and natural gas. It’s also replacing kerosene lamps and diesel generators in areas where people can’t access a power grid.

Solar photovoltaic (PV) home systems are used, for example, by 1.5 million households in Germany, by 6.6 million households in Bangladesh and by 16% of households in Australia.

But it’s calculated that wind energy stands to make the largest contribution to reducing climate change over the next three decades.

Wind farms have very small carbon footprints, are quick to build, and can be built off-shore or on-shore, while still using most of the land they stand on.

Around 6% of global electricity was supplied by wind turbines in 2020 and it’s expected to be much more. Over 10 million homes in Spain alone are powered by wind.

What drives the price of renewable energy?

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The price of renewable energies depends first on the costs of developing any new technology necessary.

Then on building production platforms, such as power plants, wind farms, solar panels, water turbines and their distribution networks.

Once built, the fuel for this energy – that’s the sun, water and wind – is free, as long as they are all naturally available where you live.

What often happens with new renewable technologies is that they are very expensive at the beginning, but then as technologies are more widely used, they become much cheaper.

For example, the cost of producing electricity using Photovoltaic (PV) solar panels reduced by around 90% between 2008 and 2019.

Particularly wind and solar power are now leading a fresh wave in green energy.

They have defied earlier expectations and are now competitive with traditional fuels, while having no or little impact on the environment.

What is biomass?

There are a lot of different sources of biomass.

In its broadest sense, biomass refers to all carbon-based organic matter, including plants and animals, living and dead.

Biomass is part of the world’s natural carbon cycle.

As plants and trees grow, they absorb carbon from the atmosphere. This is released back into the atmosphere as plants and trees decay or are burned.

Biomass can therefore contribute to limiting climate change in three ways:

  • Growing plants and trees remove carbon dioxide from the atmosphere and store it for long periods of time.
  • When managed and harvested sustainably, biomass can replace oil, coal and gas in the production of electricity.
  • When managed and harvested sustainably, biomass can replace high carbon building materials such as steel and cement.

When talking about producing renewable energy from biomass, there is a much smaller group of commonly used types of biomass.

These include:

  • crop residues, such as straw and husks;
  • animal waste, such as animal and poultry manure;
  • forest residues, such as wood chips or pellets from forest maintenance and management activities;
  • industrial waste, such as scraps, peelings and cooking water from the food industry and
  • household solid waste and sewage.

These types of biomass are used to produce bio-energy, usually as electricity, heat, or liquid fuel.

Is biomass a renewable source of energy?

Bioenergy is a renewable energy since it’s easy to replenish with more or different types of biomass.

But biomass can only contribute significantly to limiting climate change, under certain conditions (for more on this, read below).

Many biomass wastes and residues, for example in agriculture or forestry, are currently left to decompose or are burned. 

We know that in nature, organic matter left on the ground will decompose over time, releasing carbon dioxide into the atmosphere, in the natural carbon cycle.

The burning of biomass converts the stored energy into useful energy, releasing carbon dioxide into the air in a way that mimics the natural process, while being faster.

Instead of burning fossil fuels, which have taken millions of years to be created and then stored in the earth, and which can’t be replaced, we can burn materials such as straw, which have taken a few months to be produced.

To understand the potential contribution of biomass in reducing climate change, let’s consider this example of straw a little further.

When we burn the straw, it also releases carbon dioxide.

But this is carbon dioxide that was removed from the atmosphere by the straw growing last year, which is now being put back into the atmosphere.

It will be removed again by the next crop of straw growing in a few months’ time.

The carbon dioxide is drawn down from the atmosphere and then re-released year after year.

This is a natural process which is occurring all the time.

You can draw a comparison with the difference between your savings account and your cheque or current account.

When you are burning coal, oil and gas and releasing carbon dioxide that has been stored under the earth for millions of years into the atmosphere, it’s like raiding your savings account that you had put away for a rainy day.

Once it’s spent, that’s it.

You are releasing the carbon stocks into the atmosphere in a frivolous manner and causing climate change.

But when you are burning biomass, it’s more like your current or cheque account.

This money came in relatively recently. You’re spending it now, but you know you’re going to get more coming in again next month.

With biomass, you’re not releasing carbon from carbon sinks, which have held carbon in store for millions of years, causing long-term increases in carbon dioxide in the air that we associate with climate change.

Instead, you are following the flow of carbon coming in and out of the atmosphere with biomass.

And if at the same time you produce energy, then that’s beneficial.

Is biofuel clean energy?

The short answer is not always, so it’s important to know exactly how biofuel, or energy using biomass, is produced.

Biomass comes from a lot of different sources, ranging from wood pellets made from compressed wood, crops grown especially to burn for fuel, to chicken litter.

It’s transformed into fuel by various techniques that range from traditional burning processes to advanced biofuel technology.

Some of these processes have to occur at very high temperatures, others happen biologically at low temperatures.

Some processes used can consume a lot of energy in their production and their distribution.

The production, transport and consumption of biofuels can therefore release more carbon dioxide into the atmosphere overall than was drawn down from the atmosphere when the biomass was growing.

It may also release other more potent greenhouse gases, such as methane, into the atmosphere.

In other words, there are risks that biomass production could sometimes be more polluting than the alternative of fossil fuel.

Sustainable low carbon bio-energy is achieved only in certain circumstances. These include:

  • As a minimum, the production of bio-energy must be part of a system of sustainable land use, where carbon stocks in plants and soils increase over time. Biomass crops such as miscanthus, willow and poplar, for example, can build up stores of soil carbon over time and have a range of other environmental benefits.
  • Wood sourced biomass should be made up of waste wood, industrial residues and fast decaying forest residues which are not needed for maintaining carbon stocks. Wood from slow-growing forests should not be used for biomass.
  • To remain sustainable in the future, wastes must be reduced, reused or recycled as much as possible, before any residual waste is used for bio-energy production. This is because agricultural residues are needed for other uses, such as maintaining soil fertility.
  • Crops grown especially for energy need to be grown only on lower-quality land.

This suggests that many of the current uses of biomass do not reduce the amount of carbon in the atmosphere and are in sectors where there are increasingly other low-carbon alternatives that may be cheaper and easier to manage.

Other renewable energy sources may be more attractive for our future.

Is nuclear energy green?

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Nuclear energy could generate sizeable amounts of low carbon electricity.

But there are more factors to consider in deciding if this energy is really green and clean for a sustainable future.

Nuclear energy is created in a process where uranium atoms are split into two smaller and lighter atoms. Heated is created from this, which is used to produce electricity.

The advantages of nuclear energy are that it is available all the time, its low carbon and it has a very high energy density.

In fact, it’s nearly 8000 times more efficient at producing energy than traditional fossil fuels.

This means that you need far fewer nuclear power stations than wind farms to generate the same amount of electricity.

But while the energy produced by nuclear energy is renewable, the uranium isotope used in nuclear power plants is used up and is relatively hard to find. That means that it’s a non-renewable fuel.

It also produces very dangerous radioactive waste, which has to be securely stored for a very long time. The storage of waste is a major challenge facing nuclear power plants.

Nuclear accidents can and do happen. And nuclear power plants can have other negative effects on the environment (read below for more on this).

When considering these additional factors, nuclear energy is not considered green.

Is nuclear power good for the future?

There are three major factors limiting the attractiveness of nuclear fuel for the future:

(1) The cost of building a modern nuclear power station.

  • The costs are perhaps twice the amount of building a new wind farm or large solar plant.
  • While costs of new technologies usually reduce over time, this has historically not been the case with nuclear power stations in several countries.

(2) The time to build one and to decommission one.

  • It takes around ten years to build a nuclear power station. Compare this to just one year for a wind farm.
  • Considering that we need to make significant progress on tackling climate change in the new 10 years, the speed of construction is a very relevant consideration.
  • Also, stations stopping production need to be slowly wound down, or decommissioned. This takes also an average of 10 years.

(3) The lack of public acceptability and desirability, based on the creation of radioactive waste, pollution and the risks of accidents. 

  • Nuclear reactors generate radioactive waste, which is very dangerous – to man and more broadly to the natural world – and has to be securely stored for a very long period. This can’t be buried in landfills and needs special technologies for handling. Currently, it’s sealed in containers and kept underground.
  • The amount of waste produced is significant, although often underplayed. The storage of waste is a major challenge facing nuclear power plants.
  • Nuclear accidents, affecting the power plants or stored nuclear waste, can and do happen. The Chernobyl incident in April 1986 is considered the worst accident in history. And modern stations are not immune, seen when an earthquake badly damaged the nuclear power station in Fukushima in March 2011.
  • Nuclear power plants can also have other effects on the environment.

For example, the mining and enrichment of uranium are dangerous and health-threatening for the workers. It has a negative impact on the environment through e.g. greenhouse gas emissions, the creation of open pits and soil pollution. 

The cooling systems of reactors use vast quantities of water. This water is heated and then released into the oceans, adding to the already increased temperatures that marine life is challenged with. The stations are often not paying for this water use, meaning that there is reduced incentive for its efficient use, while this artificially reduces their running costs.

New technologies are currently being developed, which could result in smaller and more advanced, modular reactors.

These use different ways of cooling the reactor and different fuels, which may overcome some of the significant disadvantages of nuclear fuel to date.

But the time scales for these new technologies are uncertain, with the first station possibly being built in 2030.

No one knows how much it will cost, since nobody’s built one yet at full scale.

And there is still the problem of what to do with the radioactive waste and to ensure that accidents don’t happen…

What is energy with carbon capture?

This is when fuels are burned for energy, but any carbon dioxide produced is captured and stored in the earth, rather than being released into the atmosphere.

There is potential for this technique to be an important source of low carbon electricity in some parts of the world.

But several challenges have to be addressed first. These include:

  • Finding sufficient storage facilities to capture and store the carbon dioxide. This could be, for example, a disused oil or gas field.
  • Ensuring that the geology of underground storage sites is well understood, to guarantee that the carbon dioxide stays where it’s put for a long period and no carbon dioxide leaks out.

Any leaks again contribute to climate change and global warming.

  • The technology used to capture and store carbon is in its infancy.

Capture and storage technologies can capture up to 90% of carbon dioxide emissions, and channel them via a pipeline to a storage site.

This technology is at an early stage and cannot yet deal with large quantities. But there are a couple of large power plants operating in the United States and Canada.

  • High costs. The cost of generating electricity from fossil fuels with carbon capture and storage is expected to be at least twice as high as a unit of electricity produced using wind and solar power.

Want to know more about carbon capture? Read about the climate change and the ocean.