Energy options for the future

Introduction

This unit will explore how both renewable and non-renewable energy sources may contribute to our energy future within a context of a need to meet carbon reduction targets. It will review current energy sources and technologies and their limitations and then explore future possibilities, a hydrogen economy, the use of nuclear energy and carbon capture.

Unit authored by Bruce Heil.

Learning outcomes

By the end of this unit you should be able to:

• build a basic understanding of our future energy options;

• build an understanding of how our current fossil fuel energy options may deliver energy with lower environmental consequences in the future;

• understand what the future might be for nuclear energy in the UK;

• understand how hydrogen may offer the opportunity to deliver cleaner transport systems;

• build a basic understanding of carbon capture and storage.

1 Renewable and non-renewable energy

1.1 Renewable energy

Renewable energy is energy from natural resources or energy that can be replenished as quickly as it is used. When we think of renewable energy we usually think of solar panels on house roofs or wind turbines marching across the hills. Both make use of naturally occurring forms of energy, namely the energy in sunlight and the energy in the wind. The latter can be thought of as an indirect form of solar energy, as the differential heating of the Earth’s surface. Similarly, the wind passing over the sea creates waves and harnessing these provides another form of renewable energy, again an indirect result of sunlight.

We consider hydro-electric schemes to be renewable as well. Rain on high ground is collected in reservoirs and can be tapped to turn water turbines at a lower level to generate electricity. The climate system is generated by the sun, so again hydro power is an indirect form of solar energy. Tidal energy, by contrast, is the result of the gravitational pull of the moon and, to a lesser extent, the sun on the seas.

The other key renewable is often referred to as biomass. By this we mean plants that can be burnt to create heat but which can be replenished at the same rate as they are consumed. Sunlight, of course, provides the energy input to the plants to enable them to grow. Biomass plants are thus stored solar energy. In certain parts of the world we make use of geothermal energy, the heat within the Earth.

1.2 Non-renewable energy

By contrast, non-renewable resources cannot be replenished as quickly as they are used. In the case of the fossil fuels that we commonly use this replenishment may take millions of years. The fossil fuels coal, oil and natural gas are also stored solar energy. The solar energy enabled plants and animals to grow. As they died the plants and animals were buried under geological strata and under pressure over millions of years the carbon content has created the hydrocarbon that we are now able to mine and tap.

We can calculate from our use rate of these resources and our estimates of the remaining reserves how long they are likely to last and, hence, how quickly we need to develop alternatives. In addition, it is our burning of these fuels that is increasing the levels of carbon dioxide (CO₂) and other gases in the atmosphere and generating global warming. This, of course, is the other key driver in encouraging the development of alternative sources of energy.

The last big source of energy, and one that is also non-renewable, is nuclear energy. The energy is released from the fission of the atomic nuclei of certain materials, such as uranium. As uranium ore is a mineral with finite levels of deposits, nuclear energy is also non-renewable. We usually consider it separately from fossil fuels because it does not have the global warming impact of fossil fuels. There are, of course, other issues with nuclear power, particularly how we dispose of the radioactive materials that result from the fission process.

1.3 Fossil fuels

The fossil fuels coal, oil and natural gas are stored solar energy. Plants and animals grew using the heat and energy of the sun, died, were buried and over millions of years and under pressure formed the hydrocarbons that we utilise today. These sources of stored solar energy are clearly finite.

The UK is heavily dependent on gas and oil for both heating our homes and offices and for industrial processes requiring heat. Our transport systems are almost totally dependent on oil.

2 Alternative sources of energy

2.1 Hydrogen

Hydrogen can be used as a fuel in a fuel cell to produce electricity and heat with high efficiency and no emissions. It can also be burnt as a fuel, again with relatively no harmful emissions apart from a small amount of nitrous oxide.

However, hydrogen has to be produced, as it cannot be simply extracted from the ground like oil or natural gas. Hydrogen as an energy source is a secondary source like electricity. It has to be produced using other sources of energy; but when created it is a useful carrier of energy.

The options for producing hydrogen include:

• reforming fossil fuels, allowing the carbon to be captured and stored (see other steps on carbon capture)

• by electrolysis using electricity from renewable energy sources

• by electrolysis using electricity from nuclear plant.

One problem is generating the hydrogen. In an ideal hydrogen future we would use renewable energy to generate the hydrogen, which can then be used for space heating (replacing natural gas) or for transport (replacing oil). Clearly, currently we do not have enough renewable energy to contemplate this. One option might be to use fossil fuels like coal to generate the hydrogen, providing that carbon capture and sequestration techniques are used to minimise the atmospheric CO₂ emissions. Alternatively, nuclear energy could be used to generate the hydrogen.

Once produced, the hydrogen needs to be transported and stored, and this requires new technologies to be developed. The use in vehicles also needs new technologies that are not yet commercially available. The downside is that energy needs to be used to provide the hydrogen.

2.2 Nuclear energy

We will not consider nuclear technologies here but focus on the arguments for and against nuclear power.

3 Energy efficiency: reducing carbon emissions

3.1 Options for reduction

Chart 3 on page 20 of the Department of Energy and Climate Change’s report, 'Energy trends' dated March 2009, indicates that the two key contributors to carbon emissions are domestic use of energy and power stations. Together these account for over 40 per cent of carbon emissions.

In a general sense there are three obvious ways of reducing our carbon emissions:

• use energy more efficiently

• replace conventional carbon emitting sources with renewable energy

• clean up existing carbon-emitting technologies to reduce emissions.

3.2 Using energy more efficiently in the home

The Energy Saving Trust identifies ways to reduce the energy use in your home.

It identifies two key efficiency savings options:

• reduce heat loss from the home

• replace inefficient boilers with more efficient ones.

3.3 Tackling power station emissions

The UK had traditionally relied on coal-fired power stations to deliver electricity. During the ‘dash for gas’ the output from gas-fired power stations increased and this delivered reduced CO₂ emissions as the gas-fired stations are more efficient and gas delivers more output for less CO₂. However, gas is also a finite source and the UK will soon be importing gas. Coal may, therefore, make a comeback and, currently, new stations have been announced.

The UK government has published a strategy document dealing with reducing carbon emissions from our fossil-fuelled power stations. It is entitled ‘A strategy for developing carbon abatement technologies for fossil fuel use’.

Page 4 explores the question ‘Is it so difficult to reduce fossil fuel consumption in the UK and worldwide?’

The report’s answer is that fossil fuel power generation will be needed for the foreseeable future, particularly because of increasing demand for electricity in developing countries. It projects very large increases in demand, particularly in China and India, which would require hundreds of new power stations that will be with us for 40 to 60 years. As such, there is a very real need to identify ways to reduce the carbon emissions from these stations.

Page 5 of the report considers carbon abatement technologies (CATs) in the section headed ‘What are CATs and what are their deployment prospects?’ and identifies three CATs that might be deployed:

• higher efficiency conversion processes

• fuel switching to lower carbon alternatives

• CO₂ capture and storage (CCS).

As the data indicate, potentially the most effective of these is the last one: CCS. This technology is not yet commercially developed, but the method of long-term storage has been identified.

To conclude this brief look at CCS, read the Guardian report entitled ‘New era for fossil fuels as first carbon capturing power plant begins work’. This is the first retrofit of CCS technology to an existing power plant and will provide an opportunity to test both the capture technology and the stability of the storage reservoir.

4 Carbon capture and sequestration

4.1 The impact of fossil fuel power stations on the climate

The UK government has published a document entitled ‘A strategy for developing carbon abatement technologies for fossil fuel use: Carbon Abatement Technologies Programme’.

Page 3 explores the question ‘Why do we need a UK CAT strategy?’ and considers the impact that increasing atmospheric levels of CO₂ are having on the climate and consequently are likely to have on the UK. The document also indicates the level of CO₂ emission reductions that are necessary and the timescales involved. The UK is a minor emitter of CO₂ but, nevertheless, needs to provide a lead. The UK has a target of cutting emissions by 60 per cent by 2050.

Page 4 of the document asks ‘Is it so difficult to reduce fossil fuel consumption in the UK and worldwide?’ and indicates that worldwide demand for electricity, particularly from China and India, is set to double by 2030, which will require a massive increase in electrical generating capacity, much of which will be met by fossil-fuelled power stations.

If we are to reduce carbon emissions and the consequent impact on climate change, then the deployment of CCS techniques will be an essential part of the strategy.

4.2 Carbon capture technologies

The combustion of fossil fuels generates CO₂. Power stations that use fossil fuels are large-scale emitters of CO₂, and because they are large scale they provide an opportunity to capture and store the CO₂ rather than emitting it to the atmosphere. Small-scale emitters, like domestic gas boilers, do not provide the same opportunity, particularly for storage. Large-scale emitters make the necessary piping and infrastructure more cost effective and practicable.

Pre-combustion technology. This is where the carbon is captured from the hydrocarbon fuel before combustion, producing hydrogen, which in turn can then be used as a clean fuel.

The fuel, which might be methane or coal that has been gasified, is converted into hydrogen and carbon monoxide. The carbon monoxide is converted into CO₂ and then separated from the hydrogen ready for storage.

The BBC News article ‘BP pulls out of green power plant’ provides information on the cancellation of this project.

Post-combustion technology. As the term suggests, this involves capturing the CO₂ from the flue gases after combustion. More information, including the advantages and disadvantages of this type of capture, can be found at the Scottish Centre for Carbon Storage.

An example of a test scheme that has just started is provided by ScottishPower’s Longannet power station.

4.3 Carbon sequestration

The Scottish Centre for Carbon Storage proposes three methods of underground storage for carbon. Why is deep-ocean storage rejected at this point in time?

There is also the potential for CO₂ storage to increase the oil potential of oil wells.

A diagrammatic version of how this would work is provided by the Guardian article ‘How carbon capture and storage could work in the UK’.

Acknowledgements

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Text

Unit authored by Bruce Heil.

Unit image

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Links

All links accessed 27 November 2009.