Energy and the New Reality 2

Carbon-free Energy Supply

L. D. Danny Harvey

• Publisher: Routledge
• Year: 2010
• ISBN:
  9781136541599
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Transforming our energy supplies to be more sustainable is seen by many to be the biggest challenge of our times. In this comprehensive textbook, L. D. Danny Harvey sets out in unprecedented detail the path we must take to minimize the effects that the way we harness energy will have on future climate change.

The book opens by highlighting the importance of moving to low carbon technologies for generation, then moves on to explain the functioning, potential and social/environmental issues around:

• solar energy
• wind energy
• biomass energy
• geothermal energy
• hydroelectric power
• ocean energy
• nuclear energy.

It also covers the options for carbon capture and storage and the contexts in which low carbon energy can best be utilized (potential for community integrated systems, and the hydrogen economy). The book closes with scenarios that combine the findings from its companion volume (concerning the potential for limiting future energy demand) with the findings from this volume (concerning the cost and potential of C-free energy systems) to generate scenarios that succeed in limiting future atmospheric CO2 concentration to no more than 450 ppmv. Detailed yet accessible, meticulously researched and reviewed, this work constitutes an indispensible textbook and reference for students and practitioners in sustainable energy and engineering.

1

Introduction and Key Points from Volume 1

This introductory chapter briefly outlines the scientific basis for great concern over the global warming issue and explains why greenhouse gas (GHG) emissions must be reduced dramatically and with the greatest urgency. A framework for analysing the driving factors for industrial CO₂ emissions is then presented, followed by a brief summary of the key points from Volume 1.

1.1 The Scientific Basis for Concern about Global Warming

Emissions of carbon dioxide (CO₂) due to industrial activities and land use changes during the past 200 years have caused the CO₂ concentration in the atmosphere to increase by 40 per cent, from about 280ppmv (parts per million by volume) in 1800 to 390ppmv by 2010. Other GHGs have increased as well – methane (CH₄) by a factor of 2.5, nitrous oxide (N₂O) by 15 per cent and ozone (O₃) in the lower atmosphere by a factor of two to five (depending on location). A number of entirely artificial GHGs have been added to the atmosphere as well. All of these gases trap radiant heat emitted from the earth’s surface and so have a warming effect on the climate. The collective heat trapping of all the GHG increases so far is equivalent to that which would arise from roughly an 80 per cent increase in CO₂ alone.

The key parameter in the science of global warming is the climate sensitivity, defined as the global average temperature change resulting from a fixed doubling in the atmospheric CO₂ concentration, once the climate system has had a chance to fully adjust to the increase in CO₂. There are several independent lines of evidence (computer simulations with three-dimensional (3D) climate models, analyses of temperature changes during the past 150 years, analysis of times in the geological past when climates were quite different from today, and analysis of past slow natural variations in atmospheric CO₂) that all agree in indicating that the climate sensitivity very likely lies somewhere between 1.5 degrees Celsius (°C) and 4.5°C. Thus, with the prospect of GHG concentrations reaching the equivalent of four times the pre-industrial CO₂ concentration or larger by the end of the century under business-as-usual (BAU) emission scenarios, we face the prospect of a commitment to 3–9°C by the end of this century in the global average and a realized warming of 2–6°C. The average warming would be greater over land areas and greater still in polar regions.

The current atmospheric GHG concentrations, if sustained, would probably eventually warm the climate by 1.2–3.6°C, whereas only 0.8°C global average warming has been observed so far. The observed warming is smaller than the projected warming because pollution in the form of reflective aerosols (which are produced largely from the emission of sulphur and nitrogen oxides in association with the use of fossil fuels) has offset up to half of the heating effect from the concurrent GHG buildup, and because the oceans delay the surface warming due to the mixing of heat to great depths. The reflective aerosols are themselves associated with acid rain, so as acid rain emissions are cleaned up, or when fossil fuel use eventually decreases, there will be an acceleration in the warming as the climate system attempts to ‘catch up’ to the GHG concentrations already found in the atmosphere.

As discussed in more detail in Volume 1 (Chapter 1, subsection 1.4.1), there is a continuously increasing risk of serious impacts as the projected warming increases from 1 to 3°C and beyond. In particular:

• widespread extinction of coral reef ecosystems with 1–2°C warming above pre-industrial levels;
• possible collapse of the Greenland ice sheet with as little as 1–2°C sustained global average warming, and almost certainly with 3–4°C sustained warming;
• likely extinction of 15–30 per cent of species of life on earth due to a mere 2°C warming happening by 2050, with greater losses with greater warming;
• reduced agricultural productivity in some major food-producing regions once local warming exceeds 1–3°C (depending on the crop and location);
• severe water shortages in semi-arid regions, including the eventual loss of glacier meltwater that supplies summer water to 25 per cent of the population of China;
• acidification of the oceans as CO₂ is absorbed by the oceans, with severe and still poorly understood impacts.

Industrial CO₂ emissions reached about 8 gigatonnes of carbon per year (GtC/yr) in 2005 and land use emissions were about 1–2GtC/yr. Total human emissions of CO₂ are thus about 9–10GtC/yr, while the observed annual increase is about 4–5GtC/yr. The balance is absorbed through a combination of increased rates of photosynthesis on land and through net diffusion of CO₂ into the ocean water and its conversion to other forms of dissolved carbon (C). These are referred to as the terrestrial biosphere and oceanic sinks. In the absence of changes in the strength of the sinks, stabilization of the atmospheric CO₂ concentration requires reducing total emissions only to the point where they equal the total sink strength (a reduction of about 5GtC/yr, of which 1–2GtC/yr could be achieved by ending deforestation). However, once the atmospheric CO₂ concentration stops growing the sinks would themselves weaken over time even in the absence of climatic change. Warming induced by the GHG increases will further weaken the sink strength, such that stabilization of atmospheric CO₂ at a concentration of 450ppmv requires the near elimination of human CO₂ emissions by the end of this century. Inasmuch as a CO₂ concentration of 450ppmv in combination with minimal increases in other GHGs is the equivalent of a doubling in CO₂ concentration, and given that this is very likely to cause anywhere from 1.5°C to 4.5°C warming, with the consequences outlined above, it is clear that even an atmospheric CO₂ concentration of 450ppmv is too large. Thus, efforts will almost certainly be needed to draw down the concentration as rapidly as possible, but significant negative impacts, ecosystem losses and species extinctions will be unavoidable during the process. Depending on how quickly we act, how large the climate sensitivity is and how sensitive the Greenland and West Antarctic ice sheets are to warming, it may or may not be possible to avoid triggering an eventual 10 metres (m) or so sea level rise.

1.2 Kaya Identity and Efficiency Versus C-Free Energy Tradeoffs

Future CO₂ emissions, expressed as a mass of carbon per year, can be written as the product of the following factors:

population × GDP (gross domestic product) per year per capita × primary energy per unit GDP × carbon emission per unit of primary energy used

or, in shorthand notation:

where E/$ (primary energy use per unit of GDP) is referred to as the energy intensity of the economy and C/E (carbon emission per unit of energy) is referred to as the carbon intensity of the energy system.¹ This decomposition of CO₂ emission is referred to as the Kaya identity, in honour of the Japanese scientist who first proposed it.

In Volume 1 (Chapter 10, subsection 10.2.1) we applied the Kaya identity at the global scale, considering three scenarios of global population, two scenarios of growth in GDP/capita (one with continuous growth at 1.6 per cent/year, the other where the rate of growth decreased linearly from 1.6 per cent/year in 2000 to 0.8 per cent/year growth in 2100), various rates of decrease in energy intensity (1 per cent/year and 2 per cent/year), and various rates of increase in C-free power. The product of the first two terms of the Kaya identity gives gross world product – the size of the global economy – while the product of the first three terms gives the amount of primary energy (in J, joules) required per year. The primary energy requirement in joules per year can be divided by the number of seconds per year to give the primary power requirement (W, watts), then divided by 10¹² (the number of joules in one terawatt) to give the primary power requirement in terawatts (TW).² Figure 1.1a shows the variation in gross world product for the low and high rates of GDP/capita growth each combined with the low and high population scenario, while Figure 1.1b shows the variation in primary power for low GDP/capita and low population growth and for high GDP/capita and population growth, each combined with slow (1 per cent/year) and fast (2 per cent/year) rates of improvement of energy intensity. Gross world product grows from $56 trillion in 2005 to anywhere from $170 trillion to $420 trillion in 2100. Global primary power demand decreases from 15.3TW in 2005 to 6.9TW in 2100 for the lowest scenario, and increases to 44.7TW for the highest scenario.

Figure 1.1 (a) Growth in gross world product for the low and high population scenarios combined with low (solid lines) and high (dashed lines) GDP/capita scenarios; and (b) variation of world primary power demand for low population and GDP/capita growth or high population and GDP/capita growth combined with energy intensity reductions of 1 per cent/year (upper curves) or 2 per cent/year rate of reduction (lower curves)

CO₂ emissions are shown in Figure 1.2a for four scenarios:

1. high population, high GDP/capita, low improvement in energy intensity, low C-free power;
2. high population, high GDP/capita, high improvement in energy intensity, low C-free power;
3. high population, high GDP/capita, high improvement in energy intensity, high C-free power;
4. low population, low GDP/capita, high improvement in energy intensity, high C-free power.

Figure 1.2 Variation in CO₂ emissions for (a) Scenarios 1, 2, 3 and 4, and (b) Scenarios 1, 2a, 3a and 4

In Scenario 1, CO₂ emissions rise to 28GtC/yr and in Scenario 2 they peak at 9.7GtC/yr around 2050, while in Scenarios 3 and 4, emissions are eliminated by 2095 and 2070, respectively. Scenario 3 is consistent with the emission reductions needed to stabilize atmospheric CO₂ at 450ppmv, while Scenario 4 provides a margin of safety (given uncertain climate–carbon cycle feedbacks) for stabilization at 450ppmv.

From Figure 1.2a, it appears that the single most important factor in reducing CO₂ emissions is to increase the rate of improvement of energy intensity from 1 per cent/year to 2 per cent/year; the impact of quadrupling the rate of growth in C-free power, or the combined effect of lower population and GDP/capita growth, is substantially less. However, the relative impact of the different changes depends on the order in which they are implemented. This is illustrated in Figure 1.2b, which shows CO₂ emissions for Scenarios 1 and 4 as well as for the following:

2a low population, low GDP/capita, low energy intensity improvement, low C-free power;

3a low population, low GDP/capita, high energy intensity improvement, low C-free power.

Now, the combined effect of low population and low GDP/capita, when implemented first, is comparable to the effect of the higher rate of improvement in energy intensity when it is implemented first. Significant economic growth is of course needed in the developing countries in order to improve the material standard of living, but beyond some level of wealth, long since achieved in the developed countries, economic growth should no longer be the goal. Rather, the underlying goal should be human happiness that, once basic human needs are satisfied, is related to many non-material factors, including the diversity and richness of human relationships (family, friends, community), and not the accumulation of material wealth.

Figure 1.3a illustrates the tradeoffs between the product of future population and GDP/capita, the rate of reduction in energy intensity and the amount of C-free power that would need to be installed by 2050 in order for the CO₂ concentration not to exceed 450ppmv. Shown is the total primary power demand in 2050 as a function of the rate of reduction in energy intensity, in comparison to the fossil fuel power permitted in 2050, assuming either high population combined with high GDP/capita, or low population combined with low GDP/capita. The difference between the primary power demand and the permitted fossil fuel primary power gives the required C-free primary power, which is shown in Figure 1.3b for 2050 in comparison to the global primary power supply in 2000. Average global primary power supply in 2005 was 15.3TW, of which 12.0TW were from fossil fuels and 3.3TW from carbon-free sources. Energy intensity decreased at an average rate of 1.07 per cent/year during the period 1965–2005, and if it were to decrease at 1 per cent/year through to 2050, global primary power demand in 2050 would be 22TW and 31TW for the low and high population and GDP/capita scenarios, respectively. The permitted fossil fuel use supplies 6.0TW of primary power, so the required C-free primary power in 2050 is 16–25TW. If global average energy intensity decreases at 2.5 per cent/year, the required C-free power in 2050 is 5.2–9.6TW, or two to four times the present non-nuclear world C-free power supply of 2.45TW. The required C-free power under the low population and GDP/capita scenario is only 54 per cent that of the high population and GDP/capita scenario, which underlines the importance of low population growth and a moderation in the rate of growth of GDP/capita.

Figure 1.3 (a) Primary power demand in 2050, as a function of the rate of decrease of global energy intensity for the high population and GDP/capita or low population and GDP/capita scenarios, and the approximate permitted fossil fuel power in 2050 if atmospheric CO₂ is to be stabilized 450ppmv; and (b) amount of C-free power required in 2050 for the same conditions as in (a), and global primary power and C-free primary power supply in 2005

Volume 1 deals comprehensively with the prospects for accelerating the rate of decrease in energy intensity, and also touches upon the issues of growth in population and in GDP/capita. Volume 2 deals with the remaining factor in determining future CO₂ emissions: the rate at which C-free sources of energy can be deployed and ultimate limits on the deployment of C-free energy sources. The magnitude of the C-free challenge depends on how successful we are in reducing the growth in world energy demand. Under anything close to a BAU pathway with regard to energy demand, renewable energy sources simply will not be able to satisfy a large part of, much less all of, our energy needs within this century. It is therefore pertinent to briefly review the findings from Volume 1 concerning the potential to rein in our at present insatiable demand for ever more energy, before proceeding to assess the prospects for ramping up the C-free energy supply....

Table of contents

• Cover
• Half Title
• Title Page
• Copyright
• Dedication
• Contents
• List of figures, tables and boxes
• Preface
• Online supplemental material
• Acknowledgements
• Chapter highlights
• List of abbreviations
• Chapter 1: Introduction and Key Points from Volume 1
• Chapter 2: Solar Energy
• Chapter 3: Wind Energy
• Chapter 4: Biomass Energy
• Chapter 5: Geothermal Energy
• Chapter 6: Hydroelectric Power
• Chapter 7: Ocean Energy
• Chapter 8: Nuclear Energy
• Chapter 9: Carbon Capture and Storage
• Chapter 10: The Hydrogen Economy
• Chapter 11: Community-Integrated Energy Systems with Renewable Energy
• Chapter 12: Integrated Scenarios for the Future
• Chapter 13: Policy Sketch and Concluding Thoughts
• Appendix A Prefixes and Conversion Factors
• Appendix B Computing the Embodied Energy of Manufactured Materials
• Appendix C Financial Parameters
• Appendix D Heating Values of Fuels and Energy Equivalents
• Appendix E Websites with More Information
• Appendix F Software Tools for the Analysis of Renewable Energy
• References
• Index