World energy demand and supply

Most of the energy we use can be traced back to the Sun. In the case of fossil fuels (coal, oil and gas) it has been stored away over millions of years in the past. If wood (or other biomass including animal and vegetable oils), hydropower, wind or solar energy itself is used, the energy has either been converted from sunlight almost immediately or has been stored for at most a few years. These latter sources of energy are renewable; they will be considered in more detail later in the chapter. The other forms of energy that do not originate with the Sun are nuclear energy and geothermal energy, both of which result from the presence of radioactive elements in the Earth when it was formed.

Until the Industrial Revolution, energy for human society was provided from 'traditional' sources - wood and other biomass and animal power. Since 1860, as industry has developed, the rate of energy use has multiplied by about a factor of over 30 (Figure 11.1), at first mostly through the use of coal, followed, since about 1950, by rapidly increasing use of oil and then more recently by the use of natural gas. In 2005 the world consumption of primary energy was about 11 400 million tonnes of oil equivalent (toe). This can be converted into physical energy units to give an average rate of primary energy use of about 15 million million watts (or 15 terawatts = 15 x 1012 W).1

Great disparities exist in the amount of energy used per person in various parts of the world. The 2 billion poorest people in the world (less than $US1000 annual income per capita) each use an average of only 0.2 toe of energy annually while the billion richest in the world (more than $US22 000 annual income per capita) use nearly 25 times that amount at 5 toe per capita annually.2 The average annual energy use per capita in the world is about 1.7 toe, an average consumption of energy of about 2.2 kilowatts (kW). The highest rates of energy consumption are in North America where the average citizen consumes an average of about 11 kW. About one-third of the world's population rely wholly on traditional fuels (wood, dung, rice husks, other forms of 'biofuels') and do not currently have access to commercial energy in any of its forms.

In Figure 11.2 is shown how the energy we consume is generated and used. Also summarised are the energy flows from source to users in the main sectors and the size of the various resources that are available using conventional technologies. Taking the world average approximately 25% of primary energy is used in transport, 35% in industry and 40% in buildings (two-thirds in residential buildings and one-third in commercial buildings). It is also interesting to know how much energy is used in the form of electricity. Rather more than one-third of primary energy goes to make electricity at an average efficiency of conversion of about one-third. Of this electrical power about half,

Energy Supply Global Warming

StatoilHydra's Sleipner T gas platform off the Norwegian coast which is sequestering one million tonnes of carbon dioxide per year.

Year

Figure 11.1 Growth in the rate of primary energy use and in the sources of energy from 1860 to 2005 in thousand millions of tonnes of oil equivalent (Gtoe) per year. In terms of primary energy units, 1 Gtoe = 41.9 exajoules. Of the 'other' in 2005, approximately 1.2 Gtoe is attributed to traditional fuels, 0.7 Gtoe to nuclear energy and 0.3 Gtoe to hydropower and other renewables (source for data up to 2000: Report of G8 Renewable Energy Task Force, July 2001; from 2000 to 2005 Fig. TS 13 in IPCC AR4 WGIII 2007).

Year

Figure 11.1 Growth in the rate of primary energy use and in the sources of energy from 1860 to 2005 in thousand millions of tonnes of oil equivalent (Gtoe) per year. In terms of primary energy units, 1 Gtoe = 41.9 exajoules. Of the 'other' in 2005, approximately 1.2 Gtoe is attributed to traditional fuels, 0.7 Gtoe to nuclear energy and 0.3 Gtoe to hydropower and other renewables (source for data up to 2000: Report of G8 Renewable Energy Task Force, July 2001; from 2000 to 2005 Fig. TS 13 in IPCC AR4 WGIII 2007).

on average, is utilised by industry and the other half in commercial activities and in homes.

How much is spent on energy? Taking the world as a whole, the amount spent per year by the average person for the 1.7 toe of energy used is about 5% of annual income. Despite the very large disparity in incomes, the proportion spent on primary energy is much the same in developed countries and developing ones.

How about energy for the future? If we continue to generate most of our energy from coal, oil and gas, do we have enough to keep us going? Current knowledge of proven recoverable reserves (Figure 11.2) indicates that at current rates of use, known reserves of fossil fuel will meet demand at least until 2050. But before then, if demand continues to expand, oil and gas production will come under increasing pressure. Further exploration will be stimulated, which will lead to the exploitation of more sources, although increased difficulty of extraction can be expected to lead to a rise in price. So far as coal is concerned, there are operating mines with resources for production for well over 100 years.

Estimates have also been made of the ultimately recoverable fossil fuel reserves, defined as those potentially recoverable assuming high but not prohibitive prices and no significant bans on exploitation. Although these are bound to be somewhat speculative, they show that, at current rates of use, reserves

Electric Circuits Model House

Figure 11.2 Global energy flows (EJ in 2004) from primary energy through carriers to end-users and losses in transmission, etc. Related carbon dioxide emissions from coal, oil and gas combustion are also shown as well as the size of known resources. Further energy conversions occur in the end-use sectors. Peat is included with coal, organic waste is included with biomass. The resource efficiency ratio by which fast-neutron technology increases the power-generation capability per tonne of natural uranium varies greatly in different assessments. In this diagram the ratio used is up to 240 : 1.

Figure 11.2 Global energy flows (EJ in 2004) from primary energy through carriers to end-users and losses in transmission, etc. Related carbon dioxide emissions from coal, oil and gas combustion are also shown as well as the size of known resources. Further energy conversions occur in the end-use sectors. Peat is included with coal, organic waste is included with biomass. The resource efficiency ratio by which fast-neutron technology increases the power-generation capability per tonne of natural uranium varies greatly in different assessments. In this diagram the ratio used is up to 240 : 1.

of oil and gas are likely to be available for 100 years and of coal for more than 1000 years. In addition to fossil fuel reserves considered now to be potentially recoverable there are reserves not included in Figure 11.2, such as the methane hydrates, which are probably very large in quantity but from which extraction would be much more difficult.

Likely reserves of uranium for nuclear power stations should also be included in this list. When converted to the same units (assuming their use in 'fast' reactors) they are believed to be substantially greater than likely fossil fuel reserves (Figure 11.2).

Human-made lights which highlight developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States and Japan.

It is considerations other than availability, in particular environmental considerations, that will provide limitations on fossil fuel use.

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