Carbonfree electricity supply

We have already noted that moving as rapidly as possible to carbon-free electricity is key to achieving the level of overall reductions of carbon dioxide emissions required by 2030 and 2050. Contributions to this movement can come in five ways: (1) increases in efficiency, (2) decreases in carbon intensity, (3) by widespread deployment of carbon capture and storage, (4) by the use of nuclear energy, (5) through the use of all possible renewable energies. From the long-term point of view, (1) and (5) are the most important. I will now briefly address each in turn.

First, regarding energy efficiency, the efficiency of coal-fired power stations, for instance, has improved from about 32%, a typical value of 20 or 30 years ago, to about 42% for a pressurised, fluidised-bed combustion plant of today. Gas turbine technology has also improved providing efficiency improvements such that efficiencies approaching 60% are reached by large modern gas-turbine-combined cycle plants. Large gains in overall efficiency are also available by making sure that the large quantities of low-grade heat generated by power stations is not wasted but utilised, for instance in CHP schemes. For such co-generation, the efficiencies attainable in the use of the energy from combustion of the fuel are typically around 80%. The wider deployment therefore of CHP in building schemes or in industries where both heat and power are required is an effective way of substantially increasing efficiency at the same time as producing savings in economic terms.29

Second, regarding carbon intensity, for a given production of energy, the carbon dioxide emissions from natural gas are 25% less than those from oil and 40% less than those from coal. By switching fuel to gas, therefore, substantial emissions savings can be made.

Third, an alternative to moving away from fossil fuel sources of energy is to prevent the carbon dioxide from fossil fuel burning from entering the atmosphere by the employment of carbon capture and storage (CCS).30 Carbon dioxide capture is arranged either by removing it from the flue gases in a power station, or the fossil fuel feedstock can, in a gasification plant, be converted through the use of steam,31 to carbon dioxide and hydrogen (Figure 11.11). The carbon dioxide is then relatively easy to remove and the hydrogen used as a versatile fuel. The latter option will become more attractive when the technical and logistic problems of the large-scale use of hydrogen in fuel cells to generate electricity have been overcome - this is mentioned again later in the chapter.

Various options are possible for the disposal (or sequestration) of the large amounts of carbon dioxide that result. For instance, the carbon dioxide can be pumped into spent oil or gas wells, into deep saline reservoirs or into unminable coal seams. Other suggestions have also been made such as pumping it into the deep ocean, but these are more speculative and need careful research and assessment before they can be realistically put forward. In the most favourable circumstances (for instance when power stations are close to suitable reservoirs and when the extraction cost is relatively small), the cost of removal, although significant, is only a small fraction of the total energy cost. The IPCC has estimated a range of $US15-80 per tonne CO2 for the added cost - the cost of extraction being generally much larger than the cost of storage.

The global potential for storage in geological formations is large and has been estimated to be at least 2000 Gt carbon dioxide and possibly much larger. The likely rate of leakage is believed to be very low although more research is required into this rate and also into the risk of rapid release as a result, for instance, of seismic activity.

Figure 11.11 Schematic of infrastructure for carbon dioxide Capture, transport and Storage. It illustrates coal as the fuel, but it applies to oil- or gas-fired power plants also or to any large concentrated source of carbon dioxide.

Because of the rapid increase during the last few years in the number of new coal-fired power stations constructed globally (for instance, China is currently adding capacity of 2 GW per week), the need for CCS technology has become more acute. A substantial number of demonstration plants employing CCS need to be built before 2015 in the USA, Europe, China, Australia and other countries where coal remains a major source of power generation.32 Rapid deployment of CCS to all new coal-fired power stations would enable continuing use of fossil fuels without the deleterious effects of carbon dioxide emissions.

A fourth source of carbon-free energy is nuclear energy.33 It has considerable attractiveness from the point of view of sustainable development because it does not produce greenhouse gas emissions (apart from the relatively small amount associated with the materials employed in nuclear power station construction) and because the rate at which it uses up resources of radioactive material is small compared to the total resource available. It is most efficiently generated in large units, so is suitable for supplying power to national grids or to large urban conurbations, but not for small, more localised supplies. An advantage of nuclear energy installations is that the technology is known; they can be built now and therefore contribute to the reduction of carbon dioxide emissions in the short term. The cost of nuclear energy compared with energy from fossil fuel sources is often a subject of debate; exactly where it falls in relation to the others depends on the return expected on the upfront capital cost and on the cost of decommissioning spent power stations (including the cost of nuclear waste disposal), which represent a significant element of the total. Recent estimates are that the cost of nuclear electricity is similar to the cost of electricity from natural gas when the additional cost of capture and sequestration of carbon dioxide is added.

The continued importance of nuclear energy is recognised in the IEA energy scenarios, which assume growth in this energy source in the twenty-first century. How much growth is limited in the short term by the shortage of personnel with the necessary skills for design and construction of nuclear power systems and by the limited facilities available for building key components. In the longer term, the amount of growth realised will depend on how well the nuclear industry is able to satisfy the general public of the safety of its operations; in particular that the risk of accidents from new installations is negligible, that nuclear waste can be safely disposed of and that dangerous nuclear material can be effectively controlled and prevented from getting into the wrong hands. Despite the substantial safeguards that are in place internationally, this last possibility of the proliferation of dangerous nuclear material is the one that, in my view, presents the strongest argument for questioning the widespread growth of nuclear energy.34 However, proposals are now being pursued for a fourth generation of nuclear power plants based on more advanced reactors that promise to be safer, less productive of radioactive waste and with much less danger of leading to nuclear proliferation. None of these, however, are likely to be built before 2020 and maybe 2030.

A further nuclear energy source with great potential in the more distant future depends on fusion rather than fission (see box below p. 377).

The fifth source of carbon-free energy is from the variety of renewable energies that have been identified and that are available. To put renewable energy in context it is relevant to realise that the energy incident on the Earth from the Sun amounts to about 180 000 million million watts (or 180 000 terawatts, 1 TW = 1012 W). This is about 12 000 times the world's average energy use of about 15 million million watts (15 TW). As much energy arrives at the Earth from the Sun in 40 minutes as we use in a whole year. So, providing we can harness it satisfactorily and economically, there is plenty of renewable energy coming in from the Sun to provide for all the demands human society can conceivably make.

There are many ways in which solar energy is converted into forms that we can use; it is instructive to look at the efficiencies of these conversions. If the solar energy is concentrated, by mirrors for instance, almost all of it can be made available as heat energy. Between 1% and 2% of solar energy is converted through atmospheric circulation into wind energy, which although concentrated in windy places is still distributed through the whole atmosphere. About 20% of solar energy is used in evaporating water from the Earth's surface which eventually falls as precipitation, giving the possibility of hydropower. Living material turns sunlight into energy through photosynthesis with an efficiency of around 1% for the best crops. Finally, photovoltaic (PV) cells convert sunlight into electricity with an efficiency that for the best modern cells can be over 20%.

Around the year 1900, very early in the production of commercial electricity, water power was an obvious source and from the beginning made an important contribution. Hydroelectric schemes now supply about 18% of the world's electricity. Other renewable sources of electricity, however, have been dependent on recent technology for their implementation. In 2005, only about 4% of the world's electricity came from renewable sources other than large hydro (these are often collectively known as 'new renewables').35 Over half of this was from 'modern' biomass (called 'modern' when it contributes to commercial energy to distinguish it from traditional biomass), the rest being shared between solar, wind energy, geothermal, small hydro and marine sources.

Under the IEA BLUE Map scenario (Figure 11.12), all renewable sources will be contributing by 2050 45% of total electricity production. The main growth expected is in energy from 'modern' biomass and from solar and wind energy sources. In the following paragraphs, the main renewable sources are described in turn and their possibilities for growth considered. Most of them are employed for the production of electricity through mechanical means (for hydro and wind power), through heat engines (for biomass and solar thermal) and through direct conversion from sunlight (solar PV). In the case of biomass, liquid or gaseous fuels can also be produced.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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