| Energy and water interdependencies |
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| Friday, 06 November 2009 06:04 |
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Globally, agriculture utilises nearly 70% of the freshwater taken from rivers, lakes and aquifers, while the energy and industry sectors together consume 20% (UN World Water Development Report, WWDR-3 – see Figure 1 - See Below). On the other hand, transport (29%) and industry (27%) account for major portions of energy consumption, while agriculture uses relatively little (2%) – see Figure 2 - see below. Modern industrial societies have been accustomed to abundant and cheap sources of both elements, aside from occasional droughts and the 1970s oil crises. In many developing countries, however, energy and water shortages remain a daily challenge for millions of people. Recently, global concern about energy security and the finiteness of fossil fuels has come to the fore once again. And regional and national water security has become an increasingly prominent issue in many parts of the world, particularly in the context of climate change. While energy and water are each critically important in their own right, they are also intimately connected in many ways. Their interdependence is now coming under increasing scrutiny as sustainability challenges intensify. Energy dependencies on water The dependence of energy on water dates back to pre-industrial energy systems. Wood, as the major source of fuel, required adequate rainfall. Water was used as a power source in mills for grinding grains, while most in-land bulk transport was water-borne on rivers and canals. Modern energy systems are dependent on water to some degree. Water is used at various stages of the production process: mining, manufacturing of energy infrastructure and during power generation. Perhaps most significantly, all thermal power generation requires water for cooling. Coal-fired power stations boil water to drive steam turbines in addition to using water for cooling. Nuclear power plants also require water for cooling – but in some instances, they can be located on coastlines so as to utilise seawater instead of fresh water. Coal-to-liquids and tar sand refining consume large amounts of fresh water, too. Some renewable energy sources also rely on water inputs, the most obvious being hydroelectricity. About 20% of the world’s electrical energy is derived from hydro power. Some water-abundant countries – such as Austria and Sweden – rely on hydro for close to half of their electricity generation. Some types of solar thermal power plants need water for cooling, while others utilise water for washing mirrors. Procuring the water can be a real problem in sunshine-abundant desert areas that are otherwise obvious locations for solar farms. Geothermal power plants rely on water that is heated naturally underground to drive steam turbines. Crops produced as feedstock for biofuels – e.g. sugar cane and maize for ethanol, and rapeseed for biodiesel – need large water inputs. An estimated 2% of world irrigation water is used for biofuels production (cited in WWDR-3). It has further been estimated that each litre of biofuel requires an average of 2 500 litres of water – enough to produce food for one person for a day. The Jatropha Curcas plant has been touted as a less thirsty feedstock for biodiesel production, as it can grow in more arid areas. However, yields of the oil-bearing fruit are still related to water availability and in some areas irrigation is required to produce commercially viable yields. Another potential feedstock for biodiesel, which has yet to be successfully commercialised, is algae. Algae use sunlight to convert water and carbon dioxide into chemical energy. Fortunately, this need not be fresh water but can be waste water and for some algae species, seawater. Advocates suggest cultivating algae in large ponds in desert regions to take advantage of the abundant solar energy, but access to water is an obvious issue in such areas unless they are located along coastlines. Finally, hydrogen is an energy carrier that can be produced through the electrolysis of water. However, the availability of sufficient water would be just one of many constraints on large-scale hydrogen production. Water dependencies on energy The provision of water to agricultural, industrial and domestic consumers often requires substantial amounts of energy. According to the UN’s WWDR-3, it has been estimated that 7% of all energy is used for water extraction, treatment and distribution. In the first place, energy is used to extract groundwater, such as when electric pumps tap underground aquifers to provide irrigation for agriculture. The construction of storage and distribution infrastructure such as dams, aquifers and pipelines also consumes energy. So does the pumping of water through distribution systems that cannot rely on gravity. Purifying water and treating wastewater also consume substantial amounts of energy. Yet another significant use of energy is for heating water for domestic or commercial purposes. Desalination of seawater is performed in some water-scarce countries. This is a highly energy-intensive process that requires a cheap source of energy as well as costly infrastructure. About three-quarters of global desalination capacity is located in the Middle East, a region that is energy rich but water scarce. Globally, desalination at present utilises a minute fraction of total energy supply, and it seems unlikely to grow much due to energy and cost constraints. Spill-overs Another linkage between energy and water arises through the impact of energy production and consumption on water quality. Unfortunately, the production of energy may result in significant pollution of water sources. This can occur in various ways. Acid mine drainage is a huge drawback of coal and uranium mining, particularly where mines are proximate to cultivated lands as yields can be compromised. Oil spillages have been known to have devastating effects on water quality, ecosystems and human health in certain regions; Ecuador and Nigeria are notable examples. The production of synthetic oil from the tar sands in Canada is having a major polluting impact on some of Alberta’s river systems. Radioactive contamination of water around nuclear power plants or waste disposal sites is another potential problem. The production of bioenergy crops can impair downstream water quality if herbicides, pesticides and fertilisers are used in the farming process, as is the norm in industrialised economies. Pollution of water sources also occurs as a result of energy consumption. A prime example is acid rain from sulphur dioxide emissions from coal combustion. Another is the acidification of lakes through the absorption of carbon dioxide, a byproduct of fossil fuel consumption. Challenges to security of supply Energy and water security vary widely across the globe, but face some similar and interrelated challenges. An important distinction needs to be drawn between economic and physical aspects of resource security. At present, economic energy and water insecurity persists for hundreds of millions of people in developing countries – particularly in sub-Saharan Africa – as a result of extensive poverty at the household level and a lack of infrastructure at national levels (see Figure 3 - See Below). Currently, richer countries are able to afford the infrastructure and imports to ensure energy and water security, although some areas do already face physical water scarcity, such as the south-western United States and eastern Australia. Globally, challenges for future physical energy and water security emanate from both demand and supply sides of the equation. There are two main sources of rising demand pressure on both water and energy supplies. The first is growth in the world’s population, which is expanding by about 80 million persons a year. The second is rising affluence – as measured by per capita incomes – in many developing countries, particularly China and India. On the energy supply side, the depletion of fossil fuels – particularly the now widely acknowledged impending peak and decline in oil production – could substantially intensify competition for energy resources in the years ahead. As far as water is concerned, there are at least two main threats to future supplies. The first is the ongoing degradation of water quality resulting from polluting agricultural and industrial activities. The second challenge is climate change, which is expected to result in an increasing frequency of droughts and floods, a trend which has already been observed over the past half century, according to the WWDR-3 report. The melting of glaciers threatens stable runoffs and downstream agriculture and industry in several parts of the world, notably in South Asia and China, which rely heavily on melt-water from the Himalayan glaciers. Climate change is characterised by many feedback loops, some of which involve the energy-water linkage. Climate-related reductions in river flows in some parts of the world, such as East Africa and Asia, have constrained the generation of hydropower. In addition, the warming of river water needed for cooling nuclear power plants resulted in shutdowns of several plants in Europe during heat waves in recent years. In the face of demand and supply pressures, there is a significant risk of conflict over water and energy resources in the coming decades, both internationally and intra-nationally. Perhaps paradoxically, conflict could also arise as a result of a local abundance of some energy resource as different factions – or nations – strive to gain control. The Middle East is an obvious hot spot in this regard, given that it is home to over 60% of known and expected remaining oil reserves (Figure 4 - See below). The region is also one of the most water-stressed in the world, a fact that adds to geopolitical tensions. Southern Africa: water a limiting factor? Southern Africa in general, and South Africa in particular, are relatively well endowed with energy resources, including large coal and uranium deposits, some natural gas, and abundant solar energy. However, the region is relatively poorly endowed with water resources. The linkage between energy and water security has recently been highlighted by Dr Anthony Turton, director of Touchstone Resources. In Turton’s view, reported by Engineering News, water represents the primary constraint on the expansion of energy, and possibly on economic development more broadly. According to Turton, there is little or no scope for the construction of more dams in South Africa. At the same time, acid mine drainage and acid rain resulting from coal mining and combustion, respectively, are negatively impacting on agricultural production, particularly in prime maize-growing areas. The two largest energy producers in southern Africa, Eskom and Sasol, are also very significant consumers of water. According to Eskom’s 2008 Annual Report, the company consumes about 2% of South Africa’s fresh water annually. In view of the country’s water scarcity, Eskom has pioneered a dry cooling system at its Matimba and Kendal coal-fired power stations, which have substantially lower water consumption than other plants. Water availability could become a key constraint on the operation of some of Eskom’s coal plants, and particularly on the construction of new power stations using coal from the Waterberg fields in Limpopo. The same situation faces Sasol, which is investigating the feasibility of constructing a new coal-to-liquids plant to take advantage of these deposits. Sasol already consumes approximately 3.5% of the Vaal system water supply. At a national level, security of supply has certain parallels in the cases of energy and water. In South Africa, coal is increasingly being viewed by the government as a strategic national asset. With Eskom’s demand projected to rise from 125 million tons (mt) per year in 2007 to more than 180 mt by 2018, there are serious questions to be asked about the sustainability of current levels of coal exports. Energy is also exported indirectly via minerals, processed metals such as aluminium, and manufactured goods in general. A similar issue of national security of supply pertains to water. Although South Africa does not export water directly, it does export water in the form of agricultural produce, such as fruit and wine from the Western Cape and maize from the ‘highveld’. Manufactured exports also embody a certain volume of water. This ‘virtual’ trade in water carries a hidden opportunity cost and may come under increasing scrutiny in a water-constrained future. Climate change is expected to hit southern Africa particularly hard, with drier conditions in the western half and more extreme patterns of rainfall in the eastern half of the region. Overall, the region is set to experience hotter temperatures and intensified evaporation, which will negatively impact on water supplies. Integrated planning for sustainability The interdependencies between energy and water imply that planning and policy formulation for both resources should be integrated where possible. Otherwise, outcomes may be perverse, such as when an abundance of one element results in unsustainable rates of use of the other. For example, cheap electricity has allowed extensive irrigation from underground aquifers, which have been depleted at unsustainable rates in various parts of the world, such as the mid-western US and India. The basic principle underlying integrated planning for water and energy should be long-term sustainability – using renewable resources without degrading them. Water is a renewable resource that follows a natural cycle, but its quality needs to be preserved. In contrast, fossil fuels – which currently contribute 80% of world primary energy supply – are of course a finite endowment of a non-renewable resource and are subject to depletion. Over time, they need to be replaced by renewable energy sources of energy such as solar, wind and ocean power. These are much less polluting than fossil fuels and many are also less thirsty for water, since they do not require cooling, although some water is used at the manufacturing stage. Human societies need to adopt agricultural, industrial and domestic consumption practices that are sustainable in their use of both water and energy. Conservation of energy and water – through the identification and reduction of wastage – should be a top priority. Efforts to conserve either water or energy will bring about savings in the other resource. The natural water cycle can be augmented by recycling systems for industrial and residential consumers. Many cities already recycle water, but there is much scope for expansion – although the recycling process requires energy inputs. The next step should be to boost efficiency in the use of resources. There is huge potential for raising industrial water productivity, as illustrated in Figure 5 - See below. Ways to minimise the use of energy for delivering water supplies include the harvesting of rainwater by households and businesses; the use of gravity-based distribution and irrigation systems wherever possible; and curbs on the growth of cities that are located far from water sources. Energy efficiency can be enhanced at the production, distribution and consumption stages through the deployment of improved technologies. Cogeneration harnesses some of the residual heat from energy production processes and therefore reduces the need for water for cooling at the same time as capturing energy that is otherwise wasted. Cogeneration can also be used in combined power and desalination plants to produce potable water. In Japan and Russia, some nuclear power plants are used in this way. Conservation and efficiency measures can save consumers money and boost the competitive advantage of businesses. Government policies and regulations, such as efficiency standards and tariff structures, are important for promoting sustainable resource use. Price incentives play a pivotal role in the way that water and energy are consumed. The challenge is to strike a balance between setting tariffs that are high enough for businesses and households to value these essential resources appropriately and not waste them, while also ensuring affordability and access to these basic necessities for the poor. An option is a stepped tariff system for water and electricity which includes a free basic allowance and beyond that, rates that progressively increase with the volume of consumption. Key 21st century concerns Energy and water security may vie with each other to top political agendas this century. Societies cannot afford to treat these issues in isolation, or delay necessary actions. Water scarcity can be a limiting factor for conventional energy production. The utilisation of water-intensive, dirty fossil energy sources can compromise water quality and availability. Investing in certain renewable energies will help to bolster both energy security and water security, but other renewable technologies rely quite heavily on water. Thus conservation and efficiency measures are also essential at the production and consumption stages alike. Humanity faces the tremendous challenge of shifting toward more sustainable agricultural and industrial processes, while maintaining sufficient productivity levels and expanding provision of basic services to meet the needs of the world’s population. Jeremy Wakeford
Figure 1: World water demand by sector
Figure 4 : World oil reserves Figure 5:
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Water and energy are both fundamental requirements for the functioning and maintenance of living systems, from individual organisms to complex human societies
Eskom Power Gauge
