Shell Briefing Service Renewable energy Number one, 1994 World requirements for energy are growing, especially in the developing world where demand is likely to double over the next 30 years. Fossil fuels will remain the backbone of energy supplies for the foreseeable future, but other types of energy resources may ?nd increasing use, providing they are economically and environmentally sustainable. This Shell Brie?ng Service describes the current contribution of renewable sources of energy to world energy requirements and discusses their future potential. In the ?rst section, the prob- lems of meeting the world?s growing The Shell Brie?ng Service is produced as an information brief for companies of the Royal Dutch/Shell Group. This publication is one of a range published by Group Public Affairs, Shell International Petroleum Company Ltd, Shell Centre, London SE1 7NA, England, covering aspects of the oil, gas, coal, chemicals, metals and forestry businesses. For further copies, and for details of other titles available in English or as translations, please contact the Public Affairs Department of your local Shell company. Alternatively, write to the above address or Fax 071 934 5555 (London) quoting department reference or telephone 071 934 5293. Shell International Petroleum Company Limited (SIPC) 1994. Permission to reproduce any part of this publication should be sought from SIPC. Agreement will normally be given, provided that the source is acknowledged, except for parts shown to be from other sources. Designed by James Cook Graphics, Godalming, Surrey. Printed in England by Barwell Colour Print Ltd. 117883/25m/1.94. demands for energy in a sustainable fashion are described. The following two sections describe the various sources of renewable energy, in particular the ?new renewables solar, wind, modern biomass, geothermal and water-based systems other than conventional large scale hydropower. The ?nal section outlines some of the initiatives taken by governments and other institutions to promote sustainable energy develop- ment, including the use of renewables. It concludes that a gradual evolution towards a more complex energy supply pattern is more likely than sudden dramatic changes in energy supplies. Note on units of energy The standard unit for measuring energy is the joule (J). Multiples such as the gigajoule (109) are used throughout the energy industry. The elec- tricity industry more commonly uses units based on the kilowatt hour (lkWh 3600 kJ). A kilowatt (kW) is a ?ow of energy. A kilowatt hour (kWh) is a stock of energy. kWe kilowatt of electricity bdoe barrel a day oil equivalent toe tonne of oil equivalent (kilo) thousand (103) (mega) 106 (giga) 109 (tera) 1012 (peta) 1015 As a rough guide: 1 can run one cooker hotplate for one hour. can run a motor car for 1000 km. is the energy typically used by a medium-sized town in one day. is the energy supplied by a large nuclear power plant over about two months when operated at full load. Energy and in environment People need energy to meet basic needs such as heating and lighting, but also to provide the services which contribute to modern standards of living including rapid trans- portation, global communications and the manufacture of consumer goods. For more than a century, the world?s commercial energy needs have been met predominantly by fossil fuels ?rst coal, then oil and also, more recently, natural gas. Fossil fuels account for 85% of world demand. Nuclear energy contributes just over ?ve per cent, hydropower some six per cent, while commer- cial renewables biomass, solar power, wind, geothermal account for some four million bdoe or less than two per cent (Figure 1). However, if non-commercial energy is included, biomass is estimated to contribute some 25 million bdoe equivalent to some 14% of the world?s energy. Much of this is in the developing world which depends on biomass energy for more than a third of its total energy requirements. Demand for energy is growing to meet the needs of growing populations. The current world population of ?ve billion could Total: 168.3 million bdoe? Oil Coal Modern Nuclear Hydro renewables *Estimated Figure 1 World commercial energy demand Figure 2 Development rise to almost eight billion by 2020, more and than three-quarters of whom will live in environment developing countries. For these people, Urban 002 particulate Urban 802 emissions concentrations concentrations per head Lack of urban 8O sanitation 60 40 Waste 20 perhead 100 1000 10 000 Index GNP per head (peak 100) Source: World Bank (based on cross-section in 19803) economic development is the key to alleviating Widespread poverty and the environmental degradation that is associated With it poor housing and sanitation, polluted water supplies, deforestation caused by reliance on non-sustainable use of fuel- wood. In developing countries, the services provided by energy are directly linked to a better environment and quality of life. In the developed world, the focus is on reducing the impact of energy use on the environment. Burning fossil fuels results in emissions of sulphur dioxide, nitrogen oxides and volatile organic compounds which contribute to ?acid rain? and photochemical smogs. Fossil fuels also emit carbon dioxide (002), one of the main ?greenhouse gases?. There is concern that increased concentra- tions of COZ in the atmosphere could lead to an augmented greenhouse effect and possible global warming. Figure 2 shows how environ- mental priorities differ depending on a country?s state of economic development. Reconciling such different priorities has become a matter of increasing international debate. In the Brundtland report ?Our Common Future? published in 1987, the concept of ?sustainable development? was de?ned as meeting the needs of the present without compromising the ability of future generations to meet their own needs?. In June 1992, the UN Conference on Environment and Development (UNCED) adopted Agenda 21 which contains many proposals concerning the role of energy in sustainable develop- ment. For instance, governments are encour- aged to promote greater ef?ciency in the use of energy and resources, to develop urban transport policies to reduce transport demand and hence traf?c congestion, and to look at the implications of pricing policies which fully take into account environmental costs. A new UN Commission on Sustainable Development has been set up which will meet regularly to review governments? progress towards implementing Agenda 21. To ensure adequate energy supplies for the future, all types of energy resources which are economically and environmentally sustainable will need to be considered. Although fossil fuel resources are ultimately ?nite, there will be no shortages of fossil fuels for the foreseeable future. At current rates of production, the world?s proven oil reserves Will last for more than 40 years, natural gas for some 60 years and coal for more than 200 years. These ?gures do not take into account the fact that new reserves are still being discovered and technologies developed which enable a greater proportion of the resources to be extracted. Ultimate hydrocarbon resources, which include deposits as yet undiscovered, are even greater. The inherent bene?ts of fossil fuels are such that they are likely to continue to form the backbone of energy supplies well into the future, providing they are extracted and used ef?ciently and the negative impact of their products and any polluting discharges are minimised. In the longer term, nuclear power may make a major contribution to meeting increased energy demands. However, prob? lems of weapons proliferation, plant safety, waste disposal and rising costs have still to be solved. At present, most renewables are gener- ally too expensive, despite the fact that the costs of some technologies have already decreased and are expected to continue down- wards. For example, it is still more expensive to generate electricity from renewables than from fossil fuels and the established renew- able, hydro (Figure 3). However, as modern renewable technologies progress down the ?cost learning curve?, they bene?t from the economies already achieved by mature tech- nologies such as fossil fuel extraction. Figure 4 shows this trend for wind, which is already competitive on many sites, and photovoltaics. Photovoltaic . Solar thermal I: Tidal 5 Wave I l: Biomass El Windl Nuclear ?3 Fossil fuels ?0 Hydro la 0 2.0.49.6? Cents/kWh Note: Ranges from small scale plants (eg, PV) installed close to end use to large scale central power plants (eg, nuclear, fossil fuel) where distribution costs are not included. Although renewables offer some environ? mental bene?ts over fossil fuels, they are not free from environmental problems. For instance, wind farms occupy large land areas, have a negative visual impact, may be noisy and cause electromagnetic inter? . ference. Some of the materials in photo- voltaic (PV) cells are toxic which may cause hazards during production and disposal or if accidents such as ?res occur. Pollutants, including dioxins and chlorine, are released during direct combustion of biomass, espe- cially in the case of municipal solid waste. The impact of tidal barrages is similar to that of hydroelectric schemes namely loss of land and disruption of habitats for wildlife. If more widespread, large scale applications of renewables are introduced, the balance between their environmental bene?ts and drawbacks may change. Figure 3 Electricity generation costs, 1993 . Figure 4 Trade-offs between costs. and env1ron- Electricity from mental impact, familiar in. the context of renewables conventional energy supphes, apply cost learning increasingly to renewables. curves Costs Photovoltaics (GentS/kWh) 1976 Wind 300 200 22% 100 learning factor .- 1988 50 1982 $8 13%" 1992 learning factor 5 4' 0.1 1 10 100 1000 10,000 100,000 Cumulative sales (thousand Renewable energy is derived mainly from the sun, but also from planetary motion and from the Earth (Figure 5). Finite sources of energy are derived from the sun, nuclear reaction on the Earth and chemical reactions from mineral sources. (Fossil fuels, for instance, are stores of solar energy converted millions of years ago.) Energy from the sun for industrial processes and to generate electricity. PV systems convert sunlight directly into electric current in a semi-conductor. Solar cells, grouped together and packaged into protective enclosures called modules, form the basic building blocks of such systems. They are generally made from silicon, the Figure 5 Energy flows Source: Twidell Weir ?Renewable Energy Resources" published by Chapman Hall, UK. Figures are Infra?red radiation to space in terawatts A i 50 000 . . reflected 80 000 Sensible Solar radiation . to space heating and heating deVIces Ocean thermal energy 120 000 40 000 Latentheat absorbed Potential _p Hydropower From sun Solar on earth energy . . radiation 300 Kinetic Wind and wave energy -9 conversion 30 Photo- . l?i Blofuels From earth 30 Geothermal Geothermal Heat _p installations From planetary motion Gravitation 3 . . Orbital motion Tides i? Tidal power Renewables can be divided into: Solar energy: solar thermal systems and photovoltaics biomass wind power Hydropower and other water-based systems a Geothermal energy. Solar thermal systems use sunlight to heat water or air either directly or indirectly. Systems range from simple thermal collectors which provide low temperature heat for domestic water heating or space heating to more sophisticated systems using parabolic mirrors to provide high temperature heat second most common element in the Earth?s crust. Biomass is a collective term for plant matter created by and deriva- tives such as forest and crop residues, animal wastes and the organic content of domestic and municipal solid waste. Biomass can be used as a direct source of heat (the oldest and still the main utilisation), to produce elec- tricity or as a feedstock to produce gaseous or liquid fuels. Wind is an indirect form of solar energy since it is a result of the expansion and convection of air as solar radiation is absorbed on the Earth. Wind energy systems can be stand alone to provide mechanical energy (eg, for irrigation or drainage) or to generate electricity for local use or grid? connected, in which case a number of wind turbine generators are linked together to form part of a large electricity network. Water-based systems include hydro- power, tidal power, wave power and ocean thermal energy. Hydropower is the most highly developed of all renewables and is used to generate about a ?fth of the world?s electricity. The technology used in both large scale and ?mini? hydroelectric schemes is well established. Tidal power is similar to conventional hydroelectricity schemes apart from the fact that the head of water is obtained from the rise and fall of the tide instead of from rivers. Wave power uses the motion of water in ocean waves to move ?oating devices and generate electric power either directly or indirectly. Ocean thermal energy exists as a result of the temperature difference between the warm water at the surface of the ocean and the cold water of the ocean depths. Geothermal energy uses heat from the It is ?renewable? only if the heat extracted does not exceed that replenished from the centre of the earth and if the water which brings the heat to the surface is reinjected. Geothermal heat can be used directly for space and water heating and agriculture or to generate electricity. I History For thousands of years, renewables were virtually the only forms of energy available to humankind. Fuelwood has been used for ?res since time immemorial While Wind energy was used for sailing vessels in the Mediterranean some 5000 years ago. Windmills may have been used in India some 2500 years ago and the ancient Greeks probably used solar energy in minor ways using burning mirrors for instance. The Renaissance in Europe brought a renewed interest in technology and with it the intro- duction of several energy supply techniques based on wind and hydro power. In the 18th century, as a result of increasing shortages Figure 6 Earth?s interior such as warm water or steam trapped in underground reservoirs. of wood fuel, new processes were developed which enabled coal to be used on an indus- I I Direct solar I Biomass I Wind I Small hydro I Geothermal I Ocean Resource Magnitude laigzme Very large Large Large Large Large Distribution Worldwide Worldwide Coastal, Worldwide, Tectonic Coastal, mountains, mountains boundaries tropical plains I Variation Daily, seasonal, Seasonal, Highly Seasonal Constant Seasonal, weather- climate variable tidal dependent dependent intensity Low 1 kW /m2 Moderate Low average Moderate Low average Low peak to low 0.8 MW/km2 to low up to Technology Options Photovoltaics, Combustion, Horizontal and Low to high Steam and Low temp. low to high fermentation, vertical-aXIs head turbines binary thermodynamic temp. thermal digestion, wind-turbines and dams thermodynamic cycles, systems, gasification, wind pumps cycles, total mechanical passive liquefaction sail power flow turbines wave oscillators systems geopressured tidal dams magma and turbines Status Developmental, Some Many Mostly Some Developmental some commercial, commercial, commercial, commercial, commercial more more some developmental developmental developmental Based on Capacity <25% w/o As needed Variable intermittent High, base Intermittent World Energy factor storage, with short-term most 15-30% to base load to base load Council (WEC) intermediate biomass storage load Report 1993 'Renewable Key Materials, cost, Technology, Materials, Turbines, Exploration, Technology, Eggbgulces improvements efficiency, agriculture design, siting, cost, design, extraction, materials, Opportunities resource data and foresty resource data resource data hot dry rock and cost and management cost use, Constraints cost 1990 2020 mm Characteristics of renewables Average annual solar radiation 500?800 9 800?1100 @1100?1400 @1400?1700 01700?1900 .1900?2200 More than 2200 per square metre per year Figure 7 World average solar radiation trial scale, thus heralding the industrial revolution in northern Europe. Fossil fuels ?rst coal, then later oil and gas became increasingly dominant as industrialising societies began to enjoy the bene?ts of high quality, highly concentrated and trans- portable forms of energy. As fossil fuels became more Widely available, energy use increased dramatically and renewable energy conversion technologies such as water and Wind power were largely aban- doned in newly industrialised societies due to their low power density and relative inef?ciency. Since that time, developments in renew- ables technologies have resulted in lower costs and increased ef?ciency so that they can be regarded as potential contributors to world energy demand where the emphasis is on high quality, concentrated energy supplies. I Characteristics of renewables Renewable energy technologies range from ideas still on the drawing board to well developed techniques, from local small and medium scale systems to large engineering projects such as hydro schemes. Nevertheless, some common characteristics may be identi?ed (Figure 6). the potential resource from renewables is enormous. For instance, the total energy ?ow of sunlight intercepted by the Earth is 170 000 terawatts or about 2.5 106 million bdoe more than 10 000 times man?s annual energy requirements (Figure 5). The average annual solar radiation avail- able at the Earth?s surface varies from about 1000 kWh/m2 a year in Northern Europe to more than 2000 kWh/m2 a year in desert areas (Figure 7). Resources of renewables are dif?cult to quantify accurately as adequate surveys are not available for many countries. For instance, wind maps are often inadequate as wind regimes are affected by a range of local effects still improperly understood. Although a rough estimate of biomass resources from existing forests and crops can be made, the energy potential of these is rarely quanti?ed on the basis of possible conversion technologies. (Much biomass use eg, for fuelwood and charcoal burning is highly inef?cient.) There are few surveys of deep aquifers which may be a source of geothermal energy. The dif?culty in collecting data on renewable energy use, especially where non-commercial sources are involved, means that much of the contribu- tion of renewables goes unrecorded. Unlike fossil fuels, which are highly concentrated stores of energy, most renew- ables are diffuse energy sources. The more diffuse an energy ?ow, the harder it is to capture. As renewables have a large capture area, the collecting devices and storage systems required to harness the energy may occupy considerable land space. Capital costs of equipment are generally high, as large material and energy inputs are needed to access the wide capture area and achieve acceptable power capture. The intermittent nature of many renew- able resources may be a limitation as satis? factory storage methods have still to be found in some cases. However, such limita- tions may be overcome by using renewable supplies to meet peak daytime demands in conjunction With conventional sources or by integrating several renewables into a system where they can ?complement? each other eg, photovoltaics for peak daytime demand and biomass for base load. The potential for renewables varies on a regional scale as it is closely linked to local geography and environment. In many cases, there are ?niche? opportunities which suit particular local or regional conditions which prove economic at that level even if they do not have more general potential. Renewable energy systems are typically small to medium scale dispersed developments tailored to meet speci?c local needs. These are in complete contrast to fossil fuel developments which are based on large, international systems with a well-established infrastructure. I Potential markets for renewables The most promising markets for renewables are in heat and power generation, currently dominated by coal and gas. Between 1980 and 1990, world electricity demand increased from some 8300 a year to more than 11 500 a year. The greatest increase was in developing countries where the average annual increase in demand was three times that of developed countries. The World Bank estimates that some 600 000 of new electricity generating capacity will be needed by the end of the 1990s, more than half of which will be required by the developing countries, India and China in particular. Demand for rural electri?cation schemes for remote areas is likely to increase, especially in developing countries where many inhabitants have no access to an electricity grid. Renewables will probably take longer to make an impact on the transportation market Which is currently dominated by oil products which are versatile, easy to store and transport and have a high energy density. The internal combustion engine, run on gasoline or diesel, will continue to be the preferred choice of motorists for many years, especially given the progressive reduction in vehicle emissions achieved through improvements in vehicle technology and fuel quality. A signi?cant breakthrough in vehicle technologies such as the devel- opment of cost-effective fuel cells or elec- tricity storage devices would be required for renewables to make a major impact on transport applications. Harnessing renewable energy I Solar thermal The simplest systems for low temperature applications (less than consist of a ??at plate? collector and a storage tank. For example, in a solar water heater, water runs through pipes or channels in a collector. As the sun heats the collector, the hot water produced inside rises by natural convection to be replaced by colder water. Solar water heaters for domestic and commercial use are manufactured in many countries, especially in Australia, Israel, the USA and Japan. Solar heat can also be used as process heat for industry or agriculture (eg, crop drying) and for space heating and cooling. Where large amounts of low temperature heat are required, a solar pond may be more economic than a ?at plate collector. Solar ponds consist of several layers of salty water, with the saltiest layer on the bottom. The fresh water on top traps the heat in the higher density lower layers. As these ponds have built-in energy storage, they can be used to heat buildings in winter. They can also be used to generate electricity. To achieve higher temperatures, a solar thermal system may incorporate parabolic mirrors to concentrate sunlight. To generate electricity, the most common system is one which uses mirrors mounted in parabolic troughs to focus sunlight on pipes in which oil circulates. The heated oil provides energy to drive a turbine generator. An alternative is the ?solar power tower? which uses sun tracking mirrors called ?heliostats? to focus concentrated sunlight on to a central receiver. Demonstration ?power tower? projects have been constructed in France, Italy, Spain and the USA. I Photovoltaics PV cells are semiconductor devices which were ?rst produced in the 1950s to provide power for space satellites. Although solar cells can be produced using a variety of semi- conductor materials, most are made from silicon. The development of thin ?lm photo- voltaic technologies with low manufacturing costs is the focus of considerable research worldwide. Figure 8 illustrates the design of a typical PV cell. Most PV power devices produce energy in small quantities for a variety of purposes such as rural electri?cation schemes in developing countries, power supplies for Figure 8 A photovoltaic cell Anti- reflective coating?\ Sunlight (photons) Contact grid Electron current Junction 0.2?0.5mm c. - \7 Back contact instrumentation and telecommunications, and power for consumer goods such as calculators and watches. Over the past 20 years, the cost per peak Watt of PV modules has fallen from more than to around At the same time, production capacity has risen from around 5MW to about 60MW a year. Solar cell production capacity has been doubling every ?ve years. PV is already cost effective for small applications and further cost reductions will pave the way for wider applications. If PV module costs could be reduced to between one and two per peak Watt, PV could in many cases become cost competitive with centralised fossil fuel based power generation and could possibly meet up to a ?fth of world electricity demand without the need for storage. Even in temperate zones, this would require less than 1.5 million hectares of land, which compares favourably with land requirements for some of the world?s major food crops (Figure 9). At present, there are a few large PV arrays installed as demonstration projects, representing just a few megawatts. An alter- native would be to integrate rooftop arrays into existing grids for instance to help reduce daytime peak demand. As the power would be produced in densely populated areas, it would be used closer to production, thus minimising distribution costs. This alternative has been pursued in Switzerland where there is a policy to obtain 0.5% of the country?s primary energy from ?new? renewables by the end of the century. Residential buildings have been ?tted with roof mounted modules which are used in conjunction with dc/ac inverters and which provide metered supply in parallel with the public electricity supply system. Millions of hectares PV 20% 0 5.0 world power PV 100% Grapes 0 Coffee 0 Sugar?cane Potatoes Groundnuts Seed cotton Soya beans Source: World Bank I Biomass Biomass is the world?s fourth largest energy source and has an energy potential far exceeding current world energy use. It is available in most countries and represents a valuable indigenous resource, especially in developing countries. Providing the biomass is produced at a sustainable rate, the C02 emitted during processing and combustion balances the 002 consumed during photosyn- thesis. Thus biomass is not a net contributor to CO2 in the atmosphere except for the fuel used in its transport and does not contribute to possible global warming (Figure 10). Biomass can be divided into two cate- gories traditional and modern. Traditional I 1 100 150 200 250 390 Coarse grains I biomass is mainly fuelwood, the ?poor man?s oil?, used for domestic heating and cooking and the main source of energy for almost half the world?s population. Other traditional forms of biomass include charcoal, straw, rice husks, plant residues and animal waste. Traditional biomass can represent some 90% of energy use in some developing countries where it is not usually acquired via commer- cial markets and so rarely appears in commercial energy statistics. In parts of the world, fuelwood gathering is leading to short- ages (so that fuelwood is no longer a renew- able resource) and is causing forest damage and other environmental deterioration. Where fuelwood is scarce, animal dung may be used as a fuel rather than as a fertilizer, thus reducing agricultural ef?ciency. Modern biomass such as wood residues from industrial processes, bagasse (?bre residue from sugar-cane), energy crops and urban waste may be used on a commercial scale as solid, liquid or gaseous fuels or in power generation where they substitute or complement conventional sources of energy. Recently, interest has increased in growing energy crops on agricultural land taken out of production (?set aside? land) in Europe and the USA. Short?rotation, fast growing trees and herbaceous plants for heat and power generation are the crops receiving most attention and appear to have the best economic potential. Other proposed crops include sugar/starch crops (eg, sugar-cane, cassava, sorghum and Jerusalem artichoke) used in the production of ethanol and plants which yield oil for possible use as fuels in diesel engines such as sun?owers, soya, Figure 9 Solar energy land requirements Figure 10 Biomass recycling carbon Power plant Sun Sustainable tree plantation Processing and transport groundnut, cottonseed, rapeseed, palm oil and castor oil. Direct combustion to 002 and water is the main process used to convert biomass into useful energy. Biomass can also be used indirectly following a thermochemical or biological conversion process. The main thermochemical processes are pyrolysis, liquefaction and gasi?cation. Pyrolysis is Where a feedstock is degraded by heat to produce gas, liquid and char. Carbonisation, used for centuries to produce charcoal, is an example of slow pyrolysis. Much research has The liquefaction process, Where high pressure hydrogen is injected to liquefy the feedstock, is not yet economically Viable, due to a number of engineering and technical obstacles. In a gasi?cation process, a feed- stock is converted into a mixture consisting mainly of carbon monoxide and hydrogen. Equipment for biomass gasi?cation is already commercially available. The two main biological conversion processes are anaerobic digestion, used to produce biogas from various organic wastes and fermentation which uses starch or sugar Figure 11 been conducted into new processes of fast feedstocks to produce fuel ethanol. Converting biomass pyrolysis but as yet none has gone Figure 11 shows various conversion biomass beyond the demonstration stage. routes for biomass resources. Resources Conversion Fuels End uses Residues: Physical: Solid: 0 Forest - 0 Chipping Chips 0 Agricultural 7, Compacting 0 Pellets 0 Municipal 0 Drying 0 Briquettes solid waste 0 Charcoal .1 Chemical: 4 . - 0 Carbonisation Liquefaction Herbaceous Gasification f. crops . . . .. Gaseous . Heat/power Biological: Sugar/starch Fermentation crops . 0 Digestion ,7 . ?r Liquid . Transportation I Physical: i Oilseed crops . Crushing Biomass in power generation Biomass is already widely used to generate electricity in the forest products industries using wood wastes as fuel for steam-turbine systems. However, steam turbines are rela? tively expensive and inef?cient at the small scale to which biomass use is best suited. In addition, readily available resources of low?cost biomass are needed to make this approach economic. Integrated gasi?cation/ gas turbine technology offers a more promising route to biomass power. Hot fuel gases are generated from the biomass and used to drive a gas turbine which in turn generates electricity. Shell companies are involved in a development programme to construct a 30 biomass power demon- stration plant in Brazil fuelled by biomass from a eucalyptus plantation. The project has ?nancial support from the UN Global Environmental Facility (GEF). If the equip- ment development trials are satisfactory, construction is scheduled to start in 1995. If successful, the project could expand the potential of biomass in Brazil, especially in the sugar/alcohol industries, and encourage the use of dedicated fuelwood plantations as an important source of primary energy worldwide. Biogas Biogas, produced by anaerobic digestion and consisting mainly of methane and 002, is used principally for direct combustion and to fuel stationary internal combustion engines. Both China and India have a long history of biogas use while in Denmark, several large biogas plants produce gas mainly from manure for use in combined heat and power production. Biofuels Biomethanol, bioethanol, vegetable oils and vegetable oil esters are all potential trans- portation fuels. Bioethanol has been used neat or in blends with gasoline, notably in Brazil. Under the Brazilian Proalcool project, heavily subsidised by the govern- ment keen to reduce dependence on foreign oil supplies, ethanol produced from sugar- cane provides more than half the country?s automotive fuel. There are also ethanol programmes in the USA (ethanol from maize), Zimbabwe and Malawi. Vegetable oil esters have lower viscosities and higher cetane numbers than pure vegetable oils and thus have greater potential as diesel fuel substitutes or blends. In Europe, interest is being shown in rapeseed oil methyl ester either on its own or in a blend with diesel. 10 Although the technical performance of liquid biofuels is generally satisfactory, they have little environmental bene?t over modern oil-based transportation fuels and require very large subsidies to compete with established fuels. Several studies have shown that it is more cost effective to grow energy crops for use as solid fuels for heat or power rather than for liquid transportation fuels. I Wind power Traditional windmills have been used for centuries to drive machinery for grain milling and for simple irrigation schemes. A typical modern windmill used for electricity generation consists of a two or three-bladed rotor which rotates about a horizontal axis and is mounted at the top of a tall tower. Multiblade rotors may be used for applica- tions which require low frequency power, such as water pumping. The best sites are in remote rural, island or coastal areas where consistently good wind speeds may be expected. Figure 12 shows the areas of the world which are most attractive for wind power development. As wind generators have to be situated at an optimum distance from each other to avoid interference with wind ?ow patterns, wind farms tend to require large land areas. Although the land may still be used for agri? culture, siting wind farms in areas of scenic beauty may arouse opposition. One solution might be a wind farm based offshore, although it would have to be more robust, more corrosion resistant and need less main- tenance than a land based installation. A demonstration plant has been built offshore Denmark to investigate the technical prob? lems in detail. Horizontal axis wind turbines are tech- nically proven and may be commercially attractive for electricity production in areas with good wind conditions and local mainte? nance facilities as long as the wind energy share is less than about a quarter of total demand (to avoid the need for dedicated storage). Wind turbine technology has been developed intensively over the past 20 years and larger turbines, in the 0.25 to 0.5 range are now available. Developments such as variable speed rotors offer potential for further cost savings. Installed generating capacity has also been increasing. Current world capacity of grid- connected turbines is estimated at around 2500 more than half of which is in Westerlies N. Atlantic Westerlies Westerlies Roaring forties Howling fifties 0 Possible sites fortidal power development Regions of wind attractive for wind power development 4 Source: WEC and Twidell Weir, op. cit. Figure 12 Developing wind and tidal power possible sites California. The growth of wind power in California in the early 19805 was largely due to tax incentives. Although these were discontinued following the oil price collapse of 1986, wind power continues to grow in California but at a slower rate. Outside the USA, the largest user of wind energy is Denmark where about two per cent of electricity production is gener- ated from wind. Denmark currently has more than 400 of installed capacity, equivalent to some 65% of Europe?s total and plans to expand this to 1500 by the year 2005. Denmark is also a leading manufacturer of wind turbines, supplying about three-quarters of Europe?s needs and an estimated 45% 0f the world market. In some parts of the world, ?hybrid? systems consisting of wind turbines and diesel generators have been developed to overcome the problem of the intermittency of wind power. They are of particular interest in remote areas far from public grids where diesel generators have been used in the past for local power production. Multiple hybrid arrangements have also been designed which incorporate wind power, solar photovoltaic energy, diesel generation and conventional batteries. Over the past ten years, wind power costs have fallen, mainly as a result of improved equipment production methods, better siting and maintenance scheduling. Technical improvements, such as the devel- opment of advanced materials to provide lighter, stronger components, could reduce costs further. I Water based systems Small hydro schemes Historically, hydropower was developed on a small scale to meet local needs. As transmis- sion ef?ciency increased, power generation became concentrated into ever larger units and large scale hydro schemes bene?ted from the resulting economies of scale. Today, world hydropower capacity is estimated at some 600 000 of which around three per cent comprises small hydro schemes (ie, less than 10 World production is about 2280 a year, around two?thirds of which is in industri- alised countries. Small hydro schemes account for just under four per cent total production. A small hydro development consists of a dam, diversion weir and powerhouse 11 12 containing the equipment which transforms the energy of the water into electrical energy. New schemes are usually ?run-of?water? developments with no water storage reservoir. As small projects lack the economies of scale of larger develop- ments, costs per installed kWe may be quite high. However, they may be attractive in rural communities not connected to a grid, especially if they serve to boost other uses of water such as irrigation. Most of the world?s small hydro plants are located in China where few areas are served by transmission grids. Energy from the ocean Most technologies for harnessing energy from the ocean are immature. Tidal power Extracting energy from the tides is practi- cable only where the tides are large enough and there are favourable sites for plant construction (Figure 12). Of the very few schemes in operation around the world, the largest is in La Rance in France which has operated reliably and with a low mainte? nance requirement since the mid-1960s. Further development of tidal power is hampered by high capital investment requirements, long construction times and a potentially severe impact on the environ- ment around possible sites. Wave power Using the power of the waves has stimu- lated the imaginations of many inventors. More than 1000 patents exist worldwide for wave power devices, though few have reached prototype stages. A number of designs use an oscillating water column as an energy collector. Although some small scale devices have operated satisfactorily, the problems of large scale operation such as large storms and resistance to corrosion and marine fouling, have still to be resolved. Most research into wave power has been conducted in the UK, where the conclusion is that effort should focus on developing small shoreline devices, as large scale offshore designs are unlikely to become economic for some considerable time. Ocean thermal energy Ocean thermal energy conversion (OTEC) plants operate on an open, closed or hybrid cycle and can be mounted on a vessel or built onshore. Unlike wave or tidal energy, OTEC is not intermittent and plants are suited to baseload operation. The ?rst test plant was built in the 1930s, but there was no further interest until the 1970s when rising oil prices triggered the search for alternative sources of energy. Projects are underway or planned in a number of coun- tries to design demonstration plants to test the reliability and technical performance of the technology. However, costs would have to be reduced signi?cantly before OTEC could compete with conventional baseload power generation. I Geothermal energy Geothermal energy has long been used for therapeutic hot baths, space and water heating and agriculture. Over the past few decades, dry steam and high temperature water have been used to generate electricity on a commercial scale. Resources are concentrated along the boundaries between tectonic plates in the Earth?s crust which are prone to volcanic activity or earth? quakes. Countries known for their geo? thermal potential include Italy, (Where elec? tricity was ?rst generated from geothermal power in 1904), Japan, New Zealand, the Philippines, China, Iceland, the former Soviet Union, Mexico and the USA. The past decade has seen developments in the use of medium temperature geo- thermal water for power generation using binary cycle plants. At the beginning of the 1990s, world geothermal electric capacity was estimated at almost 6000 repre? senting a small but not insigni?cant ?niche? in the power generation market. Geothermal energy is also used directly for space and water heating, for example in district heating, greenhouse heating, crop drying and various industrial processes. Leaders are Iceland where four-?fths of the popula- tion use geothermal space heating and Hungary, where geothermal sources are widely used to heat greenhouses. Total direct use of geothermal energy is estimated at around 5.6 million toe. Technologies to ?nd and extract geo- thermal resources are based on those used in the oil and gas industries, modi?ed to take into account the high temperatures and salinity of the resource. To date, only hydrothermal resources (hot water and/or steam trapped in porous or fractured rock at depths between 100 and 4500 metres) have been exploited on a commercial scale. The development of technologies to extract energy from hot dry rock, geopressured resources (hot water aquifers) and magma (molten rock) could increase the potential of geothermal energy in the longer term. Figure 13 Renewables future trends Although some renewables do offer some environmental bene?ts over fossil fuels, they are still generally much more expensive. Their costs have declined, however, and are likely to continue to do so as these largely modern technologies progress rapidly down their cost learning curves. The pace of develop- ment could quicken if governments elect to spend large amounts of public money on further research and development. For instance, the GEF has been set up by the United Nations Development Programme (UNDP), the United Nations Environment Programme (UNEP) and the World Bank to provide grants for investment projects aimed at protecting the global environment. The Commission of the European Communities (CEC) launched a ?ve year Thermie programme in 1990, with a budget of some $630 million, to promote rational use of Current policies renewable energy sources* I Percentage Ecologically-orientated of world policies energy supply I 30 I I Traditional and new 1? 25 ?15 Newrenewable ?10 energy sources?r 1990 Year 2000 Traditional sources: Wood-burning and large-scale hydropower I New sources: Biomass, solar, wind, geothermal, wave and small-scale hydropower Source: World Energy Council op.cit. energy by developing technologies for both fossil fuels and renewables. There are two further programmes Joule and Altener. Joule supports research and development into advanced energy technologies: just over a third of its $250 million budget is allocated to renewables. Altener, with a budget of some $35 million, aims to promote an increased share of renewables in total EU energy consumption. In the USA, as part of the US National Energy Strategy, support is given for research and development on renewables and applications are encouraged partly by extending investment tax credits for renew? ables technologies. Opinions vary considerably as to how renewables will penetrate future energy markets. In a recent report, the World Energy Council considered two alternative cases up to the year 2020. Under the ?current policies? scenario, new renewables, led by biomass, are expected to rise from 1.9% of total commercial energy supply in 1990 to just 4% in 2020. If traditional biomass and hydropower are added, the ?gure would rise to just over 20% of total energy supply. The ?ecologically driven? scenario assumes large government subsidies for renewables on an international scale. Under this scenario, new renewables might account for 12%, and total renewables 30% of total commercial energy supply, with most consumption in developing countries (Figure 13). Dramatic changes in energy supply are unlikely to occur quickly, however, given the rigidities inherent in the world?s energy infrastructure, such as slow capital stock turnover. Investment in future energy supplies requires huge capital outlays with long lead times for major projects and a long? term commitment by investors. To ful?l all these requirements will result in increasingly complex trade-offs in energy policy. A gradual evolution towards a more complex energy supply pattern is the most likely path, driven by technological advances on all fronts. In the ?nal analysis, the role of renewables will be determined by their economic and environ- mental performance. 13 fzect?g?e Catalysis?" . or ezuelgrof? a r5! . today the gas industry Natural gas for power generation by Enan v.2 Gamay Renewable energy describes the current contribution of renewable sources of energy to world energy requirements and discusses their future potential. Fossil fuels will remain the backbone of energy supplies for the foreseeable future but other types of energy resources may find increasing use to meet the world?s growing energy needsProspects or plas?cs . technology maximisin reward? by integration 9 ewes . . Exploration and appraisal The an Trading Company. p.Lc. . Molecu\ar design redress' the ba\ance Developing sate pestidides by Wm Tammy Shell Briefing Service Renewable energy Numberone, 1994 Related publications Related publications which may be of interest include: Shell Briefing Service: 0 2/92: Motoring and the environment Selected Papers: 0 Sustainable biomass energy by Philip Elliott and Roger Booth Speeches: 0 Fossil fuel energy today and tomorrow by C.A.J. Information on ordering these and other publications can be found on the inside front cover of this briefing.