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  Environmental Policy Issues

Renewable Energy Issues
(Released January 2000)

 

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  1. Alternative Energy: Environmental and Economic Factors Associated with Renewable Energy and Creating New Integrated Energy Management Systems

    Kolar, JL

    Environmental Quality Management [Environ. Qual. Manage.], vol. 8, no. 3, pp. 63-82, 1999

    At best, the future of alternative and renewable energy remains uncertain. Our dependency on fossil fuels is already depleting world supplies of coal and petroleum while increasing greenhouse gas emissions. Most assuredly, the ability of alternative energy, described in this article as biomass, hydrogen, wind, solar, and geothermal power, to compete and even integrate with fossil fuels will depend on several important variables: First, developing, as well as developed, countries must be willing to direct long-term public and private funding towards innovative energy technologies by increasing research and promoting public education. Secondly, the "bottom line" economics associated with alternative energy technology must clearly show a positive cost/benefit ratio. Revenues and not deficits are paramount to the sustainability of alternative energy. Lastly, many experts argue for the environmental benefits of alternative energy by way of carbon reductions. The 1997 Kyoto Global Warming Treaty requires the United States in particular to reduce carbon dioxide emissions from fossil fuel burning by 7 percent below 1990 levels. While many experts argue that reactions to global warming and the alternative energy benefits anticipated because of them are fiscally irresponsible and not worth the billions of tax dollars intended, we can be assured that a business-as-usual attitude will continue without increased government and public support.

  2. Rays of hope and winds of change: A utility perspective on renewable energy

    Walker, Richard P; Marshall, Ward C; Champion, Brian

    Proceedings of the American Power Conference [Proc Am Power Conf], vol. 61 (I), pp. 209-214, 1999

    Positive experiences associated with the Central and South West Corporation (CSW) Renewable Energy Project along with strong customer support have led CSW to incorporate additional renewable resources into its generation mix. CSW has established a new business unit whose goal is to identify the most cost effective sources of renewable energy and to determine how best to integrate them into our resource mix. This is being done in anticipation of federal or state mandates requiring increased use of renewable energy and/or increasing markets for renewable energy driven by environmental considerations related to the use of fossil fuels.

  3. Global climate change and the challenges for renewable energy

    Jefferson, JM

    RENEWABLE ENERG, vol. 15, no. 1-4 pt 1, pp. 1-7, Dec 1998

    Despite the recent encouraging signs of interest by major industrial firms in developing renewable energy sources and technologies more quickly and on a large scale, the 1990s have so far on balance given little grounds for optimism. This is because of the slowness of effective policy developments in the wake of lack of real public support and commitments which has increased pessimism in relation to: prospects for raising the efficiency of energy use quickly; prospects for expanding renewable energy resource utilization quickly; and curbing greenhouse gas emissions and mitigating climate change. Further discussions on these issues are presented.

  4. Evaluation of renewable energy potential using a GIS decision support system

    Voivontas, D; Assimacopoulos, D; Mourelatos, A; Corominas, J

    Renewable Energy, vol. 13, no. 3, pp. 333-344, Mar 1998

    A GIS Decision Support System has been developed for the evaluation of Renewable Energy Sources potential and the financial analysis of RE investments. A GIS database with data on wind, topography, urban areas, and special activities has been developed and used for the evaluation of theoretical potential through the spatially continuous mapping of Renewable Energy Resources. The available and technological potential are evaluated by the application of availability and technological restrictions. The evaluation of economical potential is performed by a precise estimation of the expected energy output and installation cost. The financial analysis based on the Internal Rate of Return, identifies the financial viability of alternative investments. The evaluation of wind energy potential for the island of Crete, Greece and the financial analysis of a wind park installation are presented as a case study.

  5. Momentum at last: Perspectives on the U.S. renewable energy industry

    Gay, Charles F; Moon, Susan; Brown, Howard

    Energy Sources [ENERGY SOURCES], vol. 20, no. 2, pp. 97-102, Mar 1998

    The long term goal of the renewable energy community is to revolutionize the world's energy economy. This includes becoming a main contributor to the markets for grid electricity and transportation fuels. The transition to renewable energy future is particularly challenging in the U.S. since the infrastructure, spheres of influence, and ways of doing business in the energy industry are well entrenched. One of the organizations dedicated solely to developing and capturing the enormous potential of renewable energy and energy efficiency is the National Renewable Energy Laboratory (NREL). The NREL specializes in performing and managing research for public and private clients.

  6. Renewable energy technologies potential contribution to sustainable development: The example of hydro power

    Chabot, B

    Houille Blanche, no. 2, pp. 59-64, 1998

    Renewable energy technologies offer many advantages for energy supply and sustainable development. Meanwhile, their large scale deployment is often difficult to achieve due to the harsh competition with fossil fuels, both for comfort and ease of use for decision makers and users and for direct cost competitiveness, which often do not take into account the social and environmental costs. So, the example of Hydro Power which is still the main non fossil source for electricity in the world and which continues to develop strong markets is presented here as a success story which could be repeated in the short and medium term by other renewable energy technologies. Moreover, as only a small part of the world hydro technical potential has been tapped, the hydropower contribution to sustainable development will be secured in the future, as well as for large scale projects including new technologies and behaviour to lower potential impacts on local environment and for small hydropower projects well designed for rural electrification in developing countries.

  7. Dissemination of renewable energy technologies in developing countries - lessons for the future

    Marquand, CJ; McVeigh, JC; Sehgal, S

    International Journal of Ambient Energy [INT J AMBIENT ENERGY], vol. 19, no. 1, pp. 3-32, Jan 1998

    Rural areas of developing countries have long been recognized as the places where it may be cost-effective to harness renewable energy sources for power and subsistence energy requirements. However, their utilization still remains at a relatively low level. The aim of this paper is to identify the reasons why this is so, bearing in mind that the cost of renewable energy technologies has decreased significantly over the last twenty years. The other aims of this paper are to examine how governments and the private sector are involved in the scheme of things, and to reason how the dissemination of renewables may best be carried out. Private participation is becoming increasingly important in the power sector, particularly with all the renewable energies, and in the final section a possible role for multinational oil companies in the potentially huge 'renewables' market, which has been identified over the next two decades, is discussed.

  8. Green energy: The implementation and utilization of renewable energy in the United States

    Murry, Nicole L

    PROC AM POWER CONF, ILLINOIS INST OF TECHNOLOGY, CHICAGO, IL, (USA), 1998, vol. 1, pp. 592-595,

    Often referred to as `green energy', renewable energy uses the earth's natural resources to create energy. Currently, renewable energy provides only 12% of the US electricity supply. The continued implementation and utilization of renewable energy in the US are dependent the support from the Federal and State governments, utility purchase requirements if utility deregulation is passed, and consumer education on the environmental benefits of renewable energy. Renewable energy is anticipated to grow 1.8% yearly until the year 2010. This growth can increase if fossil fuel prices rise or renewable energy is utilized to reduce US greenhouse emissions.

  9. Likely market-penetrations of renewable-energy technologies

    Mackay, RM; Probert, SD

    Applied Energy [APPL ENERGY], vol. 59, no. 1, pp. 1-38, Jan 1998

    The learning-curve concept is considered to be an important tool for predicting the future costs of renewable-energy technology systems. This paper sets out the underlying rationale for learning-curve theory and the potential for its application to renewable technologies, such as photovoltaic-module and wind-power generator technologies. An indication of the data requirements for carrying out learning-curve projections is given together with an assessment of the requirements necessary for an analysis to be undertaken of the application of learning curves to other renewable-energy technologies. The paper includes a cost comparison and a figure-of-merit criterion applicable to photovoltaic-module and wind-power-turbine technologies.

  10. Integrated approach towards sustainable development

    Tompkins, William

    Journal of Canadian Petroleum Technology [J Can Pet Technol], vol. 37, no. 11, 3ppp, Nov 1998

    The economy and environment are in every aspect related. Hence, corporate economic and public policies, and the development of new petroleum technologies must considerably address environmental conservation and protection issues. In this article, a few concepts are presented outlining how a more holistic and integrated view of industry, profit-making, society and the environment can contribute to sustainable development.

  11. Next 25 years: The future of the construction industry

    Michel, Henry L

    Journal of Management in Engineering [J MANAGE ENG], vol. 14, no. 5, pp. 26-31, Oct 1998

    Some of the possible actions and challenges confronting the construction industry in the next 25 years are discussed: conservation of worldwide resources through more effective recycling and more efficient use of these resources; smaller and more fuel-efficient engines; natural gas collection instead of flaring of gases; pumped storage gases or liquids for peak power production through substitution of more readily-available materials; fiber optics replacing copper and aluminum cables and wires; alternative renewable energy sources such as solar, wind, water and safe nuclear; and integration of environmental policies on a global scale.

  12. An equity- and sustainability-based policy response to global climate change

    Byrne, J; Wang, Y-D; Lee, Hoesung; Kim, J-D

    Energy Policy, vol. 26, no. 4, pp. 335-343, Mar 1998

    Many climate models predict that an atmosphere composed of high concentrations of GHGs will result in higher surface temperatures. Although the precise magnitude and physical dynamics of the greenhouse effect remain the subject of continuing analysis, the UN-organized Intergovernmental Panel on Climate Change (IPCC) has concluded that increasing levels of GHGs are affecting recent climate patterns (IPCC, 1990; IPCC, 1996b, c). The Earth Summit held in Rio in 1992 and subsequent meetings of the Conference of Parties in Berlin (1995), Geneva (1996), and Kyoto (1997) have called for international action to address the problem. The focus of these actions is heavily on the energy sector and the fuels and technologies upon which it relies. The common denominator of most policy proposals is a shift From fossil fuels to an energy system relying increasingly on energy efficiency and renewable energy. The ensuing policy debate has raised cost and efficiency concerns in reducing GHG emissions and many have counselled a go-slow response. Broadly, two precautionary energy policy approaches 'no regrets' and 'insurance' - have been proposed. Each, in our view, has difficulties that argue against their adoption as an international policy framework. This article proposes a global energy policy alternative that adopts an equity- and sustainability-based approach to the definition and distribution of costs of changing the energy sector to avert climate change.

  13. Materials for solar energy conversion: An overview

    Granqvist, CG; Wittwer, V

    Solar Energy Materials and Solar Cells [Solar Energy Mater. Solar Cells], vol. 54, no. 1-4, pp. 39-48, Aug 1998

    We introduce the radiative properties of our natural surroundings and demonstrate how the characteristic features of thermal emission, solar irradiation, atmospheric absorption, and sensitivity of the human eye and of plant photosynthesis lead naturally to a set of solar energy materials with well-defined wavelength- and angular-dependent absorptance, emittance, reflectance, and transmittance. Specific discussions are given of antireflection through microstructuring and of overheating protection through thermotropism. The paper ends with a look in the crystal ball at some possible solar materials research in the future.

  14. Solar energy education - A viable pathway for sustainable development

    Hasnain, SM; Alawaji, SH; Elani, UA

    Renewable Energy, vol. 14, no. 1-4, pp. 387-392, Aug 1998

    The growing consumption of limited reserves of fossil fuels and their impact to the environment have raised global interest in harnessing solar energy. Proper knowledge of solar energy is lacking in many levels of society. Recently, the Energy Research Institute (ERI) of King Abdulaziz City for Science and Technology (KACST) have conducted a survey on the availability of solar energy education program around the world. It has been observed that a considerable amount of work has been done for developing solar energy technologies but relatively little attention has been paid on the role of solar energy education. This paper gives an overview of the current status of solar education program available around the globe and it also highlights the importance of the energy information network for solar education program.

  15. New world of solar energy

    Johnson, Jeff

    Chemical and Engineering News [CHEM ENG NEWS], vol. 76, no. 13, pp. 24-28, 30 Mar 1998

    After decades of life support, makers of photovoltaic (PV) electrical generating systems today are brimming with work orders and optimism. Last year, sales grew by nearly 40% and are expected to do so again in 1998. Companies that have long operated in the red are making profits, and worldwide demand now exceeds manufacturing capacity. As a result, PV companies are expanding or building new factories around the world and in the United States. The Department of Energy estimates that by year's end companies operating in the U.S. will have made capital expenditures to nearly triple PV production from two years ago. U.S. capacity will have grown from 50 MW in 1996 to more than 140 MW in 1998.

  16. Assessment of risk-based capacity benefit factors associated with wind energy conversion systems

    Billinton, R; Chen, Hua

    IEEE Transactions on Power Systems [IEEE TRANS POWER SYST], vol. 13, no. 3, pp. 1191-1196, Aug 1998

    A Wind Energy Conversion System (WECS) has a different impact on the load carry capability of a generating system than does a conventional energy conversion system. This is mainly due to the variation in wind velocity. Two risk-based capacity indices designated as Load Carrying Capacity Benefit Ratio (LCCBR) and Equivalent Capacity Rate (ECR) are introduced in this paper. These two indices can be used to indicate capacity benefit and credit of a WECS, and thus provide valuable information for energy policy makers in decision problems involving the selection and classification of wind sites. A midpoint sectionalized technique has been developed to calculate the Incremental Peak Load Carrying Capability (IPLCC) and to assess the LCCBR and ECR. The technique is effective and usually takes only a few iterations to obtain the indices. Sequential Monte Carlo simulation is utilized to estimate the adequacy of a generating systems including WECS. A small reliability test system containing WECS is utilized to illustrate the proposed technique.

  17. Power struggle: renewable technologies battle to unlock the grid

    Kneisel, Sophie

    CAN CONSULT ENG, pp. 22-23, 1995

    Now is the time to promote the assets of wind energy and other renewable technologies. Their advantages - flexibility of implementation, diversity in resource management, risk minimization, and regional development - need to be reflected immediately in practical government policies to open the energy market.

  18. Comparison of the means and cost of subsidizing wind energy

    Mitchell, C

    Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy [PROC INST MECH ENG PART A], vol. 209, no. 3, pp. 185-188, 1995

    The support mechanisms for wind in the United Kingdom, the Netherlands, Denmark and Germany are reviewed. Their cost to the consumer is calculated and compared. The benefits and disbenefits of the differing systems are discussed.

  19. Practical difficulties in raising finance for wind farms

    Johns, JH

    Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy [PROC INST MECH ENG PART A], vol. 209, no. 3, pp. 189-194, 1995

    The 15 year term of NFFO3 will significantly alter the financial structures of wind farm projects. Senior debt terms will extend to 10-12 years and returns are unlikely to reach the levels required by venture capitalists. Returns to equity investors can be enhanced by debt and equity gearing techniques, for example the introduction of preference shares. Two investment schemes and an additional capital gains relief which were introduced in the November 1993 budget could benefit potential investors in wind farms.

  20. Utilities role in deploying renewables

    Vigotti, R

    RENEWABLE ENERG, vol. 15, no. 1-4 pt 1, pp. 125-130, Dec 1998

    The aim of this paper is to review the current status and prospects of the renewable energy sources that are more suitable for the production of electricity, and to present the views of the EURE Group on the role electricity utilities could play in deploying generating plants based on these sources. In the first part of the paper, reference is made both to the renewable sources that have long been used for these purposes, such as hydro power, and to the 'new' ones, particularly bioenergy, photovoltaics and wind power. Mention is also made of other technologies that have so far been less developed or can be applied only locally (e.g. geothermal energy). In the second part, the paper advises on the way utilities could contribute to renewable energy research and how they could help promoting these sources.

  21. Biomass conversion to liquid fuel by two-stage thermochemical cycle

    Rustamov, VR; Abdullayev, KM; Samedov, EA

    Energy Conversion & Management [Energy Convers. Manage.], vol. 39, no. 9, pp. 869-875, Jul 1998

    The nature of wood thermal decomposition and notions about the influence of base effects have been studied in the presence of different solvents in the process of wood liquefaction. The possibility of consecutive stopped wood decompositions has been established according to the two competing directions: depolymerization and dehydration. The necessity of destructive processes and depolymerization of the biomass, which dominate over dehydration, has been shown to obtain liquid products (liquefaction products). The temperature limits of the depolymerization process (220-250 degree C), which precedes the two covered fields of eliminating water (240-280 degree C and 280-380 degree C), has been established. The possibility of obtaining light-boiling organic products (T sub(boil) to 150 degree C) or a mixture of the light ( similar to 150 degree C) and heavy (200-280 degree C) fractions has been shown to depend on the base concentration. At the same time, the nature of the deoxygenation processes of oxygen-containing pyrolysis products by dispersed iron has been studied.

  22. State of the art of biomass combustion

    Bhattacharya, SC

    Energy Sources [ENERGY SOURCES], vol. 20, no. 2, pp. 113-135, Mar 1998

    As a result of the growing concern over the adverse environmental impact of fossil fuels as an energy resource, there is currently a great deal of interest in biomass energy to satisfy a much larger energy demand than at present. A review of biomass combustion technologies employed for different applications in the households as well as industries with particular reference to recent development and emerging technologies is presented.

  23. Agricultural regulatory framework and biomass production

    Kuch, Peter J; Crosswhite, William M

    Biomass and Bioenergy [BIOMASS BIOENERGY], vol. 14, no. 4, pp. 333-339, 1998

    This paper examines programs and implementing regulations that provide a framework for the application of agricultural and environmental policy to biomass crop production. Administration of policies and programs is accomplished through Federal agencies including the United States Department of Agriculture, Environmental Protection Agency, National Oceanic and Atmospheric Administration, and the United States Corps of Engineers as well as State laws, regulations, permits and local plans and zoning ordinances. Impacts of the various programs and regulations on biomass production depend upon the crop, how it is grown and prior land use on the site. There is reliance on both regulations and assistance programs that provide price and income support, technical assistance and cost sharing benefits that can influence the production of biomass crops. Biomass crop production can promote greater stewardship on farms and woodlots contributing favorably to environmental improvement and use of renewable sources of energy.

  24. U.S. bioenergy crop economic analyses: Status and needs

    Walsh, Marie E

    Biomass and Bioenergy [BIOMASS BIOENERGY], vol. 14, no. 4, pp. 341-350, 1998

    U.S. bioenergy crop production cost, supply curve, and transportation cost studies are summarized and compared. Production cost estimates range from <$22/dry Mg [$20/dry ton (dt)] to more than $110/dry Mg ($100/dry ton) depending on crop, region, yield and method of analysis. A detailed description of an ORNL study is presented as a representative production cost study. Three national supply curve estimates are compared; for a quantity of 110 million dry Mg (100 million dry tons), these studies estimate marginal bioenergy crop prices of $29/dry Mg ($26/dt) (farmgate), $46/dry Mg ($42/dt) (farmgate), and $55/dry Mg ($50/dt) (delivered). Three regional supply curve analyses are also discussed. Bioenergy crop transportation costs estimates range from $5.5/Mg ($5/dt) and $8/Mg ($7.27/dt) for a haul distance of 40 km (25 miles). The paper closes with a discussion of analytical needs.

  25. Renewable Energy: Biomass Power and Biofuels as Alternative Sustainable Energy Sources

    Kolar, J

    Environmental Quality Management [Environ. Qual. Manage.], vol. 8, no. 2, pp. 35-42, 1998

    This article describes biomass fuels as renewable and sustainable energy resources in Minnesota as well as across the United States. This country has long benefited from surplus supplies of diverse energy resources, while our dependency on foreign petroleum supplies and domestic coal reserves has only recently prompted Congress to recognize the importance of renewable and alternative fuels such as biomass energy. Our further utilization of biomass power and biofuels can be an important step in altering our dependency on both coal and petroleum while simultaneously reducing carbon dioxide emissions.

  26. Possibilities for the rational use of energy from thermal waters

    Jankovic, Z

    MEMBRANES IN DRINKING AND INDUSTRIAL WATER PRODUCTION, Elsevier Science B.V., P.O. Box 211, 20 Sep 1998, p. 241, Desalination , vol. 119, no. 1-3

    Geothermal deposits, or thermal and thermomineral waters are some of the most utilized resources all over the globe, even from the earth crust below the oceans. Intensive exploitation and utilization of thermal water started over 20 years ago after the first oil crisis in 1973. Today thermal water is used in many countries for various purposes. The development of geothermal technology has been rapid. Geothermal resources are practically inexhaustible and sterile. Ecologically geothermal energy has a great future and possesses all the conditions to become the energy of the next millennium. In the Republic of Yugoslavia geothermal energy has been considered a potential source of energy due to its abundant geothermal waters (GTV). It is necessary to apply much effort into developing a GTV energy so that liquid and gas fuels can be adequately replaced. We will introduce an improved thermal energy system (TES) for the rational use of GTV energy which enables the production of thermal energy in the winter period and electrical energy in the summer season. Economics of the improved TES will be presented.

  27. Geothermal modeling of soil or mine tailings with concurrent freezing and deposition

    Nixon, JF; Holl, Nick

    Canadian Geotechnical Journal [CAN GEOTECH J], vol. 35, no. 2, pp. 234-250, Apr 1998

    A geothermal model is described that simulates simultaneous deposition, freezing, and thawing of mine tailings or sequentially placed layers of embankment soil. When layers of soil or mine tailings are placed during winter subfreezing conditions, frozen layers are formed in the soil profile that may persist with time. The following summer, warmer soil placement may not be sufficient to thaw out layers from the preceding winter. Remnant frozen soil layers may persist for many years or decades. The analysis is unique, as it involves a moving upper boundary and different surface snow cover functions applied in winter time. The model is calibrated based on two uranium mines in northern Saskatchewan. The Rabbit Lake scenario involves tailings growth to a height of 120 m over a period of 24 years. At Key Lake, tailings increase in height at a rate of 1.3 m/year. Good agreement between the observed position of frozen layers and those predicted by the model is obtained. Long-term predictions indicate that from 80 to 200 years would be required to thaw out the frozen layers formed during placement, assuming 1992 placement conditions continue. Deposition rates of 1.5-3 m/year give the largest amounts of frozen ground. The amount of frozen ground is sensitive to the assumed snow cover function during winter.

  28. Small hydropower stations control and monitoring

    Jacquemmoz, P; Tironi, D

    Houille Blanche, no. 1, pp. 15-18, 1999

    An hydropower station control and monitoring system is in charge of electromechanical devices automatic working. Until now, the EDF small stations control and monitoring was based on the other stations system. But today, in order to reduce the global cost of a station, the principles for the small stations that do not jeopardize people or electrical network, are to set up only working specifications and a guide for electrical installation. These new principles have been applied to some small stations renewing in 1997, in particular the Rabastens station.

  29. Advanced Control for Hydro-Powerplants

    Libaux, A; Irving, E

    Houille Blanche [Houille Blanche], no. 2, pp. 25-33, 1999

    This paper presents new solutions for the control design of Hydropower plants. The chosen example is a run of the river type operations. Some control problems in France or in foreign countries have lead to a verification of the existing controls in these plants, and also incited the instigation of advanced controls, carefully compared to the classical one. The need for adequate models, as well as for powerful tools and algorithms for control design is a long standing issue. Non-linear partial derivative complicate models, which have been carefully tested through experience and used for classical control design using a trial and error approach, have been in use for a long time. Subsequently, transfer functions were fulfilled by the identification of the complex numerical model time-responses. Indeed, this approach has not been efficient enough, as some dynamic term effects could not be identified due to the non-linear effects. The modelization approach using non-linear differential models based on a lumped parameter representation of the physical system is much more powerful. Linearized state space models are deduced from the non-linear ones, which allow the design of convenient classical or modern controls. It is accepted that classical PI are greatly improved by additional loops assuring positivity, but powerful design techniques are missing for a PID plus a stabilising loop. Hence, an original robust design methodology has been implemented which uses dominant poles and modulus margin placement realised by an optimisation technique. As a generalisation of this idea of additional loops. LQG control using all measurements available is particularly efficient and simulations on non-linear detailed models are presented. Finally, due to the non-linear behaviour of the plant and in order to obtain best performances at any flow rate, as at any set-point level, a gain-scheduling adaptive system using switching fixed LQG or switching fixed PI with stabilising loop has been implemented and gives excellent results for the adaptive LQG and acceptable ones for the adaptive PI. Both PI and LQG switching controls have been implemented with very efficient bumpless antisaturation components. Switching criteria have been automated according to the plant flow rate and to the maximum reservoir levels. Due to its general nature, this methodology has not only helped to solve run of the river control problems, but has also been used for speed / power control of turbine units with efficient results.

  30. The meaning of results: Comparative risk assessments of energy options

    Wilson, R; Holland, M; Rabl, A; Dreicer, M

    IAEA Bulletin [IAEA Bull.], vol. 41, no. 1, pp. 14-18, 1999

    Significant progress has been made in both the development of the techniques of comparative risk assessment, and in the use and interpretation of their results. This is particularly so for the assessment of options for electricity generation and transport. The results have become a useful aid to decision-making, though they often need to be integrated with other social, political, and economic issues before any decision may be made. The main controversies for comparative risk assessment concern global warming for fossil fuels; catastrophic accidents, particularly for nuclear and large hydropower plants; and high-level radioactive waste disposal. These issues involve technical and complex social and political questions. However, comparative risk assessment should provide information in a transparent manner so the limitations and strengths of results are correctly understood.