- Email: [email protected]
Solar energy
07 Alternative energy sources (solar energy) carbohydrates; and a pyroprobe interfaced with a gas chromatograph (GC) and mass spectrometer for product identification. In addition to monitoring the major products for each step, one also monitored and compared the temperatures corresponding to the maximum rate. From this analysis, the DTG results at 20 °C min 1 heating rate show that the temperature differences between the peak temperatures of the two decomposition steps are approx. 70, 190, and 200 °C for cellulose, pectin, and xylan, respectively. Furthermore, T G A data were used to calculate sets of biomass-specific kinetic parameters for these two steps. 03•00199 Rapeseed cake as a biomass source (~ulcuo~lu, E. et al. Energy Sources, 2002, 24, (4), 329-336. The term biomass source covers purpose-grown agricultural crops (oil seeds), conventional agricultural crops (sugar and starch), trees, and novel species (C3 and C4), as well as agricultural, forest, agroindustrial and domestic wastes, effluents, and residues. Among these sources, cakes (meals) that are residual products derived from oil seed plants have significant potential. All over the world rapeseed plant is grown widely and a significant amount of it can be obtained following rapeseed oil making. Most of the cake is evaluated as an animal meal. In this study, physical and chemical properties of rapeseed cake have been determined and presented as a biomass source candidate.
03/00200
Renewable energy crops in the UK
Collins, R. Refocus, 2002, 3, (2), 42. In the past year the U K has witnessed a veritable 'dash for (mostly offshore) wind', with major energy companies and utilities poised to enter the renewables market in a manner and scale not hitherto witnessed. In contrast, despite the grants and funding incentives which have been announced in the UK, reaction and interest in the development of energy crop generation projects has so far been more muted. Can energy crops now begin to emerge as a second major source of new renewable energy for the UK?
03/00201 Stand and site productivity response following whole-tree harvesting in early thinnings of Norway spruce (Picea abies (L.) Karst.) Nord-Larsen, T. Biomass and Bioenergy, 2002, 23, (1), 1-12. Two field experiments were established on nutrient poor, sandy soils in Klosterheden National Forest and in Mangeh0je Forest Plantation in western Denmark to quantify the effect on site productivity of wholetree harvesting in early thinnings of Norway spruce. The growth response following biomass removal was investigated for four treatments: (1) no thinning (NT), (2) whole-tree harvesting in which the felled trees were removed immediately after thinning (WTHg~,,), (3) whole-tree harvesting in which the felled trees were left to dry in the stand during the following growing season so that some of the nutrient rich parts of the tree such as needles and twigs are returned to the forest floor (WTHo,7), and (4) harvesting of stems and coarse branches with needles and twigs being threshed from the branches and left in the stand (SCB). The results indicated that WTH~r¢~, might lead to a short-term reduction in stand volume increment of the remaining stand. Comparing the mean annual increment during the first four growing seasons after treatment, using the initial standing volume as a covariate, WTHgr~, caused a significant growth reduction of 10-18% at Klosterheden and 5-17% at Mangeh0je, compared to the SCB- and WTHdry-treatments. The effect of WTHgreen was attributed to an increased removal of essential nutrients such as N, P and K. The growth response following whole-tree harvesting was confined to the first four growing seasons and the effect of different treatments was not significant when data for all ten growing seasons were analysed.
03•00202 Sustainable fermentative hydrogen production: challenges for process optimisation Hawkes, F. R. et al. International Journal of Hydrogen Energy, 2002, 27, (11-12), 1339-1347. This paper reviews information from continuous laboratory studies of fermentative hydrogen production useful when considering practical applications of the technology. Data from reactors operating with pure cultures and mixed microflora enriched from natural sources are considered, lnocula have been derived from heat-treated anaerobically digested sludge, acti~'ated sludge, aerobic compost and soil, and nonheat-treated aerobically composted activated sludge. Most studies are on soluble defined substrates, and there are few reports of continuous operation on complex substrates with mixed microflora to produce H2. Methanogenesis which consumes H2 may be prevented by operation at short hydraulic retention times (around 8-12 h on simple substrates) and/or pH below 6. Although the reactor technology for anaerobic digestion and biohydrogen production from complex substrates may be similar, there are important microbiological differences, including the need to manage spore germination and oxygen toxicity on start-up and control sporulation in adverse circumstances during reactor operation.
26 Fuel and Energy Abstracts January 2003
03100203 Tailoring optical systems to optimized photobioreactors Gordon, J. M. et al. International Journal o[ Hydrogen Energy, 2002, 27, (11-12), 1175-1184. Photobioreactor designs are commonly restricted by the ability of conventional optical systems to deliver prescribed solar intensities and flux distributions at high collection efficiency. This paper explores how non-imaging optical designs can be tailored to reactor conditions that maximize bioproductivity. Two distinct classes of photobioreactors are considered: (1) stationary outdoor units; and (2) an indoor reactor that requires the total separation of the collection and delivery of solar radiation. For practical and economic reasons, the latter obliges solar collectors of immense optical concentration. The outdoor directillumination units comprise stationary mirrored troughs placed around standard reactor shapes, and replace expensive reactors with inexpensive reflectors, while enhancing bioproductivity. For the indoor reactors, the recent innovation of dual-axis tracking solar fiber-optic mini-dish concentrators were adopted to collect, concentrate and transport sunlight to a remote reactor. Contoured polymeric light extractors distribute the light uniformly and efficiently inside the reactor. In all cases, the principal demands are: (a) accommodating reactor shapes with high ratios of irradiated surface area to volume; (b) uniform flux on the irradiated surfaces; (c) high efficiency for collecting and delivering solar radiation; (d) being based on existing and affordable technologies; and (e) compactness. Flux levels of 2000 μmolm z s i of photosynthetically active radiation are realistically attainable over the entire transparent surface of the reactor.
Geothermal energy 03/00204 Performance of supercritical cycles for geothermal binary design Gu, Z. and Sato, H. Energy Conversion and Management, 2002, 43, (7), 961-971. Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the condensing temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design.
Solar energy 03/00205
Assessment of the dye-sensitized solar cell
McConnell, R. D. Renewable and Sustainable Energy Reviews, 2002, 6, (3), 271-293. The field of solar electricity, or photovoltaics (PV), is rich in that there are many materials and concepts for converting sunlight into electricity. The technologies accepted as conventional are those well along in the process of commercialization. The dye-sensitized solar cell, developed in the 1990s, is a nonconventional solar electric technology that has attracted much attention, perhaps a result of its record cell efficiency above 10%. This paper reviews the technology, discusses new research results and approaches presented at a recent symposium of many of the world's important dye solar cell researchers, and presents an assessment of the dye-sensitized solar cell in a comparison with current conventional solar electric technologies. It concludes the dye solar cell has potential for becoming a cost-effective means for producing electricity, capable of competing with available solar electric technologies and, eventually, with today's conventional power technologies. But it is a relatively new technology and faces many hurdles on the path to commercialization. Because of its potential, this assessment recommends further funding for research and development (R&D) of the dye-sensitized solar cell technology on the basis of the promising technical characteristics of the technology, a strong US and world-wide research base, positive industry interest, and today's relatively small funding allocation for its R&D.
03/00206 Calculation of solar irradiance profiles from hourly data to simulate energy systems behaviour Notton, G. et al. Renewable Energy, 2002, 27, (1), 123-142.
07 Alternative energy sources (solar energy) Three models (constant, linear and extraterrestrial) were compared w.hich simulate an hourly profile of solar irradiance and allow the determination, with a given reliability, of minute data of global solar irradiation from hourly measured irradiations. These models are compared from the point of view of various statistical tests using data collected on a Mediterranean site. The extraterrestrial model shows very satisfying results and improves greatly the accuracy compared with a constant model.
03/00207 Design, development and performance testing of a new natural convection solar dryer Pangavhane, D. R. et al. Energy, 2002, 27, (6), 579-590. Mechanical drying of agricultural products is an energy consuming operation in the post-harvesting technology. Greater emphasis is given to using solar energy sources in this process due to the high prices and shortages of fossil fuels. For these purposes, a new natural convection solar dryer consisting of a solar air heater and a drying chamber was developed. This system can be used for drying various agricultural products like fruits and vegetables. In this study, grapes were successfully dried in the developed solar dryer. The qualitative analysis showed that the traditional drying, i.e. shade drying and open sun drying, dried the grapes in 15 and 7 days respectively, while the solar dryer took only 4 days and produced better quality raisins.
03100208 Turkey
Estimation of solar radiation parameters for Izmir,
Ulgen, K. and Hepbasli, A. International Journal of Energy Research, 2002, 26, (9), 807-823. In this study, the solar radiation parameters (global and diffuse solar radiation) are correlated with respect to ambient temperatures in the fifth-order polynomial form for Izmir in Turkey. Experimental data were measured in the Solar-Meteorological Station of Solar Energy Institute in Ege University over a 5-year period, 1994-1998. The ratios of the total daily diffuse to global radiation intensities for each month range from 0.38 to 0.45 averaged for the same period, with an average value of 0.41. It can be concluded that the present models predict the solar radiation parameters reasonably well with the correlation coefficients over 0.95 for the projections.
03/00209 Experimental study of a tubeless convex type solar collector Abu-Qudais, M. et al. Energy Conversion and Management, 2002, 43, (6), 791-797. This paper describes the design and performance of a convex type of solar water heater. The main purpose of a convex solar collector is to accomplish static tracking for the sun radiation without additional cost, that is, to collect energy efficiently in the early and later times of the day due to the low angle of incidence with a high percentage of solar radiation perpendicular to the collector plate. Two adjacent types of collectors, fiat plate and convex type with the same projected area, were constructed and tested under the same conditions. Comparisons were made of the lumped efficiency and useful energy under different conditions. The efficiency and the useful energy were considerably greater of the convex type collector than for the flat plate collector under the same environmental and insolation conditions. An additional 45% energy gain was achieved from the convex type compared to the fiat plate collector.
03•00210 Means of enhancing and promoting the use of solar energy Bahaj, A. S. Renewable Energy, 2002, 27, (1), 97-105. The development of renewable technologies in the last decade has been exceptional. In photovoltaic (PV) for example, efforts were not only limited to merely improving their efficiency but also to the reduction of the cost of cells and modules via volume production for commercial markets. There are many national schemes promoting the use of PV technology and regional targets for a share of renewable energy production. This paper describes approaches for enhancing the prospect of utilizing solar energy within our society. The issue of expansion or enhancing the utilization of solar energy can be undertaken by individuals, groups, institutions and governments. The aim of this paper is to provide some examples, which could serve as a framework in which action could be taken to promote solar technology.
03/00211 Modelling solar half-hour data using fourth order cumulants Safi, S. et al. International Journal of Solar Energy, 2002, 22, (2), 67-81. In this study, there were two key objectives. The first one was to develop a new simple and efficient technique to identify the parameters of the moving average (MA) process using the technique of higlier order cumulants. The simulation for different orders of MA in the presence of Gaussian noise, for SNR lower than 20vdB, gives satisfactory results. The second objective involved adopting the proposed method for modelling half-hour solar radiation in Marra-
kesh. Accurate design and optimization of short response time solar energy systems with storage are sensitive to the stationary and sequential characteristics of half-hourly solar radiation. In order to benefit from some characteristics of stationary processes, a preliminary transformation was performed on the original data. The proposed method was used to look for a simple and efficient model to represent solar half-hourly radiation sequences needed for many applications in the solar energy field. The Giannakis technique based on cumulant diagonal slices and the partial autocorrelation function of Box & Jenkins and Brockwell & Davis were used for selection of the model order.
03/00212 Multimedia education program for an active solar hot water system Axaopoulos, P. et al. International Journal of Solar Energy, 2002, 22, (2), 83-92. An interactive multimedia education program has been developed to study the transient behaviour of an active solar heating system for domestic hot water production. The users can explore various cases, study what happens under different operating scenarios and examine the effects of altering conditions. In addition, simulation processes are used when a more quantitative understanding of the related subjects is needed, as they offer higher perceptual fidelity (i.e. more accurate representation of the situation being modelled). The simulation accounts for a large number of parameters and can be used to investigate their effects on the thermal efficiency of the solar collector and the system. It can also be used for an extensive set of exercises in the tertiary education sector. The operating principles and performance aspects of the different components have been considered providing a basis for understanding the components interaction and total system performance. The program is a user friendly, fast, easy-touse and a powerful educational tool.
03/00213 Performance of a natural circulation solar air heating system with phase change material energy storage Enibe, S. O. Renewable Energy, 2002, 27, (1), 69-86. The design, construction and performance evaluation of a passive solar powered air heating system is presented. The system, which has potential applications in crop drying and poultry egg incubation, consists of a single-glazed flat plate solar collector integrated with a phase change material (PCM) heat storage system. The PCM is prepared in modules, with the modules equispaced across the absorber plate. The spaces between the module pairs serve as the air heating channels, the channels being connected to common air inlet and discharge headers. The system was tested experimentally under daytime no-load conditions at Nsukka, Nigeria, over the ambient temperature range of 19-41°C, and a daily global irradiation range of 4.9-19.9 MJ m " . Peak temperature rise of the heated air was about 15 K, while the maximum airflow rate and peak cumulative useful efficiency were about 0.058 kg s 2 and 22%, respectively. These results show that the system can be operated successfully for crop drying applications. With suitable valves to control the working chamber temperature, it can also operate as a poultry egg incubator.
03/00214 Photo-electrochemical hydrogen generation from water using solar energy. Materials-related aspects Bak, T. et al. International Journal of Hydrogen Energy, 2002, 27, (10), 991-1022. The present work considers hydrogen generation from water using solar energy. The work is focused on the materials-related issues in the development of high-efficiency photo-electrochemical cells (PECs). The property requirements for photo-electrodes, in terms of semiconducting and electrochemical properties and their impact on the performance of PECs, are outlined. Different types of PECs are overviewed and the impact of the PEC structure and materials selection on the conversion efficiency of solar energy are considered. Trends in research in the development of high-efficiency PECs are discussed. It is argued that very sophisticated materials engineering must be used for processing the materials that will satisfy the specific requirements for photo-electrodes. An important issue in the processing of these materials is the bulk vs. interface properties at the solid/ solid interfaces (e.g. grain boundaries) and solid/liquid interfaces (e.g. electrode/electrolyte interface). Consequently, the development of PECs with the efficiency required for commercialization requires the application of up-to-date materials processing technology. As the production of hydrogen is expected to grow greatly by 2010, seed funding already has been allocated to several national research programs aiming at the development of hydrogen technology. The countries having access to this PEC technology are likely to form the OPEC of the future.
Fuel and Energy Abstracts January 2003 27
07 Alternative energy sources (wind energy) 03/00215 Photovoltaic module quality in the Kenyan solar home systems market Duke, R. D. et al. Energy Policy, 2002, 30, (6), 477-499. As one of the largest unsubsidized markets for solar home systems (SHS) in the world, Kenya represents a promising model for rural electrification based on private purchases of clean decentralized photovoltaic technologies. Small amorphous-silicon modules dominate the market and most brands provide high quality and affordable service. Product quality varies widely, however, and the public has limited capacity to distinguish among competing brands. This imposes direct hardships on households with the misfortune to purchase lowquality equipment, and it constrains sales as some customers refrain from purchasing solar equipment due to the associated performance uncertainty. This article analyses market failure associated with photovoltaic module quality in the Kenyan SHS market and develops strategies to address the problem - emphasizing that similar quality problems may exist for other SHS components and in other markets. The principal conclusion is that domestic pro~]uct testing with public disclosure represents an inexpensive low-risk strategy, but it may prove inadequate. Mandatory product quality standards based on international testing regimes (e.g. IEC standards), augmented with a basic domestic testing option, would provide stronger assurance, but the risks associated with this intervention suggest caution. An emerging multilateral SHS market support effort (PVMTI) should ensure quality for the credit-based sales it promotes in Kenya; however, the long-term impact of this approach is not yet clear and is unlikely to address quality problems associated with the existing unsubsidized sales-based markets for SHS. Finally, fee-for-service models would decisively address quality problems, but launching this model in the Kenyan market would likely require large subsidies.
03•00216 Useful solar heat gains in multi-zone nondomestic buildings as a function of orientation and thermal time constant Yohanis, Y. G. and Norton, B. Renewable Energy, 2002, 27, (1), 87-95. Two parameters affecting useful solar absorption are orientation and thermal mass. Solar energy absorption in buildings depends on these parameters in a complex manner particularly when considering large glazing ratios and large direct components of insolation. Therefore, where parameters of different zones in a multi-zone building vary, useful solar absorption will also vary. For higher northern latitudes, compared with south orientation, useful solar absorption differs by about 2, 4 and 6% between large and small time constants for east, west and north orientations, respectively. The smallest and largest differences are for east and north orientations, respectively. Fenestration design should be a consequence of orientation and overshading, seeking to balance daylight, solar gains and heat losses.
Wind energy 03/00217
A next generation wind power technology?
behaviour of wind parks erected during 1985-1995 in Greece, significantly improved the accuracy of predictions in comparison with the results based on time-mean values of the corresponding parameters. Finally, the proposed model satisfactorily explains the evolution of wind energy applications in Greece during the last 15 years, on the basis of pure economic terms.
03100219 Investigation on wind power potential on Hong Kong islands - an analysis of wind power and wind turbine characteristics Lu, L. et al. Renewable Energy, 2002, 27, (1), 1-12. This paper discusses the potential for electricity generation on Hong Kong islands through an analysis of the local weather data and typical wind turbine characteristics. An optimum wind speed, Uop, is proposed to choose an optimal type of wind turbine for different weather conditions. A simulation model has been established to describe the characteristics of a particular wind turbine. A case study investigation allows wind speed and wind power density to be obtained using different hub heights, and the annual power generated by the wind turbine to be simulated. The wind turbine's capacity factor, being the ratio of actual annual power generation to the rated annual power generation, is shown to be 0.353, with the capacity factor in October as high as 0.50. The simulation shows the potential for wind power generation on the islands surrounding Hong Kong.
03/00220 Management of fluctuations in wind power and CHP comparing two possible Danish strategies Lund, H. and Clark, W. W. Energy, 2002, 27, (5), 471J,83. Both CHP (combined heat and power production) and wind power are important elements of Danish energy policy. Today, approximately 50% of both the Danish electricity and heat demand are produced in CHP and more than 15% of the electricity demand is produced by wind turbines. Both technologies are essential for the implementation of Danish climate change response objectives, and both technologies are intended for further expansion in the coming decade. Meanwhile, the integration of CHP and wind power is subject to fluctuations in electricity production. Wind turbines depend on the wind, and CHP depends on the heat demand. This article discusses and analyses two different national strategies for solving this problem. One strategy, which is the current official government policy known as the export strategy, proposes to take advantage of the Nordic and European markets for selling and buying electricity. In this case, surplus electricity from wind power and CHP simply will be sold to neighbouring countries. Another strategy, the self-supply strategy, runs the CHP units to meet both demand and the fluctuations in the wind scheduling. In this case, investments in heat storages are necessary and heat pumps have to be added to the CHP units. Based on official Danish energy policy and energy plans, this article quantifies the problem for the year 2015 in terms of the amount of surplus electricity, and investments in heat pumps, etc. needed to solve the problem are calculated. Based on these results between the two different strategies, the conclusion is that the self-supply strategy is recommended over the official export strategy.
03•00221 art
Offshore wind in Europe: the current state of the
Weisbrich, A. L. Refocus, 2002, 3, (2), 26-29. Present day wind turbines (large blade Props on Pole or POPs) have continued to evolve to ever larger sizes requiring massive blades, gearboxes or large, complex customized generators. This continuous increase in size has subsequently increased the costs and complexity of manufacturing, transporting, constructing and maintaining these systems. This article discusses an alternative wind power technology design, the Wind Amplified Rotor Platform which uses many identical smaller vertically integrated modules as opposed to one large generator. The modular design can be easily and relatively inexpensively volume produced and implemented both in traditional electric utility scale wind farms as well as in marine based offshore wind farms sites.
Henderson, A. R. R¢[ocus, 2002, 3, (2), 4 17. After several decades of theoretical developments, desk studies, experimental wind turbines and prototype windfarms, the first largescale commercial developments of offshore windfarms are now being built. To support and accelerate this development, the European Commission funded a project, 'Concerted Action on Offshore Wind Energy in Europe' (CA-OWEE), which aimed to gather and distribute knowledge on all aspects of offshore wind energy, including: offshore technology, electrical integration, economics, environmental impacts and political aspects. The partners are from a wide range of fields and include developers, utilities, consultants, research institutes and universities.
03/00218 An integrated time-depending feasibility analysis model of wind energy applications in Greece Kaldellis, J. K. Energy Policy, 2002, 30, (4), 267-280.
03/00222 Small wind turbines: the unsung heroes of the wind industry Anon, Refocus, 2002, 3, (2), 30.
An integrated time-depending feasibility analysis is presented in order to improve the reliability of the computational methods to simulate the e c o n o m i c behaviour of commercial wind parks in Greece, in view of the continuous technological improvements of the sector and the important world-wide political and economic transformations. According to the proposed model, the time-dependency of the governing parameters is taken into account based data from the local market records covering almost 20 years. In addition, information from several European and local wind parks is also incorporated. The application of the developed computational frame to several cases, concerning the economic
26
Fuel and Energy Abstracts January 2003
Most discussions concerning wind energy usually focus on utility-size projects on a megawatt scale and how to get such projects off the ground. Whilst silently whirring away in the background are the millions of small (less than 100 kW) and micro-turbines (less than 5 kW) that have been installed on a huge scale for decades making significant contributions to supplying electricity in off-grid and grid connected areas. This article takes a closer look at these unsung heroes of wind, issues surrounding their installation and use, and highlight companies around the world that manufacture a variety of small and micro-wind turbines for a range of applications.
03/00200
Renewable energy crops in the UK
Collins, R. Refocus, 2002, 3, (2), 42. In the past year the U K has witnessed a veritable 'dash for (mostly offshore) wind', with major energy companies and utilities poised to enter the renewables market in a manner and scale not hitherto witnessed. In contrast, despite the grants and funding incentives which have been announced in the UK, reaction and interest in the development of energy crop generation projects has so far been more muted. Can energy crops now begin to emerge as a second major source of new renewable energy for the UK?
03/00201 Stand and site productivity response following whole-tree harvesting in early thinnings of Norway spruce (Picea abies (L.) Karst.) Nord-Larsen, T. Biomass and Bioenergy, 2002, 23, (1), 1-12. Two field experiments were established on nutrient poor, sandy soils in Klosterheden National Forest and in Mangeh0je Forest Plantation in western Denmark to quantify the effect on site productivity of wholetree harvesting in early thinnings of Norway spruce. The growth response following biomass removal was investigated for four treatments: (1) no thinning (NT), (2) whole-tree harvesting in which the felled trees were removed immediately after thinning (WTHg~,,), (3) whole-tree harvesting in which the felled trees were left to dry in the stand during the following growing season so that some of the nutrient rich parts of the tree such as needles and twigs are returned to the forest floor (WTHo,7), and (4) harvesting of stems and coarse branches with needles and twigs being threshed from the branches and left in the stand (SCB). The results indicated that WTH~r¢~, might lead to a short-term reduction in stand volume increment of the remaining stand. Comparing the mean annual increment during the first four growing seasons after treatment, using the initial standing volume as a covariate, WTHgr~, caused a significant growth reduction of 10-18% at Klosterheden and 5-17% at Mangeh0je, compared to the SCB- and WTHdry-treatments. The effect of WTHgreen was attributed to an increased removal of essential nutrients such as N, P and K. The growth response following whole-tree harvesting was confined to the first four growing seasons and the effect of different treatments was not significant when data for all ten growing seasons were analysed.
03•00202 Sustainable fermentative hydrogen production: challenges for process optimisation Hawkes, F. R. et al. International Journal of Hydrogen Energy, 2002, 27, (11-12), 1339-1347. This paper reviews information from continuous laboratory studies of fermentative hydrogen production useful when considering practical applications of the technology. Data from reactors operating with pure cultures and mixed microflora enriched from natural sources are considered, lnocula have been derived from heat-treated anaerobically digested sludge, acti~'ated sludge, aerobic compost and soil, and nonheat-treated aerobically composted activated sludge. Most studies are on soluble defined substrates, and there are few reports of continuous operation on complex substrates with mixed microflora to produce H2. Methanogenesis which consumes H2 may be prevented by operation at short hydraulic retention times (around 8-12 h on simple substrates) and/or pH below 6. Although the reactor technology for anaerobic digestion and biohydrogen production from complex substrates may be similar, there are important microbiological differences, including the need to manage spore germination and oxygen toxicity on start-up and control sporulation in adverse circumstances during reactor operation.
26 Fuel and Energy Abstracts January 2003
03100203 Tailoring optical systems to optimized photobioreactors Gordon, J. M. et al. International Journal o[ Hydrogen Energy, 2002, 27, (11-12), 1175-1184. Photobioreactor designs are commonly restricted by the ability of conventional optical systems to deliver prescribed solar intensities and flux distributions at high collection efficiency. This paper explores how non-imaging optical designs can be tailored to reactor conditions that maximize bioproductivity. Two distinct classes of photobioreactors are considered: (1) stationary outdoor units; and (2) an indoor reactor that requires the total separation of the collection and delivery of solar radiation. For practical and economic reasons, the latter obliges solar collectors of immense optical concentration. The outdoor directillumination units comprise stationary mirrored troughs placed around standard reactor shapes, and replace expensive reactors with inexpensive reflectors, while enhancing bioproductivity. For the indoor reactors, the recent innovation of dual-axis tracking solar fiber-optic mini-dish concentrators were adopted to collect, concentrate and transport sunlight to a remote reactor. Contoured polymeric light extractors distribute the light uniformly and efficiently inside the reactor. In all cases, the principal demands are: (a) accommodating reactor shapes with high ratios of irradiated surface area to volume; (b) uniform flux on the irradiated surfaces; (c) high efficiency for collecting and delivering solar radiation; (d) being based on existing and affordable technologies; and (e) compactness. Flux levels of 2000 μmolm z s i of photosynthetically active radiation are realistically attainable over the entire transparent surface of the reactor.
Geothermal energy 03/00204 Performance of supercritical cycles for geothermal binary design Gu, Z. and Sato, H. Energy Conversion and Management, 2002, 43, (7), 961-971. Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the condensing temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design.
Solar energy 03/00205
Assessment of the dye-sensitized solar cell
McConnell, R. D. Renewable and Sustainable Energy Reviews, 2002, 6, (3), 271-293. The field of solar electricity, or photovoltaics (PV), is rich in that there are many materials and concepts for converting sunlight into electricity. The technologies accepted as conventional are those well along in the process of commercialization. The dye-sensitized solar cell, developed in the 1990s, is a nonconventional solar electric technology that has attracted much attention, perhaps a result of its record cell efficiency above 10%. This paper reviews the technology, discusses new research results and approaches presented at a recent symposium of many of the world's important dye solar cell researchers, and presents an assessment of the dye-sensitized solar cell in a comparison with current conventional solar electric technologies. It concludes the dye solar cell has potential for becoming a cost-effective means for producing electricity, capable of competing with available solar electric technologies and, eventually, with today's conventional power technologies. But it is a relatively new technology and faces many hurdles on the path to commercialization. Because of its potential, this assessment recommends further funding for research and development (R&D) of the dye-sensitized solar cell technology on the basis of the promising technical characteristics of the technology, a strong US and world-wide research base, positive industry interest, and today's relatively small funding allocation for its R&D.
03/00206 Calculation of solar irradiance profiles from hourly data to simulate energy systems behaviour Notton, G. et al. Renewable Energy, 2002, 27, (1), 123-142.
07 Alternative energy sources (solar energy) Three models (constant, linear and extraterrestrial) were compared w.hich simulate an hourly profile of solar irradiance and allow the determination, with a given reliability, of minute data of global solar irradiation from hourly measured irradiations. These models are compared from the point of view of various statistical tests using data collected on a Mediterranean site. The extraterrestrial model shows very satisfying results and improves greatly the accuracy compared with a constant model.
03/00207 Design, development and performance testing of a new natural convection solar dryer Pangavhane, D. R. et al. Energy, 2002, 27, (6), 579-590. Mechanical drying of agricultural products is an energy consuming operation in the post-harvesting technology. Greater emphasis is given to using solar energy sources in this process due to the high prices and shortages of fossil fuels. For these purposes, a new natural convection solar dryer consisting of a solar air heater and a drying chamber was developed. This system can be used for drying various agricultural products like fruits and vegetables. In this study, grapes were successfully dried in the developed solar dryer. The qualitative analysis showed that the traditional drying, i.e. shade drying and open sun drying, dried the grapes in 15 and 7 days respectively, while the solar dryer took only 4 days and produced better quality raisins.
03100208 Turkey
Estimation of solar radiation parameters for Izmir,
Ulgen, K. and Hepbasli, A. International Journal of Energy Research, 2002, 26, (9), 807-823. In this study, the solar radiation parameters (global and diffuse solar radiation) are correlated with respect to ambient temperatures in the fifth-order polynomial form for Izmir in Turkey. Experimental data were measured in the Solar-Meteorological Station of Solar Energy Institute in Ege University over a 5-year period, 1994-1998. The ratios of the total daily diffuse to global radiation intensities for each month range from 0.38 to 0.45 averaged for the same period, with an average value of 0.41. It can be concluded that the present models predict the solar radiation parameters reasonably well with the correlation coefficients over 0.95 for the projections.
03/00209 Experimental study of a tubeless convex type solar collector Abu-Qudais, M. et al. Energy Conversion and Management, 2002, 43, (6), 791-797. This paper describes the design and performance of a convex type of solar water heater. The main purpose of a convex solar collector is to accomplish static tracking for the sun radiation without additional cost, that is, to collect energy efficiently in the early and later times of the day due to the low angle of incidence with a high percentage of solar radiation perpendicular to the collector plate. Two adjacent types of collectors, fiat plate and convex type with the same projected area, were constructed and tested under the same conditions. Comparisons were made of the lumped efficiency and useful energy under different conditions. The efficiency and the useful energy were considerably greater of the convex type collector than for the flat plate collector under the same environmental and insolation conditions. An additional 45% energy gain was achieved from the convex type compared to the fiat plate collector.
03•00210 Means of enhancing and promoting the use of solar energy Bahaj, A. S. Renewable Energy, 2002, 27, (1), 97-105. The development of renewable technologies in the last decade has been exceptional. In photovoltaic (PV) for example, efforts were not only limited to merely improving their efficiency but also to the reduction of the cost of cells and modules via volume production for commercial markets. There are many national schemes promoting the use of PV technology and regional targets for a share of renewable energy production. This paper describes approaches for enhancing the prospect of utilizing solar energy within our society. The issue of expansion or enhancing the utilization of solar energy can be undertaken by individuals, groups, institutions and governments. The aim of this paper is to provide some examples, which could serve as a framework in which action could be taken to promote solar technology.
03/00211 Modelling solar half-hour data using fourth order cumulants Safi, S. et al. International Journal of Solar Energy, 2002, 22, (2), 67-81. In this study, there were two key objectives. The first one was to develop a new simple and efficient technique to identify the parameters of the moving average (MA) process using the technique of higlier order cumulants. The simulation for different orders of MA in the presence of Gaussian noise, for SNR lower than 20vdB, gives satisfactory results. The second objective involved adopting the proposed method for modelling half-hour solar radiation in Marra-
kesh. Accurate design and optimization of short response time solar energy systems with storage are sensitive to the stationary and sequential characteristics of half-hourly solar radiation. In order to benefit from some characteristics of stationary processes, a preliminary transformation was performed on the original data. The proposed method was used to look for a simple and efficient model to represent solar half-hourly radiation sequences needed for many applications in the solar energy field. The Giannakis technique based on cumulant diagonal slices and the partial autocorrelation function of Box & Jenkins and Brockwell & Davis were used for selection of the model order.
03/00212 Multimedia education program for an active solar hot water system Axaopoulos, P. et al. International Journal of Solar Energy, 2002, 22, (2), 83-92. An interactive multimedia education program has been developed to study the transient behaviour of an active solar heating system for domestic hot water production. The users can explore various cases, study what happens under different operating scenarios and examine the effects of altering conditions. In addition, simulation processes are used when a more quantitative understanding of the related subjects is needed, as they offer higher perceptual fidelity (i.e. more accurate representation of the situation being modelled). The simulation accounts for a large number of parameters and can be used to investigate their effects on the thermal efficiency of the solar collector and the system. It can also be used for an extensive set of exercises in the tertiary education sector. The operating principles and performance aspects of the different components have been considered providing a basis for understanding the components interaction and total system performance. The program is a user friendly, fast, easy-touse and a powerful educational tool.
03/00213 Performance of a natural circulation solar air heating system with phase change material energy storage Enibe, S. O. Renewable Energy, 2002, 27, (1), 69-86. The design, construction and performance evaluation of a passive solar powered air heating system is presented. The system, which has potential applications in crop drying and poultry egg incubation, consists of a single-glazed flat plate solar collector integrated with a phase change material (PCM) heat storage system. The PCM is prepared in modules, with the modules equispaced across the absorber plate. The spaces between the module pairs serve as the air heating channels, the channels being connected to common air inlet and discharge headers. The system was tested experimentally under daytime no-load conditions at Nsukka, Nigeria, over the ambient temperature range of 19-41°C, and a daily global irradiation range of 4.9-19.9 MJ m " . Peak temperature rise of the heated air was about 15 K, while the maximum airflow rate and peak cumulative useful efficiency were about 0.058 kg s 2 and 22%, respectively. These results show that the system can be operated successfully for crop drying applications. With suitable valves to control the working chamber temperature, it can also operate as a poultry egg incubator.
03/00214 Photo-electrochemical hydrogen generation from water using solar energy. Materials-related aspects Bak, T. et al. International Journal of Hydrogen Energy, 2002, 27, (10), 991-1022. The present work considers hydrogen generation from water using solar energy. The work is focused on the materials-related issues in the development of high-efficiency photo-electrochemical cells (PECs). The property requirements for photo-electrodes, in terms of semiconducting and electrochemical properties and their impact on the performance of PECs, are outlined. Different types of PECs are overviewed and the impact of the PEC structure and materials selection on the conversion efficiency of solar energy are considered. Trends in research in the development of high-efficiency PECs are discussed. It is argued that very sophisticated materials engineering must be used for processing the materials that will satisfy the specific requirements for photo-electrodes. An important issue in the processing of these materials is the bulk vs. interface properties at the solid/ solid interfaces (e.g. grain boundaries) and solid/liquid interfaces (e.g. electrode/electrolyte interface). Consequently, the development of PECs with the efficiency required for commercialization requires the application of up-to-date materials processing technology. As the production of hydrogen is expected to grow greatly by 2010, seed funding already has been allocated to several national research programs aiming at the development of hydrogen technology. The countries having access to this PEC technology are likely to form the OPEC of the future.
Fuel and Energy Abstracts January 2003 27
07 Alternative energy sources (wind energy) 03/00215 Photovoltaic module quality in the Kenyan solar home systems market Duke, R. D. et al. Energy Policy, 2002, 30, (6), 477-499. As one of the largest unsubsidized markets for solar home systems (SHS) in the world, Kenya represents a promising model for rural electrification based on private purchases of clean decentralized photovoltaic technologies. Small amorphous-silicon modules dominate the market and most brands provide high quality and affordable service. Product quality varies widely, however, and the public has limited capacity to distinguish among competing brands. This imposes direct hardships on households with the misfortune to purchase lowquality equipment, and it constrains sales as some customers refrain from purchasing solar equipment due to the associated performance uncertainty. This article analyses market failure associated with photovoltaic module quality in the Kenyan SHS market and develops strategies to address the problem - emphasizing that similar quality problems may exist for other SHS components and in other markets. The principal conclusion is that domestic pro~]uct testing with public disclosure represents an inexpensive low-risk strategy, but it may prove inadequate. Mandatory product quality standards based on international testing regimes (e.g. IEC standards), augmented with a basic domestic testing option, would provide stronger assurance, but the risks associated with this intervention suggest caution. An emerging multilateral SHS market support effort (PVMTI) should ensure quality for the credit-based sales it promotes in Kenya; however, the long-term impact of this approach is not yet clear and is unlikely to address quality problems associated with the existing unsubsidized sales-based markets for SHS. Finally, fee-for-service models would decisively address quality problems, but launching this model in the Kenyan market would likely require large subsidies.
03•00216 Useful solar heat gains in multi-zone nondomestic buildings as a function of orientation and thermal time constant Yohanis, Y. G. and Norton, B. Renewable Energy, 2002, 27, (1), 87-95. Two parameters affecting useful solar absorption are orientation and thermal mass. Solar energy absorption in buildings depends on these parameters in a complex manner particularly when considering large glazing ratios and large direct components of insolation. Therefore, where parameters of different zones in a multi-zone building vary, useful solar absorption will also vary. For higher northern latitudes, compared with south orientation, useful solar absorption differs by about 2, 4 and 6% between large and small time constants for east, west and north orientations, respectively. The smallest and largest differences are for east and north orientations, respectively. Fenestration design should be a consequence of orientation and overshading, seeking to balance daylight, solar gains and heat losses.
Wind energy 03/00217
A next generation wind power technology?
behaviour of wind parks erected during 1985-1995 in Greece, significantly improved the accuracy of predictions in comparison with the results based on time-mean values of the corresponding parameters. Finally, the proposed model satisfactorily explains the evolution of wind energy applications in Greece during the last 15 years, on the basis of pure economic terms.
03100219 Investigation on wind power potential on Hong Kong islands - an analysis of wind power and wind turbine characteristics Lu, L. et al. Renewable Energy, 2002, 27, (1), 1-12. This paper discusses the potential for electricity generation on Hong Kong islands through an analysis of the local weather data and typical wind turbine characteristics. An optimum wind speed, Uop, is proposed to choose an optimal type of wind turbine for different weather conditions. A simulation model has been established to describe the characteristics of a particular wind turbine. A case study investigation allows wind speed and wind power density to be obtained using different hub heights, and the annual power generated by the wind turbine to be simulated. The wind turbine's capacity factor, being the ratio of actual annual power generation to the rated annual power generation, is shown to be 0.353, with the capacity factor in October as high as 0.50. The simulation shows the potential for wind power generation on the islands surrounding Hong Kong.
03/00220 Management of fluctuations in wind power and CHP comparing two possible Danish strategies Lund, H. and Clark, W. W. Energy, 2002, 27, (5), 471J,83. Both CHP (combined heat and power production) and wind power are important elements of Danish energy policy. Today, approximately 50% of both the Danish electricity and heat demand are produced in CHP and more than 15% of the electricity demand is produced by wind turbines. Both technologies are essential for the implementation of Danish climate change response objectives, and both technologies are intended for further expansion in the coming decade. Meanwhile, the integration of CHP and wind power is subject to fluctuations in electricity production. Wind turbines depend on the wind, and CHP depends on the heat demand. This article discusses and analyses two different national strategies for solving this problem. One strategy, which is the current official government policy known as the export strategy, proposes to take advantage of the Nordic and European markets for selling and buying electricity. In this case, surplus electricity from wind power and CHP simply will be sold to neighbouring countries. Another strategy, the self-supply strategy, runs the CHP units to meet both demand and the fluctuations in the wind scheduling. In this case, investments in heat storages are necessary and heat pumps have to be added to the CHP units. Based on official Danish energy policy and energy plans, this article quantifies the problem for the year 2015 in terms of the amount of surplus electricity, and investments in heat pumps, etc. needed to solve the problem are calculated. Based on these results between the two different strategies, the conclusion is that the self-supply strategy is recommended over the official export strategy.
03•00221 art
Offshore wind in Europe: the current state of the
Weisbrich, A. L. Refocus, 2002, 3, (2), 26-29. Present day wind turbines (large blade Props on Pole or POPs) have continued to evolve to ever larger sizes requiring massive blades, gearboxes or large, complex customized generators. This continuous increase in size has subsequently increased the costs and complexity of manufacturing, transporting, constructing and maintaining these systems. This article discusses an alternative wind power technology design, the Wind Amplified Rotor Platform which uses many identical smaller vertically integrated modules as opposed to one large generator. The modular design can be easily and relatively inexpensively volume produced and implemented both in traditional electric utility scale wind farms as well as in marine based offshore wind farms sites.
Henderson, A. R. R¢[ocus, 2002, 3, (2), 4 17. After several decades of theoretical developments, desk studies, experimental wind turbines and prototype windfarms, the first largescale commercial developments of offshore windfarms are now being built. To support and accelerate this development, the European Commission funded a project, 'Concerted Action on Offshore Wind Energy in Europe' (CA-OWEE), which aimed to gather and distribute knowledge on all aspects of offshore wind energy, including: offshore technology, electrical integration, economics, environmental impacts and political aspects. The partners are from a wide range of fields and include developers, utilities, consultants, research institutes and universities.
03/00218 An integrated time-depending feasibility analysis model of wind energy applications in Greece Kaldellis, J. K. Energy Policy, 2002, 30, (4), 267-280.
03/00222 Small wind turbines: the unsung heroes of the wind industry Anon, Refocus, 2002, 3, (2), 30.
An integrated time-depending feasibility analysis is presented in order to improve the reliability of the computational methods to simulate the e c o n o m i c behaviour of commercial wind parks in Greece, in view of the continuous technological improvements of the sector and the important world-wide political and economic transformations. According to the proposed model, the time-dependency of the governing parameters is taken into account based data from the local market records covering almost 20 years. In addition, information from several European and local wind parks is also incorporated. The application of the developed computational frame to several cases, concerning the economic
26
Fuel and Energy Abstracts January 2003
Most discussions concerning wind energy usually focus on utility-size projects on a megawatt scale and how to get such projects off the ground. Whilst silently whirring away in the background are the millions of small (less than 100 kW) and micro-turbines (less than 5 kW) that have been installed on a huge scale for decades making significant contributions to supplying electricity in off-grid and grid connected areas. This article takes a closer look at these unsung heroes of wind, issues surrounding their installation and use, and highlight companies around the world that manufacture a variety of small and micro-wind turbines for a range of applications.