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Thermal Efficiency (thermal + efficiency)
Selected AbstractsComparison of drying behaviour, quality and yield of copra processed in either a solar hybrid dryer on in an improved copra kilnINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2007Thiruchelvam Thanaraj Summary Drying copra in a solar hybrid dryer reduces the moisture content from around 50% to 7% after 71 h of continuous drying. The copra was graded as 73% white copra, 21% Milling Ordinary Grade II (M.O.GII) and the remaining 6% M.O.GIII (dusty copra). Thermal efficiency was about 10%. In the Coconut Research Institute copra kiln, the moisture content of copra was reduced from around 52% to 8% in 62 h of intermittent dying. The copra was graded as about 82% M.O.GI and the remaining 18% M.O.GIII (burnt copra). Thermal efficiency was about 15.5%. High quality white copra could be processed in solar hybrid drying. However, no white copra could be processed in kiln drying. [source] Theoretical performance analysis of the multi-stage gas,solid fluidized bed air preheaterINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2001Sang Il Park Abstract The multi-stage fluidized bed can be used to preheat the combustion air by recovering the waste heat from the exhaust gas from industrial furnaces. The dilute-phase fluidized bed may be formed to exclude the excessive pressure drop across the multi-stage fluidized bed. But, in this case, the solid particles do not reach to the thermal equilibrium due to relatively short residence time in each layer of fluidized bed. In this study, a theoretical analysis on the dilute phase multistage fluidized bed heat exchanger was performed. A parameter related to the degree of thermal equilibrium between gas and solid particles at the dilute-phase fluidized beds was derived. Using this parameter, a relatively simple expression was obtained for the thermal efficiencies of the multi-stage fluidized bed heat exchanger and air preheater. Copyright © 2001 John Wiley & Sons, Ltd. [source] Materials Selection for Optimal Design of a Porous Radiant Burner for Environmentally Driven Requirements,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Jaona Randrianalisoa Combustion supports which optimize a porous radiant burner are identified using a material selection approach. The optimization requirements account for the environmental aspect such as lower pollution. It was shown that high porosity metallic materials such as FeCrAlY foam, is always preferable in terms of pollution. From the viewpoint of thermal efficiency, metallic foams are better at high in-flux while Mullite foam takes over at low in-flux. [source] The heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (the heat transfer and pressure loss characteristics of the heat exchanger with wing fin)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2007Kiyoshi Kawaguchi Abstract In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods of improving thermal efficiency by recovering latent heat. This paper described the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having a wing fin (fin pitch: 4 mm, fin length: 65 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of heat exchanger, and the heat transfer coefficient between outer fin surface and gas. The effects of condensate behavior in the fins on heat transfer and pressure loss characteristics were clarified. Furthermore, the equations for predicting the heat transfer coefficient and pressure loss which are necessary in the design of the heat exchanger were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 215,229, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20154 [source] An experimental investigation on manifold-injected hydrogen as a dual fuel for diesel engine system with different injection durationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2009N. Saravanan Abstract Stringent emission norms and rapid depletion of petroleum resources have resulted in a continuous effort to search for alternative fuels. Hydrogen is one of the best alternatives for conventional fuels. Hydrogen has both the benefits and limitation to be used as a fuel in an automotive engine system. In the present investigation, hydrogen was injected into the intake manifold by using a hydrogen gas injector and diesel was introduced in the conventional, mode which also acts as an ignition source for hydrogen combustion. The flow rate of hydrogen was set at 5.5,l,min,1 at all the load conditions. The injection timing was kept constant at top dead center (TDC) and injection duration was adjusted to find the optimized injection condition. Experiments were conducted on a single cylinder, four stroke, water-cooled, direct injection diesel engine coupled to an electrical generator. At 75% load the maximum brake thermal efficiency for hydrogen operation at injection timing of TDC and with injection duration of 30°CA is 25.66% compared with 21.59% for diesel. The oxides of nitrogen (NOX) emission are 21.7,g,kWh,1 for hydrogen compared with diesel of 17.9,g,k,Wh,1. Smoke emissions reduced to 1 Bosch smoke number (BSN) in hydrogen compared with diesel of 2.2 BSN. Hydrogen operation in the dual fuel mode with diesel exhibits a better performance and reduction in emissions compared with diesel in the entire load spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Energy efficiency improvement strategies for a diesel engine in low-temperature combustionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2009Ming Zheng Abstract The lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and soot simultaneously, which can be implemented by the heavy use of exhaust gas recirculation (EGR) or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low-temperature combustion (LTC) cycles is commonly compromised by the high levels of hydrocarbon and carbon monoxide emissions. More seriously, the scheduling of fuel delivery in HCCI engines has lesser leverage on the exact timing of auto-ignition that may even occur before the compression stroke is completed, which may cause excessive efficiency reduction and combustion roughness. New LTC control strategies have been explored experimentally to achieve ultralow emissions under independently controlled EGR, intake boost, exhaust backpressure, and multi-event fuel-injection events. Empirical comparisons have been made between the fuel efficiencies of LTC and conventional diesel cycles. Preliminary adaptive control strategies based on cylinder pressure characteristics have been implemented to enable and stabilize the LTC when heavy EGR is applied. The impact of heat-release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with engine cycle simulations. This research intends to identify the major parameters that affect diesel LTC engine thermal efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modeling and optimization of a novel pressurized CHP system with water extraction and refrigerationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008J. R. Khan Abstract A novel cooling, heat, and power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a vapor absorption refrigeration system (VARS). The semi-closed Brayton cycle is called the high-pressure regenerative turbine engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400°C. This thermal efficiency, is in addition to the large external cooling load, generated in the combined cycle, which is 13% of the net work output. In addition, it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd. [source] The influence of rotary valve distribution systems on the energetic efficiency of regenerative thermal oxidizers (RTO)INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2008Mario Amelio Abstract On,off valve systems, commonly used in regenerative thermal oxidizer (RTO) plants, generate, during the opening time, a mass flow rate (MFR) which is constant. On the contrary, rotary valve systems, which are increasingly adopted in RTO plants, are characterized by variable MFR profiles. In this work, the energy requirements of two RTO systems, equipped with on,off or rotary valves, were determined using a home-developed numerical code. Energy performances were evaluated by calculating the thermal efficiency and pressure drop within structured or random packed bed RTO systems, at the same mean MFR. The results demonstrated that thermal efficiency was only moderately influenced by the valve system, and is slightly lower for the RTO with on,off valve. On the other hand, the study revealed that energy requirements of all RTO systems were basically unaffected by cycle duration, allowing valve rotational velocity to be freely set to maximize for other technical requirements. On the contrary, pressure drop was greatly influenced by the valve type and increased as variability in MFR function augmented. Moreover, the type of regenerator, structured or random packed bed, affected differently the total energy requirements (basically pumping energy plus auxiliary fuel). Energy requirements of structured and random regenerators were comparable only when volatile organic compounds concentration was lower than typical values encountered in the industrial practise. In other cases, structured regenerators RTO were more competitive. Finally, structured regenerators are usually the best choice when rotating valve distribution systems are adopted. Copyright © 2007 John Wiley & Sons, Ltd. [source] Comparative thermal performance evaluation of an active solar distillation systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2007G. N. Tiwari Abstract In this paper, thermal models of all types of solar collector-integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35,N, 77°12,E, 216 m above MSL). The thermal model of flat-plate collector integrated with active solar still was validated using the experimental test set-up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m,2 day,1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermodynamic analysis of spark-ignition engine using a gas mixture model for the working fluidINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2007E. Abu-Nada Abstract This paper presents thermodynamic analysis of spark-ignition engine. A theoretical model of Otto cycle, with a working fluid consisting of various gas mixtures, has been implemented. It is compared to those which use air as the working fluid with variable temperature specific heats. A wide range of engine parameters were studied, such as equivalence ratio, engine speed, maximum and outlet temperatures, brake mean effective pressure, gas pressure, and cycle thermal efficiency. For example, for the air model, the maximum temperature, brake mean effective pressure (BMEP), and efficiency were about 3000 K, 15 bar, and 32%, respectively, at 5000 rpm and 1.2 equivalence ratio. On the other hand, by using the gas mixture model under the same conditions, the maximum temperature, BMEP, and efficiency were about 2500 K, 13.7 bar, and 29%. However, for the air model, at lower engine speeds of 2000 rpm and equivalence ratio of 0.8, the maximum temperature, BMEP, and efficiency were about 2000 K, 8.7 bar, and 28%, respectively. Also, by using the gas mixture model under these conditions, the maximum temperature, BMEP, and efficiency were about 1900 K, 8.4 bar, and 27%, i.e. with insignificant differences. Therefore, it is more realistic to use gas mixture in cycle analysis instead of merely assuming air to be the working fluid, especially at high engine speeds. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance enhancement of gas turbines by inlet air-cooling in hot and humid climatesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2006Majed M. Alhazmy Abstract In this paper, a model to study the effect of inlet air-cooling on gas turbines power and efficiency is developed for two different cooling techniques, direct mechanical refrigeration and an evaporative water spray cooler. Energy analysis is used to present the performance improvement in terms of power gain ratio and thermal efficiency change factors. Relationships are derived for an open gas turbine cycle with irreversible compression and expansion processes coupled to air-cooling systems. The obtained results show that the power and efficiency improvements are functions of the ambient conditions and the gas turbine pressure ratio. The performance improvement is calculated for, ambient temperatures from 30 to 50°C, the whole range of humidity ratio (10,100%) and pressure ratio from 8 to 12. For direct mechanical refrigeration air-cooling, the power improvement is associated with appreciable drop in the thermal efficiency. The maximum power gain can be obtained if the air temperature is reduced to its lowest limit that is the refrigerant evaporation temperature plus the evaporator design temperature difference. Water spray cooling process is sensitive to the ambient relative humidity and is suitable for dry air conditions. The power gain and efficiency enhancement are limited by the wet bulb temperature. The performance of spray evaporative cooler is presented in a dimensionless working graph. The daily performance of the cooling methods is examined for an ABB-11D5 gas turbine operating under the hot humid conditions of Jeddah, Saudi Arabia. The results indicate that the direct mechanical refrigeration increased the daily power output by 6.77% versus 2.57% for the spray air-cooling. Copyright © 2005 John Wiley & Sons, Ltd. [source] A new type of EFHAT power generation system with effective utilization of latent heatINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2005Hongguang Jin Abstract On the basis of synergetic integration of an externally fired humid air turbine (EFHAT) cycle and effective recovery of latent heat from the exhaust gas of gas turbine, we have proposed a new type of EFHAT power generation system with effective utilization of latent heat, different from traditional EFHAT system. Due to use of clean humid air as working substance, latent heat can be recovered and utilized to generate hot water for the humidifier. This will enhance the humidification ability, giving rise to performance improvement of the system. As a result, at the turbine inlet temperature of 1123 K, the thermal efficiency of this new system may be expected to be as high as 47,48%. Additionally, we obtained the analytical expressions of system performance, and disclosed the relative relationship of system efficiency between the new EFHAT system and the pure externally fired power system. Copyright © 2005 John Wiley & Sons, Ltd. [source] Parametric study of chemical looping combustion for tri-generation of hydrogen, heat, and electrical power with CO2 captureINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2005J. Wolf Abstract In this article, a novel cycle configuration has been studied, termed the extended chemical looping combustion integrated in a steam-injected gas turbine cycle. The products of this system are hydrogen, heat, and electrical power. Furthermore, the system inherently separates the CO2 and hydrogen that is produced during the combustion. The core process is an extended chemical looping combustion (exCLC) process which is based on classical chemical looping combustion (CLC). In classical CLC, a solid oxygen carrier circulates between two fluidized bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO2 separation occurs. In exCLC the oxygen carrier circulates along with a carbon carrier between three fluidized bed reactors, one to oxidize the oxygen carrier, one to produces and separate the hydrogen, and one to regenerate the carbon carrier. The impacts of process parameters, such as flowrates and temperatures have been studied on the efficiencies of producing electrical power, hydrogen, and district heating and on the degree of capturing CO2. The result shows that this process has the potential to achieve a thermal efficiency of 54% while 96% of the CO2 is captured and compressed to 110 bar. Copyright © 2005 John Wiley & Sons, Ltd. [source] Influence of the heat recovery steam generator design parameters on the thermoeconomic performances of combined cycle gas turbine power plantsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2004Manuel Valdés Abstract This paper proposes a methodology to identify the most relevant design parameters that impact on the thermal efficiency and the economic results of combined cycle gas turbine power plants. The analysis focuses on the heat recovery steam generator (HRSG) design and more specifically on those operating parameters that have a direct influence on the economic results of the power plant. These results are obtained both at full and part load conditions using a dedicated code capable of simulating a wide number of different plant configurations. Two different thermoeconomic models aimed to select the best design point are proposed and compared: the first one analyzes the generating cost of the energy while the second one analyzes the annual cash flow of the plant. Their objective is to determine whether an increase in the investment in order to improve the thermal efficiency is worth from an economic point of view. Both models and the different HRSG configurations analysed are compared in the results section. Some parametric analysis show how the design parameters might be varied in order to improve the power plant efficiency or the economic results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Analysis of an unconventional cycle as a new comparison standard for practical heat engines: the circular/elliptical cycle in T,S diagramINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2004Bahri Sahin Abstract An unconventional cycle analysis in the T,S diagram has been carried out and the cycle characteristics such as thermal efficiency, work density (defined as the ratio of the network output to the maximum volume in the cycle), maximum volume and maximum pressure are determined. The obtained results for the unconventional cycle are compared with those of the Carnot cycle. It is proposed that the analysed unconventional cycle may be used as a better comparison standard than the Carnot cycle for practical heat engines when both size and thermal efficiency are considered. Copyright © 2004 John Wiley & Sons, Ltd. [source] Recovery of CO2 with MEA and K2CO3 absorption in the IGCC systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2004Baoqun Wang Abstract Recovery of CO2 with monoethanolamine (MEA) and hot potassium carbonate (K2CO3) absorption processes in an integrated gasification combined cycle (IGCC) power plant was studied for the purpose of development of greenhouse gas control technology. Based on energy and exergy analysis of the two systems, improvement options were provided to further reduce energy penalty for the CO2 separation in the IGCC system. In the improvement options, the energy consumption for CO2 separation is reduced by about 32%. As a result, the thermal efficiency of IGCC system is increased by 2.15 percentage-point for the IGCC system with MEA absorption, and by 1.56 percentage-point for the IGCC system with K2CO3 absorption. Copyright © 2004 John Wiley & Sons, Ltd. [source] Friction effect on the characteristic performance of Diesel enginesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2002Lingen Chen Abstract An irreversible model for an air standard Diesel engine is presented in this paper. This model takes into account the finite-time evolution of the cycle's compression and power strokes and it considers global losses lumped in a friction-like term. The relations between the power output and the compression ratio, as well as between the thermal efficiency and the compression ratio are derived. The maximum power output with the corresponding efficiency, and the maximum efficiency with the corresponding power output are calculated versus compression ratio. Copyright © 2002 John Wiley & Sons, Ltd. [source] Toward a Microfluidic-Based Rapid Amylase Assay SystemJOURNAL OF FOOD SCIENCE, Issue 6 2009Richard J. Holmes ABSTRACT:, This article describes work into a prototype system for the assay of amylase, using microfludic technologies. The new system has a significantly shorter cycle time than the current laboratory methods, which generally use microtitre plates, yet is capable of generating significantly superior results. As such, we have shown that sensitivity is enhanced by a factor of 10 in the standard assay trials, and by a factor of 2 in the real-sample lab trials. In both assays, the use of a microreactor system reduced the reaction time by a factor of 6.2, from 20 min incubation to 3.2 min. Basing the conclusion on the Megazyme Cerealpha Standard Method, and using the Cerealpha units as a measure of assay efficiency, the typical response for the microfluidic assay was shown to be 1.0 × 10,3 CU/mL (standard deviation [SD] 2.5 × 10,4 CU/mL), compared to 2.56 × 10,4 CU/mL (SD 5.94 × 10,5 CU/mL) for the standard macroassay. It is believed that this improvement in the reaction schematics is due to the inherent advantages of microfluidic devices such as superior mixing, higher thermal efficiency, and enhanced reaction kinetics. [source] Methane steam reforming at microscales: Operation strategies for variable power output at millisecond contact timesAICHE JOURNAL, Issue 1 2009Georgios D. Stefanidis Abstract The potential of methane steam reforming at microscale is theoretically explored. To this end, a multifunctional catalytic plate microreactor, comprising of a propane combustion channel and a methane steam reforming channel, separated by a solid wall, is simulated with a pseudo 2-D (two-dimensional) reactor model. Newly developed lumped kinetic rate expressions for both processes, obtained from a posteriori reduction of detailed microkinetic models, are used. It is shown that the steam reforming at millisecond contact times is feasible at microscale, and in agreement with a recent experimental report. Furthermore, the attainable operating regions delimited from the materials stability limit, the breakthrough limit, and the maximum power output limit are mapped out. A simple operation strategy is presented for obtaining variable power output along the breakthrough line (a nearly iso-flow rate ratio line), while ensuring good overlap of reaction zones, and provide guidelines for reactor sizing. Finally, it is shown that the choice of the wall material depends on the targeted operating regime. Low-conductivity materials increase the methane conversion and power output at the expense of higher wall temperatures and steeper temperature gradients along the wall. For operation close to the breakthrough limit, intermediate conductivity materials, such as stainless steel, offer a good compromise between methane conversion and wall temperature. Even without recuperative heat exchange, the thermal efficiency of the multifunctional device and the reformer approaches ,65% and ,85%, respectively. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Steady-state multiplicity, flashback, and control issues in CH4 radiant burnersAICHE JOURNAL, Issue 9 2004M. Bizzi Abstract Methane is widely employed as a source of energy in combustion systems. Among the currently available technologies, radiant heaters offer high thermal efficiency and low environmental impact in comparison with atmospheric burners. The present work deals with the modeling of methane combustion in a noncatalytic metal fiber burner, represented by means of one-dimensional transient equations. The model accounts for a detailed reaction mechanism, radiation within the porous medium, longitudinal heat and mass transfer. After its validation, the model was employed to analyze a typical stability problem that affects these systems: under given operating conditions (low specific power inputs and excess of air) the occurrence of flashback may in fact preclude the safe operation of the system. As a consequence of energy radiation in the upstream direction, the burner upstream surface and the plenum chamber might become hot enough to heat in turn the gas feedstock, thus eventually determining flashback. In this paper, the mechanism of flashback is numerically investigated as a function of the burner structure and operating conditions by means of a model analysis so as to single out regions of flashback occurrence and a criterion for safe operation. Finally, some guidelines are outlined for a cheap and effective control of the system, paving the way for possible improvement of currently adopted control systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2276,2286, 2004 [source] Enhancing thermal, electrical efficiencies of a miniature combustion-driven thermophotovoltaic systemPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2009Yueh-Heng Li Abstract Methods to enhance the thermal and electrical efficiencies through novel design of combustion and thermal management of the combustor in a miniature thermophotovoltaic (TPV) system are proposed, discussed, and demonstrated in this paper. The miniature TPV system consists of a swirling combustor surrounded by GaSb PV cell arrays. The swirl combustor design, along with a heat-regeneration reverse tube and mixing-enhancing porous-medium fuel injection, improves the low illumination and incomplete combustion problems associated with typical miniature TPV systems. A reverse tube is used to enforce swirling flame attachment to the inner wall of the emitter by pushing the swirl recirculation zone back into the chamber and simultaneously redirecting the hot product gas for reheating the outer surface of the emitter. The porous medium fuel injector is used as a fuel/air mixing enhancer and as a flame stabilizer to anchor the flame. The miniature TPV system, using different combustor configurations, is tested and discussed. Results indicate that the proposed swirling combustor with a reverse tube and porous medium can improve the intensity and uniformity of the emitter illumination, and can increase the thermal radiant efficiency. Consequently, the overall thermal efficiency and electrical output of the miniature TPV system are greatly enhanced. Copyright © 2009 John Wiley & Sons, Ltd. [source] PV thermal systems: PV panels supplying renewable electricity and heatPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2004Dr. Wim G. J. van Helden Abstract With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat-collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set-up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost-effective manner than separate PV and solar thermal systems and thus contribute to the long-term international targets on implementation of renewable energy in the built environment. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||