Façade solar collectors

Rational use of energy in buildings leads to a concept of active energy façades such as transparently insulated massive walls, solar thermal or PV façades, advanced glazings for daylighting purposes or double ventilated façades. The paper is concerned with the façade-integrated solar thermal collectors concept for water heating in the existing building stock in the Czech Republic (panel and brick blocks of flats), which are ready for major renovations. Thermal behavior of façade collectors compared with standard roof-located collectors in solar DHW systems was investigated. Façade solar collectors should have an area increased by approximately 30% to achieve the usual 60% solar fraction compared with conventional roof solar collectors with a 45° slope. Further increases in the solar fraction above 70% lead to a required area comparable with roof collectors but with less stagnation periods compared with roof collectors. Application of façade solar collectors affects the indoor comfort in buildings in a reasonable range. Indoor temperatures increase by no more than 1 K in all investigated configurations. Building behavior is not strongly affected by façade collectors when sufficient insulation layers are present.     

Wind energy potential of the region of Trás-os-Montes and Alto Douro, Portugal

The main objective of this paper is to present a study on the wind energy potential that is being developed in the Region of Trás-os-Montes and Alto Douro. This study started in July 1996 and will continue until the end of 1998.In order to have an adequate characterisation of the wind energy potential in this region it is necessary to measure the wind speed and direction in several places. At this moment the data are being collected at nine places. Due to lack of space, only four places will be addressed in this article.The Region of Douro and Alto Trás-os-Montes has an area of 12,235 km². It is located in the Northeast part of Portugal and represents 57.7% of the North Region.Other projects refer to this region as having great potential in the field of renewable energies. From the analysis of the collected data, it seems that wind energy in Marão and Alvão mountains is one of the most interesting renewable energies.     

Chlorin-based supramolecular assemblies for artificial photosynthesis

Photosynthetic reaction center models consisting of zinc 9-desoxo-pyrochlorophyllide a primary electron donors, ZC, that are directly bonded at their 3-position to the 5-position of a 2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin ZP, which is in turn bonded at its 15-position to 2-triptycenenaphthoquinone, 2-triptycenebenzoquinone, 1-triptycenebenzoquinone, or N-(4-phenyl),N′-(n-octyl)-1,4,5,8-naphththalediimide 1, 2, 3, and 4, respectively, were prepared. Steric hindrance between adjacent substituents positions the π system of the chlorophyll perpendicular to that of the porphyrin. In turn, the π system of the chlorophyll is held about 60° to that of the O-O axis of the quinones in 1 and 2, parallel to the quinone O-O axis in 3, and parallel to the N-N axis in the diimide acceptor in 4. The resulting structures place the ZC donors in 1, 2, 3 and 4 at fixed center-to-center distances of 20, 18, 14, and 21 å from the acceptors, respectively. Photoexcitation of 1-4 in 2-methyltetrahydrofuran glass at 77K results in a single observable electron transfer reaction: ZC-ZP-X^1* ZC-ZP-X → ZC⁺-ZP-X⁻, where X = benzoquinone (BQ), naphthoquinone (No) or naphthalenediimide (NI), that occurs with τ = 4.5, 3.3, 2.0, and 2.0 ps for 1, 2, 3, and 4, respectively. The final ZC⁺-ZP-X⁻ radical pairs live for 12.7, 8.4, 2.5, and 10 ms at 77K in 1, 2, 3, and 4, respectively, and exhibit spin-polarized EPR spectra characteristic of spin-correlated radical pairs. The EPR spectra of 1-4 can be simulated using the distances and orientations of the radicals relative to one another determined from the molecular structures of 1-4. These long-lived, spin-polarized radical ion pairs closely mimic the bacteriochlorophyll cation - quinone anion radical pair produced in photosynthetic reaction centers and provide a useful tool for studying the interaction of the surrounding medium with the charge separated radical ion pair.     

Ruthenium (II) complexes with π expanded ligand having phenylene–ethynylene moiety as sensitizers for dye-sensitized solar cells

Ruthenium(II) complexes by introducing phenylene–ethynylene subunit into a tpy (tpy=2,2′:6′,2″-terpyridine) ligand were newly synthesized, and their photophysical and photochemical properties were characterized. The molar extinction coefficients of these dyes were larger than that of black dye. The photovoltaic performances of the solar cells based on these synthesizing dyes were investigated under AM 1.5 irradiation (100 mW cm^?2). The conversion efficiencies of 1a and 1b were 5.7% and 2.4%, respectively.     

Investment cost for geothermal power plants

Stepwise development strategy is considered a suitable method for securing a cost-effective way for the development of geothermal power plants. This strategy has been in use in Iceland for the last decade. Geothermal high-temperature fields are developed in steps of 20–30 MW. About 6 years are required for each step in the development. Parallel development of several fields in a country might be preferable, especially when a rapid increase of the generation capacity is required in that country. The capacity factor of geothermal power plants depends on the mix of power plants serving the electricity grid. Where geothermal power plants can be operated as base load, the capacity factor is usually in excess of 0.9. The investment cost of geothermal power plants is divided into the cost of surface equipment and activities and the cost of subsurface investment. The surface costs include the cost of surface exploration, and the plant and steam-gathering system, while the cost of subsurface investment is that of drilling. Surface equipment costs can be estimated with the same accuracy as other construction works at the surface (buildings, roads, bridges), whereas higher uncertainty might be associated with the cost of drilling. Analyses of the surface costs of five power plants in Iceland show that the investment cost of the surface equipment is linear with size, in the range 20–60 MW. Surface costs were found to be about 1000 USD/kW with a relative error of 10%. Stefánsson (Stefánsson, V., 1992. Success in geothermal development. Geothermics 21, 823–834) published a statistical study of the drilling results in 31 high-temperature fields in the world. Using these results, it is possible to estimate the expectation value and its limits of error for the subsurface investment in an arbtitrary geothermal field. The results obtained for the range 20–60 MW are summarized as follows:

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Spatial assessment of the bioenergy potential of forest residues in the western province of Spain, Caceres

The present work is mainly devoted to provide a rigorous analysis on the quantification, the mapping and the management of the bioenergy potential of forest residues from the most representative forestry species of the west-central region of Spain (Cáceres).An appropriate methodological approach for the estimate of potential biomass and potential bioenergy as well as the use of GIS for data process are both crucial for the design of thermal plants and for the accurate estimate of biomass collection and transportation costs, according to the scale economy of the plant.The total forest residues in the province of Cáceres are estimated as 463 000 t y⁻¹. The availability of such major biomass potential for energy production is strongly conditioned to the inherent difficulties during the extraction process. This way, an energy potential of 139 000 toe y⁻¹ would be achieved if the above-mentioned biomass collection rate is assumed.The method to optimise the search for suitable locations for thermal plants as well as for biomass extraction/collection areas, based on the combined use of GIS and spatial analysis techniques, is also described.     

Ecoulement de fluides non newtoniens a travers des elargissements brusques

The present paper is concerned with non newtonian pseudoplastic fluid flow across an abrupt enlargement. Basic equations are integrated by a finite volume scheme. The obtained results clearly display the stabilizing effect of fluid pseudoplasticity. The recirculation zone and re-establishment length diminish when behaviour index decreases. It is noticed that there is an agreement between the numerical results and the results of experimental study carried out in our laboratory.

Résumé

La présente étude concerne l'écoulement de fluides non newtoniens pseudoplastiques à travers des élargissements brusques. Les calculs sont effectués par un code aux volumes finis. L'effet stabilisant du caractère rhéofluidifiant du fluide est mis en évidence. La zone de recirculation et la longueur d'établissement diminuent quand l'indice de structure décroît. Il y a un bon accord entre nos résultats numériques et les résultats des études expérimentales réalisées dans notre laboratoire.     

Geochemical monitoring of the Krafla and Námafjall geothermal areas, N-Iceland

The Krafla and Námafjall high-temperature geothermal areas in N-Iceland have been exploited for steam production since the late and early 1970s, respectively. Power generation at Krafla was 30 MW until 1998, when it was increased to 60 MW. At Námafjall the steam has been utilized for operating a 3 MW back-pressure turbine unit, drying of diatomaceous earth and heating of fresh water for space heating. A total of 34 wells have been drilled at Krafla, of which 18 are producing at present. At Námafjall 12 wells have been drilled but only three are productive. The highest temperatures recorded downhole are 320 and 350 °C at Námafjall and Krafla, respectively. Geochemical monitoring in the two fields during the last 20–25 years has revealed decreases in the Cl concentrations in the water discharged from most of the wells that have been producing for more than 10 years. The cause is enhanced colder water recharge into the producing aquifers of these wells due to depressurization by fluid withdrawal from the geothermal reservoir. Such recharge is particularly pronounced in the central part of the Leirbotnar wellfield at Krafla but it is also extensive in the only producing well in the Hvíthólar wellfield. At Námafjall incursion of cold groundwater into the reservoir was particularly intense subsequent to the volcanic-rifting event in the area in 1977. Solute (quartz, Na/K, Na/K/Ca) geothermometry temperatures have decreased significantly in those wells where Cl concentrations have decreased but only to a limited extent in those wells which have remained constant in Cl. This indicates that the changes in the concentrations of the reactive components, on which these geothermometers are based, is largely the consequence of colder water recharge and not partial re-equilibration in the depressurization zone around wells where cooling of the fluid occurs in response to extensive boiling. Aqueous SO₄ concentrations increase as Cl concentrations decrease. Except for the hottest wells, which are low in SO₄, sulphate concentrations are controlled by anhydrite solubility. Increase in SO₄ concentrations is a reflection of cooling as anhydrite has retrograde solubility with respect to temperature. H₂S-temperatures are similar to the solute geothermometry temperatures for wells with a single feed. They are, on the other hand, higher, for wells with multiple feeds, if the feed zones have significantly different temperatures. H₂-temperatures are anomalously high for most wells due to the presence of equilibrium steam in the producing aquifers. The equilibrium steam fraction amounts to 0–2.2% by wt. of the aquifer fluid (0–47% by volume). CO₂ temperatures are anomalously high for some Krafla wells due to high flux of CO₂ from the magma intruded into the roots of the geothermal system during the 1975–1984 volcanic-rifting episode. During the early phase of this episode the Leirbotnar wells were the ones most affected. The new magma gas flux has migrated eastwards with time. Today some wells in the Sudurhlídar wellfield are the ones most affected whereas the Leirbotnar wells have recovered partly or fully. The depth level of producing aquifers in individual wells at Krafla and Námafjall has been evaluated by combining data on temperature and pressure logging and geothermometry results. The majority of wells at Krafla receive fluid from a single aquifer, or from 2–3 aquifers having similar temperature. The same applies to two of the three productive wells at Námafjall.     

Calcul des flux aux parois présentant des singularités

Nous présentons une étude du transfert thermique dans des domaines possédant des singularités en flux aux frontières. Après une mise un évidence des deux types de singularités que l'on peut rencontrer, une méthode de calcul des flux aux parois utilisant des volumes de contrôle aux frontières est proposée. Des exemples numériques en conduction et en convection nous permettent d'illustrer l'importance des erreurs commises d'une part et les gains en précision que la méthode proposée permet d'obtenir d'autre part. Nous terminons par une discussion sur la zone d'influence de la singularité qui conditionne le choix de la taille des volumes de contrôle.This paper deals with the calculation of heat fluxes at singular boundaries. We show that accurate evaluation of these fluxes can be made by using a heat balance on boundary control volumes. Numerical examples in heat diffusion and natural convection problems are considered to assess the correctness of the proposed method. Finally, the region of influence of the singularity is discussed.     

Experimental assessment of the performance of an active transparent façade during actual operating conditions

Results of an extensive measurement campaign performed on an active transparent façade during actual operating conditions are presented. The main aims of the research were: to assess the actual façade performance, both in terms of energy savings and enhanced comfort conditions, to obtain more detailed knowledge of its thermofluid dynamic behaviour and to highlight the weak points of this relatively new technology that still requires further improvement. The analysed component consists of a transparent mechanically ventilated façade integrated with an HVAC system. The façade is used as the exhaust outlet of the HVAC system. The temperatures, heat fluxes and air velocities in the ventilated façade were continuously monitored, over a period of 2 years, using a monitoring system with 34 sensors. In the paper, attention is focused on the measurement techniques that were adopted and on the critical analysis of the experimental data.     

Isotopic zoning and origin of the aquifers in the discharge area of the geothermal fields of ahuachapán and Chipilapa, El Salvador

The northern discharge areas of the Ahuachapán, and Chipilapa geothermal fields can be subdivided into four different zones based on their structural position, and the isotopic and chemical composition of their waters. In general, the contribution of geothermal waters from these two fields was estimated to be less than 10%. Elevation effects are of little importance, whereas a slight trend towards higher isotopic values with increasing water temperatures may exist.The NNW-SSE-trending Escalante and Agua Caliente faults represent lateral groundwater barriers, and provide vertical conduits for the ascending geothermal waters. The western discharge areas seem to be more influenced by the Ahuachapán, geothermal field, whereas those to the east are more influenced by the Chipilapa field.Groundwaters in the Northern Plain are mainly from shallow northward-flowing aquifers. These waters show temperature effects, mixing with geothermal waters and are affected by the geology of the area. However, none of these factors alone can explain the isotopic variations observed in the waters of the northern discharge areas.     

Kinetics of non-premixed hydrogen–oxygen catalytic recombination reaction at ambient temperature

This study proposes the use of the hydrogen–oxygen catalytic recombination reaction to safely eliminate the leaked hydrogen in a confined environment. Experiments on the hydrogen–oxygen reaction catalyzed by using Pt/C as a catalyst are conducted at ambient temperature in a small cylindrical vessel. The macroscopic kinetic process of the hydrogen–oxygen recombination reaction is investigated, and the effects of the reaction parameters, such as the initial hydrogen volume fraction and catalyst layer position, on the reaction temperature and hydrogen conversion are examined. The reaction temperature and temperature rise rate are shown to reach the maximum values when the initial hydrogen fraction is 70 vol%. When the initial hydrogen fraction is ≤ 67 vol%, the hydrogen conversion reaches 100%. After the initial hydrogen fraction is > 67 vol%, the hydrogen conversion decreases significantly, and the hydrogen conversion is only 53% for the initial hydrogen fraction is up to 80 vol%. Moreover, the position of the catalyst layer has a significant effect on the reaction rate and heat distribution inside the vessel. When the catalyst layer is near the bottom of the reaction vessel, the reaction rate is accelerated and the released heat accumulates at the bottom of the vessel. The influence law of the aforementioned factors can provide a technical reference for applications of the hydrogen–oxygen catalytic reaction.     

From a scholar city to a solar city

Located on “Bartolomé Masó” municipality on the north part of “Sierra Maestra” in “Granma” province, the Scholar City “Camilo Cienfuegos”, represents a paradigm of the real ideals of the Cuban Revolution related to education. The paper presents the results of a work developed by a team of professors and students of the Faculty of Architecture and Mechanic Engineering in the Polytechnic University of Havana (ISPJAE) in 1997, which includes a diagnosis of its current situation as a consequence of its historical development, and an strategy for its transformation into a sustainable city.The proposed strategy deals with economic and social sustainability, preservation of natural resources, energy conservation, and appropriate technology, considered in 3 main concepts: Habitat city, Cultural city, and Sustainable city, which are finally integrated into a Solar City as a symbolic term. As part of the proposal, a Master Plan, urban and architectural design criteria and steps for the future development are presented.     

The influence of ångström parameters on calculated direct solar spectral irradiances at high turbidity

This work analyzes the influence of ångström parameters on modeled spectral solar irradiance data. The ångström parameters are obtained in the same way as in the Volz method but using continuous record of spectral direct solar irradiance measures in the 400–1000 nm spectral range. Different pairs of α-β values are obtained depending on the two selected wavelengths. The comparison between the calculated irradiance data with these different α-β pairs and experimental data show important differences that may be taken into account in irradiance models.     

Triphenylamine-substituted methanofullerene derivatives for enhanced open-circuit voltages and efficiencies in polymer solar cells

A new class of triphenylamine substituted methanofullerene derivatives, bis(4'-(diphenylamino)biphenyl-4-yl)methanofullerene (1) and the bisadduct (2), were synthesized. The incident photon to current efficiency (IPCE) studies revealed that the diphenylamino components have contribution to the photocurrent that expands the light harvesting window around 400 nm. When being blended with poly (3-hexylthiophene) (P3HT) to fabricate the solar cell, the device of P3HT:1 (1:0.7) shows high open circuit voltage (V_oc) of 0.69 V under the illumination of AM 1.5, 100 mW/cm² with high power conversion efficiency (PCE) of 3.16%, which is about 0.1 V higher than that of the corresponding [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) devices. This indicates that the arylamine substituents on 1 have played some special roles on the high V_oc performance. Similar effects are also observed for 2. The device of P3HT:2 (1:1) shows even higher V_oc of 0.87 V with the PCE of 1.83%. These results indicate that 1 and 2 are alternative high performance acceptors.     

A comparison between one year of daily global irradiation from ground-based measurements versus METEOSAT images from seven locations in Tunisia

Three numerical images from METEOSAT B2 per day have been processed over a period of 12 months, from October 1985 to September 1986, to estimate the daily values of available solar radiation in Tunisia. The methodology used, GISTEL, on the images of the “visible” channel of METEOSAT, is described. Results are compared with measured radiation values from seven stations of the “Institut de la Météorologie de Tunisie.” Among more than 2200 measured-estimated daily pairs, a high percentage, 89%, show a relative error of + or −10%. Many figures concerning Sidi-Bou-Saïd, Kairouan, Thala, and Gafsa are presented to show the capability of GISTEL to map the daily available solar radiation with a sufficient spatial resolution in countries where radiation measurements are too scarce.     

Carbon emission mitigation measures in Brazil—case study of biomass policy for a ferroalloy plant in Ceará State

The present work aims at discussing the possibilities of atmospheric carbon emissions mitigation in the scope of the United Nations Framework Convention on Climate Change (UNFCCC) in the forest sector using a case study in the Northeast of Brazil. Taking Ceará State as an example and based on the Ceará State Energy Balances for 1980, 1984 and 1987, the Carbon (C-CO₂) Emission Balances were drawn up covering these same years. An exercise was carried out in order to draw up carbon emissions mitigation proposals through both Environmental Education and reforestation policies replacing forest clearing. The first, environmental education and forest management practices, involves more efficient practices in the woody sector. The second, reforestation policies, instead of felling native forests for fuel-wood burned to produce charcoal, is discussed from the economic point of view. An estimate was drawn up of the carbon abatement costs, using a case study for charcoal production based on reforestation instead of deforestation, for a ferroalloy plant in Ceará State.