Domestic hot water consumption vs. solar thermal energy storage: the optimum size of the storage tank

Many efforts have been made in order to adequate the production of a solar thermal collector field to the consumption of domestic hot water of the inhabitants of a building. In that sense, much has been achieved in different domains: research agencies, government policies and manufacturers. However, most of the design rules of the solar plants are based on steady state models, whereas solar irradiance, consumption and thermal accumulation are inherently transient processes. As a result of this lack of physical accuracy, thermal storage tanks are sometimes left to be as large as the designer decides without any aforementioned precise recommendation. This can be a problem if solar thermal systems are meant to be implemented in nowadays buildings, where there is a shortage of space. In addition to that, an excessive storage volume could not result more efficient in many residential applications, but costly, extreme in space consumption and in some cases too heavy. A proprietary transient simulation program has been developed and validated with a detailed measurement campaign in an experimental facility. In situ environmental data have been obtained through a whole year of operation. They have been gathered at intervals of 10 min for a solar plant of 50 m2 with a storage tank of 3 m3, including the equipment for domestic hot water production of a typical apartment building. This program has been used to obtain the design and dimensioning criteria of DHW solar plants under daily transient conditions throughout a year and more specifically the size of the storage tank for a multi storey apartment building. Comparison of the simulation results with the current Spanish regulation applicable, “Código Técnico de la Edificación” (CTE 2006), offers fruitful details and establishes solar facilities dimensioning criteria.

Identification procedure of mealy apples by instrumental means. Extraction of storage features.

Mealiness is a negative attribute of sensory texture that combines the sensation of a disaggregated tissue with the sensation of lack of juiciness. Since January 1996, a wide EC Project entitled : "Mealiness in fruits. Consumers perception and means for detection'" is being carried out. Within it, three sensory panels have been trained at : the Institute of Food Research (IFR, United Kingdom), the Instituto de Agroquímica y Tecnología de los Alimentos (IATA, Spain) and the Institut voor Agrotechnologisch Onderzoek (ATO-DLO, Netherlands) to assess mealiness in apples. In all three cases, mealiness has been described as a multidimensional sensory descriptor capable of gathering the loss of consistency (of crispness and of hardness) and of juiciness. Also within the EC Project several instrumental procedures have been tested for mealiness assessment. In this sense the Physical Properties Laboratory (ETS1A-UPM) has focused its aims in a first stage on performing instrumental tests for assessing some textural descriptors as crispiness, hardness and juiciness. The results obtained within these tests have shown to correlate well with the sensory measurements (Barreiro et Ruiz-Altisent, 1997) in apples, but also have succeed when trying to generate several texture degradation levels on peaches from which mealiness appears to be the last stage (Ortiz et al. 1997).

Fruit by fruit identification of mealy peaches. Extraction of storage features.

Mealiness is a negative attribute of sensory texture, characterised by the lack of juiciness decrease in the total amount of of water content of tissues. Peach mealy textures are known as \ and leatheriness. Besides the lack of juiciness and flavour, that characterises mealy fruits, in associated with internal browning near the stone and an incapacity of ripening although there i ripe appearance. It is considered as a physiological disorder that appears in stone fruits probably < unbalanced pectolitic enzyme activity during storage. Since January 1996, a wide EC Project entitled: "Mealiness in fruits. Consumer perception and i detection" is being carried out. Within it, the Physical Properties Laboratory (ETSIA-UPM) working to develop instrumental procedures to detect mealiness in different types of fruits (s contributions by Barreiro to AgEng). The results obtained have shown to correlate well with \ measurements in apples (Barreiro et al), also we have succeeded in identifying individual mealy j the basis of instrumental measurement in peaches. The definition of these texture categories will be used in further studies as a base for new individual classification.

Explosion risk in coke, coal and sulphur storage

The self-ignition of all kind of powdery substances is a topic studied over the years, especially if the dusty substance is coal or substances related with coal because it may be a cause of energetic materials and human losses. But it is important to note that this is not the only risk in industrial plants that generate or store solid substances. Every combustible powders are potentially explosive and they may cause serious consequences if all the necessary factors are developed. Due to this potentially risk, it is essential a good characterization and knowledge of all the parameters involved in those processes.

Flammability properties of dry sewage sludges

Dry sewage sludge are being considered as a possible energy source for direct firing. They have interesting properties to be used as an alternative fuel, but also other characteristics must be considered from the point of view of its safe operation: the most important are ignition sensitivity, explosion severity, thermal sensitivity and thermal stability. The aim of this study was to determine if sewage sludge have different characteristics due to different locations or seasons and how this influences their flammability properties. To study these characteristics sludge samples were selected from different locations in Spain, taken during different seasons. In addition, relationships between flammability parameters and chemical analysis were observed. Some parameters can be controlled during normal operation, such as granulometry or humidity, and may mean a decrease in the risk of explosion. Those relationships are well known for other dusts materials, like coal, but not yet for sewage sludge dusts. Finally, properties related to spontaneous combustion were determined (thermal susceptibility and stability). The addition of those properties to the study provides an overview of the thermal behavior of sewage sludge during their utilization, including transport and storage.

Comparisson of hydrogen applications for storage and energy vector

For the decades to come can be foreseen that electricity and water will keep be playing a key role in the countries development, both can be considered the most important energy vectors and its control can be crucial for governments, companies and leaders in general. Energy is essential for all human activities and its availability is critical to economic and social development. In particular, electricity, a form of energy, is required to produce goods, to provide medical assistance and basic civic services in education, to assure availability of clean water, to create conducive environment for prosperity and improvement, and to keep an acceptable quality of life. The way in which electricity is generated from different resources varies through the different countries. Nuclear energy controlled within reactors to steam production, gas, fuel-oil and coal fired in power stations, water, solar and wind energy among others are employed, sometimes not very efficiently, to produce electricity. The so call energy mix of an individual country is formed up by the contribution of each resource or form of energy to the electricity generation market of the so country. During the last decade the establishment of proper energy mixes for countries has gained much importance, and energy drivers should enforce long term plans and policies. Hints, reports and guides giving tracks on energy resources contribution are been developed by noticeable organisations like the IEA (International Energy Agency) or the IAEA (International Atomic Energy Agency) and the WEC (World Energy Council). This paper evaluates energy issues the market and countries are facing today regarding energy mix scheduling and panorama. This paper revises and seeks to improve methodology available that are applicable on energy mix plan definition. Key Factors are identified, established and assessed through this paper for the common implementation, the themes driving the future energy mix methodology proposal. Those have a clear influence and are closely related to future environmental policies. Key Factors take into consideration sustainability, energy security, social and economic growth, climate change, air quality and social stability. The strength of the Key Factors application on energy system planning to different countries is contingent on country resources, location, electricity demand and electricity generation industry, technology available, economic situation and prospects, energy policy and regulation

Diffuse soil CO2 flux to assess the reliability of CO2 storage the reliability of CO2 storage in the Mazarrón-Gañuelas Tertiary Basin (Spain)

In the framework of a global investigation of the Spanish natural analogues of CO2 storage and leakage, four selected sites from the Mazarrón?Gañuelas Tertiary Basin (Murcia, Spain) were studied for computing the diffuse soil CO2 flux, by using the accumulation chamber method. The Basin is characterized by the presence of a deep, saline, thermal (?47 ?C) CO2-rich aquifer intersected by two deep geothermal exploration wells named ?El Saladillo? (535 m) and ?El Reventón? (710 m). The CO2 flux data were processed by means of a graphical?statistical method, kriging estimation and sequential Gaussian simulation algorithms. The results have allowed concluding that the Tertiary marly cap-rock of this CO2-rich aquifer acts as a very effective sealing, preventing any CO2 leak from this natural CO2 storage site, being therefore an excellent scenario to guarantee, by analogy, the safety of a CO2 storage.

Storage stability of SBS/sulfur modified bitumens at high temperature: influence of bitumen composition and structure

Polymer modified bitumens, PMBs, are usually prepared at high temperature and subsequently stored for a period of time, also at high temperature. The stability of PMBs, in these conditions, has a decisive influence in order to obtain the adequate performances for practical applications. In this article the attention is focused in the analysis of the factors that determine the stability of styrene–butadiene–styrene copolymer (SBS)/sulfur modified bitumens when the mixtures are maintained at high temperature. Bitumens from different crude oil sources were used to prepare SBS/sulfur modified bitumens. Changes in the values of viscosity, softening point, as well as in the morphology of PMB samples, stored at 160 °C, were related to the bitumen chemical composition and to the amount of asphaltene micelles present in the neat bitumen used in their preparation El trabajo se centra en el estudio de la influencia de la estructura /composición del betún sobre la compatibilidad del sistema betún/SBS. Cuatro betunes provenientes de dos crudos distintos se seleccionaron y sus mezclas se utilizaron para preparar betunes modificados con contenidos de SBS del 3% en peso

Steady state analysis of a storage integrated solar thermophotovoltaic (SISTPV) system

This paper presents the theoretical analysis of a storage integrated solar thermophotovoltaic (SISTPV) system operating in steady state. These systems combine thermophotovoltaic (TPV) technology and high temperature thermal storage phase-change materials (PCM) in the same unit, providing a great potential in terms of efficiency, cost reduction and storage energy density. The main attraction in the proposed system is its simplicity and modularity compared to conventional Concentrated Solar Power (CSP) technologies. This is mainly due to the absence of moving parts. In this paper we analyze the use of Silicon as the phase change material (PCM). Silicon is an excellent candidate because of its high melting point (1680 K) and its very high latent heat of fusion of 1800 kJ/kg, which is about ten times greater than the conventional PCMs like molten salts. For a simple system configuration, we have demonstrated that overall conversion efficiencies up to ?35% are approachable. Although higher efficiencies are expected by incorporating more advanced devices like multijunction TPV cells, narrow band selective emitters or adopting near-field TPV configurations as well as by enhancing the convective/conductive heat transfer within the PCM. In this paper, we also discuss about the optimum system configurations and provide the general guidelines for designing these systems. Preliminary estimates of night time operations indicate it is possible to achieve over 10 h of operation with a relatively small quantity of Silicon.

Carbon dioxide adsorption in chemically activated carbon from sewage sludge

In this work, sewage sludge was used as precursor in the production of activated carbon by means of chemical activation with KOH and NaOH. The sludge-based activated carbons were investigated for their gaseous adsorption characteristics using CO2 as adsorbate. Although both chemicals were effective in the development of the adsorption capacity, the best results were obtained with solid NaOH (SBAT16). Adsorption results were modeled according to the Langmuir and Freundlich models, with resulting CO2 adsorption capacities about 56 mg/g. The SBAT16 was characterized for its surface and pore characteristics using continuous volumetric nitrogen gas adsorption and mercury porosimetry. The results informed about the mesoporous character of the SBAT16 (average pore diameter of 56.5 Å). The Brunauer-Emmett-Teller (BET) surface area of the SBAT16 was low (179 m2/g) in comparison with a commercial activated carbon (Airpel 10; 1020 m2/g) and was mainly composed of mesopores and macropores. On the other hand, the SBAT16 adsorption capacity was higher than that of Airpel 10, which can be explained by the formation of basic surface sites in the SBAT16 where CO2 experienced chemisorption. According to these results, it can be concluded that the use of sewage-sludge-based activated carbons is a promising option for the capture of CO2. Implications: Adsorption methods are one of the current ways to reduce CO2 emissions. Taking this into account, sewage-sludge-based activated carbons were produced to study their CO2 adsorption capacity. Specifically, chemical activation with KOH and NaOH of previously pyrolyzed sewage sludge was carried out. The results obtained show that even with a low BET surface area, the adsorption capacity of these materials was comparable to that of a commercial activated carbon. As a consequence, the use of sewage-sludge-based activated carbons is a promising option for the capture of CO2 and an interesting application for this waste.

Influence of duration of storage on protein quality traits of soybean meals

Two experiments were conducted to determine the influence of duration of storage of soybean meal (SBM) on variables that define the quality of the protein fraction. Urease activity, protein dispersibility index (PDI), KOH protein solubility (KOHsol), and trypsin inhibitor activity were determined. In experiment 1, 8 samples of SBM, ranging in CP content from 55.4 to 56.5% DM, were collected from a US crushing plant at weekly intervals and analyzed at arrival to the laboratory and after 30, 60, 90, and 120 d of storage. In experiment 2, 7 samples of SBM, ranging in CP content from 49.0 to 55.0% DM, were collected from different Argentinean crushers and analyzed at arrival and after 24, 48, 80, and 136 wk of storage. In both experiments, samples were stored in hermetic glass containers in a laboratory room at 12 ± 2°C and a relative humidity of 70 ± 3%. Duration of storage did not affect urease activity or trypsin inhibitor activity values in either of the 2 experiments. However, PDI values decreased linearly with time of storage in both experiments (P menor que 0.001). Also, KOHsol decreased linearly (P menor que 0.05) with duration of storage in experiment 2 (long-term storage) but not in experiment 1(shorter term storage). Therefore, PDI values might not be adequate to compare protein quality of commercial SBM samples that have been stored for different periods of time. The KOHsol values are less affected by length of storage of the meals under current commercial practices.

Energy Storage Systems for Electric Vehicles: Performance Comparison based on a Simple Equivalent Circuit and Experimental Tests

The decision to select the most suitable type of energy storage system for an electric vehicle is always difficult, since many conditionings must be taken into account. Sometimes, this study can be made by means of complex mathematical models which represent the behavior of a battery, ultracapacitor or some other devices. However, these models are usually too dependent on parameters that are not easily available, which usually results in nonrealistic results. Besides, the more accurate the model, the more specific it needs to be, which becomes an issue when comparing systems of different nature. This paper proposes a practical methodology to compare different energy storage technologies. This is done by means of a linear approach of an equivalent circuit based on laboratory tests. Via these tests, the internal resistance and the self-discharge rate are evaluated, making it possible to compare different energy storage systems regardless their technology. Rather simple testing equipment is sufficient to give a comparative idea of the differences between each system, concerning issues such as efficiency, heating and self-discharge, when operating under a certain scenario. The proposed methodology is applied to four energy storage systems of different nature for the sake of illustration.

Sampling strategies using the "accumulation chamber" for monitoring geological storage of CO2

Fundación Ciudad de la Energía (CIUDEN) is carrying out a project of geological storage of CO2, where CO2 injection tests are planned in saline aquifers at a depth of 1500 m for scientific objectives and project demonstration. Before any CO2 is stored, it is necessary to determine the baseline flux of CO2 in order to detect potential leakage during injection and post-injection monitoring. In November 2009 diffuse flux measurements of CO2 using an accumulation chamber were made in the area selected by CIUDEN for geological storage, located in Hontomin province of Burgos (Spain). This paper presents the tests carried out in order to establish the optimum sampling methodology and the geostatistical analyses performed to determine the range, with which future field campaigns will be planned.

Flammability properties of thermally dried sewage sludge

The treatment and disposal of sewage sludge is becoming an urgent need whereby different technologies were developed and integrated into the waste cycle all over the world. One of the most used technologies is the thermal drying of the sludge. Thermally dried sewage sludge has interesting properties that allow its use as an alternative fuel, but also needs some consideration from the point of view of its safe operation. The aim of this study was the research on the flammability properties of sewage sludge, including ignition sensitivity, explosion severity, thermal sensitivity and thermal stability. Furthermore relationships among those properties and composition parameters have been determined, added to the study of their variation depending on their origin or season. Finally, properties related to spontaneous combustion were determined. To study these relationships and characteristics sludge samples were selected from different locations in Spain and taken during different seasons.

Pre-investigation of water electrolysis for flexible energy storage at large scales: the case of the Spanish power system

This report analyzes the basis of hydrogen and power integration strategies, by using water electrolysis processes as a means of flexible energy storage at large scales.