Desalination with a solar-assisted heat pump : an economic optimization

The solar-assisted heat pump (SAHP) desalination, based on the Rankin cycle, operates in low temperature and utilizes both solar and ambient energy. An experimental SAHP desalination system has been constructed at the National University of Singapore, Singapore. The system consisted of two main sections: an SAHP and a water distillation section. Experiments were carried out under the different meteorological condition of Singapore and results showed that the system had a performance ratio close to 1.3. The heat pump has a coefficient of performance of about 8, with solar collector efficiencies of 80% and 60% for evaporator and liquid collectors, respectively. Economic analysis showed that at a production rate of 900 L/day and an evaporator collector area of around 70m2 will have a payback period of about 3.5 years.

Solar evaporator-collectors : analyses and applications

Taking into consideration of growing energy needs and concern for environmental degradation, clean and inexhaustible energy source, such as solar energy, is receiving greater attention for various applications. The use of solar energy system reduces pollution, waste and has little or no harmful effects on the environment. It is appreciated that this source of energy can be complementary rather than being competitive to conventional energy sources. In order to collect and harness energy from the sun, a solar collector is essential. A solar collector is basically a heat exchanger that transforms solar radiant energy into heat or thermal energy. Improvement of performance is essential for commercial acceptance of their use in such applications. Many studies have been undertaken on the enhancement of thermal performance of solar collectors, using diverse materials of various shapes, dimensions and layouts. In the literature, various collector designs have been proposed and tested with the objective of meeting these requirements [1-8]. Omer et al. [1] found the efficiency of a solar collector of about 70% in a solar assisted heat pump system. Traditional solar collectors are single phase collectors, in which the working fluid is either air or water. Different modifications are suggested and applied to improve the heat transfer between the absorber and working fluid in a collector. These modifications include the use of absorber with fins attached [2,3], corrugated absorber [4,5], matrix type absorber [6], V-groove solar air collector [7]. Karim et al. [8] approached a review of design and construction of three types (flat, vee-grooved, and finned) of air collectors. Two-phase collectors, on the other hand, have significant potential for continuous operation round the clock, when used in conjunction with a compressor, as found in a solar assisted heat-pump cycle.

Intelligent thermal energy meter cum controller for solar water heating systems

A microcontroller based, thermal energy meter cum controller (TEMC) suitable for solar thermal systems has been developed. It monitors solar radiation, ambient temperature, fluid flow rate, and temperature of fluid at various locations of the system and computes the energy transfer rate. It also controls the operation of the fluid-circulating pump depending on the temperature difference across the solar collector field. The accuracy of energy measurement is +/-1.5%. The instrument has been tested in a solar water heating system. Its operation became automatic with savings in electrical energy consumption of pump by 30% on cloudy days.

Comments on "Full-sphere simulations of circulation-dominated solar dynamo: Exploring the parity issue" - Reply

We respond to Dikpati et al.'s criticism of our recent solar dynamo model. A different treatment of the magnetic buoyancy is the most probable reason for their different results.

Full Sphere Axisymmetric Simulations of the Solar Dynamo

We explore a full sphere (2D axisymmetric) kinematic solar dynamo model based on the Babcock-Leighton idea that the poloidal field is generated in the surface layers from the decay of tilted bipolar solar active regions. This model incorporates the helioseismically deduced solar rotation profile and an algorithm for buoyancy motivated from simulations of flux tube dynamics. A prescribed deep meridional circulation plays an important role in the advection of magnetic flux. We specifically address the parity issue and show that – contrary to some recent claims – the Babcock-Leighton dynamo can reproduce solar-like dipolar parity if certain reasonable conditions are satisfied in the solar interior, the most important requirement being that the poloidal field of the two hemispheres be efficiently coupled across the equator.

COST AND PERFORMANCE TRADEOFFS OF ALTERNATIVE SOLAR-DRIVEN S-CO2 BRAYTON CYCLE CONFIGURATIONS

This paper evaluates cost and performance tradeoffs of alternative supercritical carbon dioxide (s-CO2) closed-loop Brayton cycle configurations with a concentrated solar heat source. Alternative s-CO2 power cycle configurations include simple, recompression, cascaded, and partial cooling cycles. Results show that the simple closed-loop Brayton cycle yielded the lowest power-block component costs while allowing variable temperature differentials across the s-CO2 heating source, depending on the level of recuperation. Lower temperature differentials led to higher sensible storage costs, but cycle configurations with lower temperature differentials (higher recuperation) yielded higher cycle efficiencies and lower solar collector and receiver costs. The cycles with higher efficiencies (simple recuperated, recompression, and partial cooling) yielded the lowest overall solar and power-block component costs for a prescribed power output.

Utilização de coletor de composto parabólico de concentração solar na indústria de asfalto.

Esta dissertação apresenta a avaliação térmica, econômica e ambiental de um sistema de aquecimento solar (SHS) que é usado em uma usina de asfalto, através de simulação computacional com TRNSYS. O processo escolhido é o aquecimento do betume a partir da temperatura de armazenamento até a temperatura de mistura, usando óleo mineral como fluido de transferência de calor (HTF). Os componentes do sistema são o trocador de calor HTF-betume, o coletor concentrador solar parabólico composto (CPC), o aquecedor auxiliar e a bomba de circulação. A simulação no TRNSYS calcula os balanços de massa e energia no circuito fechado do HTF a cada hora. Dados horários do Ano Meteorológico Típico (TMY) do Rio de Janeiro foram utilizados para executar este trabalho. Em muitos casos, a temperatura do HTF ultrapassou 238C, mostrando que o CPC é apropriado para esta aplicação. Economia de combustível e emissões evitadas foram consideradas para as análises economica e ambiental. Este trabalho descreve as fontes renováveis de energia, os tipos de usinas de asfalto e de aquecedores de betume. Ele também mostra a fração brasileira de algumas destas fontes. Os resultados, portanto, mostram ser possível encorajar políticas públicas ambientalmente corretas para incentivar o uso de energia solar na indústria de asfalto. Além disso, este trabalho pode ajudar na redução da elevada emissão dos gases de efeito estufa a partir da utilização dos combustíveis fósseis nesta indústria.

A case for facade integrated solar thermal systems.

This paper explores the potential for façade located solar thermal collectors. Building typologies with limited roof space area are highlighted. A relationship exists between hot water consumption and the solar collector area; hence, a literature review of the hot water consumption of different building typologies is conducted. The review showed that there is a paucity of information on the hot water consumption of buildings, primarily attributed to the difficulty in quantifying it. The hot water consumption is typically describedusing liters per capita per day (Lcd) units, with a broad range of values existing, dependent, primarily on the building's function and location. Asimulation-based study is conducted to size solar thermal systems for different buildings and their associated hot water loads. High solar fractions,for buildings with high levels of hot water consumption, could only be achievedby using significantly largercollector surface areas. As a result, façade located solar thermal collectors are required for certain high-rise buildings that aim to provide for their hot water needs using a considerable portion of solar energy.

The distribution of solar wind speeds during solar minimum: calibration for numerical solar wind modeling constraints on the source of the slow solar wind

It took the solar polar passage of Ulysses in the early 1990s to establish the global structure of the solar wind speed during solar minimum. However, it remains unclear if the solar wind is composed of two distinct populations of solar wind from different sources (e.g., closed loops which open up to produce the slow solar wind) or if the fast and slow solar wind rely on the superradial expansion of the magnetic field to account for the observed solar wind speed variation. We investigate the solar wind in the inner corona using the Wang-Sheeley-Arge (WSA) coronal model incorporating a new empirical magnetic topology–velocity relationship calibrated for use at 0.1 AU. In this study the empirical solar wind speed relationship was determined by using Helios perihelion observations, along with results from Riley et al. (2003) and Schwadron et al. (2005) as constraints. The new relationship was tested by using it to drive the ENLIL 3-D MHD solar wind model and obtain solar wind parameters at Earth (1.0 AU) and Ulysses (1.4 AU). The improvements in speed, its variability, and the occurrence of high-speed enhancements provide confidence that the new velocity relationship better determines the solar wind speed in the outer corona (0.1 AU). An analysis of this improved velocity field within the WSA model suggests the existence of two distinct mechanisms of the solar wind generation, one for fast and one for slow solar wind, implying that a combination of present theories may be necessary to explain solar wind observations.

Ensemble downscaling in coupled solar wind-magnetosphere modeling for space weather forecasting

Advanced forecasting of space weather requires simulation of the whole Sun-to-Earth system, which necessitates driving magnetospheric models with the outputs from solar wind models. This presents a fundamental difficulty, as the magnetosphere is sensitive to both large-scale solar wind structures, which can be captured by solar wind models, and small-scale solar wind “noise,” which is far below typical solar wind model resolution and results primarily from stochastic processes. Following similar approaches in terrestrial climate modeling, we propose statistical “downscaling” of solar wind model results prior to their use as input to a magnetospheric model. As magnetospheric response can be highly nonlinear, this is preferable to downscaling the results of magnetospheric modeling. To demonstrate the benefit of this approach, we first approximate solar wind model output by smoothing solar wind observations with an 8 h filter, then add small-scale structure back in through the addition of random noise with the observed spectral characteristics. Here we use a very simple parameterization of noise based upon the observed probability distribution functions of solar wind parameters, but more sophisticated methods will be developed in the future. An ensemble of results from the simple downscaling scheme are tested using a model-independent method and shown to add value to the magnetospheric forecast, both improving the best estimate and quantifying the uncertainty. We suggest a number of features desirable in an operational solar wind downscaling scheme.

Accelerated aging of thick glass second surface silvered reflectors under sandstorm conditions

Concentrated solar power systems are expected to be sited in desert locations where the direct normal irradiation is above 1800 kWh/m2.year. These systems include large solar collector assemblies, which account for a significant share of the investment cost. Solarreflectors are the main components of these solar collector assemblies and dust/sand storms may affect their reflectance properties, either by soiling or by surface abrasion. While soiling can be reverted by cleaning, surface abrasion is a non reversible degradation.The aim of this project was to study the accelerated aging of second surface silvered thickglass solar reflectors under simulated sandstorm conditions and develop a multi-parametric model which relates the specular reflectance loss to dust/sand storm parameters: wind velocity, dust concentration and time of exposure. This project focused on the degradation caused by surface abrasion.Sandstorm conditions were simulated in a prototype environmental test chamber. Material samples (6cm x 6cm) were exposed to Arizona coarse test dust. The dust stream impactedthese material samples at a perpendicular angle. Both wind velocity and dust concentrationwere maintained at a stable level for each accelerated aging test. The total exposure time in the test chamber was limited to 1 hour. Each accelerated aging test was interrupted every 4 minutes to measure the specular reflectance of the material sample after cleaning.The accelerated aging test campaign had to be aborted prematurely due to a contamination of the dust concentration sensor. A robust multi-parametric degradation model could thus not be derived. The experimental data showed that the specular reflectance loss decreasedeither linearly or exponentially with exposure time, so that a degradation rate could be defined as a single modeling parameter. A correlation should be derived to relate this degradation rate to control parameters such as wind velocity and dust/sand concentration.The sandstorm chamber design would have to be updated before performing further accelerated aging test campaigns. The design upgrade should improve both the reliability of the test equipment and the repeatability of accelerated aging tests. An outdoor exposure test campaign should be launched in deserts to learn more about the intensity, frequencyand duration of dust/sand storms. This campaign would also serve to correlate the results of outdoor exposure tests with accelerated exposure tests in order to develop a robust service lifetime prediction model for different types of solar reflector materials.

Solar energy exhibits at the popular science park Teknoland

The new Popular Science Park TEKNOLAND in Falun contains a number of interactive solar energy exhibits, including The Solar Heated Chess Board, The Solar Electric Playhouse, The Sudanese Solar Oven, and Solar Collector Optics. The TeknoTrix tutored children activities include solar thermal activities. Some related interactive exhibits are planned to be included during the summer and during coming years.

Teknoland - popular science park with solar energy exhibits

The new Popular Science Park TEKNOLAND in Falun contains a number of interactive solar energy exhibits, including The Solar Heated Chess Board, The Solar Electric Playhouse, The Sudanese Solar Oven, and Solar Collector Optics. The TeknoTrix tutored children activities include solar thermal activities. Some related interactive exhibits are planned to be included during the summer and during coming years.

Load and Season Adapted Solar Collectors

In Sweden solar irradiation and space heating loads are unevenly distributed over the year. Domestic hot water loads may be nearly constant. Test results on solar collector performance are often reported as yearly output of a certain collector at fixed temperatures, e g 25, 50 and 75 C. These data are not suitable for dimensioning of solar systems, because the actual performance of the collector depends heavily on solar fraction and load distribution over the year.At higher latitudes it is difficult to attain high solar fractions for buildings, due to overheating in summer and small marginal output for added collector area. Solar collectors with internal reflectors offer possibilities to evade overheating problems and deliver more energy at seasons when the load is higher. There are methods for estimating the yearly angular irradiation distribution, but there is a lack of methods for describing the load and the storage in such a way as to enable optical design of season and load adapted collectors.This report describes two methods for estimation of solar system performance with relevance for season and load adaption. Results regarding attainable solar fractions as a function of collector features, load profiles, load levels and storage characteristics are reported. The first method uses monthly collector output data at fixed temperatures from the simulation program MINSUN for estimating solar fractions for different load profiles and load levels. The load level is defined as estimated yearly collector output at constant collector temperature divided be yearly load. This table may examplify the results:CollectorLoadLoadSolar Improvementtypeprofile levelfractionover flat plateFlat plateDHW 75 %59 %Load adaptedDHW 75 %66 %12 %Flat plateSpace heating 50 %22 %Load adaptedSpace heating 50 %28 %29 %The second method utilises simulations with one-hour timesteps for collectors connected to a simplified storage and a variable load. Collector output, optical and thermal losses, heat overproduction, load level and storage temperature are presented as functions of solar incidence angles. These data are suitable for optical design of load adapted solar collectors. Results for a Stockholm location indicate that a solar combisystem with a solar fraction around 30 % should have collectors that reduce heat production at solar heights above 30 degrees and have optimum efficiency for solar heights between 8 and 30 degrees.

Design of gas filled solar collectors

With a suitable gas filling used between cover glass and absorber in a flat plate solar collector, it is possible achieving better thermal performance at the same time as the distance betweenabsorber and glass can be reduced. Though, even if there is no vacuum inside the box, there will be potential risks for exhaustion due to stresses depending on the gas volume varies as the temperature varies. This study found out that it is possible build such a collector with less material in the absorber and the tubes and still getting better performance, without risks for exhaustion.