Electrically switchable chromogenic materials for external glazing

The development of chromogenic materials is important for their potential applications as electrically adjustable or thermally self-adjusting light and heat filters in the external glazing of buildings. Recently, we have reported our investigations on electrolyte-liquid crystal dispersions, which show independent electro-optical and electrochromic properties characterized by fast bleaching times. Nevertheless, for the external glazing of buildings, it is recommended to have a transparent off state, which turns opaque upon application of the external field. In this paper, we present our efforts to homeotropically align by rough surfaces fluid mixtures of a low molecular mass liquid crystal with a negative dielectric anisotropy, a liquid crystalline monomer, and electrolyte molecules in order to obtain transparent films after a polymerization process. Upon application of an ac electric field, the device becomes opaque and if a dc field is added, the cell changes colour too. We have also investigated the relationship between electro-optical/chromogenic response and physical chemical properties of the components.     

High-efficiency multistable switchable glazing using smectic A liquid crystals

Presently, nematic polymer dispersed liquid crystals (PDLCs) that are used in switchable glazing technology require constant power to operate and, moreover, exhibit unwanted haze at wide viewing angles. In this paper, a novel switchable glazing technology, based around a bistable electro-optic effect in the Smectic A liquid crystal phase, is described which does not require constant power to operate or exhibit haze. The application of a low-frequency (100 Hz) voltage induces an optically opaque state due to the motion of ionic material whereas the application of a higher frequency AC (1 kHz) voltage induces a haze-free clear state. Multistable (greyscale) operation is possible through the application of intermediate frequencies or voltages; the threshold voltages of the effect were found to range from 36 to 66 V rms. Any voltage-induced state is preserved indefinitely after removal of the voltage leading to low power consumption.     

Optimum glazing combination for solar space heating

A study is made for comparing the maximum seasonal energy yield obtainable by solar collectors for space heating application. Different glazing combinations with glass and plastic as glazing materials are considered. The study is made for four different locations. The performance of eight glazing combinations with covers ranging in number from one to three is compared to obtain the optimum combination for each location. The results show that selecting the optimum glazing combination improves the performance significantly. In general, plastic covers give higher yield. The study confirmed that the use of two covers is justified in cold, cloudy climates while a single cover is suitable for temperate climates. In most cases three covers lead to a significant reduction in the yield. Replacing plastic by glass as a top cover for longer life results in a small yield reduction. Some of the other conclusions are that the ratio of average to normal transmittance-absorptance product changes significantly with location and month of the year. However, the seasonal average value of this ratio is almost constant for any number of covers but changes with location.     

Visual and energy performance of switchable windows with antireflection coatings

The aim of this project was to investigate how the visual appearance and energy performance of switchable or smart windows can be improved by using antireflective coatings. For this study clear float glass, low-e glass and electrochromic glass were treated with antireflection (AR) coatings. Such a coating considerably increases the transmittance of solar radiation in general and the visible transmittance in particular. For switchable glazing based on absorptive electrochromic layers in their dark state it is necessary to use a low-emissivity coating on the inner pane of a double glazed window in order to reject the absorbed heat. In principle all surfaces can be coated with AR coatings, and it was shown that a thin AR coating on the low-e surface neither influences the thermal emissivity nor the U-value of the glazing. The study showed that the use of AR coatings in switchable glazing significantly increases the light transmittance in the transparent state. It is believed that this is important for a high level of user acceptance of such windows.     

Transmittance-absorptance product of solar glazing with transparent insulation materials

The transmittance-absorptance product of solar glazing containing the transparent insulation material (TIM) of square celled honeycomb is investigated. A method is developed for the determination of transmittance-absorptance product of beam, sky and ground diffuse solar radiations using the individual transmittances of cellular array and encapsulating covers; the internal reflections are taken into account. Three practical cases; cellular array, cellular array with top cover, and cellular array with top and bottom covers are considered. The results are presented for beam radiation as a function of angle of incidence and sky and ground diffuse radiation as a function of tilt angle. The predicted results are tested by measuring the global radiation transmittance of commercial TIM; the predicted results deviate from the measurements by an average of 2.0%.     

Smart solar tanks for small solar domestic hot water systems

Investigation of small SDHW systems based on smart solar tanks are presented. The domestic water in a smart solar tank can be heated both by solar collectors and by means of an auxiliary energy supply system. The auxiliary energy supply system––in this study electric heating elements––heats up the hot-water tank from the top and the water volume heated by the auxiliary energy supply system is fitted to the hot-water consumption and consumption pattern. In periods with a large hot-water demand, the volume is large; in periods with a small hot-water demand, the volume is small.Two small SDHW systems, based on differently designed smart solar tanks and a traditional SDHW system were investigated by means of laboratory experiments and theoretical calculations. The investigations showed that the yearly thermal performance of SDHW systems with smart solar tanks is 5–35% higher than the thermal performance of traditional SDHW systems. Estimates indicate that the performance/cost ratio can be improved by up to 25% by using a smart solar tank instead of a traditional tank when the backup energy system is electric heating elements. Further, smart solar tanks are suitable for unknown, variable, large or small hot-water consumption and the risk of oversized solar heating systems and oversized tank volumes is reduced by using smart solar tanks. Based on the investigations it is recommended to start development of smart solar tank units with an oil-fired boiler or a natural gas burner as auxiliary energy supply system.     

Fiber-optic solar energy transmission and concentration

Fiber-optic solar energy transmission and concentration provide a flexible way of handling concentrated solar energy. The high flux solar energy transmission by a flexible fiber-optic bundle and the research on the associated compound parabolic concentrator will largely expand the existing field of applications of solar energy concentrators. We report on a flexible light guide which consists of 19 optical fibers and is capable of transmitting up to 60 W of optical power, with 60% efficiency. A flexible fiber-optic solar energy transmission and concentration scheme by using one single fiber, 2 and 7 fiber bundles is also reported.     

A glazing unit for solar control, daylighting and energy conservation

The glazing unit for solar control, daylighting and energy conservation is a system consisting of two prismatic panes. The prismatic ribs of the panes are inclined by a certain angle to the horizontal within the window plane, exhibit identical cross-sections in the shape of a rightangle-triangle with a certain basic prism angle, are facing each other and are positioned such that just a small gap remains between the two panes. The lower rib faces of the outer prismatic pane are coated with a specularly reflecting layer and the upper rib faces of the inner prismatic pane are coated with a diffusely reflecting layer. The prismatic glazing unit can be used for common window tilt angles and for window directions with significant solar irradiation at sites with a temperate climate. It does not reduce the view to the outside appreciably and achieves — in comparison to other window panes — relatively uniform illumination of a room with daylight. During the summer and the transitional seasons it provides improved protection against solar irradiation and distinctly reduced irradiated heat fluxes. The reflecting surfaces of the prismatic ribs do not create glare.     

A survey on control schemes for distributed solar collector fields. Part I: Modeling and basic control approaches

This article presents a survey of the different automatic control techniques that have been applied to control the outlet temperature of solar plants with distributed collectors during the last 25 years. Different aspects of the control problem involved in this kind of plants are treated, from modeling and simulation approaches to the different basic control schemes developed and successfully applied in real solar plants. A classification of the modeling and control approaches is used to explain the main features of each strategy.     

A survey on control schemes for distributed solar collector fields. Part II: Advanced control approaches

This article presents a survey of the different advanced automatic control techniques that have been applied to control the outlet temperature of solar plants with distributed collectors during the last 25 years. A classification of the modeling and control approaches described in the first part of this survey is used to explain the main features of each strategy. The treated strategies range from classical advanced control strategies to those with few industrial applications.     

Evaluation of control strategies for different smart window combinations using computer simulations

Several studies have shown that the use of switchable windows could lower the energy consumption of buildings. Since the main function of windows is to provide daylight and visual contact with the external world, high visible transmittance is needed. From an energy perspective it is always best to have the windows in their low-transparent state whenever there are cooling needs, but this is generally not preferable from a daylight and visual contact point of view. Therefore a control system, which can be based on user presence, is needed in connection with switchable windows. In this study the heating and cooling needs of the building, using different control mechanisms were evaluated. This was done for different locations and for different combinations of switchable windows, using electrochromic glazing in combination with either low-e or solar control glazing. Four control mechanisms were investigated; one that only optimizes the window to lower the need for heating and cooling, one that assumes that the office is in use during the daytime, one based on user presence and one limiting the perpendicular component of the incident solar irradiation to avoid glare and too strong daylight. The control mechanisms were compared using computer simulations. A simplified approach based on the balance temperature concept was used instead of performing complete building simulations. The results show that an occupancy-based control system is clearly beneficial and also that the best way to combine the panes in the switchable window differs depending on the balance temperature of the building and on the climate. It is also shown that it can be beneficial to have different window combinations for different orientations.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

Enhancing information for solar and wind energy technology deployment in Brazil

Brazil's primary energy matrix is based on more than 47% of renewables, and more than 85% of its electricity is generated by hydro power sources. Despite this large fraction of renewable energy resources, less than 0.3% of the national energy supply comes from solar or wind sources. This paper presents a diagnostic review on the penetration of the solar and wind energy technologies in Brazil. It also includes a survey of the latest government policies and incentives for renewable energies deployment by entrepreneurs, industry and commercial and residential consumers. In addition, the paper analyses how to best meet the requirements for policy support and information technology to boost the deployment of solar technology and wind energy in Brazil. This study was mostly based on results of a widely distributed survey covering key issues, and also by personal interviews carried out with key stakeholders in order to better understand the issues highlighted in the survey responses. The study pointed out some of the main obstacles to effectively promote and improve government policies and actions for investment in solar and wind energy market in Brazil.     

A new and inexpensive open source data acquisition and controller for solar research: Application to a water-flow glazing

A water-flow window consists of two glass panes making up a chamber in which a water layer flows in a controlled way. Such windows may be considered as Building-Integrated Solar Thermal (BIST) collectors, and could assist to incorporate renewable energy systems in buildings, improving their energy efficiency, especially when they are properly managed by a control system. Despite the need of an automatic controller for this kind of window and the advantages of microprocessor-based control for solar systems, only differential controllers have been described. A novel controller based on an inexpensive open source microcontroller board has been designed, built, programmed and installed in an experimental prototype water-flow window. The proposed data acquisition and control system, the code sequence steps, a model algorithm, and a comparison between the data collected by the system and a commercial datalogger are presented. The advantages of using an open source board for the proposed control system are analysed and the benefits of using a control system based on a microcontroller are discussed.     

Development co-operation and solar energy

The applications of energy in Colombia, India and Upper Volta, for which an improvement in the situation is the most urgent, are described. to a more limited extent these applications have also been investigated with respect to Niger, Pakistan and Senegal. the technical economic possibilities of achieving these improvements by means of solar energy in the period up to 1985 are discussed. Concerning those cases which offer a reasonable chance of the use of solar energy, the investigation then turns to the kind of co-operative programmes between industrialized countries and the developing countries being considered which might contribute to putting these opportunities into practice. This study has revealed the following programmes as offering the best possibilities. 1. Small thermal electric generators powered by concentrated sunlight at an operating temperature of about 300°C, the principal application being the driving of pumps for irrigation in India and Pakistan. 2. Small absorber cooling systems for India and Pakistan. 3. Drinking-water purification for Niger, Pakistan, Senegal and Upper Volta. 4. Battery-charging systems for India and Pakistan. 5. Reforestation for firewood production, close to the major towns of the Sahel countries. Furthermore, much importance is found to attach to the improving of the efficiency of cooking.     

Desalination using solar energy: Towards sustainability

This paper describes the theoretical rationale for a new low temperature phase-change desalination process, and six examples of applications to illustrate how this process can be engineered for sustainable desalination. In this process, brackish water is evaporated at near-ambient temperatures under near-vacuum pressures created by the barometric head without any mechanical energy input. Thermodynamic advantages and benefits of low temperature phase-change desalination are discussed and results from simulation studies and a prototype test system are presented. Three of the examples illustrate how the proposed process can be driven by solar energy: a) utilizing direct solar energy; b) inclusion of an external reflector; c) utilizing photovoltaic energy during non-sunlight hours. The other examples illustrate how the proposed process can be driven by waste heat: i) waste heat rejected by an absorption refrigeration unit driven by grid power; ii) waste heat rejected by an absorption refrigeration unit driven by solar collectors; and iii) waste heat rejected by an absorption refrigeration unit supported by a photovoltaic array. Merits of utilizing solar energy and process waste heat in reducing energy consumption and greenhouse gas emissions are discussed in detail.     

Smart energy solutions with hydrogen options

We are in an era where everything is now requested to be smart. Here are some examples, such as smart materials smart devices, smartphones, smart grid, and smart metering. In regard to energy portfolio, we need to make it in line with these under smart energy solutions. With the developed cutting-edge technologies and artificial intelligence applications, we need to change the course of action in dealing with energy matters by covering the entire energy spectrum under five categories, namely, energy fundamentals and concepts, energy materials, energy production, energy conversion, and energy management. It is important to highlight the importance of a recent event. On 17 January 2017 a total of thirteen leading energy, transport and industry companies in the World Economic Forum in Davos (Switzerland) have launched a global initiative, so-called: Hydrogen Council, to voice a united vision and long-term ambition for hydrogen to foster the energy transition. It has aimed to join the global efforts in promoting hydrogen to help meet climate goals. This is a clear indication that smart solutions are not possible without hydrogen options. This study focuses on introducing and highlighting smart energy solutions under the portfolio pertaining to exergization, greenization, renewabilization, hydrogenization, integration, multigeneration, storagization, and intelligization. Each one of these plays a critical role within the smart energy portfolio and becomes key for a more sustainable future. This study also focuses on the newly developed smart energy systems by combining both renewable energy sources and hydrogen energy systems to provide more efficient, more cost-effective, more environmentally benign and more sustainable solutions for implementation. Furthermore, a wide range of integrated systems is presented to illustrate the feasibility and importance such a coupling to overcome several technical issues. Moreover, numerous studies from the recent literature are presented to highlight the importance of sustainable hydrogen production methods for a carbon-free economy.     

Exergy analysis of solar energy applications

Solar energy is a clean, abundant and easily available renewable energy. Usage of solar energy in different kinds of systems provides scope for several studies on exergy analysis. In the present work, a comprehensive literature review has been carried out on exergy analysis of various solar energy systems. The systems considered under study are solar photovoltaic, solar heating devices, solar water desalination system, solar air conditioning and refrigerators, solar drying process and solar power generation. The summary of exergy analysis and exergetic efficiencies is presented along with the exergy destruction sources.     

Design,development and testing of an improved multipurpose solar energy device

This paper reports the design, development and testing of an improved multipurpose solar energy device. The novel feature of the device is that it can be used as a solar water heater and solar still simultaneously and, when required, as a solar cabinet dryer by incorporating minor changes.