Development of novel approaches toward energy-efficient photochemistry in continuous flow

The research outlined in this thesis was directed towards the development of novel methodologies to perform photochemical transformations in continuous flow. A meticulous approach was adopted to design reactor systems that would optimize photon utilization, thereby enhancing productivity, while simultaneously minimizing energy consumption.The work described in this manuscript can be divided into three main research lines. First, a focus was placed on the development of photochemical reactors capable of concentrating photons gathered from sunlight. A large scale reactor was first built to produce chemicals in an autonomous fashion under fluctuating solar irradiation. Sensors provide a feedforward system to adapt the flows of reagents to the incoming light and provide a consistent product output. Then, a second reactor design is presented using luminescent coatings. This smaller scale system is used for fast prototyping and rapid screening of reaction conditions.In the second part of this thesis, the emphasis shifts toward CO2 conversion assisted by solar simulated light. Special attention is paid to the reactor design to aid the characterization of the different catalysts. Various catalysts are tested and optimized for carbon monoxide or methane production. The product is then used and valorised into follow-up transformations.Finally, the third segment of this thesis shifts its focus toward the development of laboratory-scale photoreactors. The design of 3D printable flow and batch systems provides tools to perform efficient and reproducible photochemical transformations. Combining ray-tracing simulations and chemical actinometry experiments, the reactors were extensively characterized

Development of novel approaches toward energy-efficient photochemistry in continuous flow

The research outlined in this thesis was directed towards the development of novel methodologies to perform photochemical transformations in continuous flow. A meticulous approach was adopted to design reactor systems that would optimize photon utilization, thereby enhancing productivity, while simultaneously minimizing energy consumption.The work described in this manuscript can be divided into three main research lines. First, a focus was placed on the development of photochemical reactors capable of concentrating photons gathered from sunlight. A large scale reactor was first built to produce chemicals in an autonomous fashion under fluctuating solar irradiation. Sensors provide a feedforward system to adapt the flows of reagents to the incoming light and provide a consistent product output. Then, a second reactor design is presented using luminescent coatings. This smaller scale system is used for fast prototyping and rapid screening of reaction conditions.In the second part of this thesis, the emphasis shifts toward CO2 conversion assisted by solar simulated light. Special attention is paid to the reactor design to aid the characterization of the different catalysts. Various catalysts are tested and optimized for carbon monoxide or methane production. The product is then used and valorised into follow-up transformations.Finally, the third segment of this thesis shifts its focus toward the development of laboratory-scale photoreactors. The design of 3D printable flow and batch systems provides tools to perform efficient and reproducible photochemical transformations. Combining ray-tracing simulations and chemical actinometry experiments, the reactors were extensively characterized

Solar Window Innovations: Enhancing Building Performance through Advanced Technologies

Building-integrated photovoltaic (BIPV) glazing systems with intelligent window technologies enhance building energy efficiency by generating electricity and managing daylighting. This study explores advanced BIPV glazing, focusing on building-integrated concentrating photovoltaic (BICPV) systems. BICPV integrates concentrating optics, such as holographic films, luminescent solar concentrators (LSC), Fresnel lenses, and compound parabolic concentrators (CPCs), with photovoltaic cells. Notable results include achieving 17.9% electrical efficiency using cylindrical holographic optical elements and crystalline silicon cells at a 3.5× concentration ratio. Dielectric CPCs showed 97.7% angular acceptance efficiency in simulations and 94.4% experimentally, increasing short-circuit current and maximum power by 87.0% and 96.6%, respectively, across 0° to 85° incidence angles. Thermochromic hydrogels and thermotropic smart glazing systems demonstrated significant HVAC energy savings. Large-area 1 m2 PNIPAm-based thermotropic window outperformed conventional double glazing in Singapore. The thermotropic parallel slat transparent insulation material (TT PS-TIM) improved energy efficiency by up to 21.5% compared to double glazing in climates like London and Rome. Emerging dynamic glazing technologies combine BIPV with smart functions, balancing transparency and efficiency. Photothermally controlled methylammonium lead iodide PV windows achieved 68% visible light transmission, 11.3% power conversion efficiency, and quick switching in under 3 min. Polymer-dispersed liquid crystal smart windows provided 41–68% visible transmission with self-powered operation

A study of the solar energy systems and storage devices

Includes abstract.Includes bibliographical references.Following the 2008 severe electricity shortage in South Africa, domestic and industrial users faced incessant periods of blackouts. It is generally believed to be associated with lack of generation capacity. Since then research efforts have been directed towards boosting the generation capacity of the South African network by investing in a mix of power generation projects which include coal, nuclear and renewable energy schemes such as solar and wind. The renewable energy resources are considered a more viable option because of their many advantages such as lower greenhouse gas emissions, inexhaustible, reliable and even cheaper energy cost on the long term. Africa has huge potentials of solar power because of the abundance of direct sunshine in most days of the year. The rising cost of the fossil electricity has made the solar power an attractive option bearing in mind that the cost of the solar power has plummeted steadily in the past few years. Two main technologies are prevalent in the solar power research. These are photovoltaic (PV) systems and the concentrated solar power (CSP). The PV systems are made of solar panels and power electronic circuits. They are mostly economical in small residential units. The CSPs on the other hand which are made of solar field, thermal storage and steam turbine/generator units are economical only in large scale. In this thesis, a 2.5 kW Residential PV system and a 100 MW Molten Salt Power Tower Concentrated Solar Power were developed. The technical model of the photovoltaic panel and the power electronic circuits that connect it to the grid were also developed with Matlab/Simulink while the economic simulation of the PV, as well as the Concentrated Solar Power were carried out with Systems Advisor Model (SAM) using the climate data of Cape Town. The simulation results of this work compared the cost of PV electricity first with Renewable Energy Feed-in Tariff (REFIT) of National Energy Regulator of South Africa (NERSA), and then with the residential tariff charged by the City of Cape Town. Also the cost of electricity using CSP is compared NERSA`s REFIT. Finally the cost of PV electricity is compared with that of CSP. We therefore conclude that, with government incentives, CSP and PV are viable technologies however electricity produced by CSP is cheaper than that of the PV

Structured luminescent solar energy concentrators : a new route towards inexpensive photovoltaic energy

The solar energy market has grown considerably over the last decade due to increasing global awareness of environmental issues, the effects of greenhouse gases and fossil fuel shortages. More and more areas are now perceived as potential markets for solar energy conversion devices with the ultimate goal of replacing traditional power generating methods. However, in order for electricity generated by a photovoltaic module to be viable for industrial electricity production, the cost should be about $0.06/kWh according to the US department of Energy. The lowest cost of electricity generated by standard silicone photovoltaic modules (US$0.25/kWh) today is still a factor of two to three higher than conventional grid-connected electricity. An attractive alternative to the expensive photovoltaic panels and concentrated photovoltaic systems is the simple, colorful and cost efficient luminescent solar concentrator (LSC). LSCs consist of a transparent substrate embedded with fluorescent dyes or with the dyes as a thin film coating on top of the substrate. Generally, polymeric plates that are commercially available in large quantities for a low price are used as the transparent substrates. The fluorescent dyes in the LSC act as a light converter that absorbs sunlight and emits light at longer wavelengths. A fraction of the emitted light is directed towards the edges of the plastic plate where photovoltaic cells are attached to convert light energy into usable electricity. The simplicity and low material prices of LSCs potentially result in low energy costs (~US $0.30/Wp). However, the luminescent solar concentrator exhibits several potential light loss mechanisms that limit its efficiency and practicality for many potential applications. In this work, the possibility of producing a more efficient luminescent solar concentrator is explored by reducing the intrinsic losses of the system using inexpensive and straightforward methods. First, the behavior of standard dye-embedded and thin film coated LSCs was studied as a function of absorbance and dye concentration. Both theoretical and experimental results demonstrated that increases in dye concentration above a critical point leads to a negligible increase in edge emission and a decrease in emitted photon to absorbed photon efficiency. The decrease in efficiency is mainly a result of internal re-absorption losses, which also increases the external surface losses. The former refers to light emitted from dye molecules that is re-absorbed by neighboring dyes, and the latter refers to light lost through the top and bottom surfaces of the fluorescent substrate. To broaden the absorption range of the LSCs, stacked LSC systems consisting of two substrates doped with different fluorescent dyes was simulated theoretically and compared to experimental results. The total edge emission of the stacked LSCs was found to be more than double that of the single substrate devices. To reduce the probability of re-absorption in the luminescent solar concentrators, the thin film dye coating was patterned to create line and square dye arrays. The surface area coverage of the dye coating was reduced through patterning, which in turn decreases the probability of emitted light encountering other dye molecules, leading to a decrease in re-absorption losses in the LSC system. This concept was confirmed experimentally and theoretically as the emitted photon to absorbed photon efficiency of the patterned LSC systems increased with decreasing dye coverage. However, a significant fraction of light was lost through the clear regions of the patterned waveguide and the edge emission (in absolute light intensities) decreased as dye coverage is reduced. A possible solution for recovering light lost through the clear regions of the patterned waveguide is to use a lens array to focus incident light on the patterned dye areas. The objective of the lens array design was to maximize the acceptance angle while simultaneously minimizing the focal spot size, which dictates the size of the dye areas required. The resulting lens, designed using ray-tracing techniques, was aspherical in shape and exhibits an acceptance angle of 30¿. Subsequently, the lens array was combined with a line patterned LSC to form an integrated system. Experimental results demonstrated that the addition of a lens array resulted in better performing systems where the edge emission exceeded a fully covered standard luminescent solar concentrator by more than 20%. Introducing a lens array to the patterned LSCs induces preferred emission at two opposite edges of the substrate, and this effect was further enhanced by aligning the dye molecules using liquid crystals in a guest-host system. Three different dye alignments, isotopic, homeotropic and planar, were studied using patterned LSCs. The planar aligned systems demonstrated higher emission-to-absorption power efficiency than both isotropic and homeotropic aligned systems. In addition, emission was enhanced from two edges in the planar aligned dye system, which exceeded the edge emission of isotropic systems by 20%. These planar aligned dye systems are potentially advantageous for reducing the material cost of LSC solar modules as the preferred emission allows photovoltaic cells to be attached to two edges of the waveguide instead of four. A large fraction of emitted photons is lost through the top and bottom surfaces of the waveguide in the patterned luminescent solar concentrator systems with and without a lens array. To limit the surface losses and to further enhance the edge emission of the patterned and lens array integrated system, wavelength-selective chiral nematic (cholesteric) liquid crystal reflectors were employed. The addition of the cholesteric reflectors generally increased the edge emission of the patterned LSC system, both with and without the lens array, when the position of the reflection band of the cholesteric was chosen correctly. The increase in edge emission was higher at low dye coverage, which suggests that the cholesteric reflectors are more suitable for LSC systems with little re-absorption losses. The LSC studied in this work primarily use inexpensive materials and fabrication methods, and may be suitable for applications in energy generating rooftop installations in both urban and remote areas. The relatively low cost of energy generated by LSCs compared to standard silicon PV panels makes them an attractive alternative for large-area installations. For example, the large area of industrial building rooftops allows a vast number of LSC systems to be installed to produce the required amount of energy. In addition, the integrated patterned and lens system are relatively flat compared to standard concentrating photovoltaic systems, which makes them more visually appealing in urban environments. The ability of LSCs to alter the solar spectrum, as well as the flexibility in material choices, open new potential applications in areas such as modern agriculture where LSC plates can be used to built energy generating greenhouses

Power generation from thermoelectric cells by using solar parabolic concentration dish.

Thermoelectric and solar-energy technologies are the focus of significant research, and can make a major contribution to the need to find alternative methods of power generation, heating and cooling. Thermoelectric technology is often overlooked, but can be used in applications where other technologies could not be used, or in combination with other alternative technologies. The thermoelectric devices can utilize solar thermal power and waste heat to generate electricity, and are friendly to the environment as no any refrigerant gas is used, so they have attracted increasing attention as a green and flexible source of electricity able to meet a wide range of power requirements. Contemporary problems surrounding climate change will act as a stimulus for the development of thermoelectric, and the technology is successful in cooling, refrigeration and space-craft power, with potential for growth in power generation applications. In this thesis, the potential of thermo electric cells as concentrator solar power generation system has been discussed in detail, and an abundant knowledge as well as information about the thermoelectric technology and solar thermal system has been also illustrated

A survey of photovoltaic systems

Solar photovoltaic manufacturers and suppliers are listed. Data sheets on specific products and typical operating, installation, or maintenance instructions and procedures are appended

Energy: A continuing bibliography with indexes, issue 15

This bibliography lists 1112 reports, articles, and other documents introduced into the NASA scientific and technical information system from July 1, 1977 through September 30, 1977