Potentials and challenges of the fuel cell technology for ship applications. A comprehensive techno-economic and environmental assessment of maritime power system configurations

The decarbonization of the global ship traffic is one of the industry’s greatest challenges for the next decades and will likely only be achieved with new, energy-efficient power technologies. To evaluate the performances of such technologies, a system modeling and optimization approach is introduced and tested, covering three elementary topics: shipboard solid oxide fuel cells (SOFCs), the benefits of decentralizing ship power systems, and the assessment of potential future power technologies and synthetic fuels. In the following, the analyses’ motivations, scopes, and derived conclusions are presented. SOFCs are a much-discussed technology with promising efficiency, fuel versatility, and few operating emissions. However, complex processes and high temperature levels inhibit their stand-alone dynamic operation. Therefore, the operability in a hybrid system is investigated, focusing on component configurations and evaluation approach corrections. It is demonstrated that moderate storage support satisfies the requirements for an uninterrupted ship operation. Depending on the load characteristics, energy-intensive and power-intensive storage applications with diverging challenges are identified. The analysis also emphasizes to treat degradation modeling with particular care, since technically optimal and cost-optimal design solutions differ meaningfully when assessing annual expenses. Decentralizing a power system with modular components in accordance with the load demand reduces both grid size and transmission losses, leading to a decrease of investment and operating costs. A cruise-ship-based case study considering variable installation locations and potential component failures is used to quantify these benefits. Transmission costs in a distributed system are reduced meaningfully with and without component failure consideration when compared to a central configuration. Also, minor modifications ensure the component redundancy requirements, resulting in comparably marginal extra expenses. Nowadays, numerous synthetic fuels are seen as candidates for future ship applications in combination with either combustion engines or fuel cells. To drive an ongoing technology discussion, performance indicators for envisioned system configurations are assessed in dependence on mission characteristics and critical price trends. Even if gaseous hydrogen is often considered not suitable for ship applications due to its low volumetric energy density, resulting little operating costs are accountable for its superior performance on short passages. For extended missions, fuel cells operating on methanol or ammonia surpass hydrogen economically

Techno-economic and Environmental Comparison of Internal Combustion Engines and Solid Oxide Fuel Cells for Ship Applications

In order to quantify the economic and environmental impact of technology selection in ship power systems, four different battery-supported hybrid configurations including diesel and gas combustion engines, as well as natural gas fueled solid oxide fuel cells (SOFCs) are modeled and analyzed. The investigations include component investments, maintenance and operational costs, as well as the components’ and fuels’ carbon footprints, operational greenhouse gases and other relevant emissions. Dynamic energy system models are used to derive economically optimal system designs for an appropriate technology comparison in a cruise ship case study. The assessment is conducted for a cruise ship case study with technology parameters for the near future and 2050. Results indicate that the auxiliary power system based on diesel combustion is inferior both economically and environmentally compared to SOFCs or gas combustion engines. While latter are the most cost efficient, SOFC application provides an environmental improvement without the need for a new fuel such as hydrogen. In a final outlook for the year 2050, SOFCs economically overtake gas combustion engines on the condition that their investment costs decrease and synthetic fuels are introduced to the market as a low emission solution

Brightening of Long, Polymer-Wrapped Carbon Nanotubes by sp3^{3} Functionalization in Organic Solvents

The functionalization of semiconducting single-walled carbon nanotubes (SWNTs) with sp$^{3}$ defects that act as luminescent exciton traps is a powerful means to enhance their photoluminescence quantum yield (PLQY) and to add optical properties. However, the synthetic methods employed to introduce these defects are so far limited to aqueous dispersions of surfactant-coated SWNTs, often with short tube lengths, residual metallic nanotubes and poor film formation properties. In contrast to that, dispersions of polymer-wrapped SWNTs in organic solvents feature unrivaled purity, higher PLQY and are easily processed into thin films for device applications. Here, we introduce a simple and scalable phase-transfer method to solubilize diazonium salts in organic nonhalogenated solvents for the controlled reaction with polymer-wrapped SWNTs to create luminescent aryl defects. Absolute PLQY measurements are applied to reliably quantify the defect-induced brightening. The optimization of defect density and trap depth results in PLQYs of up to 4 % with 90 % of photons emitted through the defect channel. We further reveal the strong impact of initial SWNT quality and length on the relative brightening by sp$^{3}$ defects. The efficient and simple production of large quantities of defect-tailored polymer-sorted SWNTs enables aerosol-jet printing and spin-coating of thin films with bright and nearly reabsorption-free defect emission, which are desired for carbon nanotube-based near-infrared light-emitting devices

Extrapolation of the intensity autocorrelation function of a quantum-dot micropillar laser into the thermal emission regime

We present investigations on the coherence of the emission from the fundamental mode of an AlGaInAs/GaAs quantum-dot microcavity laser. We measure the first-order field-correlation function g((1))(tau) with a Michelson interferometer, from which we determine coherence times of up to 20 ns for the highest pump powers. To fully characterize the coherence properties of the cavity emission, we apply a phenomenological model that connects the first-and second-order correlation functions. Hereby it is possible to overcome the limited sensitivity of the streak camera used for photon-correlation measurements, and thus to extend the accessible excitation-power range for g((2))(tau) down to the thermal regime. (C) 2011 Optical Society of America</p

Variability of Inducible Expression across the Hematopoietic System of Tetracycline Transactivator Transgenic Mice

The tetracycline (tet)-regulated expression system allows for the inducible overexpression of protein-coding genes, or inducible gene knockdown based on expression of short hairpin RNAs (shRNAs). The system is widely used in mice, however it requires robust expression of a tet transactivator protein (tTA or rtTA) in the cell type of interest. Here we used an in vivo tet-regulated fluorescent reporter approach to characterise inducible gene/shRNA expression across a range of hematopoietic cell types of several commonly used transgenic tet transactivator mouse strains. We find that even in strains where the tet transactivator is expressed from a nominally ubiquitous promoter, the efficiency of tet-regulated expression can be highly variable between hematopoietic lineages and between differentiation stages within a lineage. In some cases tet-regulated reporter expression differs markedly between cells within a discrete, immunophenotypically defined population, suggesting mosaic transactivator expression. A recently developed CAG-rtTA3 transgenic mouse displays intense and efficient reporter expression in most blood cell types, establishing this strain as a highly effective tool for probing hematopoietic development and disease. These findings have important implications for interpreting tet-regulated hematopoietic phenotypes in mice, and identify mouse strains that provide optimal tet-regulated expression in particular hematopoietic progenitor cell types and mature blood lineages