The flow through a forced circulation Z-type flat plate solar collector was investigated by means of combined experimental measurements and numerical simulations. The efficient operation of such collectors depends on the uniformity of the flow rate distribution among their riser tubes, while low pumping power demand is also sought. Mass flow rate measurements in the riser tubes were performed, utilizing a specially adapted ultrasound instrument for various values of total flow rates in the collector. By means of a commercial Computational Fluid Dynamics (CFD) code, laminar and turbulent flow models in different computational grids were tested and validated against the experiments. Appropriate metrics were introduced to quantify flow rate distribution non-uniformity among the risers, and pressure drop through the manifold was calculated. Parametric studies for flow conditions outside the experimental window were performed utilizing the CFD method in order to assess the effect of the Reynolds number in the flow distribution among the riser tubes. Furthermore, aiming to enhance flow rate uniformity, a methodology based on modifying the diameter of each riser tube was applied and successfully demonstrated. The proposed method can be employed in large solar collector arrays, either as stand-alone systems or as belonging to hybrid alternative sources of energy (ASE) systems, aiming to optimize their overall efficiency.

Pursuing net-zero emission operations in the shipping industry are quintessential for this sector to mitigate the environmental impact caused by hydrocarbon fuel combustion. Significant contributions to this are expected from the substitution of conventional marine fuels by alternative, emission-free fuels with lower emission footprints. This study aims to conduct a comprehensive literature review for delineating the main characteristics of the considered alternative fuels, specifically focusing on hydrogen, methanol, and ammonia, which have recently attracted attention from both industry and academia. This study comparatively assesses the potential of using these fuels in marine engines, and their subsequent performance characteristics as well as the associated environmental benefits. In addition, the required storage conditions, space, as well as the associated costs, are reviewed. Special attention is given to the safety characteristics and requirements for each alternative fuel. The results of this study demonstrate that the environmental benefits gained from alternative fuel use are pronounced only when renewable energy is considerably exploited for their production, whereas the feasibility of each fuel depends on the vessel type used and pertinent storage constraints. Hydrogen, ammonia, and methanol are considered best-fit solutions for small scale shipping, requiring minimal on-board storage. In addition, the need for comparative assessments between diesel and alternative fuels is highlighted and sheds light on marine engines’ operational characteristics. Moreover, using combinations of alternative and diesel fuels is identified as a direction towards decarbonisation of the maritime sector; intensifying the need for optimisation studies on marine engine design and operation. This study concludes with recommendations for future research directions, thus contributing to fuel research concepts that can facilitate the shipboard use of alternative fuels.

No abstract

The scarcity of water is a long-standing problem in Greek islands. The government, as a temporary solution adopted the transportation of water using tanker ships. This type of water is of low quality non-potable and in some cases inappropriate for any use. Apart from that water transportation increases the carbon footprint of the islands that it is already stained due to the big thermal power plants that feed the grid using fossil fuels (mainly diesel). Apart from the environmental issues the economic consequences are extremely high. The cost of transported water in Dodecanese and Cyclades reached a total of 73,5 million € from 2002 to 2010. The aim of this paper is to bring forward the proposed solutions for desalination of sea water using renewable energy sources, as Greek islands have a great wind and solar potential that is hard to find in any other place on Europe. A Life Cycle Assessment is been conducted between two different desalination technologies (RES and Diesel operating desalination) to fully understand the impact these units have to the environment.

The shipping sector decarbonisation has attracted great attention due to the sector contribution to worldwide carbon emissions. This study aims at investigating the techno-economic–environmental performance of different ship power plants to identify sustainable solutions for a case study cargo ship. Four scenarios, considering conventional and hybrid power plants, the latter with installed batteries, both using marine gas oil and ammonia fuels, are analysed to estimate the pertinent lifetime key performance indicators characterising their economic and environmental performance. Additionally, taxation schemes of varying extent are considered, and a sensitivity analysis is carried out on the most uncertain input parameters, namely, fuel prices and capital cost. This study results demonstrate that the hybrid plant using ammonia exhibits the lowest environmental footprint associated with 66% carbon emission reduction, whilst increasing the lifetime cost by 40%. Taxation schemes close to 340 EUR per CO2 tonne are required to render it economically viable whilst meeting the IMO targets for 2050 on CO2 emissions reduction. The sensitivity analysis reveals that the economic parameters is highly sensitive to fuel price and the capital expenditure.