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A mathematical model was developed to simulate solar drying of grapes, integrating heat and mass transfer models solved by an explicit finite differences method, considering changing boundary conditions. The model simultaneously incorporated shrinkage of the product, changes in effective moisture diffusivity and dependence of thermal properties on water content and temperature. Field experiments were carried out in a mixed mode solar dryer located in the North of Portugal, with pre-blanched grapes. A good prediction of experimental solar drying curves was attained. The mathematical model can be applied for simulating solar drying of different foods, once known their specific thermo-physical properties. Simulations obtained with the developed model can be valuable for predicting accurate drying times and consequently to design, control and optimise the production of dried foods.

Abstract The integration of distributed generation (DG) units into traditional distribution grids causes several significant changes in their characteristics like power flow direction, voltage profile and short circuit level. Therefore, the currently used control and protection strategies can no longer work properly and have to be revised and modified. The most important protection problems are e.g. blinding of protection, false tripping, unsynchronized reclosing. For a reliable and efficient protection system, both transient and steady states of fault current contributions should be considered. In this paper, in order to study the real impact of DG units on a given protection scheme, the fault current contributions generated with exact models of DG units including their interfaces with the grid and control system (photovoltaic generator, PSMG with full size converter, DFIG with partial size converter, commonly met on Belgian grids, and directly connected IG) are presented and compared with the ones that are generated by ideal models of DGs in the same conditions. The PSCAD software is used for the simulation of transient contributions of DGs under several faulty conditions in a tested medium voltage distribution grid.

Abstract This work aims to get a better insight into the behaviour of CECO, an oscillating-body wave energy converter that presents a singular feature: the motion of its oscillating part is restricted to translations along an inclined axis. In order to study in the time domain the response of CECO for a wide range of wave conditions, a hybrid numerical approach based on the Boundary Element Method (BEM) and the Morison’s equation was used. The effects of the power take-off system were included in the numerical model and calibrated with the results from previous wave basin experiments. The results show that CECO is able to capture up to 40% of the incident wave energy when the direction of translation is 45°. However, if the direction of translation is vertical, the amount of captured wave energy decreases almost three times. This investigation demonstrates the advantage of limiting the oscillation of the CECO floating part to an inclined direction and reaffirms the concept as a promising technology for wave energy conversion.

Abstract In the present study, the effect of different degumming processes on the phosphorus content of Crambe abyssinica oil and resultant biodiesel was evaluated. The non-edible oil was submitted to water degumming and chemical degumming with different concentrations of phosphoric acid and varying the acid to oil volume percentages. Phosphorus content of the products was measured by UV spectroscopy after sample calcination, according to NP 1994:2000. Biodiesel was produced by transesterification using a 6:1 methanol to oil molar ratio and 1 wt% sodium hydroxide as catalyst at 65 °C, during 1 h. The biodiesel produced directly from the crude oil presented high phosphorus concentration (>20 ppm); consequently, a degumming process was required to fulfil the quality standard (

Abstract This paper addresses a strategy for decision-making of sustainable aggregation for clean energy participating in a day-ahead electricity market. The clean energy consists of wind turbines, photovoltaic arrays and energy storage, contributing to a better resilience of the system. The power delivered by a wind turbine or by a photovoltaic array is most certainly in deviation from the value associated with the bid accepted at a closing of a day-ahead electricity market. The deviation is due to the unpredicted variable nature of the respective sources of energy, leading to uncertainty and may imply a risk of loss of profit. So, uncertainty must be considered, and the addressed strategy considers uncertainty by scenarios of historical data and risk by the conditional value at risk. The strategy is a unified approach based on a risk-constrained and a two-stage stochastic optimization problem rewritten as a mixed-integer linear programming problem. A case study is presented to illustrate the main result and drive conclusions.

To generate a substantial amount of power, Wave Energy Converters (WECs) are arranged in several rows or in a ‘farm’. Both the power production and cost of a farm are lay-out dependent. In this paper, the wave power redistribution in and around three farm lay-outs in a near shore North Sea wave climate, is assessed numerically using a time-dependent mild-slope equation model. The modelling of the wave power redistribution is an efficient tool to assess the power production of a farm. Further, for each lay-out an optimal (low cost) submarine cable network is designed. The methodology to assess the power production and cost of a farm of WECs is applied to the Wave Dragon Wave Energy Converter (WD–WEC). The WD–WEC is a floating offshore converter of the overtopping type, which captures the water volume of overtopped waves in a basin above mean sea level and produces power when the water drains back to the sea through hydro turbines.It is observed that the cable cost is relatively small compared to the cost of the WD–WECs. As a result, WD–WECs should be installed in a lay-out to increase power production rather than decrease cable cost, taking spatial and safety considerations into account. WD–WECs arranged in a single line produce the highest amount of power, but require an available sea area with a large width (51 km). Installing a single line of WD–WECs in front of a farm of wind turbines increases the time window for accessing the wind farm (applied to Horns Rev II – significant wave height smaller than 1–2 m during 8 h at minimum) by 9–14%.

Woody crops such as orchards and olive groves require annual pruning operations, which leave abundant residues on the ground. These must be removed both for disease control and for facilitating the following tending activities. The resulting biomass can be managed as a waste or a by-product, in both cases incurring in a cost for farmers. A harvester prototype for collecting and comminuting apple pruning residues was tested and compared to a traditional mulcher. In particular, the study aimed at: 1) quantifying productivity and costs of the two systems, 2) evaluating the possible influence of apple variety, tree age and machine type on the productivity per hectare, and 3) estimating and comparing the energy balance of the two working options.

Abstract This paper addresses the importance of the probabilistic analysis in determining the wave energy potential to support the design of electrical generators for wave energy conversion. The irregular activity of ocean waves induces variable frequencies and amplitudes of operation for point absorbers electrical generators, which may lead to the construction of inefficient electrical machines. Applying probabilistic models to describe the ocean wave's behavior allows the determination of the values most likely to be sampled for ocean-state parameters. Knowing these values, the most expected ocean wave potential can be determined and a proper device design can be performed. This work also refers to the importance of using the joint probability models instead of the marginal ones. Seven locations at the Portuguese coast are evaluated in order to determine their wave energy resource potential.