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Abstract Building-integrated photovoltaics (BIPV) is a growing reality worldwide and its development involves implementing techniques to log and estimate the solar resources available. In this paper an easy methodology for the pre-classification of facades in BIPV projects has been described. This step is previous to the calculation of the complete solar potential in a building, and don't include the shape and shading factors. The proposed methodology covers the development of a new model that allows the irradiation factor (IF) to be estimated on facades with only 2 input parameters: the latitude of the place and the azimuth angle of the photovoltaic generator. The necessary tools to assess the “Energetic Efficiency Rating” for BIPV facades are provided, as an initial stage to be applied by architects and engineers.

Abstract Wave trends have been shown to be relevant to energy generation in various areas of the world. Accordingly, this article describes the impact of wave trends on the design of oscillating water column wave energy converters. First, wave trends across the North-East Atlantic Ocean are analysed based on the ERA5 reanalysis. In addition, an empirical model that provides the capture width of an oscillating water column is employed, identifying an approximately linear relationship between the average wavelength and the optimal width of the chamber. Thus, combining wave trends and the empirical model, the optimal size of the chamber is found to vary significantly between different geographical locations and over the four decades between 1979 and 2018. Differences between the original geometry and the geometry optimised considering wave trends, reach up to 15% in some locations. As a consequence, oscillating water column chambers designed based on past available resources rather than the resource corresponding to the time when the device is to be deployed are demonstrated to be inefficient, with a significant difference in the optimal width and absorbed energy of the chamber. Accounting for changes in resource availability over time may assist in cost optimisation of unconventional renewable energy technologies.

Kinetics of cellulose hydrothermal carbonization was investigated over different reactions times and temperatures, developing a first order-reaction model, where chemical and heat transfer processes were connected and resolved simultaneously. According to the model, mass species evolutions are described by sigmoid curves and the presence of an induction period confirms the importance of taking into account the heat-up time and not only the T-constant period during the experiments. Moreover, the model indicates that temperature plays a main role on cellulose HTC (hydrothermal carbonization) reaction, affecting both pre-exponential and exponential factors of the kinetic constant. Finally, it is interesting to remark, from a practical viewpoint, that the model was able to describe the changes in H/C, O/C and high heating value taking place during cellulose hydrocarbonization, allowing the chemical composition and energy densification to be forecasted.

Abstract Among biofuel production processes using microalgae biomass, biogas generation seems to be the least complex. Nevertheless, its efficiency is hampered due to the hard cell wall. In order to enhance its anaerobic biodegradability, the present investigation evaluated the effect of two pretreatments (low temperature autohydrolysis at 50 °C for 24 and 48 h incubation and alkaline (0.5, 2 and 5% w/w NaOH dosages)) on Chlorella vulgaris and Scenedesmus sp. The autohydrolysis resulted in 16 and 6% chemical oxygen demand (COD) solubilisation for Chlorella and Scenedesmus , respectively. During thermoalkaline pretreatment, COD in soluble phase (CODsol) was increased up to 19% for Chlorella and 17% for Scenedesmus sp. The highest carbohydrates solubilisation corresponded to 2 and 5% w/w NaOH dosage for 48 h at 50 °C for Chlorella (20%) and Scenedesmus (40–43%). When compared to Chlorella , Scenedesmus biomass exhibited higher carbohydrates solubilisation, although methane yield enhancement was low for both substrates. Best case scenario for Scenedesmus sp. (20% increase) was attained with 5% NaOH at 50 °C for 24 h. Despite the lower carbohydrates solubilisation observed for Chlorella , similar methane yields were similar to Scenedesmus sp. The low methane production enhancement was ascribed to the fact that the organic matter solubilised were exopolymers released during pretreatments rather than intracellular material.

Abstract The objective of this work is to investigate the impact of a wave farm on the nearshore wave climate quantifying, for the first time, the interaction of the WECs (Wave Energy Converters) with the waves using ad hoc laboratory tests. To accomplish this objective, a procedure consisting of three main steps is implemented and illustrated with a case study: a wave farm of WaveCats (a lateral overtopping WEC) proposed for the Death Coast (NW Spain). First, the wave climate in the wave farm area is characterised and reference wave conditions are established. Second, wave-WEC interaction and, more specifically, wave energy transmission is determined by means of 3D physical model tests. Third, on the basis of the results of the laboratory tests, the impact of different layouts of the wave farm (single-row and two-row arrays) on the nearshore wave climate is computed using a high-resolution spectral wave model. The results indicate that the difference between the two layouts is negligible at a distance of 5000 m or greater past the farm. Although the case study concerns a specific WEC and area of deployment, the procedure is entirely general in that it can be applied to other WECs and areas of interest.

Abstract Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy.