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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 This paper presents a theoretical and experimental investigation about the modelling of a 1:45 scale prototype Wave Energy Converter (WEC). An analytical model is implemented to describe its behaviour in a wave tank. The aim is to provide a contribution to modelling tools used for WEC characterisation and design. Hydrodynamic characterisation software is avoided in favour of a simpler and more versatile design tool destined to a wider range of users. Therefore, an alternative approach is presented, based on mechanical analogies and the use of Matlab/Simulink/SimMechanics environment. This analytical model was constructed using linear wave theory, coupled with a non-linear model for the device and its power take-off system (PTO). Assumptions on incident waves and geometric properties of the device were required and implemented on the basis of literature of naval architecture, ships stabilization and control issues. Simulation results were compared and validated with those obtained in the same range of experimental tests of the prototype in wave tank. Trends and values of both investigation techniques show a good agreement, indicating the validity of the methodology adopted and leaving space for future improvements of the same. Finally, as example of application, the model was applied in a show case in order to estimate the energy yield by the WEC if scaled to real size, using Froude scaling. Results are encouraging and show the viability of the proposed design.

This paper combines random forests with physics-based models to forecast the electricity output of the Mutriku wave farm on the Bay of Biscay. The period analysed was 2014-2016, and the forecast horizon was 24 h in 4-h steps. The Random Forest (RF) machine-learning technique was used, with three sets of inputs: i) the electricity generated at Mutriku, ii) the wave energy flux (WEF) prediction made by the ECMWF wave model at Mutriku's nearest gridpoint, and iii) ocean and atmospheric data for the Bay of Biscay. For this last input, extended empirical orthogonal functions (EOFs) were calculated to reduce the dimensionality of these data, while retaining most of the information. The forecasts are evaluated using the R-Squared, Mean Absolute Error (MAE), and Mean Absolute Percentage Error (MAPE). The model easily outperforms a persistence forecast at 8-10 h and beyond. The most accurate forecasts are achieved by using all three of these inputs. This approach may help to effectively integrate wave farms into the electricity market. This work has been financially supported by the Spanish Government through the MINECO project CGL2016-76561-R, (MINECO/ERDF, UE) and the University of the Basque Country (UPV/EHU, GIU 17/002). ERA5 hindcast data have been downloaded at no cost from the MARS server of the ECMWF. All the calculations have been carried out within the framework of R (R Core Team, 2018). Special thanks to the Basque Energy Agency (EVE www.eve.eus) for kindly providing the data from the Mutriku wave farm used in this study.

In this paper we study a community or firm considering to diversify its investment in two distinct renewable energy technologies, namely wind and solar PV electricity. We assume technological learning curves as a function of cumulative capital investment. A real options approach is applied as it takes into account uncertainty about prices and learning, as well as irreversibility associated with investment decisions. We investigate three different cases, dealing with uncertainty about future electricity prices, and uncertainty about the speed with which learning drives the costs of wind and solar electricity down. We assess the minimum threshold for the stochastic price and the maximum electricity production cost that makes it optimal for the firm to invest in the two technologies. The results show that the learning rate affects the option to invest in but reducing critical threshold for exercising it. The greater the amount of capital invested, the more learning stimulates earlier exercising of the option to invest. The firm will then anticipate the option to invest and exercise it for lower critical threshold values if all capital is invested in one technology. If capital investment is diversified, the option should be exercised at a higher critical threshold. More uncertainty in energy prices or technology costs postpones the option to invest. Although investing in both solar and wind may be profitable under particular conditions of price and cost uncertainty, the theoretically optimal strategy is generally investing in only one technology, that is, solar or wind, depending on their relative initial costs and learning rates. This suggests that the practice in most countries of diversifying renewable energy may reflect a mistaken strategy.

Abstract This article presents the results obtained in the combustion of samples of biofuels using a commercial burner. We first provide the chemical and physical characterisation of the most abundant biofuels in Spain whose combustion we intend to study: glycerine, used vegetable oil, sunflower oil, rapeseed oil, soya oil and Animal By-products Not Intended for Human Consumption (ABNIHC) category 1 and 3 fats. We then classify the technologies used in the combustion of liquid fuels, specifying the main parameters that characterise their working parameters and the physical features of the liquid fuel, as recommended by the leading burner manufacturers. For each biofuel described, we choose the most appropriate burner technology for combustion, adopting two criteria, and we obtain suitable pulverisation as well as stable combustion. Finally, we present the results obtained in the combustion of the samples in a low pressure auxiliary air fluid pulverisation burner, the type of burner able to burn the widest range of biofuels.

Continuous phosphorus discharges in bodies of water, generated by human activities, such as agriculture, domestic effluences or wastewater from industrial processes, produce contaminated water and eutrophication. For this reason, efficient and low-cost systems that can remove phosphorus from contaminated water are necessary. In addition, it is important to generate renewable energy such as the energy produced in biomass power plants, taking advantage of the available biomass waste in each place. When producing this renewable energy, the resulting ash is a residue that can be used for phosphorus removal by adsorption processes. Moreover, according to the concept of the circular economy, the ash waste generated in this bio energy process should be reduced as much as possible. One of the advantages of this research being that surplus phosphorus-laden ash can be reused as fertilizer in agricultural fields. Considering this, the efficiency of reed ash (RA) (Phragmites australis) has been analysed in batch experiments, as well as the effect of several parameters on the removal of phosphate, such as contact time, phosphate-ash ratio, ash dose and temperature. Significant results obtained show that RA can be used to improve water quality.

The marine environment has been in the spotlight of economic development due to the growing demand for areas to promote activities associated with the concept of Blue Economy. This is the case of the renewable energy and aquaculture sectors, whose expansion towards offshore is determined by the increase global demand for energy and food, and by exceeding of the carrying capacity of coastal and terrestrial systems. In this context, the multi-use strategy can be an alternative to minimize conflicts between activities and impacts on the surrounding social-ecological environment. This contribution presents a preliminary approach to identify opportunities for individual exploitation and the possibilities of multi-use between wind energy, wave energy and aquaculture in Brazil?s Exclusive Economic Zone. Technical, operational, and biological aspects were evaluated, through a Suitability Index validated in previous works, to identify zones with favorable conditions for energy exploitation and farming of six fish species. Additionally, overlaps between conservation areas and multi-use zones were considered to analyze possible spatial conflicts. Zones with multi-use possibilities with different combinations between these sectors were identified: i) wave energy and aquaculture presented the largest areas for multi-use, distributed in the south, southeast and northeast; ii) possibility of combining wind energy and aquaculture was identified in the northeast; and iii) multi-use possibilities in the south for marine energies. Zones with multi-use possibilities were identified in protection and conservation areas, such as the combination of wave exploitation and Greater Amberjack farming, with 63% overlap. Therefore, this case study is a guide for future local studies in the marine region of Brazil, mainly in the selection of sites for analysis. The present contribution represents a starting point for the discussion about multi-use in the country C.V.C. Weiss is grateful to the Brazilian National Council for Scientific and Technological Development (CNPq) for the PDJ (Pós-doutorado Junior) fellowship granted (151228/2020–5), and the financial support from the Universidad de Cantabria (UC) through the Agusto González de Linares and Margarita Salas Grants (POS-UC-2019-06 and RMS-04, respectively). J. Bonetti is a Research Fellow of CNPq (Grant 306633/2019–1). Raúl Guanche acknowledges the Grant RYC-2017-23260 funded by MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future”. This work is framed in the project “ACUFLOT”, supported by the Biodiversity Foundation of the Ecological Transition and Demographic Challenge Ministry of Spain and the IHCantabria - Instituto de Hidráulica Ambiental de la Universidad de Cantabria

The basis of a novel method for passive solar water heating homologous to the traditional thermosyphon but driven by salinity gradient induced by changes of salinity gradient induced by evaporation at the collector is outlined. Its purpose, likewise than a thermosyphon, is to simplify the transfer of liquid while avoiding the cost and complexity of a conventional pump. However, in this concept, the fluid motion is not obtained from the tendency of a less dense fluid to rise above a denser fluid (natural convection) but rather by taking advantage of the energy released during the spontaneous mixing of the low-concentration (evaporated fraction) solution and the high-concentration (no-evaporated fraction) solution, which have been previously separated into two streams in the evaporator module. Finally, the possibility of driving the thermal osmosis by the strong thermal dependence of the solubility featured by many solutions rather than evaporation is envisaged. One important point in favor of the proposed thermosyphon driven by thermo-osmosis is that makes possible downward heat and mass transfer, i.e., heat and mass transport from the top roofs (where solar collectors are generally placed) to the bottom (inside the homes), and then the use of expensive and voluminous tanks so characteristic of current thermosyphons driven by natural convection is no longer needed.