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Abstract A series of Ultraviolet-B broadband solar irradiance, 280–315 nm, measured during the period 2002–2011 in Valladolid (Spain) is analysed. UV-B daily values follow the pattern of the solar elevation angle. Daily maximum value occurred in June, 50.29 kJ m −2 , and minimum, 0.88 kJ m −2 , in December. The total accumulated UV-B irradiation along a mean year reached 7.1 MJ m −2 . The elemental statistical characteristics of hourly and daily irradiation show that the inter-quartile range is small in winter and increases in spring; maximum stability in UV-B takes place at solar noon and around summer; it can be concluded that this maximum may be considered representative of the UV-B irradiance values. The monthly-integrated UV-B irradiation values show a large annual cycle with a maximum in July, when the influence of the annual ozone column diminishes and summer solstice occurs. The results show that the harmonic analysis permits constructing long-term monthly UV-B values under clear and all sky conditions and from low number of parameters. The UV-B percentage attenuated by the atmosphere increases from winter to summer, a maximum value of 8% is obtained in summer and a minimum of 2% in winter. The cloudiness effects on the surface solar UV-B radiation are strong during the winter months, being the cloud transmittance 0.7 in December and 0.94 in July.

Abstract The Ria de Muros is a large coastal embayment on the north-western coast of Spain in which the peak tidal currents exceed 2 m/s. It is therefore a promising site for tidal stream power. The key point when assessing this resource is the accurate estimation of the tidal currents. In this work a finite difference numerical model is used for this purpose. The model solves the vertically integrated Navier–Stokes hydrodynamics and transport equations. It is validated with in situ velocity measurements performed by means of an acoustic Doppler current profiler (ADCP). Thereafter the tidal flow velocities and the corresponding power densities are computed. The largest values are found in a section of the inner ria, in which two points are selected for a detailed assessment of the resource. The model is then run to compute the tidal stream and the corresponding power density at these points during a 14-day period, so as to cover the spring–neap cycle. The power density curve thus obtained is numerically integrated to compute the annual energy output that can be obtained by a tidal stream power plant at each location.

Abstract Solar energy, as main energy supply that sustains life on Earth, is also an unavoidable component of the complex strategy in achieving a clean and fair energy transition and goals for sustainable development by 2030. The present work studies the potential of installing Photovoltaic Distributed Generation at Universidad Politecnica de Madrid – Ciudad Universitaria campus. To this end, the study focuses on the electricity generation, carbon reduction and economic feasibility of solar photovoltaic systems installation using and comparing two different approaches based on data input with different time resolution, simulation software and level of details. Results show that the optimal photovoltaic power that maximizes emissions savings also ensures the best economic return, and in addition coincides with the maximum solar potential of the Campus, which is about 3.3 MW. At campus level, approximately 77% of the photovoltaic electricity production would be consumed locally, which would suppose a coverage of about 40% of the total electricity consumption. Emissions savings could reach 30% and an in-depth economic analysis indicates that the project is highly profitable. These results and methodology could be used to assess the feasibility of photovoltaic systems at other universities and help entities study the solar potential of their buildings.

Abstract This paper proposes a new methodology for determining the geometrical parameters and the optimal distribution of small-scale linear Fresnel reflectors on flat roofs of urban buildings. This engineering problem is highly complex as it involves 21 variables; in contrast to present-day studies available in the literature, our method provides a global solution. The algorithm involves several stages, in which it uses multiple objective functionals: maximization of the used area of the roof, minimization of the cost, minimization of losses. The solution found by this method combines all the relevant aspects from the technical and/or economic point of views and obtains, as the final objective, the maximization of the absorbed annual energy for the stated problem.

Abstract Mexico is an oil-producing country which has both fossil and renewable resources. The Gulf of Mexico is its primary source of conventional resources. The economic and environmental uncertainties arising from the widespread use of hydrocarbons, oil and natural gas make it necessary to develop indigenous renewable sources to promote the transition to a diversified energy mix, thus achieving a more sustainable energy model. Solar resources are important because of the high radiation levels throughout the country. Although use of solar power is conditioned by the climatic and meteorological characteristics of the area, it is likely to be applied in both electrical and thermal systems. The coastal region of the Gulf of Mexico is characterized by a warm, humid climate and rugged terrain, with elevations over 1000 m. These conditions mean that in the central and southern areas, solar radiation is mainly diffuse. However, studies indicate that in spring and summer global irradiation can reach 4 kWh/m 2 day in the central and southern regions, and ascend to 6.7 kWh/m 2 day in the northwest. These levels are suitable for the development of solar photovoltaic energy and low temperature thermal installations, since the degree of cloud cover in these zones complicates the use of Concentrated Solar Power technology.

Abstract Monthly average daily data over the period 1989–1992 for eight meteorological parameters in Valencia are presented. Using a multiple regression method, equations to calculate the monthly average daily data for six parameters as a function of the month of the year were obtained.

Abstract This paper presents a control strategy for sun trackers which adapts continuously to different sources of error, avoiding the necessity of any kind of calibration by analyzing the produced electric power to sense the position of the Sun. The proposed strategy is able to meet the strict specifications for HCPV sun trackers despite of mechanical uncertainties (misalignments in the structure itself, misalignment of the solar modules with respect to the wing, etc.) and installation uncertainties (misalignments of the platform with respect to geographical north). Experimental results with an industrial-grade solar tracker showing the validity of the proposed control strategy under sunny and moderate cloudy conditions, as well as with different installation precisions by un-calibrating the system on purpose are exposed.

Abstract This paper describes and assesses a behavioral model for grid-connected photovoltaic inverters. The model allows us to simulate the electrical behavior of commercial single-phase and three-phase inverters in accordance with the limits of EN50160 power quality. Regarding power strategies for current inverters, both voltage and current control loops have been explicitly modeled, providing suitable simulations of the injected AC-current waveform under either power dynamics or grid voltage disturbances. Additionally, irradiance oscillations and dynamic Maximum Power Point Tracking performance have been also considered in the proposed solution. Internal inverter variables are not needed to fit the model parameters, being estimated from basic data-sheet information provided by manufacturers and simple AC-collected values from the PV power plants. This characteristic avoids any additional DC-side measurement, being a significant contribution in comparison with previous approaches. The proposed model is assessed using real data collected in Spanish photovoltaic power plants along several years. The obtained results are compared with previous behavioral model approaches and also included in the paper.