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The integration of residential photovoltaic (PV) systems for self-consumption is expected to unlock a variety of economic, technical and social benefits, such as the creation of local work and the reduction of the price of electricity, CO2 emissions and electrical power losses in the transmission network. In spite of all these advantages, regulatory barriers prevented the development of renewable self-consumption in Spain prior to October 2018, when a new regulation introduced the right to self-consume electrical energy without charges. This work aims to estimate the effect of residential self-consumption on the Iberian electricity market. To achieve this goal, a ceteris paribus approach was adopted, the accumulated scattered PV self-production was turned into a reduction of the aggregate demand in the market and the new clearing point was established. Based on 2017 market data, the results showed that a 1% curtailment of the annual demand due to PV self-consumption could reduce the cost of the market-traded energy by almost 2%. European Commission, Horizonte 2020 SI-1778/12/ 2018

Abstract In this paper we propose a time-dependent, three-dimensional model for the efficiency of a nanofluid-based direct-absorption parabolic trough solar collector under a turbulent flow regime. The model consists of a system of equations: a partial differential equation for conservation of energy, and a time-dependent radiative transport equation describing the propagation of solar radiation through the nanofluid. Writing the model in dimensionless form reveals four controlling dimensionless numbers: one describing the relative importance of conduction and advection and three describing the heat loss to the surroundings. Realistic parameter values are applied to reduce the model further and these indicate that two of the dimensionless groups have a much smaller impact on the performance of the solar collector. We use the resulting solution for the temperature to calculate an analytic expression for the collector’s efficiency. This expression permits optimisation of design parameters such as particle loading, incoming radiative intensity, receiver dimensions, the inlet temperature, and solar concentration ratio.

Abstract An algorithm for mapping Direct Normal Irradiance (DNI) in thermosolar power plants using a Mobile Robotic Sensor Network (RSN) is presented. The algorithm selects measurement spots and allocates the RSN accordingly to carry out the dynamic estimation of DNI. A generic thermosolar power plant with a fleet of vehicles is used as a simulated case study to assess the performance of the algorithm. The results show that the proposed method allows us to obtain a spatial estimation of the DNI that could improve the performance of the plant, and that outperforms estimations based on a single pyrheliometer.

Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja.

Abstract A theoretical study of the heat transfer process that takes place in a special calorimeter of conical cavity named CAVICAL is presented. This instrument is used to measure the thermal power of a point focus solar concentrator system named DEFRAC, developed at the Center for Energy Research of the National University of Mexico. The DEFRAC concentrator has a power of 1.3 kWth and a very fine optical system. The calorimeter has a cavity opening of 8.24 cm 2 . A detailed heat transfer study was done using FLUENT code. The heat transfer processes taken into account for the analysis were the radiative energy absorbed by the inner cavity wall, the energy transfer from the outer cavity wall to the air by natural convection, the energy transferred by conduction through the inner metallic wall of the calorimeter, and by forced convection to the fluid in the cooling system. The calorimetric information gathered allowed determining the thermal power that the concentrator is able to capture. Temperature and velocity fields have been calculated for each of the thermal fluids considered inside of the calorimeter. The analysis gave thermal losses and measured the thermal efficiency of the device. The information generated is useful to further optimize the design of the calorimeter.

Different decomposition models have been developed to estimate hourly direct and diffuse solar irradiance from hourly global irradiance measurements. Besides clearness index kt, other geometric and meteorological variables have been tested as predictors of hourly diffuse fraction, k, or hourly beam transmittance index, kb, by means of piecewise correlations. The recent volcanic eruption of Mount Pinatubo (June 1991) was responsible for important modifications in the solar radiation fluxes. In this article we address the effect of the volcanic aerosols on the performance of some well-known empirical models, using a data set including different radiometric and meteorological variables. The study has revealed that the more pronounced performance changes affected the higher kt intervals associated with the lower levels of cloud cover. After the eruption, all the models present a general tendency to overestimate the direct component and underestimate the diffuse component.

A linear correlation between UV-A and 380 nm was developed by means of the TUV 4.1 radiative transfer model. The prediction error of the correlation was evaluated with data from Buenos Aires, Argentina, 2001, and from 2006, Almeria, Spain. Percent random mean square error (RMSE%) was calculated for intervals of 10° of solar zenith angles, ranging 4.75% at 20° to 37.70% at 90° in clear days and 22.16% at 20° to 26.17% at 90° for cloudy days in Buenos Aires Argentina, and 1.27% at 20° to 11.27% at 90° for clear days in Almeria, Spain. Clouded days were not assessed with the data from Spain. In Argentina, the UV-A radiometer is located in a rural area and the 380 nm radiometer is located in an urban area 6 km away. Hence the real error of the proposed model is closer to that found in Spain were both measurements were performed at the same site. The objective of the work is to achieve a simple and precise method to assess UV-A availability for environmental applications of solar energy, particularly for solar water treatment, at any desired latitude.

In this paper, a detailed model for the transient simulation of solar cavity receivers for concentrating solar power plants is presented. The proposed model aims to consider all the major phenomena influencing the performance of a cavity receiver, including radiation, convection and conduction heat transfer mechanisms. For the radiation heat exchange within the cavity, the radiosity method is implemented, where the view factor calculation for all the active and passive surfaces is performed by a ray tracing algorithm programmed in a free software environment for statistical computing, namely R. A one-dimensional modeling approach is used for the tubes constituting the receiver active panels, through which the heat transfer fluid (HTF) is pumped. The governing partial differential equations are solved numerically by applying the finite volume method. Convective heat losses are modeled through different correlations for natural and forced convection heat losses from the specific literature. Once the thermal behavior has been haracterized, the geometry of the model is later fixed to check the consistency of the model and to study its dynamic characteristics. A specific 51.6 MWth, PS10 like receiver is used in this paper, although the implemented model has the flexibility to allow a variable number of panels and geometric configurations. At last, an adaptive neural controller, designed and trained offline, controls the outlet temperature of the molten salts to the desired operating value. Results for transient simulations are shown in the paper, demonstrating the plausibility of the estimations obtained with the developed model. The proposed model has been implemented in the Modelica language and based on the Modelica Standard Library (MSL) modeling approach.