A normalized variability index of daily solar radiation

AIP Conference Proceeding 2303, 180005-1–180005-8The Variability Index (VI) is widely used to quantify the intra-day solar radiation variability. It compares the length of the global horizontal irradiance (GHI) or direct normal irradiance (DNI) profiles with the length of the corresponding clear sky GHI/DNI profiles. The VI is not a normalized index, it shows dependency on the day of the year, geographic location and time resolution. Thus, the quantification of the intra-day variability of the solar resource between different locations or different seasons could be mistaken. In this work, we propose a novel definition of the VI in order to normalize it (VI’). Moreover, we suggest a methodology to assess the dependencies of the intra-day solar resource variability quantifiers with the day of the year, geographic location and time resolution. We evaluate and compare the performance of both indexes in two different locations along two synthetic years and a measured annual dataset in different time resolutions

Impact of the intra-day variability of the DNI on the energy yield of CSP plants

AIP Conference Proceeding 2126, 190009-1–190009-7The operation and the electricity yield of CSP plants in two days with the same daily-accumulated DNI, even with the same Aperture Normal Irradiance (ANI) can be very different depending on other parameters such as the variability and distribution of the solar radiation. In this paper, we intend to quantify the impact of the intra-daily variability of the DNI on the production of CSP plants. To that end, we use the ND model [1] to generate several synthetic years with similar distribution and daily energy to a reference measured year but different levels of intra-daily variability. We use System Advisor Model (SAM, https://sam.nrel.gov/) to simulate the performance of two parabolic trough (PT) plants, with and without thermal storage and common configurations for the location of Seville, Spain. To test the influence of the DNI variability, we simulate the measured and the synthetic years and we compare the daily gross power produced. As result, a clear decrease in the gross production of the PT plant without TES system is observed when the intra-daily variability increases, with daily average differences of 47% respect to the case with lowest variability. This difference is reduced with the use of the TES system to 6 %, damping the dynamic effects of the DNI variability on the global response of the plant

Conditions in which a photovoltaic system is more viable than a low-temperature solar thermal system.

Permiso para subir el documento obtenido por la instituciónPhotovoltaic (PV) and low-temperature solar thermal (LT-STH) are the most widely used technologies in the building sector. This study determines, depending on the most influential parameters, the conditions in which a PV system is more beneficial than a LT-STH system from an economical, energetic and environmental point of view. The parameter used for economically evaluated both technologies is the levelized cost of energy (LCOE). Moreover the Greenhouse Gas Emissions factor is employed for an environmental evaluation. The main results shown on this study reveal that in most cases PV is economically and environmentally more viable than LT-STH, although it would be necessary to analyze the particular conditions of each site

Cloud transient characterization in different time steps

AIP Conference Proceeding 1850, 140016-1–140016-7In this paper we evaluate the cloud transients by analyzing the dynamics of the direct fraction index kb for one year of solar radiation data in different time steps. We use instant 5-sec data integrated data and compare the number and percentage of occurrences of the different defined sky conditions. We find that the most common situation is a progressive transient and that the average transient lasts between one and 5 minutes. We also perform a cloud transient duration analysis observing that the denser clouds have greater persistence

Photovoltaic energy balance estimation based on the building integration level

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).The photovoltaic module building integration level affects the module temperature and, consequently, its output power. In this work, a methodology has been proposed to estimate the influence of the level of architectural photovoltaic integration on the photovoltaic energy balance with natural ventilation or with forced cooling systems. The developed methodology is applied for five photovoltaic module technologies (m-Si, p-Si, a-Si, CdTe, and CIGS) on four characteristic locations (Athens, Davos, Stockholm, and Würzburg). To this end, a photovoltaic module thermal radiation parameter, PVj, is introduced in the characterization of the PV module technology, rendering the correlations suitable for building-integrated photovoltaic (BIPV) applications, with natural ventilation or with forced cooling systems. The results show that PVj has a significant influence on the energy balances, according to the architectural photovoltaic integration and climatic conditions

Process Heat Generation Potential from Solar Concentration Technologies in Latin America: The Case of Argentina

This paper evaluates the potential of solar concentration technologies—compound parabolic collector (CPC), linear Fresnel collector (LFC) and parabolic trough collector (PTC)—as an alternative to conventional sources of energy for industrial processes in Latin America, where high levels of solar radiation and isolated areas without energy supply exist. The analysis is addressed from energy, economic and environmental perspective. A specific application for Argentina in which fourteen locations are analyzed is considered. Results show that solar concentration technologies can be an economically and environmentally viable alternative. Levelized cost of energy (LCOE) ranges between 2.5 and 16.9 c /kWh/m2 and greenhouse gas (GHG) emissions avoided range between 33 and 348 kgCO2/(m2 year). CPC technology stands out as the most recommendable technology when the working fluid temperature ranges from 373 K to 423 K. As the working fluid temperature increases the differences between the LCOE values of the CPC and LFC technologies decrease. When 523 K is reached LFC technology is the one which presents the lowest LCOE values for all analyzed sites, while the LCOE values of PTC technology are close to CPC technology values. Results show that solar concentration technologies have reached economic and environmental competitiveness levels under certain scenarios, mainly linked to solar resource available, thermal level requirements and solar technology cos

Assessment of a Global-to-Direct empirical model for the long-term characterization of Direct Normal Insolation

The statistical characterization of the solar resource (direct normal solar radiation) is a key point in the initial phases of a solar thermal electricity (STE) plant project. Ideally, this characterization should be based on long time series (at least 8 years) of on-site measured data of Direct Normal Insolation (DNI) and other meteorological parameters. Unfortunately, there are very few places around the world where such time series are available, so alternative methods have to be used. Most of them rely on the application of global-to-direct conversion models to long time series of Global Horizontal Insolation (GHI), measured or derived from satellite images, to estimate the long-term resource. Usually, a meteorological station including sensors for the measurement of DNI is installed at the selected project site at the beginning of the project. The data collected during the measurement campaign, which normally extends between a few months and 2 years, are used to adjust the conversion models and to correct the estimates. In this paper, a simple empirical model that relates monthly clearness index and monthly direct normal fraction is used to estimate monthly and annual long-term DNI from statistically representative monthly values of GHI. This model is adjusted with GHI and DNI data collected during measurement campaigns of different durations. We show that the accuracy of the proposed model is under +-5% and that this accuracy improves sharply with the duration of the test campaign. For this purpose, we have used 13 years of high quality DNI and GHI data from the radiometric station of the Group of Thermodynamics and Renewable Energies (GTER) of the University of Seville, Spain. The results suggest that, this simple empirical model is a good alternative to the present methodologies when short DNI measurement campaign but long-term GHI values are available

Analysis of the distribution of measured and synthetic DNI databases and its effect on the expected production of a parabolic trough plan

The generation of a Typical Meteorological Year (TMY) is a common practice in solar energy projects. Therefore it is desirable that the TMY provides not only a good estimate of the solar resource in the long term, but also an adequate input for the estimation of the performance of the project during its lifetime. The main goal of this work is to analyze and compare the effect of using synthetic and measured time series on the statistical relationships between the annual Direct Normal Insolation (DNI) values and the corresponding electricity generation of a Solar Thermal Electricity (STE) plant. For this purpose we have used two DNI databases: (a) terrestrial database with thirteen years (2000 to 2012) of 5-second measurements for the location of Seville, Spain, and (b) synthetic database generated with the Meteonorm® V 6.1.0.23 software, by applying GHI-DNI conversion models to the measured monthly values of GHI for the same location. We have used the EOS code to estimate the electricity generation of a 50 MW parabolic trough plant with 8 equivalent hours of thermal energy storage (TES) capacity. The results show that the use of synthetic series introduces an additional uncertainty that has to be analyzed for each project, being in this study the differences between the measured and synthetic data around a 2-3% for the annual values and for the main statistical parameters

Una aproximación a la gestión pública de la empresa pública: el caso de Canarias

Las entidades públicas tienen como objetivo principal brindar servicios a la sociedad, estas tienen que rendir cuentas de todas sus acciones al Gobierno, el cual también aprueba todas las tomas de decisiones en cuanto a la misma. En contrapartida, en las empresas privadas su cometido principal radica en la obtención de beneficio, la toma de decisiones recae en su junta directiva y tienen mayor libertad de actuación. La privatización de la empresa pública provoca un debate de argumentos y contraargumentos, mientras unos consideran que con este método la empresa obtiene una mayor eficacia y su venta proporciona ingresos para el Estado, otros estiman que antes de su venta el Estado tiene que sanearla o comprometerse a una serie de gastos. No obstante, se puede optar por un proceso intermedio como es el caso de la empresa mixta. La pandemia actual del COVID-19 ha afectado en mayor medida al sector privado.The main objective of public entities is to provide services to society. All actions of this type of organisation must be supervised by the government, which has the final say in any decision or policy adopted. On the other hand, private company operation are based on maximising profits, and organizational decisions are made by the board of directors, which have greater freedom of action. The privatisation of public companies is a controversial issue that has both opponents and defenders. While some consider that privatisation would help the organisation to obtain greater effectiveness and its sale would provide income to the state. Opponents believe that the state should commit to assist and bear certain expenses before privatising the entity. However, public entities may not be fully privatised, leading to a mixed privatisation entity. The current COVID-19 pandemic has influenced the private sector to a greater exten