146 research outputs found
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
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
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
An improved model for the synthetic generation of high temporal resolution direct normal irradiation time series
Several studies have confirmed the relevant impact of the resolution and frequency distribution of solar radiation data on the results of detailed production models. Many of the available direct normal irradiance (DNI) databases generated from the satellite images have an hourly resolution. In the present work, we have proposed improvements to an existing model for the generation of 10-min synthetic DNI data from the hourly average DNI values. In the original model, the irradiance is divided into a deterministic and a stochastic component, i.e., the contribution from the hourly mean and stochastic fluctuation obtained from the mean depending on the sky condition, respectively. We have implemented several improvements, and the most relevant is the consistency of the synthetic data with the state of the sky. The adaptation and application of the model to the location of Seville show significant improvements over its predecessor as it achieved 7% rRMSD in hourly values and 1% rRMSD in daily values and presented a realistic frequency distribution in the 10-min resolution. In comparison with the original model, the application of the improved model showed significant performance improvements without any further adaptations to other locations with different climatological characteristics than Seville
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
A novel storage system for cooling stand-alone photovoltaic installations
Stand-alone photovoltaic systems usually use batteries to adjust energy yield to energy demand. An alternative energy storage system for stand-alone photovoltaic installations is proposed for three cooling applications: air conditioning, food preservation and freezing. A thermally insulated storage tank with ammonia in saturated mixture phase is integrated into the vapour-compression cooling cycle. A thermodynamic model and an economic assessment based on typical costs and cost sensitivity are included to assess the proposed system performance in comparison with a conventional stand-alone photovoltaic system with a vapour-compression cycle. Results show that the proposed storage strategy is an affordable option, especially in hot climates and for food preservation and freezing applications.Junta de Andalucía PI-1454/40/201
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
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