Downscaling of spatial irradiance based on cloud advection using transfer functions

Spatiotemporal aggregation of solar irradiance occurs when a spatially distributed receiver (e.g. a PV generation facility) collects variable geographically distributed irradiance and reduces it to a single electrical generation output. Models of this phenomenon exist, and are designed to take variability from a single point irradiance monitor and predict how that variability will be reduced by aggregation. We have applied these models in a revered manner to assess whether the models can be used to predict the variability of a single point measurement given an aggregate irradiance time series as an input. Results for an advection-based model show that this approach leads to overprediction of the high frequency variability due to overprediction of the site-to-site correlation. Incorporating predictions of site pair decorrelation from the wavelet variability model can temper the degree of overprediction and produces more realistic point time series. Further work may be warranted to further improve upon these efforts and enable reliable, transfer function-based downscaling of irradiance data

Cloud advection model of solar irradiance smoothing by spatial aggregation

Solar generation facilities are inherently spatially distributed and therefore aggregate solar irradiance in both space and time, smoothing its variability. To represent the spatiotemporal aggregation process, most existing studies focus on the reduced correlation in solar irradiance throughout a plant's spatial distribution. In this paper, we derived a cloud advection model that is instead based upon lagging correlations between upwind/downwind portions of a distributed plant, induced by advection of a fixed cloud pattern over the plant. We use the model to calculate a plant transfer function that can be used to predict the smoothing of the time series. The model was validated using the distributed HOPE-Melpitz measurement dataset, which consisted of 50 solar irradiance sensors at 1 s temporal resolution over a 3 × 2 km2 bounding area. The initial validation showed that the advection-based model outperforms other models at predicting the smoothed irradiance time series during manually identified, advection dominated conditions. We also conducted validation on the model against additional advection dominated periods in the dataset that were identified algorithmically. The cloud advection model's performance compared well to models in literature, but degraded slightly as larger cross-wind plant distributions were investigated. The results in this paper highlight the need to incorporate advection effects on spatial aggregation during advection dominated conditions. Future development of spatiotemporal aggregation models is needed to unify advective models with existing correlation reduction models and to identify regimes where each dominate

Cloud Advection and Spatial Variability of Solar Irradiance

A model for predicting smoothing of solar irradiance by spatially distributed collectors was analyzed. The model assumed cloud advection dominates the relationship between sites and represented the distributed plant with a transfer function. The transfer function representing the smoothing effect was shown to be the Fourier transform of the plant's spatial distribution, and as such, the plant represents a low-pass filter. Comparison with measured data from the HOPE-Melpitz campaign showed that the model is able to replicate dynamics present in the measured plant transfer function and showed good frequency domain agreement. Generalization of the approach is needed for broader applicability, as the current analysis only validated against one-dimensional, advection dominated conditions. However, the approach warrants further study as it has demonstrated an ability to reveal frequency domain characteristics not currently reflected by state-of-the-art models

MUPIC: MULTIDISCIPLINARY PROJECT IN AN INTERNATIONAL CONTEXT

peer reviewed4. Quality educatio

XMM-Newton observations of the interacting galaxy pairs NGC7771/0 and NGC2342/1

We present XMM-Newton X-ray observations of the interacting galaxy pairs NGC7771/7770 and NGC2342/2341. In NGC7771, for the first time we are able to resolve the X-ray emission into a bright central source (L(X)~10^41 erg/s), plus two (L(X)>10^40 erg/s) ultraluminous X-ray sources (ULXs) located either end of the bar. The soft emission of the central source is well-modelled by a two-temperature thermal plasma with kT=0.4/0.7 keV. The hard emission is modelled with a flat absorbed power-law (Gamma~1.7, NH~10^22 cm^2), and this together with a low-significance (1.7 sigma) ~300 eV equivalent width emission line at ~6 keV are the first indications that NGC7771 may host a low-luminosity AGN. For the bar ULXs, a power-law fit to X-1 is improved at the 2.5 sigma level with the addition of a thermal plasma component (kT~0.3 keV), while X-2 is improved only at the 1.3 sigma level with the addition of a disc blackbody component with T(in)~0.2 keV. Both sources are variable on short time-scales implying that their emission is dominated by single accreting X-ray binaries (XRBs). The three remaining galaxies, NGC7770, NGC2342 and NGC2341, have observed X-ray luminosities of 0.2, 1.8 & 0.9x10^41 erg/s respectively (0.3-10 keV). Their integrated spectra are also well-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Gamma=1.8-2.3 that are likely to represent the integrated emission of populations of XRBs as observed in other nearby merger systems. A comparison with other isolated, interacting and merging systems shows that all four galaxies follow the established correlations for starburst galaxies between X-ray, far-infrared and radio luminosities, demonstrating that their X-ray outputs are dominated by their starburst components.Comment: 15 pages,7 figures. Accepted for publication in MNRA

Enhanced star formation rates in AGN hosts with respect to inactive galaxies from PEP-Herschel observations

We compare the average star formation (SF) activity in X-ray selected AGN hosts with mass-matched control inactive galaxies,including star forming and quiescent sources, at 0.5<z<2.5. Recent observations carried out by PACS, the 60-210um Herschel photometric camera, in GOODS-S, GOODS-N and COSMOS allow us to unbiasedly estimate the far-IR luminosity, and hence the SF properties, of the two samples. Accurate AGN host stellar masses are measured by decomposing their total emission into the stellar and nuclear components. We find a higher average SF activity in AGN hosts with respect to non-AGNs. The level of SF enhancement is modest (~0.26dex at ~3sigma) at low X-ray luminosities (Lx10sigma) for bright AGNs. However, when comparing to star forming galaxies only, AGN hosts are broadly consistent with the locus of their `main sequence'. We investigate the relative far-IR luminosity distributions of active and inactive galaxies, and find a higher fraction of PACS detected, hence normal and highly star forming systems among AGN hosts. Although different interpretations are possible, we explain our findings as a consequence of a twofold AGN growth path: faint AGNs evolve through secular processes, with instantaneous AGN accretion not tightly linked to the current total SF in the host, while luminous AGNs co-evolve with their hosts through periods of enhanced AGN activity and SF, possibly through major mergers. While an increased SF with respect to non-AGNs of similar mass is expected in the latter, we interpret the modest SF offsets measured in low-Lx AGN hosts as either a) generated by non-synchronous accretion and SF histories in a merger scenario or b) due to possible connections between instantaneous SF and accretion that can be induced by smaller scale (non-major merger) mechanisms. Far-IR luminosity distributions favour the latter scenario.Comment: Final versio

Massive star formation in Wolf-Rayet galaxies. V: Star formation rates, masses and the importance of galaxy interactions

(Abridged) We have performed a comprehensive analysis of a sample of 20 starburst galaxies, most of them classified as Wolf-Rayet galaxies. In this paper, the last of the series, we analyze the global properties of our galaxy sample using multiwavelength data (X-ray, FUV, optical, NIR, FIR, and radio). The agreement between our Ha-based SFR and those provided by indicators at other wavelengths is remarkable, but we consider that the new Ha-based calibration provided by Calzetti et al. (2007) should be preferred over older calibrations. The FUV-based SFR provides a powerful tool to analyze the star-formation activity in both global and local scales independently to the Ha emission. We provide empirical relationships between the ionized gas mass, neutral gas mass, dust mass, stellar mass, and dynamical mass with the B-luminosity. Although all mass estimations increase with increasing luminosity, we find important deviations to the general trend in some objects, that seem to be consequence of their particular evolutionary histories. We investigate the mass-metallicity relations and conclude that both the nature and the star-formation history are needed to understand the relationships between both properties. The majority of the galaxies follow a Schmidt-Kennicutt scaling law of star-formation that agrees with that reported in individual star-forming regions within M~51 but not with that found in normal spiral galaxies. We found a relation between the reddening coefficient and the warm dust mass indicating that the extinction is mainly internal to the galaxies. Considering all data, we found that 17 up to 20 galaxies are clearly interacting or merging with low-luminosity dwarf objects or HI clouds. We conclude that interactions do play a fundamental role in the triggering mechanism of the strong star-formation activity observed in dwarf starburst galaxies.Comment: 33 pages, 21 figures, accepted for publication by A&

Configurations of renewable power generation in cities using open source approaches: With Philadelphia case study

In this paper, an open source tool is introduced to represent urban energy infrastructure in the City of Philadelphia, and different renewable energy scenarios are compared with respect to minimization of the standard deviation of the residual load. Renewable energy sources play a critical role in the world’s ongoing energy transition in response to climate change. Urban Energy Systems may be particularly sensitive to this transition due to the high energy demand density associated with urban environments. Open energy analysis and modeling tools can provide important information that can be used by urban energy planners, policy makers, and other stakeholders during this transition. In the present study, we apply FlexiGIS, an open energy modeling tool developed in a European context, to a case study in the City of Philadelphia. Due to the importance of open access to energy data, we pay particular attention to open energy data sources. Notably, OpenStreetMap was incomplete in its spatial coverage, but alternate open data resources were identified. This work conducts an optimization of the renewable energy mix to minimize the amount of balancing energy required for the residual load. We observe that Philadelphia has an optimal mix of renewables that favors a roughly even share of wind and solar, but that, compared to a previous case study in Oldenburg, Germany, requires more balancing energy at comparable levels of renewable penetration