35 research outputs found
Geometrical Optimisation of Receivers for Concentrating Solar Thermal Systems
In concentrated solar thermal technologies, the receiver converts
concentrated solar radiation into high-temperature heat. Solar
receivers are commonly simulated with a stochastic integration
method: Monte-Carlo ray-tracing. The optimisation of the geometry
of receivers is challenging when using existing optimisation
methods for two reasons: each receiver evaluation using
Monte-Carlo ray-tracing requires significant computational effort
and the outcome of a simulation involves uncertainty.
A series of novel optimisation techniques are proposed to enable
gradient-free, stochastic and multi-objective optimisation
adapted to such problems. These techniques address the
computational load difficulty and the challenge of conducting
stochastic optimisation based on uncertain evaluations by
introducing the concepts of “Progressive Monte-Carlo Evaluation
(PMCE)”, “Intermediate Ray Emission Source (IRES)” and
adaptive view-factor calculation. A new “Multi-Objective and
Evolutionary PMCE Optimisation (MOEPMCE-O)” method is then
built around PMCE to enable multi-objective geometrical
optimisation of receivers.
PMCE is shown to be able to reduce the computational time of a
random search optimisation by more than 90% and is used in the
geometrical design of a new receiver for the Australian National
University SG4 dish concentrator that achieved 97.1% (±2.2%) of
thermal efficiency during on-sun testing. MOE-PMCE-O is applied
to a multi-objective tower receiver problem where liquid sodium
is used as the receiver heat-carrier in a surround configuration
heliostat field. A series of useful geometrical concepts emerge
from the results, with geometrical features able to maintain high
efficiency while keeping acceptable incident peak flux values
with a moderate receiver total mass.
Finally, a more fundamental look at the impact of the interaction
of concentrating optics on the exergy of radiation available at
the receiver location highlights the major role played by
concentrator surface slope error in lowering the exergy in
concentrated solar thermal systems and quantifies the exergy loss
associated with non-ideal match between flux and surface
temperature in receivers
Limits of the cylindrical absorber design for a sodium receiver
The applicability of the cylindrical arrangement of vertical tube banks is evaluated for liquid sodium concentrating solar thermal receivers and compared with a molten salt reference case through a series of parametric studies. It is shown that sodium receivers experience less thermo-elastic stress load and can operate under higher flux which presents advantages in terms of size reduction and efficiency. While the cylindrical receiver configuration cannot reach the efficiency target of 91% in a high temperature configuration (480 °C to 640 °C), there is potential to improve efficiency by improving heliostat field optics. Flux limitations due to thermo-elastic stresses are less stringent due for sodium receivers due to the better heat transfer properties, and consequently better heliostat field optics would benefit sodium receiver concepts more than molten salts ones
Waypoint Planning for Autonomous Aerial Inspection of Large-Scale Solar Farms
Solar energy is seen as a sustainable and nondepletable source of energy supply. Worldwide, large-scale solar
power infrastructure is being installed every day. Such structures
can suffer from many faults and defects that degrade their energy
output during their operational life. Detecting such faults and
defects requires regular inspection over physically large and distributed solar infrastructure. On-site manual human inspection
tends to be impractical, risky and costly. As such, replacing
humans with autonomous robotic aerial inspection systems has
great potential. In this work, we propose an unmanned aerial
vehicle (UAV) waypoint generation system that is specifically
designed for aerial inspection of solar infrastructure. Our system
takes into consideration the physical structure and the dynamic
nature of sun-tracking solar modules and generates waypoints
with the right camera viewing pose and drone orientation.
Statistical methods are used to generate a randomly selected
set of modules as a representation of the entire solar farm. The
set is guaranteed to satisfy a user-defined confidence level and
margin of error requirements. A path is generated to visit selected
modules in an optimal way by deploying the traveling-salesman
shortest path algorithm, allowing the vehicle to maximize battery
use. Illustrative flights and preliminary inspection results are
presented and discussed.This research was supported by the Australian Renewable
Energy Agency (ARENA), through Grant G00853 “A robotic
vision system for rapid inspection and evaluation of solar plant
infrastructure”
Experimental Testing of a High-Flux Cavity Receiver
A new tubular cavity receiver for direct steam generation, ‘SG4’, has been built and tested on-sun based on integrated optical and thermal modelling. The new receiver achieved an average thermal efficiency of 97.1±2.1% across several hours of testing, and reduced the losses by more than half, compared to the modelled performance of the previous SG3 receiver and dish. Near-steady-state outlet steam temperatures up to 560°C were achieved during the testsFunding from the Australian Renewable Energy Agency (project 1-UFA006) is gratefully acknowledged
Development of ASTRI high-temperature solar receivers
Three high-temperature solar receiver design concepts are being evaluated as part of the Australian Solar Thermal Research Initiative (ASTRI): a flux-optimised sodium receiver, a falling particle receiver, and an expanding-vortex particle receiver. Preliminary results from performance modelling of each concept are presented. For the falling particle receiver, it is shown how particle size and flow rate have a significant influence on absorptance. For the vortex receiver, methods to reduce particle deposition on the window and increase particle residence time are discussed. For the sodium receiver, the methodology for geometry optimisation is discussed, as well as practical constraints relating to containment materialsThis research was performed as part of the Australian Solar Thermal Research Initiative (ASTRI), a project
supported by the Australian Government, through the Australian Renewable Energy Agency (ARENA)
SolarPACES Task III Project: Analyze Heliostat Field
In recent years, great efforts have been made to reach a consensus on heliostat testing best practices. A specific SolarPACES task was launched to provide a Heliostat Testing Guidelines document for single heliostat evaluation with a focus on prototype validation and qualification. Such guidelines are not well-suited for heliostat evaluation in operating commercial heliostat fields. The commercial implementation of the Central Receiver technology is burdened by the lack of a demonstrated cost-effective methodology to test solar fields, particularly during the commissioning and operation phases of the plant. To address heliostat characterization challenges, the SolarPACES funded Project Analyze
Heliostat Field aims to set the basis towards a SolarPACES guideline for Heliostat Field Performance testing under a common framework. This is by means of a review of the existing methodologies, R&D and industrial stakeholders information sharing and preparation of a future quantitative comparison and validation plan. As part of the development of this project, several meetings and a workshop involving the SolarPACES community was organized to share knowledge and experience in the measurement and characterization of heliostat fields using a range of technologies and
procedures. Research centers and companies from 5 different and distant countries have actively participated in these meetings, sharing their experiences, needs and interests. This paper summarizes the outcome of this international collaborative effort and the prospects for future close collaborations sustained over time
Comparison of open and robotic-assisted partial nephrectomy approaches using multicentric data (UroCCR-47 study)
We compared the outcomes of robotic-assisted partial nephrectomy (RPN) and open partial nephrectomy (OPN) using contemporary data to respond to unmet clinical needs. Data from patients included in the registry who underwent partial nephrectomy between January 01, 2014 and June 30, 2017 within 20 centres of the French Network for Research on Kidney Cancer UroCCR were collected (NCT03293563). Statistical methods included adjusted multivariable analyses. Rates of peri- and post-operative transfusion, and of surgical revision, were lower in the RPN (n = 1434) than the OPN (n = 571) group (2.9% vs. 6.0%, p = 0.0012; 3.8% vs. 11.5%, p < 0.0001; 2.4% vs. 6.7%, p < 0.0001, respectively). In multivariable analyses, RPN was independently associated with fewer early post-operative complications than OPN (overall: odds-ratio [95% confidence interval, CI] = 0.48 [0.35–0.66]; severe: 0.29 [0.16–0.54], p < 0.0001 for both) and shorter hospital stays (34% [30%; 37%], p < 0.0001). RPN was also a significantly associated with a decresedrisk of post-operative acute renal failure, and new-onset chronic kidney disease at 3 and 12 months post-surgery. There were no between-group differences in oncological outcomes. In comparison with OPN, RPN was associated with improved peri- and post-operative morbidity, better functional outcomes, and shorter hospital stays. Our results support the use of RPN, even for large and complex tumours
Erratum to: Methods for evaluating medical tests and biomarkers
[This corrects the article DOI: 10.1186/s41512-016-0001-y.]
Evidence synthesis to inform model-based cost-effectiveness evaluations of diagnostic tests: a methodological systematic review of health technology assessments
Background: Evaluations of diagnostic tests are challenging because of the indirect nature of their impact on patient outcomes. Model-based health economic evaluations of tests allow different types of evidence from various sources to be incorporated and enable cost-effectiveness estimates to be made beyond the duration of available study data. To parameterize a health-economic model fully, all the ways a test impacts on patient health must be quantified, including but not limited to diagnostic test accuracy. Methods: We assessed all UK NIHR HTA reports published May 2009-July 2015. Reports were included if they evaluated a diagnostic test, included a model-based health economic evaluation and included a systematic review and meta-analysis of test accuracy. From each eligible report we extracted information on the following topics: 1) what evidence aside from test accuracy was searched for and synthesised, 2) which methods were used to synthesise test accuracy evidence and how did the results inform the economic model, 3) how/whether threshold effects were explored, 4) how the potential dependency between multiple tests in a pathway was accounted for, and 5) for evaluations of tests targeted at the primary care setting, how evidence from differing healthcare settings was incorporated. Results: The bivariate or HSROC model was implemented in 20/22 reports that met all inclusion criteria. Test accuracy data for health economic modelling was obtained from meta-analyses completely in four reports, partially in fourteen reports and not at all in four reports. Only 2/7 reports that used a quantitative test gave clear threshold recommendations. All 22 reports explored the effect of uncertainty in accuracy parameters but most of those that used multiple tests did not allow for dependence between test results. 7/22 tests were potentially suitable for primary care but the majority found limited evidence on test accuracy in primary care settings. Conclusions: The uptake of appropriate meta-analysis methods for synthesising evidence on diagnostic test accuracy in UK NIHR HTAs has improved in recent years. Future research should focus on other evidence requirements for cost-effectiveness assessment, threshold effects for quantitative tests and the impact of multiple diagnostic tests