Concentrated solar thermal (CST) systems, capable of driving high-temperature processes up to 2000 K, hold significant potential for chemical and industrial applications. This paper reviews methods for measuring concentrated solar flux, focusing on their role in calculating key optical performance metrics such as concentration ratio and optical efficiency. It also explores the challenges associated with these measurements. Flux measurement methods are categorized into direct and indirect approaches. Direct methods use heat flux gauges positioned on a stationary or moving target to measure solar flux, while indirect methods rely on a CCD or CMOS camera, a Lambertian target, and a heat flux gauge. The camera captures images of solar radiation, which are calibrated to heat flux values using readings from the heat flux gauge. Heat flux gauges are a critical component of both direct and indirect measurement methods. This study also reviews and compares various types of heat flux gauges, including Gardon radiometers, Schmidt-Boelter gauges, Kendall radiometers, heat flux microsensors, and calorimeters. The comparison considers factors such as maximum flux rating, response time, durability, water-cooling requirements, cost, and measurement uncertainty. Calibration techniques for these gauges are also discussed. It is observed that indirect methods are commonly used for measuring concentrated solar flux due to their higher resolution, which enables them to identify hot spots and measure concentrated solar flux more accurately than direct methods. The key challenges in measuring concentrated solar flux include calibrating sensors under solar conditions, ensuring sensor durability, accounting for environmental factors, and managing cost considerations.

Efficient plant operation can be achieved by properly loading and sequencing available chillers to charge and discharge thermal energy storage (TES) reservoirs at optimal rates and times. TES charging sequences are often determined by heuristic rules that typically aim to reduce utility costs under the time-of-use rates. However, such rules of thumb may result in significantly suboptimal performance on some days. Rigorous optimization, on the other hand, is computationally expensive and can be unreliable if not carefully implemented. A novel receding-horizon control (RHC) algorithm is developed to reliably compute near-optimal control for charging and discharging the stratified sensible cool storage reservoir of a chiller plant. The algorithm provides a constant coefficient-of-performance (or cost-per-ton-hour) 24 h dispatch plan under which chillers operate at higher capacity during more favorable weather conditions. The algorithm uses a one-dimensional search requiring at most N2/2 evaluations per day of chiller performance where N is the number of planning horizon time-steps and chiller performance is modeled as a function of capacity fraction and ambient wet- or dry-bulb temperature. Analysis of four hot climates, ranging from dry to humid, indicates 2.4–2.6% energy savings under a flat electricity rate relative to the same plant operating without TES. Annual cost savings from 6% to 9% were found for electricity billed under a simple (10 a.m.–10 p.m.) time-of-use rate with no demand or ratchet components.

Concentrating solar power (CSP) with thermal energy storage (TES) presents the major advantage over solar photovoltaics of dispohability. High thermodynamic efficiencies achieved by collecting and storing heat at higher temperatures, and recent maturing of the technology, are making molten-salt central receiver plants the preferred option for CSP. To explore potential further improvements in CSP efficiency and cost the world's first direct absorption molten salt volumetric receiver/storage system was built at pilot scale, commissioned and monitored. In this demonstration a 100 kWth beam-down tower directs solar radiation through a final concentrator into the open aperture of a 1.94 m high and 1.25 m internal diameter tank receiver situated near the ground. The receiver tank is filled with 3,800 kg of 60-40 wt% NaNO3-KNO3 and serves as a stratified or mixed single tank thermal store that can satisfy evening peak loads or provide baseload power through the night. Compared to the parasitic loads of a conventional tower-receiver plant, the energy needed for salt transport from receiver to TES and morning preheat is negligible for this new system. The hot-spot problem of tubular receivers is eliminated and. the combined receiver/storage tank reduces component costs. In-situ initial melting was accomplished using solar energy as the primary input. Thermal stratification was maintained by daily cycling of a divider plate and occasional mixing plate actions and hot spots were never observed during several months' operation between 250 and 500 C. Three cycles of complete salt freezing and in-situ on-sun re-melting were tested with no operational difficulty and no discernible damage.

In many cities that have experienced rapid growth like Abu Dhabi, urban microclimate scenarios evolve rapidly as well and it is important to study the urban thermal dynamics continuously. The Local Climate Zone (LCZ) classification considers factors related to the physical properties like surface cover and surface structure of the city which allow to analyze urban heat flows. Abu Dhabi city is rapidly expanding and is characterized by highly heterogeneous types of built forms that comprise mainly of old mid-rise and modern high-rise buildings with varied degrees of vegetation cover in different parts of the city. The fact that it is a coastal city in a desert environment makes it quite unique. This paper presents an approach of studying urban heat flows in such heterogeneous setup. First, the city is classified into local climate zones using images acquired by Landsat Satellite. Numerical simulations are performed in the designated LCZs using a computational fluid dynamics software, Envi-met. The results of Envi-met are calibrated and validated using in-situ measurements across all four seasons. The calibrated models are then applied to study entire Abu Dhabi island across different seasons. The results indicate a clear presence of urban heat island (UHI) effect when averaged over the full day which is varying in different zones. The zones with high vegetation do not show large average UHI effect whereas the effect is significant in densely built zones. The study also validates previous observations on the inversion of UHI effect during the day and in terms of diurnal response.

Efficient plant operation can be achieved by properly loading and sequencing available chillers to charge a thermal energy storage (TES) reservoir. TES charging sequences are often determined by heuristic rules that typically aim to reduce utility costs under time of use rates. However, such rules of thumb are in most cases far from optimal even for this task. Rigorous optimization, on the other hand, is computationally expensive and can be unreliable as well if not carefully implemented. Model-predictive control (MPC) that is reliable, as well as effective, in TES application must be developed. The goal is to develop an algorithm that can reach similar to 80% of achievable energy efficiency and peak shifting capacity with very high reliability. A novel algorithm is developed to reliably achieve near optimal control for charging cool storage in chiller plants. Algorithm provides a constant COP (or cost per ton-hour) for 24-hr dispatch plan at which plant operates during most favorable weather conditions. Preliminary evaluation of this novel algorithm has indicated up to 6% improvement in plant annual operating cost relative to the same plant operating without TES. TOU rate used in both cases charges 7.4cents/kWh during off peak hours and 9.8cents/kWh during peak hours (Peak hours are 10 am to 10 pm).

The beam-down solar concentrator at the Masdar Institute Solar Platform (Abu Dhabi, United Arab Emirates) is optimally coupled with a final optical element (FOE) to maximize the net power recovered by an upward-facing solar receiver. The FOE is designed as a converging reflective passage of hexagonal cross-section to further concentrate the solar flux onto the solar receiver. We develop efficient ways to optimize the orientation of the tower central reflectors simultaneously with the geometry and size of the FOE. Net power recovered by the receiver and optimized dimensions of the FOE designs are presented as a function of FOE internal surface reflectivity and the height of its inlet with respect to the ground. Setups where the receiver aperture is 3 m above the ground that are optimized simultaneously with an 85%-reflective FOE absorb 20% additional power incoming from the central reflector than equal setups optimized without an FOE. Such optimal FOE designs remain feasible, with inlet-to-outlet lengths below 2 m. The results may be applied to the design of other beam-down projects with planar central reflectors.

To improve the energy efficiencies of building cooling systems, manufacturers are increasingly utilizing variable speed drive (VSD) motors in system components, e.g. compressors and condensers. While these technologies can provide significant energy savings, these benefits are only realized if these components operate as intended and under proper control. Undetected faults can foil efficiency gains. As such, it's imperative to monitor cooling system performance to both identify faulty conditions and to properly inform building or multi-building models used for predictive control and energy management. This paper presents nonintrusive load monitoring (NILM) based "mapping" techniques for tracking the performance of a building's central air conditioning from smart electrical meter or energy monitor data. Using a multivariate linear model, a first mapping disaggregates the air conditioner's power draw from that of the total building by exploiting the correlations between the building's line-current harmonics and the power consumption of the air conditioner's VSD motors. A second mapping then estimates the air conditioner's heat rejection performance using as inputs the estimated power draw of the first mapping, the building's zonal temperature, and the outside environmental temperature. The usefulness of these mapping techniques are demonstrated using data collected from a research facility building on the Masdar City Campus of Khalifa University. The mapping techniques combine to provide accurate estimates of the building's air conditioning performance when operating under normal conditions. These estimates could thus be used as feedback in building energy management controllers and can provide a performance baseline for detection of air conditioner underperformance.

In a previous paper, we presented a novel approach to validate the capability of the biometeorological index, Universal Thermal Climate Index (UTCI), to predict the likelihood of urban dwellers to be outside in a public space for the heating dominated climate of Cambridge, MA. Occupancy patterns were recorded based on Wi-Fi data. The present study extends this approach to the hot and arid climate of United Arab Emirates (UAE) to evaluate the effect of outdoor evaporative coolers on resident presence in a public courtyard. Over a period of ten months, outdoor Wi-Fi access point data was collected in the public courtyard located on a university campus in Abu Dhabi. An analysis of the resulting MacID probes yields a population of 1200 regulars and 3800 visitors present in the courtyard at some point during the study period. Coincident UTCI simulations using ENVI-met strongly correlated with the number of regulars present during lunchtime both during times when the evaporative coolers were on (R-2 = 75%) and off (R-2 = 61%). Lunchtime attendance peaked for UTCI values in the thermal comfort range of around 24 degrees C during all seasons. The outdoor evaporative coolers were able to bring the UTCI down from very strong heat stress to between thermal comfort and moderate heat stress range. These findings confirm that UTCI can be used as a reliable environmental performance metric to support the design and preservation of comfortable outdoor spaces both in a hot and a cold climate, across a variety of cultural settings.

The city of Abu Dhabi is growing every year in population, urban extent and energy demand. This research focuses on the application of two simulation programs to estimate changes in urban climate associated with continued development in Abu Dhabi: The Urban Weather Generator (UWG) and ENVI-met. Simulation with these two software packages are validated with the site data measured in downtown Abu Dhabi. A comparison analysis (in the different seasons) between the rural data, the simulation output, and the site measurements shows the variations of the UHI in this Middle Eastern city and the potential of the validated tools. The main aims of this study are: (a) to make a seasonal validation of the UWG for the city of Abu Dhabi (referring to urban-rural available data). The tool was previously validated for a year (no seasonal division) for Abu Dhabi, Toulouse, Basel, Singapore, Rome and Barcelona. The simulations are based on the 2016 version of the Urban Weather Generator. The analysis is separated into three main seasons (instead of the full year): winter, spring, summer. (b) To make a seasonal validation and improve the second tool evaluated in this study, ENVI-met 4.0. The software can simulate urban temperature, humidity and wind speed. Guides are proposed for the enhancement of the accuracy of both estimation procedures. Referring to the results, UWG tends to overestimate the canyon temperature during the summer and has a more realistic estimation on the winter season. ENVI-met has better estimations of temperatures during the summer season compared to UWG. Finally, the UWG weather file contributes a more detailed energy model on a mesoscale model. It considers the seasonal effect and shows the impact of the climate on profiling the UHI phenomena. ENVI-met needs improvement in calculating the anthropogenic heat and in calculation of the mean radiant temperature.

In this chapter, various aspects related to Internet of Things (IoT) based sensor node development for urban microclimate monitoring are presented. The discussion is focused on software development, relevant methodologies, hardware modules, and platforms. A typical sensor node consists of sensors, computing/controlling unit, and a communication unit. There is a large variety of environmental sensors (temperature, wind, humidity, etc.), computing units (single-board computers and microcontrollers), and communication units. With the rise of Internet-enabled devices, the ideas of IoT are being incorporated into sensor node development.

Urbanization is driving rapid growth of mechanical cooling around the world, much of it in hot climates. Adoption of minimum energy performance standards can significantly reduce global growth of electricity demand associated with cooling. Performance standards aim to minimize equipment life-cycle cost by setting performance levels appropriate fora given climate. A typical UAE 8760-hour cooling bad profile is developed A component-based chiller model is validated by monitored data from a baseline chiller that meets the highest MEPS currently in effect of SCOP=3.5 W/W. Performance maps are produced fora series of progressively higher performance chiller designs and LCC analysis is carried out using component costs and annual simulation results until the least life-cycle-cost design is found. A high performance air-cooled chiller minimum performance level of SCOP>5.0 W/W is life-cycle cost-effective in UAE's hot climate.

Reference solar irradiance spectra are needed to specify key parameters of solar technologies such as photovoltaic cell efficiency, in a comparable way. The IEC 60904-3 and ASTM G173 standards present such spectra for Direct Normal Irradiance (DNI) and Global Tilted Irradiance (GTI) on a 37 degrees tilted sun-facing surface for one set of clear-sky conditions with an air mass of 1.5 and low aerosol content. The IEC/G173 standard spectra are the widely accepted references for these purposes. Hence, the authors support the future replacement of the outdated ISO 9845 spectra with the IEC spectra within the ongoing update of this ISO standard. The use of a single reference spectrum per component of irradiance is important for clarity when comparing and rating solar devices such as PV cells. However, at some locations the average spectra can differ strongly from those defined in the IEC/G173 standards due to widely different atmospheric conditions and collector tilt angles. Therefore, additional subordinate standard spectra for other atmospheric conditions and tilt angles are of interest for a rough comparison of product performance under representative field conditions, in addition to using the main standard spectrum for product certification under standard test conditions. This simplifies the product selection for solar power systems when a fully-detailed performance analysis is not feasible (e.g. small installations). Also, the effort for a detailed yield analyses can be reduced by decreasing the number of initial product options. After appropriate testing, this contribution suggests a number of additional spectra related to eight sets of atmospheric conditions and tilt angles that are currently considered within ASTM and ISO working groups. The additional spectra, called subordinate standard spectra, are motivated by significant spectral mismatches compared to the IEC/G173 spectra (up to 6.5%, for PV at 37 tilt and 10-15% for CPV). These mismatches correspond to potential accuracy improvements for a quick estimation of the average efficiency by applying the appropriate subordinate standard spectrum instead of the IEC/G173 spectra. The applicability of these spectra for PV performance analyses is confirmed at five test sites, for which subordinate spectra could be intuitively selected based on the average atmospheric aerosol optical depth (AOD) and precipitable water vapor at those locations. The development of subordinate standard spectra for DNI and concentrating solar power (CSP) and concentrating PV (CPV) is also considered. However, it is found that many more sets of atmospheric conditions would be required to allow the intuitive selection of DNI spectra for the five test sites, due in particular to the stronger effect of AOD on DNI compared to GTL The matrix of subordinate GTL spectra described in this paper are recommended to appear as an option in the annex of future standards, in addition to the obligatory use of the main spectrum from the ASTM G173 and IEC 60904 standards.

Three dimensional secondary concentrators are exposed to high radiation fluxes, part of which is absorbed by the reflecting material, leading to elevated wall temperatures which may cause reflectance degradation and mechanical distortion. Temperature monitoring and thermal management is required. Existing 3D secondary concentrators used in beam-up or beam-down tower plants use water-based convective cooling for which failures and leaks have been reported. The present work tested two alternative non-liquid-based cooling strategies: enhanced radiative cooling using a high-emissivity paint and forced-air convective cooling. The concentrator under no cooling enhancement reached temperatures above the acceptable limit, indicating the need for better cooling. Forced-convective cooling had the most noticeable effect and proved sufficient for the considered testing conditions. The impact of radiative cooling enhancement was lower in the considered incident flux conditions, as the initial temperature without enhancement was relatively low.

Back-silvered glass mirrors exposed in Abu Dhabi outdoor conditions for 7 years along with corresponding asreceived mirrors from the same manufacturing batch which were preserved in a warehouse are analyzed in the present study. The availability of both the as-received mirrors and the exposed ones over a time longer than that in previous studies presents an opportunity to validate accelerated aging tests through comparison with naturally aged mirrors. The exposed mirrors showed substantial reflectance degradation. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) was used to characterize both as-received and exposed samples and compare the as-received sample to a reference mirror from the state-of-the-art commercial solar mirrors. The analyses identified 5 possible causes of the rapid degradation observed for the mirrors in question in comparison to the lifetime expectation for commercial solar mirrors. The findings will serve to guide ongoing and future accelerated-aging studies on the same mirrors.

Simulation models play an important role in the design, analysis, and optimization of modern energy and environmental systems at building or urban scale. However, due to the extreme complexity of built environments and the sheer number of interacting parameters, it is difficult to obtain an accurate representation of real-world systems. Thus, model calibration and uncertainty analysis hold a particular interest, and it is necessary to evaluate to what degree simulation models are imperfect before implementing them during the decision-making process. In contrast to the extensive literature on the calibration of building performance models, little has been reported on how to automatically calibrate physics-based urban microclimate models. This paper illustrates a general methodology for automatic model calibration and applies it to an urban microclimate system. The Urban Weather Generator (UWG) is selected as the underlying simulation engine for an optimization-aided calibration based on the urban outdoor air temperature in an existing district area located in downtown Abu Dhabi (UAE) during 2017. In particular, given the time-constrained nature of engineering applications, an online hyper-heuristic evolutionary algorithm (EA) is proposed and developed in order to accelerate the calibration process. The validation results show that, in single-objective optimization, the online hyper-heuristics could robustly help EA produce quality solutions with smaller uncertainties at much less computational cost. In addition, the resulting calibrated solutions are able to capture weekly-average and hourly diurnal profiles of the urban outdoor air temperature similar to the measurements for certain periods of the year.

Direct expansion (DX) dedicated outdoor air system is shown to be a cost-effective energy efficient complement to ductless variable refrigerant flow and radiant cooling systems by providing conditioned ventilation air at the required set point temperature and relative humidity in an energy efficient manner. We compare five balanced flow dedicated outdoor air system configurations under typical office/lab ventilation loads coupled to an air-cooled outdoor unit for 24 Gulf Cooperation Council (GCC) locations representing GCC climates. All configurations use an enthalpy recovery wheel (ERW) to remove heat and moisture from intake air before it reaches the active DX dehumidification element-by passive heat and mass transfer to the exhaust stream. It is found that of two run-around heat exchanger configurations, using a rotary heat wheel across the evaporator is a more efficient configuration than placing the heat wheel (HW) between the supply and return air streams. Furthermore, adding a subcooling coil for reheat in parallel to the HW results in higher efficiency than adding the coil in series with the HW. The Life cycle cost optimized ERW and HW effectiveness for the configuration with HW between supply and return air was found to be 0.86 while the ranges for run-around HW configurations with subcooling/reheat were found to be 0.8-0.85 for ERW and 0.74-0.82 for HW in GCC climates with significant dehumidification loads. Thus, the evaporator run-around HW reduces the volume, mass and cost of the DOAS unit while providing higher overall efficiency. (C) 2017 Elsevier B.V. All rights reserved.

To assure the quality of accelerated aging tests for solar concentrators, their standardization is crucial. It guarantees the employment of adequate testing, measurement and characterization procedures and the comparability between results. A committee of the Spanish AENOR standardization agency is working on the draft "Reflector Panels for Concentrating Solar Technologies". This work focuses on the evaluation of the procedures defined in this standard. The reflector material from the Japanese company Nishio Glass Mirror Co., which showed severe degradation after 7 years of outdoor exposure in Abu Dhabi, is tested according to the AENOR standard to check if its poor outdoor performance could have been predicted by accelerated aging testing. However, after completion of the accelerated tests, in some cases even for considerably longer test durations than the minimum required by AENOR, no considerable degradation was detected. The results suggest that the proposed testing program by AENOR is not aggressive enough to identify material failure. Ways to improve the current standard are proposed through development of more realistic tests.

A beam down solar system is adjusted to maximize the power collected through a final optical element concentrator. The power reaching the outlet of the final optical element is studied as a function of the reflectivity of its facets, and the height of the central ray convergence point of the beam down central reflector. A configuration that maximizes the energy fed to the solar receiver during the experimental campaign of the CSPonD Demo project is chosen and implemented at the beam down installation at the Masdar Institute Solar Platform.

This work investigates the transient response of a certain type of direct contact heat exchanger (DCHX) that consists of packing (Raschig Rings) to increase the surface area for effective heat transfer between molten salt and air. Molten salt from the hot tank enters the heat exchanger (HX) and exit after heating the air still in the molten form. Thermal capacitance of the HX, mainly due to packing and resident salt inside the HX, results in strong transient response. Pure delay from salt residence time may also impact transient response. Both phenomena have been modelled in this paper. A Proportional-Integral controller (PI control) performance has been evaluated to maintain the minimum salt temperature above avoid crystallization temperature of the salt.

Levelized Cost of Electricity (LCOE) is an important metric which provides one way to compare the economic competitiveness of different electricity generation systems, calculated simply by dividing lifetime costs by lifetime production. Hidden behind the simplicity of this formula are various assumptions which may significantly alter results. Different LCOE studies exist in the literature, although their assumptions are rarely explicitly stated. This analysis gives all formulas and assumptions which allow for inter-study comparisons. The results of this analysis indicate that CSP LCOE is reducing markedly over time and that given the right location and market conditions, the SunShot 6c/kWh 2020 target can be reached. Increased industrial cooperation is needed to advance the CSP market and continue to drive down LCOE. The results also indicate that there exist a country and technology level learning effect, either when installing an existing CSP technology in a new country or when using a new technology in an existing CSP country, which seems to impact market progress.