High Solar Radiation Research Articles

Solar Irradiance Modulates the Asian Summer Monsoon—ENSO Relationship Over the Last Millennium

AbstractThe Asian summer monsoon (ASM) is teleconnected to the El Niño Southern Oscillation (ENSO), but this relationship is nonstationary and has shifted significantly in recent decades. Characterizing the drivers of such shifts is crucial for improving ASM prediction and extreme event preparedness. Paleoclimate records indicate a link between ASM strength and solar activity on multidecadal‐to‐centennial timescales, but 20th‐century data are too short to test mechanisms. Here we evaluate how solar irradiance influences the ASM‐ENSO relationship using last‐millennium paleoclimate data assimilation reconstructions and model simulations. We find that high solar irradiance weakens the ENSO‐East Asian summer monsoon (EASM) correlation, but strengthens the ENSO‐South Asian summer monsoon (SASM) correlation. Solar irradiance likely influences the strength of the ENSO‐EASM and ENSO‐SASM teleconnections via changes in the Western Pacific Subtropical High and the amplitude of ENSO events, respectively. We suggest a need for considering solar activity in decadal ASM rainfall predictions under global warming scenarios.

Agrivoltaic arrays can maintain semi-arid grassland productivity and extend the seasonality of forage quality

The co-location of photovoltaic energy generation and agricultural land use (Agrivoltaics, AV) has become increasingly popular in recent years. Although the benefits of AV in croplands have great promise, the development of AV systems has primarily occurred in former grasslands and sites now managed as grasslands, because of their relatively flat topography and consistently high solar irradiation. Evidence is accumulating that grassland productivity can be maintained within solar arrays, but how grassland productivity responds to grazing within solar arrays is largely unknown, despite the prevalence of grazing as a vegetation management option. Here, we report the results of a study aimed at quantifying how a semi-arid C3 grassland growing beneath an AV system in Colorado (USA) responded to simulated grazing treatments (canopy removal in June or July). In the absence of simulated grazing, there were no differences between aboveground primary production in the AV grassland vs. an adjacent control grassland. However, simulated grazing in June and July had a compensatory effect and, in some cases, annual productivity exceeded that in the control grassland. Additionally, we found that simulated grazing increased forage protein content later into the growing season compared to un-grazed AV and control sites. Overall, our results indicate that grazing within a grassland AV array is unlikely to negatively impact forage production, and that forage quality in this semi-arid region may even be increased later into the growing season with grazing.

High Resolution WRF Modelling of Extreme Heat Events and Mapping of the Urban Heat Island Characteristics in Athens, Greece

In recent decades, large-scale urbanisation has developed rapidly, resulting in significant changes in the local and regional environment and climate. Large metropolitan areas worldwide induce significant changes in local atmospheric circulation and boundary layer meteorology by modifying the underlying surface characteristics and through the emission of anthropogenic heat and pollutants into the atmosphere. We investigate the urban heat island (UHI) characteristics in the city of Athens, Greece, which is one of Europe’s largest metropolitan complexes with a population of approximately 3.7 million inhabitants. The UHI effect is intense due to the city’s size, dense construction, high incident solar radiation, and almost complete lack of natural vegetation, with previous studies suggesting a temperature rise of 4 °C on average in the city centre compared to summer background conditions. We used high-resolution WRF simulations (1-km horizontal grid) driven with ERA5 reanalysis data to produce surface temperature maps in the city of Athens and the surrounding areas (Region of Attiki) during the summer period of 1 July–20 August 2021. Different model parameterizations were tested, both with respect to urban characteristics and physical parameters. The daily minimum and maximum temperatures (Tmin and Tmax) derived from the model were validated against observational data from a dense network of weather stations covering metropolitan Athens and surrounding locations. We further investigate the influence of different meteorological conditions on the UHI gradients as produced by the model and the observational dataset, including the extreme heat wave of 28 July–5 August 2021, during which persistent maximum temperatures of >40 °C were recorded for nine consecutive days. The results indicate a strong correlation between WRF output and recorded minimum and maximum temperatures throughout the test period (R ranges from 0.80 to 0.93), with an average mean absolute bias (MAB) of 1.5 °C, and reveal the intensity and spatiotemporal variability of the UHI phenomenon in the city of Athens, with UHI magnitude reaching 8–9 °C at times. Our work aims to maximise the potential of using high-resolution WRF modelling for simulating extreme heat events and mapping the UHI effect in large metropolitan complexes.

High-contrast energy-efficient flexible electrochromic devices based on viologen derivatives and their application in smart windows and electrochromic displayers

Electrochromic materials and corresponding devices display reversible optical changes under applied voltage. While inorganic and organic electrochromic materials are extensively studied, enhancing their performance is crucial. This study presents a high-contrast energy-efficient flexible electrochromic device based on viologen derivatives and driven by film solar cell. The aims are to foster applications in smart windows, displays, and energy-efficient technologies. Two symmetric viologen derivatives of 1,1′-bis(4-(dimethylamino) phenyl)- [4,4′-bipyridine]dihexafluorophosphate (DNPV) and 1,1′-bis(4-acetamidophenyl)-[4,4′-bipyridine]dihexafluorophosphate (DAcPV) and two asymmetric viologen derivatives of 1-benzyl-1'-(4-(dimethylamino)phenyl)-[4,4′-bipyridine]dihexafluoro-phosphate (Bn-NPV) and 1-(4-acetamidophenyl)-1′-benzyl-[4,4′-bipyridine]dihexa-fluorophosphate (Bn-AcPV) were synthesized. These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices (ECDs). After applying voltage of 1.0 V, both of flexible and rigid ECDs based on DNPV and Bn-NPV exhibited reversible color change from purple to deep purple and red to deep viologen respectively, while ECDs based on DAcPV and Bn-AcPV exhibited a color change from yellow to black and pale yellow to green under applied voltage of 1.2 V, respectively. After 1000 cycles, flexible and rigid ECDs showed good stability. Especially, the flexible ECDs maintained good performance after 1000 bending cycles. In additional, the ECDs based on these viologen derivatives were prepared to displayer, which showed clear display function. And ECDs driven by solar cells demonstrated good stability after 100 cycles. Furthermore, it showed that the rigid ECD based on DAcPV with high solar irradiation modulation of 70.3 %, holds great potential in smart window applications.

Study of the Effect of Different Atmospheric Conditions on the Temporal Evolution of the Mixing Layer over Madrid during the Year 2020 by Means of Two Different Methods: Ceilometer Signals and the ECMWF-IFS Meteorological Model

Atmospheric aerosols are one of the main factors that contribute to poor air quality. These aerosols are mostly concentrated within the atmospheric boundary layer (ABL) and mixing layer (ML). The ABL extends from ground level to the lowest level of the troposphere directly affected by surface temperature, solar irradiance, the orography and its proximity to coastal areas, causing turbulence in a daily cycle. This turbulence controls the vertical mixing of aerosols and pollutants and their dispersion in the ML. Therefore, proper characterization of these layers is of crucial importance in numerical weather forecasting and climate models; however, their estimation nowadays presents some spatial and temporal limitations. In order to deal with these limitations and to assess the influence of different meteorological conditions on the temporal evolution of the aforementioned layers, the evolution of the ML over Madrid (Spain) has been studied for the year 2020 by means of ceilometer profiles fed into the STRATfinder algorithm. This algorithm is able to give reliable estimates of the height of the ABL (ABLH) and ML (MLH). The results are compared with the ECMWF-IFS model predictions, which is able to compute the MLH under any meteorological condition. Then, the influence of the meteorology in the estimation of MLHs was established by classifying data based on the season and six different prevalent synoptic meteorological situations defined using ground-level pressure fields, as well as by splitting the days into four periods (morning, daytime, evening and nighttime). Our results show that both datasets, the STRATfinder values and the ECMWF-IFS model computations, are very sensitive to the meteorological conditions that play a main role in the MLH temporal evolution. For instance, high solar irradiance and ground radiation cause high turbulence and convection that lead to a well-developed ML. In cases in which the ML is well developed, both methods show similar results, and there are therefore better correlations between them. On the contrary, the results presented here show that the presence of high relative humidity and low temperatures hamper the growth of the ML, causing different errors in both MLH estimations and poor correlations between them. Furthermore, the ECMWF-IFS model has shown a sharp decrease, identified as an artificial behavior from 16:00 UTC, because of the influence of low solar zenith angles and the temporal interpolation. The STRATfinder algorithm also shows a sharp decrease just before the sunset because of the way the algorithm distinguishes between the ML and the residual layer. Thus, this study concludes that the MLH temporal evolution still needs to be characterized using complementary tools, since the methods presented here are strongly affected by the meteorological conditions and do not show enough reliability to work individually. However, ceilometer measurements offer great potential as a correction tool for ABL heights derived from models involved in air pollution dispersion assessments.

Variety and year: Two key factors on amino acids and biogenic amines content in grapes

Amino acids have proved to play a key role in the development of volatile compounds present in wine with determining repercussions on the final wine bouquets. Biogenic amines originate from the chemical transformations of amino acids found in various foods, a phenomenon that has given rise to several health-related concerns among consumers. In the present research, the evaluation of two of the most influential factors: variety (genetic) and year (climatic conditions) on these compounds in grapes has been performed. Eight Vitis vinifera varieties have been collected during three years and the content of nineteen amino acids, two biogenic amines, and the ammonium ion has been quantified using the HPLC-PDA technique. The genetic factor has proved to be an influential variable (p-value < 0.05) with mean values of amino acids ranging from 896.89 to 1713.79 mg/L and of biogenic amines ranging from 10.61 to 22.28 mg/L. The climatic conditions have shown to be an influential factor as well (p-value < 0.05), being the low temperatures and rainfall and the high solar radiation favour the development of the amino acid and avoid biogenic amines accumulation in grapes.

Photovoltaic energy sharing: Implementation and tests on a real collective self-consumption system

This research study analyses different types of photovoltaic (PV) energy sharing in a collective self-consumption (CSC) real-case in the Izarbel technological park in France. The analysis is carried out above all from the point of view of the self-consumption rate (SCR) and the savings.After explaining the emergence of the self-consumption concept for the integration of renewable energies, the study case is described. The PV energy is produced in ESTIA1 building and consumed in ESTIA1, 2 and 4 buildings. The main IoT components used to implement the CSC are smart meters and the Tecsol TICs; devices based on the LoRa protocol to retrieve production and consumption data. Then, the characteristics of PV energy sharing in France are explained, in particular the three possible types of energy sharing/allocation (static, dynamic by default and customised dynamic) and the structure of the electricity bill. Finally, the three types of sharing are compared in four scenarios (without and with a data centre, for low and high solar radiation). The results show that the dynamic allocations lead to increases of the SCR and that the customised dynamic sharing increases savings.

Solar Radiation Drives Potential Demographic Collapse in a Perennial Bunchgrass via Dramatically Reduced Seedling Establishment

Many perennial plants in semiarid rangelands have experienced population declines, and understanding the ecological and demographic processes behind these declines is important to slowing or reversing them. Although anthropogenic disturbances drive many declines, other sorts of environmental variability, such as the differences in solar radiation with aspect, may impact population success locally. We experimentally assessed the role of solar radiation in driving an apparent decline in a common perennial bunchgrass, bluebunch wheatgrass (Pseudoroegneria spicata), on south-facing slopes at a site in the Columbia Basin of North America. Across three separate experiments on south-facing slopes, we observed dramatically (5−36 ×) higher seedling success in plots shaded to approximate the solar radiation of north-facing slopes relative to adjacent open (unshaded) plots. When we applied the rates of seedling success from these experiments to demographic models from this site, we found that seedling success in unshaded plots was often too low to allow a stable population on south-facing slopes, but that seedling success in shaded plots was often high enough to allow a stable or increasing population on north-facing slopes. We originally hypothesized that the primary mechanism driving this effect was water stress caused by greater evaporation from hotter open plots. However, despite soils in open plots being consistently hotter than soils in shaded plots, we did not observe a clear pattern of greater soil moisture in shaded plots. Therefore, it appears that higher solar radiation or higher temperatures on south-facing slopes may be sufficient to dramatically reduce seedling survival, and that the higher density of bluebunch wheatgrass on north-facing slopes relative to south-facings slopes may be driven primarily by this low survival of seedlings. As climate warms, the reduced seedling survival that threatens our bluebunch wheatgrass population may be expected to threaten many other species of perennials in similar rangelands.

An advanced exhausting airflow photovoltaic curtain wall system coupled with an air source heat pump for outdoor air treatment: Energy-saving performance assessment

Building integrated photovoltaic (BIPV) and air source heat pump (ASHP) technologies have emerged as promising solutions for building energy conservation. However, traditional solar buildings face limitations such as overheating, limited efficiency, and singular functionality; additionally, ASHPs suffer from a low coefficient of performance (COP) due to high condensing temperatures or low evaporating temperatures; the process of outdoor air handling proves energy-intensive. To address these challenges, this study proposes an innovative exhausting ventilation PV curtain wall system coupled with ASHP units (EVPV-HP) for outdoor air treatment. This system features a fine combination of PV cooling, supply air reheating, and heat recovery from both the PV facade and exhaust air. The mathematical model of the BIPV curtain wall, based on energy balance equations, is developed and solved using Matlab programming. This model is then combined with the ASHP system model established in TRNSYS to predict the year-round energy performance of the hybrid system. The findings demonstrate that the EVPV-HP system achieves seasonal energy efficiencies of 5.08 for cooling and 4.06 for heating operation modes. Compared to a conventional system, the EVPV-HP system enhances yearly energy efficiency by 17.05 % owing to increased PV production, reduced air-conditioning load, and improved COP. Furthermore, parametric analysis suggests that the system exhibits improved performance under higher solar irradiation and hotter weather conditions during summer. Conversely, in winter, the system performs better under lower ambient temperatures with incident radiation around 800 W/m2.

Performance investigation of a standalone renewable energy system using response surface methodology (RSM): 4E analysis and multi-objective optimization

This study aimed to identify and present novel findings in the field of hybrid renewable energy systems tailored for off-grid operation through a numerical-experimental investigation. The objective of the research was to contribute to the current knowledge of energy systems by addressing critical aspects of energy, exergy, economic, and environmental (4E) evaluations. The system described in the study is designed to meet the electricity demands of a telecom tower by integrating various components, including a photovoltaic (PV) unit, proton exchange membrane electrolyzer (PEME), proton exchange membrane fuel cell (PEMFC), and battery storage unit. An organic Rankine cycle (ORC) is also incorporated to efficiently recover waste heat from the PEMFC. The PV unit serves as the primary power source, with excess solar power directed to the PEME during periods of high solar irradiation. The PEME generates hydrogen and oxygen, while the PEMFC is fueled by hydrogen stored in metal hydride tanks. This setup ensures consistent power generation year-round. The study employs response surface methodology (RSM) to create regression equation models and utilizes the desirability function approach for multi-objective optimization. The optimal parameters identified include a 12:35 PM time setting, PEMFC current density of 0.693 A/cm2, PEME inlet water temperature of 326.2 K, and ORC turbine inlet pressure of around 580 kPa. These parameters result in impressive 4E outcomes: 50.9 % energy efficiency, 54.7 % exergy efficiency, a $0.53 levelized cost of energy, and a sustainability index of 2.1.

Headwater stream temperature response to forest harvesting: Do lower flows cause greater warming?

AbstractThis study addressed two hypotheses regarding the relationship between stream temperature response to shade removal and streamflow: (a) that temperature response increases as flow declines and (b) that the relationship can be complicated by shifts in dominant streamflow sources and pathways during low‐flow periods. The study was based on a paired‐catchment design in rain‐dominated headwater catchments in the southern Coast Mountains of British Columbia, Canada, and focused on the effect of a 50% thinning treatment on daily maximum temperature in June, July and August for three sites within the harvest treatment. At the two upstream sites, the treatment response exhibited a negative relationship with daily mean streamflow, especially for days with high incident solar radiation. This result suggests that the effectiveness of forest practice rules for protecting cold‐water habitat may be reduced under future climatic conditions characterized by more frequent extended drought. However, stream temperature response at the most downstream site exhibited a pronounced inverted‐U‐shaped relationship with streamflow measured at a weir. It is hypothesized that the response at the most downstream temperature logger was controlled by the existence of a stable, relatively cool inflow just upstream of the logger, which represented an increasing fraction of flow as streamflow generated higher up in the catchment declined through time. There was a lack of convergent surface topography upstream of the logger, and it is hypothesized that localized inflow may have been controlled by the topography of the soil‐till interface and/or originated as hyporheic discharge.

Impact of aging on the physical-chemical and phenolic stability of tropical red wines from Brazil produced with grapes harvested in the summer season

The São Francisco Valley in the Brazilian Northeast is characterized by the production of tropical wines from grapes obtained from at least two annual harvests. Previous studies showed that wines made with grapes harvested from the second semester (summer season, with high temperatures and solar radiation, as well as low rainfall) presented a shorter shelf-life than those made from grapes harvested in the first semester (winter season). This study aimed to characterize the changes in the chemical composition of three red wines from the summer season, during aging. Wines elaborated with grapes harvested between November and December 2014, with the main red varieties commercially used, were analyzed 12, 24 and 36 months after bottling. Decreases occurred in the concentrations of anthocyanins, flavonols, organic acids, potassium, and condensed tannins, as well as increases in polymerized pigments, hue, turbidity, and calcium. Flavanols and flavonols were associated with Syrah and Touriga Nacional wines, while myricetin was the metabolite considered to be the main indicator of the aging of ‘Alicante Bouschet’ wines. Rootstock vigor was affected by variety. This study showed that the choice of rootstock and variety combination could increase the wine stability after bottling, using grapes harvested from the second semester.

A Dual-Stage Solar Power Prediction Model That Reflects Uncertainties in Weather Forecasts

Renewable energy sources are being expanded globally in response to global warming. Solar power generation is closely related to solar radiation and typically experiences significant fluctuations in solar radiation hours during periods of high solar radiation, leading to substantial inaccuracies in power generation predictions. In this paper, we suggest a solar power generation prediction method aimed at minimizing prediction errors during solar time. The proposed method comprises two stages. The first stage is the construction of the Solar Base Model by extracting characteristics from input variables. In the second stage, the prediction error period is detected using the Solar Change Point, which measures the difference between the predicted output from the Solar Base Model and the actual power generation. Subsequently, the probability of a weather forecast state change within the error occurrence period is calculated, and this information is used to update the power generation forecast value. The performance evaluation was restricted to July and August. The average improvement rate in predicted power generation was 24.5%. Using the proposed model, updates to weather forecast status information were implemented, leading to enhanced accuracy in predicting solar power generation.

Fungal Diversity and Distribution in the Biodiversity Hotspots of the Western Himalayas

The western Himalayan region is a biodiversity hotspot. Although much of the flora and fauna has been documented, there are very few studies on fungal diversity. We present the statistical analyses of the sample collections from the last 150 years of data in the fungarium of the Forest Research Institute. We found that the host tree species—pine, oak, deodar, and spruce, had very high Shannon diversity (SD) and species richness (SR), while Dalbergia and Rhododendron had moderate to low SD and SR values; although sal occurs at lower altitudes, it has high SD and SR values. Among fungal families, the highest SD and SR value was found in Polyporaceae. Hymenochaetaceae, Peniophoraceae, Coleosporiaceae, and Stereaceae also showed SD with moderate SR. Fomitopsidaceae, Cronartiaceae, Ganodermataceae, and Thelephoraceae have low biodiversity and species. Thelephoraceae are distributed above 2000 m altitude, and Ganodermataceae and Hymenochaetaceae have wider distribution ranges, namely, 0–3500 m and 0–5000 m, respectively. The Polyporaceae show diverse variations in species distribution and occur between 0 and 4500 m; Coleosporiaceae and Cronartiaceae around 2000 m; Stereaceae, Meruliaceae, Peniophoraceae, and Fomitopsidaceae occur between 1700 and 1800 m, with all Stereaceae and Fomitopsidaceae having different distribution ranges of up to 5000 m. We found that areas with relatively low rainfall had lower species richness, and vice versa, and that high solar radiation negatively affected fungal density and SR, as observed in the distribution of Thelephoraceae. While families with high SD and SR values such as Polyporaceae were found under relatively high rainfall, moderate solar radiation, and high temperatures. Similar studies need to be undertaken in other parts of the Himalayas and the importance of fungi in ethnobotany needs to be understood to ensure sustainable use.

Direct-expansion solar-assisted heat pump coupled with crystallisation-controlled supercooled PCM for shifting building electricity demand

This paper proposes a novel approach for improving the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) system by integrating a crystallisation controllable phase change material (PCM) and building energy demand shifting strategy. The proposed system aims to reduce buildings' energy consumption while utilizing solar energy efficiently. Sodium acetate trihydrate (SAT) as the crystallisation controllable supercooled PCM has a promising feature of releasing the stored latent heat when it is externally triggered, allowing the user to control the stored heat whenever needed. In the study, the PCM can store the thermal energy generated by the DX-SAHP during peak solar hours in an efficient way. This stored energy can be released when solar energy is unavailable, but the heating is requested. This approach not only reduces the load on the heat pump system but also makes efficient use of the stored thermal energy by crystallisation controllable PCM. A detailed controlling methodology of the system is given, and heating output is controlled considering the level of solar irradiance. The proposed system was modelled and simulated using MATLAB, and the results show that the integration of crystallisation controllable PCM and building demand shifting strategy can significantly reduce the energy consumption of the buildings. On the low solar radiation day, the COP improvement compared to the air source heat pump system was found 9.4%, this improvement value can reach 77% on high solar radiation days. The system can also effectively utilize solar energy and reduce the overall carbon footprint of buildings.

Differential Antioxidant Response to Supplemental UV-B Irradiation and Sunlight in Three Basil Varieties.

Three basil plant varieties (Ocimum basilicum var. Genovese, Ocimum × citriodorum, and Ocimum basilicum var. purpurascens) were grown under moderate light (about 300 µmol photons m-2 s-1) in a glasshouse or growth chamber and then either transferred to an open field (average daily dose: 29.2 kJ m-2 d-1) or additionally exposed to UV-B irradiation in a growth chamber (29.16 kJ m-2 d-1), to reveal the variety-specific and light-specific acclimation responses. Total antioxidant capacity (TAC), phenolic profile, ascorbate content, and class III peroxidase (POD) activity were used to determine the antioxidant status of leaves under all four light regimes. Exposure to high solar irradiation at the open field resulted in an increase in TAC, total hydroxycinnamic acids (HCAs, especially caffeic acid), flavonoids, and epidermal UV-absorbing substances in all three varieties, as well as a two-fold increase in the leaf dry/fresh weight ratio. The supplemental UV-B irradiation induced preferential accumulation of HCAs (rosmarinic acid) over flavonoids, increased TAC and POD activity, but decreased the ascorbate content in the leaves, and inhibited the accumulation of epidermal flavonoids in all basil varieties. Furthermore, characteristic leaf curling and UV-B-induced inhibition of plant growth were observed in all basil varieties, while a pro-oxidant effect of UV-B was indicated with H2O2 accumulation in the leaves and spotty leaf browning. The extent of these morphological changes, and oxidative damage depended on the basil cultivar, implies a genotype-specific tolerance mechanism to high doses of UV-B irradiation.

Evaluation of the Performance of Polycrystalline and Monocrystalline PV Technologies in a Hot and Arid Region: An Experimental Analysis

In arid regions, the behavior of solar panels changes significantly compared to the datasheets provided by the manufacturer. Therefore, the objective of this study is to determine the performance of both polycrystalline and monocrystalline solar modules in an arid region characterized by a large potential for solar irradiation and high temperatures. The influence of environmental parameters, such as temperature and dust, on the output power of solar modules with different technologies (monocrystalline and polycrystalline) has been investigated. The Artificial Hummingbirds Algorithm (AHA) has been used to extract parameters for PV modules. As a result, it has been demonstrated that for high solar irradiation, the polycrystalline PV module experiences a smaller decrease in output power than the monocrystalline PV module as the module temperature increases. The percentage drop in output power is approximately 14% for the polycrystalline PV module and nearly 16% for the monocrystalline PV module. However, for low solar irradiation, it is advisable to use monocrystalline modules, as a 21% decrease in power was observed for polycrystalline modules compared to a 9% decrease for monocrystalline modules. Additionally, the monocrystalline PV module was more affected by dust than the polycrystalline PV module under high solar irradiation conditions, while under low incident solar radiation, the polycrystalline PV module was more affected by dust than the monocrystalline PV module. The power drop of the monocrystalline PV module was greater than that of the polycrystalline PV module for high solar radiation (&gt;500 W/m2). Therefore, the advantage of this proposed work is to recommend the use of polycrystalline solar panels in regions characterized by high solar irradiation and high temperatures instead of monocrystalline solar panels, which are more efficient in regions worldwide characterized by low solar irradiation and low temperatures.

Analyzing the impact of various factors on leaf surface temperature based on a new tree-scale canopy energy balance model

Trees are one of the effective ways to regulate the microclimate, while the environmental parameters influence their transpiration rate. These complex processes manifest at the macro scale through leaf surface temperature (LST). Therefore, the key to studying the influence of trees on the microclimate is to calculate the LST. In this paper, we propose a new tree-scale canopy energy balance (CEB) model related to tree canopy height based on the big-leaf model to calculate the LST and analyze the influence of various factors on both LST and each sub-term of CEB. The results indicate that air temperature and solar radiation have a greater effect on LST than relative humidity on it. When the total solar radiation flux remains constant, air parameters primarily affect the latent heat flux of trees through the vapor pressure deficit between leaves and the air. The transpiration rate of trees is influenced not only by air parameters, but also by stomatal resistance. Solar radiation can directly determine the magnitude of the net radiation flux in the CEB, while its influence on latent heat flux is insignificant. Under high solar radiation flux conditions, an increase in wind speed can mitigate the rise of LST.

Evaluating the Technical, Economic, and Environmental Performance of Solar Water Heating System for Residential Applications–Comparison of Two Different Working Fluids (Water and Glycol)

The use of solar water heaters (SWH) in both residential and commercial facilities is one of the possible ways to reduce electricity bills and the release of greenhouse gases (GHG). This study assessed the technical, economic, and environmental performance of a SWH system at six different locations in China (i.e., Lhasa, Lauchang, Wuhan, Kashi, Yumen, and Harbin). A comparison between two different working fluids (i.e., water and glycol) were modeled in the System Advisor Model in all six cities. A sensitivity analysis was conducted on some key technical and economic parameters to assess the impact of such parameters on the performance of SWH systems in the country. According to the results, Lhasa recorded the highest capacity factor of 11% and 10.70% using water and glycol as the working fluid, respectively. Lhasa was identified as the best location among the studied locations due to its high solar irradiation. The optimization study indicates that the optimum azimuth for China is 190°. It was also found that a 25% reduction in the outlet set temperature of the water can reduce the capacity factor from 11% to about 9.2%. Using the SWH as simulated in this study can reduce carbon dioxide emissions from 1252.87–2014.85 kg per year to 138.20–330.23 kg per year; the extent of reduction depends on the location of the SWHS, and the solar energy available at the area. Net electricity bill savings of $156–296 could be obtained if SWH systems were installed and used at the studied locations.

To aspirate or not to aspirate – Impact of active versus passive ventilation on urban heat (island) indicators

The present paper reports on the impact of ventilation mode – active versus passive – of instrument screens for air temperature measurements on canopy urban heat (island) indicators. This is done using air temperature data gathered in the Antwerp (Belgium) area in July 2013, in an experimental set-up composed of an urban and a nearby rural climate station, each equipped with both actively and passively ventilated temperature sensors. The resulting data shows an air temperature bias between the passively and actively ventilated measurements of up to approximately 2 °C, the highest values occurring under conditions of a high solar radiation load and low wind speed. Yet, the canopy urban heat island (UHI) increment, i.e., the urban-rural air temperature difference, is hardly affected by the ventilation method, which is ascribed to the fact that high UHI increments occur mainly at night when, in absence of solar radiation, active ventilation has a lesser influence on measured temperature. Conversely, urban heat indicators involving daytime air temperature, such as heatwave degree days (HWDD) or Steadman's apparent temperature, tend to produce overly high values when use is made of passively ventilated temperature measurements.