Typical Sunny Day Research Articles

Modeling and Evaluation of a Solar Trigeneration System With Thermal Energy Storage

In the present study, an on-demand solar combined cooling, heating, and power (CCHP) system with parabolic trough collector (PTC) and solid-state thermal energy storage (TES) is investigated, which will be demonstrated on-site in 2024 at the Administration Building of the Lavrio Technological and Cultural Park (LTCP) in Attica, Greece, covering the energy needs of the building in form of heating and electricity in winter and cooling during summer. The system is based on a combined Organic Rankine Cycle and an Ejector Cooling Cycle (ORC-ECC), which is modeled and simulated in a steady-state manner while the PTC and TES systems are modeled dynamically, i.e., they are influenced by the thermal inertia of the components, the variable weather conditions of the location, and the defined operating strategies. The ORC-ECC simulation results show an efficiency of up to 14.20 % for the ORC system and a Coefficient of Performance (COP) of 0.10 for the ECC system under defined conditions. The dynamic simulations for the specified operating strategies indicate that on typical sunny days up to 100 % of the consumers' electricity consumption can be covered by the system.

Performance assessment of the curved-type multi-channel PV roof for space-heating and electricity generation in winter

The curved-type PV roof integrated with flexible PV tiles is a novel attempt to implement the building-integrated photovoltaic/thermal technology into diverse genres of architectural design. To explore its performance in the function of electricity generation and space-heating, different ventilation configurations of the air channels are adopted in the design of the multi-air-channels of the system; two working modes (fresh-air-heating - FAH and recirculated-air-heating - RAH) are applied in the system's operation. The case study is based on a residential building linked with the system in Hefei, China. The performance assessment is conducted on a typical sunny winter day and through the winter of the Typical Meteorological Year. The investigation results indicate that RAH mode has the potential to raise the indoor air temperature to a greater extent. However, the electrical power output shows a disadvantage due to the relatively poor PV cooling effect; increasing the connection air channels could enhance the indoor air heating but add the fan power consumption. The prediction throughout winter manifests that the all-in-parallel connection produces 1827.63 kWh (FAH) and 1574.55 kWh (RAH) of total energy, whereas the 6-in-series connection produces 2085.91 kWh (FAH) and 1618.99 kWh (RAH).

Biogenic volatile organic compounds in forest therapy base: A source of air pollutants or a healthcare function?

Air pollution poses a significant threat to public health, while biogenic volatile organic compounds (BVOCs) play a crucial role in both aspects. However, the unclear relationship between BVOCs and air pollutants in the under-canopy space limits the accuracy of air pollution control and the exploitation of forest healthcare functions. To clarify the variation of BVOCs in forest therapy bases, and their impacts on ozone (O3) and fine particulate matter (PM2.5) at nose height, total VOCs (TVOCs) in the forest were collected during typical sunny days, while air pollutants and meteorological factors were observed simultaneously. The results showed that the branch-level emissions of P. tabuliformis were dominated by healthcare-effective monoterpenoids, with only α-pinene having relative air concentrations of over 5 % in forest air samples. The correlation between concentrations of under-canopy TVOCs and emission rates of BVOCs from P. tabuliformis was weak (p > 0.09) in all seasons. However, the correlation between concentrations of TVOCs and the concentrations of O3 and PM2.5 showed clear seasonal differences. In spring, TVOCs only showed a significant negative correlation with PM2.5 in the forest (p < 0.01). In summer and autumn, TVOCs were significantly negatively correlated with both O3 (p < 0.001) and PM2.5 (p < 0.01). Specifically, the negative linear relationships were more pronounced for O3 and oxygenated VOCs in autumn (R2 = 0.40, p < 0.001) than for other relationships. The relationship between air pollutant concentrations inside and outside the forest also showed significant seasonal differences, generally characterized by a weaker correlation between them during seasons of strong emissions. Therefore, BVOCs in coniferous forests are health functions as they can provide healthcare effects and mitigate the concentration of air pollutants in the forest, and the establishment of forest therapy bases in rural areas with low NOx can be a sensible approach to promote good health, well-being, and sustainable development.

Typhoon- and temperature-induced responses of a cable-stayed bridge

Long-span bridges are subjected to wind and temperature actions. Wind action is generally the governing load of long-span bridges in design, while temperature action is also significant. Accurate separation of typhoon- and temperature-induced responses is thus necessary for in-depth investigation of their effects and comprehensive evaluation of structural performance. This paper separates the temperature- and typhoon-induced responses of the Qingzhou Bridge by using a unified global analysis approach. The field-monitored meteorological data and structural responses collected from the structural health monitoring system installed on the bridge are analyzed in detail, with emphasis on the comparison of those during typhoon Higos (Signal No. 9) and a typical sunny day after the typhoon. Results show that the quasi-static variation of displacement and stress responses are higher on a typical sunny day than those during the typhoon period, which is out of intuition. Through the unified analysis, the temperature-induced responses are calculated, and the typhoon-induced responses can be separated. The temperature- and typhoon-induced longitudinal displacement, mid-span deflection, and stress of the girder are compared. The temperature-induced response accounts for a large part of the total quasi-static recording either on a typical sunny day or during the typhoon period, whereas typhoon caused significant dynamic responses. The typhoon-induced quasi-static and dynamic responses are also in good agreement with the wind tunnel test results. This case study demonstrates the effectiveness of the unified global analysis in separating the temperature effect.

Variation in canopy conductance of Cunninghamia lanceolata forest and its response to environmental factors after an extreme rainfall event

AbstractCanopy conductance (gc) is a crucial parameter in simulating evapotranspiration and modulating water exchange, but its variation mechanism has regional uncertainties and complex environmental co‐controls. In addition, the effect of extreme rainfall on gc cannot be ignored under the changing climate. Here, we investigated the variation and environmental controls on gc and the effect of extreme rainfall events in a Cunninghamia lanceolata forest across the subtropical area of Southern China. In July 2020, an extreme rainstorm hit the source area of the Xin'an River, with the cumulative rainfall on July 7 and 8 reaching 216.6 mm. The thermal diffusion probe method was used to measure the density of sap flow, and the environmental factors such as air temperature (Ta), net solar radiation (Rn) and soil water content (SWC) were monitored during the growing seasons of 2020 and 2021. Ultimately, gc obtained by the Penman‐Monteith equation was adopted since the result from the Köstner equation was overestimated. gc showed a unimodal curve on the diurnal scale, and this characteristic was more obvious after the extreme rainfall. Daily gc appeared a fluctuating pattern with a maximum in summer. gc was simultaneously affected by Ta, Rn, water vapour pressure difference (VPD), SWC, among which Ta was the most significant driving factor at both the diurnal and daily timescales. The regulation of Ta, VPD and SWC on gc had obvious thresholds, and the most definite response mode was VPD (2020: 1.25 kPa; 2021: 0.95 kPa). SWC and Ta were the dominant factors after the rainfall period, and the promotion effect of VPD on post‐rainy days turned to inhibition effect on typical sunny days. These findings will further reveal the water exchange mechanism between atmosphere and vegetation and impacts of environmental factors in subtropical coniferous forests, especially after the extreme rainfall events.

Design and Development of a Biomimetic Solar Tree for Sustainable Cogeneration: An Energy and Exergy Assessment

Solar energy is becoming an increasingly popular and important source of renewable energy. Solar trees have emerged as a novel and innovative approach to harvesting solar energy. Solar trees are artificial structures that mimic the shape and function of trees, with branches or leaves that contain photovoltaic cells to convert sunlight into electricity. The solar tree generates both electrical and thermal energy from solar radiation. The present study tested the thermal (module temperature, heat loss coefficient), electrical (power output), and operating parameters of a solar tree at Universiti Malaysia Pahang, Pekan, Malaysia, on a typical sunny day. First-law analysis and second-law analysis were carried out to determine exergy losses during the photovoltaic conversion process of solar trees. The data obtained from the experiment is utilized to determine the energy and exergy efficiencies of the solar tree. The energy efficiency ranges from 16.8% to 8.3% throughout the day, displaying some variability. However, as for the exergy efficiency of the photovoltaic solar tree under consideration, it is observed to be lower, ranging from 16.1% to 6.6% for electricity generation. It is observed that the exergy losses increased with increasing module temperature and a drop in exergy efficiency.

Comprehensive investigation of a building integrated crossed compound parabolic concentrator photovoltaic window system: Thermal, optical and electrical performance

Integrating PV solar cells with concentrators into window systems can not only generate electricity for a building, but also has the potential to enhance the thermal resistance of the building's windows without a significant sacrifice of light transmittance for passive daylight. A novel system, known as the crossed compound parabolic concentrator photovoltaic window, has been recently studied for its electrical properties. However, its thermal and optical performance, particularly in terms of the overall heat transfer coefficient (U-value) and total optical transmittance when integrated into a building, remains unexamined. These factors are crucial for predicting the system's impact on a building's energy efficiency and indoor comfort. Therefore, this paper aims to investigate the U-value of this window system under various temperature scenarios and the optical transmittance of the window at different incident angles. The thermal conductance was assessed through numerical simulations using a computational fluid dynamics model, which was validated by experimental measurements conducted in a large climate chamber. The optical transmittance was investigated using a validated 3D ray-tracing model. The total optical transmittance and electricity generation were calculated for typical sunny days in winter and summer under London's climate conditions. Additionally, alternative designs were developed to explore the impact of pitch between adjacent optics on the thermal conductance and optical transmittance of the window. The results showed that the window with a configuration of Dx = Dy = 5 mm (where Dx and Dy represent the horizontal and vertical pitches, respectively, between two adjacent solar optics) achieved the lowest U-value (2.566 W/m2·K). This U-value is slightly lower than that of the original window design, which has a U-value of 2.575 W/m2·K. The original window configuration with Dx = Dy = 1.77 mm produces the highest power output. Specifically, it generates 499.25 Wh/m2 on a typical sunny day in winter and 162.73 Wh/m2 on a typical sunny day in summer. However, it exhibits the lowest transmittance (14.6 % on a typical sunny day in winter and 25.2 % on a typical sunny day in summer, respectively), indicating that it is more suitable for buildings with a higher window-to-wall ratio to ensure an adequate amount of natural light. For buildings with a lower window-to-wall ratio, the CCPC-PV window should be designed with a larger horizontal pitch, such as 15 mm and 30 mm, to meet indoor illuminance requirements while also providing enhanced thermal performance and additional power output.

Differences and mechanisms on water use of Pinus sylvestris var mongolica forests with different origins

Determining the differences of water use characteristics of a tree species with different origins (natural forests and introduced plantations) is significantly important for forest sustainable management. Pinus sylvestris var. mongolica is an important tree species of afforestation in the 'Three North' project in China. In this study, with Pinus sylvestris var. mongolica from two origins, we monitored the sap flow velocity of sapwood (Js) of trees by thermal dissipation sap flow probes, and analyzed the relationship between water transportation and the environmental factors during the growing season. The results showed that under the typical sunny day, daily sap flow velocity (Js-daily) of trees from plantations was significantly higher than that from natural forests. The mean value of Js-daily was 132.98 and 114.86 cm·d-1 for the two origins, respectively. Trees from plantations showed higher water transportation potential than natural forests. Vapor pressure deficit (VPD) mainly showed the driving effect on the water use process of trees from natural forests. In the plantations, there was an obvious threshold effect, and the inflection point of VPD was about 1.91 kPa, with the boundary function of Js-hour increased to the maximum of 17.88 cm·h-1. Atmospheric driven transpiration potential (Js-hour/VPD) of P. sylvestris var. mongolica trees with two origins decreased with the aggravation of soil drought, but sensitivity to drought was higher in the plantations than in the natural forests, suggesting the strong ability of Pinus sylvestris var. mongolica to regulate water use process.

Lightweight extensive green roof for building renovation: Summer performance analysis and application in a living laboratory

Extensive green roofs are considered an effective energy conservation measure for increasing buildings’ energy efficiency and reducing the heat wave effect in dense build environments. In this context the present work has a two-fold objective: the first is to test and analyse a commercial extensive lightweight green roof sample through an experimental monitoring campaign carried out in a hot climate during the summer time; the second is to provide a practical case study application showing the architectural integration of the extensive green roof technology for existing buildings. The experimental monitoring campaign has been set for analyzing the temperature levels of an extensive green roof compared with a traditional horizontal roof finished with cement tile. The temperature levels have been analysed through a set of sensors positioned at different levels to characterise the green roof response to the climatic forces during summer. The results show that the air temperature in proximity to the green surface (15 cm above the greenery) is warmer than the undisturbed ambient air temperature during the day and lower during the night by 2–2.5 °C. The soil substrate and the vegetative layer contribute to increase ambient air humidity levels. As expected, the evapotranspiration of the green layer increases during a typical sunny day resulting in more water content in the air above the vegetative level of about 4–8 %. The surface temperature of the ground below the vegetation layer and the temperature of the ground layer (8 cm deep) shows beneficial attenuation and time shift properties with respectively 12–15 °C and 3–4 h. Compared to the traditional cement tiles the green roof shows lower intralayer temperature with differences ranging from 6 to 8 °C. Moreover, the renovation case study represents a practical example of green roof technology integration in a real environment. The study has high replicability, and it is meant to be an interesting example for researchers and professionals to boost the green roof technology application for higher-quality built environments.

Development of a Solar-Tracking System for Horizontal Single-Axis PV Arrays Using Spatial Projection Analysis

Uniaxial trackers are widely employed as the frame for solar photovoltaic (PV) panel installation. However, when used in sloping terrain scenarios such as mountain and hill regions, it is essential to apply a solar-tracking strategy with the sloping factors considered, to eliminate the shading effects between arrays and reduce the electricity production loss due to terrain changes. Based on a uniaxial tracker on the sloping terrain of a PV farm located in Ningxia, this study established a uniaxial solar-tracking strategy for sloping terrain by integrating a spatial projection model with a dynamic shadow assessment method. In the proposed strategy, the optimal tilt angle of the PV array and related desirable adjustment are identified taking into consideration major parameters such as the shadow area ratio S and the average solar irradiance intensity G. A tool underpinned by Matlab Simulink has also been developed to realize the proposed solar-tracking strategy. With the input of a simulated ramp signal β and the dynamically changed time parameters, the tracking angle of PV arrays over the simulated duration is accurately predicted, followed by a series of experimental validations conducted on the winter solstice and a typical sunny day (15 September). Moreover, the study also explored the terrain impacts on solar tracking by comparing the sloping terrain and flat terrain applications. The analytic and experimental results indicate that (a) the maximum value of the G(β) function could serve as the input to identify the optimal tracking angle; (b) the application of the flat terrain tracking (FTT) strategy in sloping terrain would result in a reduction of average solar irradiance intensity harvested by the PV arrays with varying degrees; (c) in the context of an east–west −7° sloping terrain, compared with the FTT strategy, the sloping terrain tracking (STT) strategy enabled anti-shading tracking, and then increased the daily PV electricity yield by 0.094 kWh/kWp, which is around 1.48% of the daily energy production; (d) given a measurement with annual scale, the STT strategy could cause a 1.26% increase in the energy harvesting with a flat uniaxial PV array on a −7° slope terrain, achieving an annual increase of 25.16 kWh/kWp. The experimental comparative analysis validated the precision of the proposed solar-tracking model, which has far-reaching significance for achieving automatic solar-tracking of PV modules, as well as improving the capacity and efficiency of PV systems.

Analysis of cooling performance and energy consumption of nocturnal radiation and natural ventilation combined mechanical refrigeration system for outdoor prefabricated substation

To make full use of renewable energy and reduce cooling energy consumption, a new structure nocturnal radiation board was designed, modeled and experimentally studied, and a combined refrigeration system of air/water-cooled chiller, nocturnal radiation board and natural ventilation unit was proposed and simulated with the building model of a prefabricated substation in Zhenjiang city in China. The research results of the nocturnal radiation board show that the average cooling heat fluxes are about 40.24, 70.40 and 37.84 W/m2 on a typical sunny summer day, a cool autumn day and a rainy summer day, respectively. The average cooling heat flux ratio of experimental results to calculating results is about 0.75, which can be taken as the model modification coefficient to predict the cooling heat flux of the nocturnal radiation board. The hourly dynamic simulation results of the combined refrigeration system show that the energy saving rates of 37.65%, 44.80% and 62.24% can be achieved on a typical summer day, a cool autumn week and the whole year when compared with the conventional air-cooled chiller system. The annual coefficient of performance of the combined refrigeration system is about 15.31, which is more than 2.7 times that of the conventional air-cooled chiller system. The proposed nocturnal radiation board and combined refrigeration system can make full use of nocturnal radiation energy and air energy for space cooling and significantly reduce the cooling energy consumption.

Development of a Photovoltaic-Based Module for Harvesting Solar Energy from Pavement: A Lab and Field Assessment

The concurrent worldwide energy crisis has become a strong incentive for researchers, governments, and industry professionals to focus on sustainable energy solutions. Consequently, pavement photovoltaic energy harvesting technologies, as one of the most common sustainable energy solutions, have recently seen a significant improvement, especially in the new innovative designs of pavement solar panels. In this study, an innovative design for a prototype energy harvesting system was proposed based on thin-film photovoltaic solar panels. In addition, the feasibility of utilizing the generated power of the proposed system to illuminate a pedestrian crosswalk to enhance the safety of an at-grade intersection was also analyzed. The designed prototype consists of a thin-film solar panel, a transparent cover to protect the solar panel, and a wooden frame to support the panel and distribute the load. Different materials for the transparent covering plates were investigated, including polycarbonate with varying thicknesses, textured GlassGrit, and textured float glass with corundum skid-resistant coating on the surface. Finite element analysis was also conducted to analyze the behavior of solar panel-incorporated layered asphalt pavement subjected to dynamic wheel loading. The results showed that the suggested model could sustain the structural loads of a moving wheel without failure. Experimental results of the study showed that considering the seven hours of operation on a typical sunny day, the proposed system could generate approximately 699 Watt-hour of power during 7 h of operation (9 a.m.–4 p.m.) from the 304.8 mm (12 inches) × 304.8 mm (12 inches) pavement solar panel.

Dynamics of shaded areas in a typical-shaped solar greenhouse and their effects on tomato growth—A case study in winter

The side walls and fixed insulation quilt of a solar greenhouse helped reduce heat loss from the room at night but produced shadows on the greenhouse floor during the day, affecting the growth and development of crops. In the present study, a method to calculate the projected area of the side walls and fixed insulation quilt in the greenhouse was derived. Then, a typical-shaped solar greenhouse and tomatoes were used as experimental research objects to investigate the spatial and temporal variation of indoor solar radiation intensity and tomato growth. The results showed that: 1) The average absolute error between the calculated and measured values of the ground shade of the solar greenhouse on four typical sunny days was 1.12%, 2.65%, and 2.02%, respectively. The area of selected greenhouse was 450m2, the maximum shaded area could account for 20.3% of the total area of the greenhouse, the shaded area projected by the insulation onto the greenhouse floor remained constant at different times, and that projected by the wall decreased and then increased parabolically with time. 2) The average solar radiation intensity in the greenhouse at the winter solstice tended to increase and then decrease with time, with a maximum value of 41,374.0 Lux. The uniformity of solar radiation distribution was reduced in the morning, evening and midday hours. 3) The tomato plant height, stem diameter, leaf area index and yield were 36.9%, 14.7%, 63.1% and 125.4% higher, respectively, in the high than in the low solar radiation zone. The results of the study can provide a theoretical basis for clarifying the dynamics of shaded areas and the spatial and temporal distribution of solar radiation intensity in greenhouses, and for optimizing the structural parameters of solar greenhouses.

The impacts of roughness length on the simulation of land-atmosphere water and heat exchanges over the Yarlung Zangbo Grand canyon region

Precipitation has a significant influence on the topsoil moisture and further impacts the land-atmospheric water and heat exchange process over the Yarlung Zangbo Grand Canyon region (YGC) where exhibits one of the highest frequencies of convective activity in China. The simulated performance of the Community Land Model version 5.0 (CLM5.0) on turbulent fluxes under seven roughness heights for heat transfer (Z0h) schemes at Motuo and Pailong stations over the YGC was evaluated. The results indicate that the CLM5.0 significantly overestimates the surface sensible heat flux (H) while the simulation performance of surface latent heat flux (LE) is better than H. By comparing and analyzing the simulation results, the Z0h schemes suitable for the YGC are selected optimally. The Zeng et al. (J. Hydrometeorol., 2012, 13, 1359–1370) scheme (Z12) is more suitable for the simulations of H, with the simulated RMSE of H at Motuo and Pailong stations on typical sunny days being only 21.63 and 15.13 W m−2, respectively, 81.51% and 76.96% lower than the original Z0h scheme of CLM5.0. The Garratt, J., R and Francey, R., J (Boundary. Layer. Meteorol., 1978, 15, 399–421) scheme (G78) is more suitable for simulating LE in the YGC. The simulated BIAS and RMSE of LE at Motuo station were 9.80% and 21.90% lower than that under the default scheme of CLM5.0 on typical cloudy days. In addition, except for the G78 and CLM5.0 default scheme, the Z0h under the other schemes showed obvious diurnal variation characteristics, and H was positively sensitive to Z0h, while LE was the opposite. Consequently, the optimal Z0h schemes are of great application value for further comparative analysis of the water and heat exchange process between the Grand Canyon land surface and the atmosphere, to better reveal the mechanism of land-atmosphere interactions in the YGC.

Heat Transfer Characteristics of Modular Heat Storage Wall Solar Greenhouse Based on Active Heat Storage System

The modular heat storage wall is a new type of solar greenhouse wall structure, which has the advantages of fast construction and good heat storage ability. This study provides data reference and practical value for producing modular heat storage wall in the construction of a solar greenhouse. In this paper, we used different heat storage materials to construct the modular wall. In the winter thermal environment test, soil module solar greenhouse (SG) and stone module solar greenhouse (PG) were controlled against each other in two greenhouses. The test results for 28 consecutive days (31 January 2021 9:00 to 28 February 2021 9:00) showed that both greenhouses could effectively increase the temperature in greenhouse by 10–12 °C. The average temperature of SG was 0.86 °C lower than that of PG during the daytime (09:00–17:00) and 0.44 °C higher than that of PG during the nighttime (17:00–09:00). Under typical sunny conditions, the average temperature differences between the inlet and outlet of SG in the heat storage and exothermic stage was less than that of PG, and the relative humidity difference was greater than that of PG. This indicated that SG had a better performance of heat preservation than PG and could raise the nighttime temperature rapidly. Under the condition of a typical cloudy day, the average temperature difference between the inlet and outlet was SG &lt; PG and the relative humidity difference was SG &gt; PG in the exothermic stage, which was consistent with the conclusion of sunny days. In the storage and exothermic stages of typical sunny days and cloudy days, the total heat exchange of SG was 464.87, 110.44 and 54.82 MJ and the total heat exchange of PG was 264.16, 61.60 and 46.89 MJ, respectively. Moreover, the heat storage and release of SG were more than that of PG in all stages. In summary, the thermal performance of the modular heat storage wall heliogreenhouse could meet the growth of tomato crop, in which the heat transfer performance of SG was optimum.

Development and Tests of the Water Cooling System Dedicated to Photovoltaic Panels

Among all the energy production technologies based on renewables, the photovoltaic panels are the ones with the highest rate of development and applications worldwide. In this context, significant efforts are put into research on innovative materials in order to improve the performance of photovoltaic cells. Nevertheless, possibilities available to enhance the energy yield of existing technologies also exist and are explored, such as the cooling of photovoltaic modules. This approach can decrease the mean operation temperature of photovoltaic cells, leading to an increase in efficiency and energy produced. In the present paper, this method is investigated by developing and testing a dedicated water cooling system for photovoltaic panels. In order to investigate the performance of the cooling system, two market-available monocrystalline photovoltaic panels with a power of 50 and 310 Wp were tested under laboratory and real operation conditions, respectively. Based on the results obtained under laboratory conditions, the most promising variant of the cooling system was selected and assessed under real operation conditions. For this system, the maximum temperature of the water-cooled 310 Wp panel was lower by approx. 24 K compared to an uncooled panel, as pointed out by a measurement performed during a typical sunny day when solar irradiation was approximately 850 W/m2. This improvement of the cell temperature led to a 10% increase in power generated by the water-cooled photovoltaic panel compared to the uncooled one. The economic analysis revealed that the estimated simply payback time for installing the cooling system in typical domestic photovoltaic installations can be less than 10 years, while from the point of view of net present value, the introduction of the water cooling system can be a profitable option for a 10-year period when a discount rate of 5% is considered.

A Photovoltaic Panel Integrated with Phase Change Material as Peak Shaving for Domestic Hot Water Energy Demand

Phase change materials (PCMs) applied to photovoltaic (PV) panels are a promising solution to recover the large share of energy from the incident radiation, not converted into electricity. PCMs can store a huge amount of energy, exploiting the solid-liquid phase change, which occurs at a nearly constant temperature. In addition, reducing the temperature of a PV panel increases its electric conversion efficiency. This papers experimentally investigates the match between the heat production of a PV-PCM system and the domestic hot water (DHW) demand of a typical residential building. Different curves of demand are analyzed, all have a peak in the evening period. The solar radiation profile of a typical sunny day is reproduced under a solar simulator. Once the PCM is fully melt, a hydraulic circuit, which connects the heat exchanger immersed in the PCM to a water tank, is activated to extract the heat stored. Different tests are performed by varying the size of the water tank storage. Results show that a storage volume of 50 L, 75 L, 100 L and 125 L ensures a reduction of energy demand of 15.3%, 21.2%, 22% and 21.5% respectively, compared to traditional electric water heaters.

Effects of Agrivoltaic Systems on the Surrounding Rooftop Microclimate

Agrivoltaic systems have the potential to maximize the usefulness of spaces in building rooftops. Urban farming systems improve the microclimatic conditions, which are beneficial to solar photovoltaic (PV) systems, as they lower the operating temperatures, resulting in a higher operating efficiency. Microclimate simulations by means of ENVI-met simulation showed that between 0800 h and 1800 h, PV temperatures in the plot that has crops below the PV system were on average lower by 2.83 °C and 0.71 °C as compared without crops on a typical sunny and cloudy day, respectively. Hence, we may see PV efficiency performance improvement of 1.13–1.42% and 0.28–0.35% on a sunny day and cloudy day, respectively. Data collected from a physical prototype of an agrivoltaic system suggested that evaporative cooling was responsible for the reduction in ambient temperatures. The presence of crops growing underneath the PV canopy resulted in the agrivoltaic prototype generating between 3.05 and 3.2% more energy over the day as compared to a control system with no crops underneath.

Adjusting optical and fluorescent properties of quantum dots: Moving towards best optical heat-rejecting materials

Quantum dots (QDs) coatings have recently attracted attentions as novel nano-scale fluorescent cooling materials with adjustable thermo-optical properties for urban overheating mitigation application. In this paper, a mathematical method for the prediction of impact of optical and fluorescent properties (i.e. absorption edge wavelength (λAE) and quantum yield (QY)) on fluorescent cooling indicators including re-emitted energy (QPL), effective solar reflection (ESR), and PL-related surface temperature reduction was proposed. The experimental thermal evaluation testing on three PbS QDs sample with different fluorescent properties and their corresponding non-fluorescent samples was performed to assess the accuracy of the proposed predictive model and evaluate the impact of fluorescent/optical properties on their cooling potential. The validated model was then used to optimize the fluorescent cooling potential for QDs samples with different fluorescent/optical properties. According to the model results, surface temperature reduction potential through PL effect demonstrates its highest value for QDs with solar absorption and QY near to unity, and λAE at around 1300 nm. QDs coatings with the optimal solar absorption, QY, and λAE showed up to 35 °C lower surface temperature than their corresponding non-fluorescent reference sample in a typical sunny day in Sydney. The maximum fluorescence contribution (Effective solar reflection (ESR)- Solar reflection (R)) is also estimated to be 0.44 for the fluorescent material with optimal optical and fluorescent property. Results of this study will support the next phase of research on fluorescent cooling.

Experimental and Numerical Study of an Active Solar Heating System with Soil Heat Storage for Greenhouses in Cold Climate Zones

Root temperature is an important ecological factor affecting plant growth. A solar greenhouse with an active solar heating system was built in Jinan, in the cold climate zone of northern China. Experiments encompassing the complete cycle of heat collection, heat storage, and heat release were carried out. Using the experimental data, the numerical simulation of soil heat storage with a variable heat flow was executed using the ANSYS (ANSYS Inc., Pittsburgh, PA, USA) Fluent software. Soil temperature fields were studied on typical sunny days and typical cloudy days in the transition season and winter. The solar collector efficiency and coefficient of performance of the system were investigated. The applicability of this active solar soil heating system with soil heat storage for cold areas was evaluated. The results showed that the system effectively maintained suitable ground temperatures to prevent plant growth inhibition caused by low ground temperatures in winter. During the experimental period, the solar collector efficiency was 47% and the system’s coefficient of performance was 67.70. The thermal performance of the system was much better than a traditional energy system. This study showed that this active solar heating system with soil heat storage is an economic and feasible way to increase soil temperatures in solar greenhouses in cold areas.