Search

Photovoltaic systems have a reliable method to generate electrical power from direct solar irradiance. Their efficiency is only up to 20% in real operating circumstances and is affected adversely by the inevitable temperature rise in their surface. Passive, active or combined cooling methods are applied to reduce operating temperature to a suitable level, depending on specific application. A Great body of literature has been investigating different PV cooling methods and techniques to reach optimized system efficiency and cooling effect. It is critical for both researchers and practitioners to have a thorough understanding and awareness of the most recent advances and existing gaps. Although there are certain review papers in this field, it is necessary to have up-to-date reviews of the most recent progress and research since the previous ones. In the present work, the main focus was to provide a review of the most recent studies and to compare their outcomes to provide a reference for practitioners and researchers. The holistic classification and evaluation of all the possible cooling technologies were provided in order to draw a comparison between various cooling approaches. Based on the analysis obtained, cooling techniques can ensure improvement in electrical efficiency in a range from 1% to 53% with expected decrease in the photovoltaic panel's surface operating temperature from 1.8 °C to 46 °C. It was also found that spectrum filtering and jet impingement indicated highly remarkable enhancements. The other factors, such as the size of the examined photovoltaic panel, photovoltaic technology, as well as climate circumstances have a strong impact on the cooling performance besides the selection of the specific coolant. The necessity for integral evaluation (performance, economic and environmental) of cooling techniques was also identified as key issue.

An innovative bioclimatic metric based on the Universal Thermal Climate Index (UTCI) is developed to quantify human thermal physiological heat stress. The Heat Stress Exposure (HSE) metric includes both duration and intensity dimensions of heat exposure, and in this paper it is applied to the Sydney Australia climatology. Geographic Information Systems (GIS) were used to spatially represent and visualize Sydney's HSE. The first stage of the analysis collated observed meteorological data from 10 weather stations across the Sydney metropolitan region, extending from coastal Sydney to approximately 50 km inland in 2017. The second stage of the analysis integrated the radiative meteorological data into estimates of hourly Mean Radiant Temperature which were then applied to UTCI. In the final stage, a threshold UTCI value of 26 °C was selected for the calculation of HSE, which was then cumulated to represent the duration of heat exposure throughout the year. The difference between each UTCI hourly reading and the 26 °C threshold defined a UTCI exceedance (ΔUTCI; °C). The cumulative total of all ΔUTCI throughout the year defined ∑ΔUTCI in units of degree hours (°C.hr), thereby capturing both intensity and duration of exposure to heat stress. Weather systems driving westerly winds from the Australian continent's central deserts brought the highest HSE to Sydney's inland western suburbs, with values ranging between 4,000–6,000 ∑ΔUTCI (°C.hr). Coastal eastern Sydney experienced considerably lower HSE values ranging from 1,600–3,000 ∑ΔUTCI (°C.hr), reflecting the moderating influences of sea breezes and evaporative cooling.

Urban overheating (UO) may interact with synoptic-scale weather conditions. The association between meteorological parameters and UO has already been a subject of considerable research, however, the impact of synoptic-scale weather conditions on UO magnitude, particularly in a coastal city that is also near the desert landmass (Sydney) has never been investigated before. The present research examines the influence of synoptic-scale weather conditions on UO magnitude in Sydney by utilizing the newly developed gridded weather typing classification (GWTC). The diurnal, and seasonal variations in suburban-urban temperature contrast (ΔT) in association with synoptic-scale weather conditions, and ΔT response to synoptic air-masses during extreme heat events are investigated in three zones of Sydney. Generally, an exacerbation in UO magnitude was reported at daytime over the years, whereas the nocturnal UO magnitude was alleviated over time. The humid warm (HW), and warm (W) air-masses were found primarily responsible for exacerbated daytime UO during extreme heat events and in all other seasons, raising the mean daily maximum ΔT to 8–10.5 °C in Western Sydney, and 5–6.5 °C in inner Sydney. The dry warm (DW), and W conditions were mainly responsible for urban cooling (UC) at nighttime, bringing down the mean daily minimum ΔT to − 7.5 to − 10 °C in Western Sydney, and − 6 to − 7.5 °C in inner Sydney. The appropriate mitigation technologies can be planned based on this study to alleviate the higher daytime temperatures in the Sydney suburbs.

“Net-zero energy”, a burning concept of the current world, has been being considered and applied on a building scale for the last few decades, however, there are significant advantages to moving to the community level. This study identifies the technological advancements of net-zero energy communities through in-depth literature review study. 23 case study settlements have been identified and analyzed based on their design methodology along with some practical applications around the globe. The focus of this work is on technologies and measures utilized for the reduction of energy consumption, minimization of greenhouse gas (GHG) emissions, and the generation of electrical and thermal energy by renewables. We identified different mitigation strategies adopted for outdoor heat sources, building adaptation techniques, and renewable energy technologies along with control strategies. The study reveals that all the settlements mainly focus on the onsite energy generation, while 17 settlements among them, additionally, consider various adaptation techniques that have significantly lessened the energy demand of the buildings. A few studies (4 settlements only) incorporate some mitigation strategies to mitigate the outdoor heat sources that enable to lower the ambient temperature along with diminishing the GHGs emissions as well as minimizing the energy demand of the community. In addition, the climate zones have significant impacts on selecting the building adaptation tools and measures. Alongside the energy balance, we have also epitomized the effects of various energy management and control strategies adopted for the smooth operation of energy. Finally, we shed light on the problems and challenges of existing net-zero energy settlements and make recommendations by considering the environment, energy, and economy towards achieving the net-zero energy purpose at the community level.

Overheated outdoor environments adversely impact urban sustainability and livability. Urban areas are particularly affected by heat waves and global climate change, which is a serious threat due to increasing heat stress and thermal risk for residents. The tropical city of Darwin, Australia, for example, is especially susceptible to urban overheating that can kill inhabitants. Here, using a modeling platform supported by detailed measurements of meteorological data, we report the first quantified analysis of the urban microclimate and evaluate the impacts of heat mitigation technologies to decrease the ambient temperature in the city of Darwin. We present a holistic study that quantifies the benefits of city-scale heat mitigation to human health, energy consumption, and peak electricity demand. The best-performing mitigation scenario, which combines cool materials, shading, and greenery, reduces the peak ambient temperature by 2.7 °C and consequently decreases the peak electricity demand and the total annual cooling load by 2% and 7.2%, respectively. Further, the proposed heat mitigation approach can save 9.66 excess deaths per year per 100,000 people within the Darwin urban health district. Our results confirm the technological possibilities for urban heat mitigation, which serves as a strategy for mitigating the severity of cumulative threats to urban sustainability.

Urban overheating affects the energy, health, power, survivability and environmental quality of cities. We calculated the magnitude of overheating in Sydney, Australia, at close to 9 °C, which causes a cooling penalty of up to 16% and an increase in the indoor overheating levels of up to 56%. We developed and evaluated eight heat mitigation scenarios based on the use of reflective surfaces, additional greenery, an increase in the evapotranspiration rate and several combinations of these factors. We estimated that mitigation can decrease the peak ambient temperature by up to 2.9 °C, reduce the maximum annual cooling consumption by up to 1.5 TWh, decrease the CO2 emissions by as much as 1.21 MT CO2, reduce indoor overheating by up to 80%, decrease the heat-related morbidity by 1.07–1.49, and decrease the heat-related mortality anomaly by as much as 1.39 per 100,000 citizens. We estimated the associated water penalty range to be between 80 and 100 Gl/year or between 13 and 16.7% of the water consumption in Sydney.

In building performance simulations it is typically assumed that outdoor HVAC equipment is exposed to air at the outdoor ‘ambient’ temperature, obtained from a weather file. However, in reality, significant spatial variations in the outdoor air temperature can exist close to buildings. This simplification may lead to significant errors, especially when comparing simulations of buildings with and without cool roofs, since the colder surface of the cool roof would reduce above-roof air temperatures, thereby influencing the energy consumption of rooftop HVAC equipment. Above-roof temperature variations were measured in detail at three shopping centre buildings, and the experimental data was used to develop a model that can estimate air temperatures above hot or cold roof surfaces. The model requires only four input variables, all of which are available in typical building simulation tools. Implementation of the model in a set of case-study simulations revealed that above-roof air temperatures can have a large effect on the predicted performance of cool roofs. In cases where cooling equipment and ventilation inlet ducts were both located on the roof, the electricity savings and gas ‘penalties’ attributable to cool roofs would have been underestimated by 44–85% (61% on average) if above-roof air temperature variations had not been modelled accurately.

By strongly reflecting solar radiation and being highly emissive within the atmospheric window, daytime radiative coolers can achieve sub-ambient temperature under direct sunlight. Radiative cooling performance is strongly coupled to specific climatic conditions since cooling efficiency is strongly affected by ambient air temperature, wind speed, and solar and ambient radiation intensity. In this paper, using a well-validated thermal model, the cooling performance of three radiative cooling materials with varying optical properties was evaluated under three distinct and representative climates. This analysis permits us to better understand the sensitivity of daytime radiative cooling materials to different climatic conditions, present strategies for selecting the ideal spectral properties of materials and investigate how to enhance cooling performance under adverse climatic conditions. It is shown that radiative cooling materials have better performance in hot and arid climates. Most radiative cooling materials exhibit the greatest response to changes in ambient radiation. Higher ambient air temperatures correspond to larger sub-ambient temperature of the surfaces, but this change is lower than that of the corresponding air temperature. Furthermore, by coupling a special optical grating window onto the surface of a radiative cooler, cooling performance can be significantly enhanced by asymmetrically reflecting incoming radiation but permitting outgoing emission. While an ideal material that only emits in the atmospheric window wavelengths presents the best performance under a large range of solar radiation, ambient radiation, and air temperature, the broadband ideal emitter exhibits higher cooling potential when coupled with the optical grating window.

There is no consensus regarding the change of magnitude of urban overheating during HW periods, and possible interactions between the two phenomena are still an open question, despite the increasing frequency and impacts of Heatwaves (HW). The purpose of this study is to explore the interactions between urban overheating and HWs in Sydney, which is under the influence of two synoptic circulation systems. For this purpose, a detailed analysis has been performed for the city of Sydney, while considering an urban (Observatory Hill), in the Central Business District (CBD), and a non-urban station in Western Sydney (Penrith Lakes). Summer 2017 was considered as a study period, and HW and Non-Heatwave (NHW) periods were identified to explore the interactions between urban overheating and HWs. A strong link was observed between urban overheating and HWs, and the difference between the peak average urban overheating magnitude during HWs and NHWs was around 8 ◦C. Additionally, the daytime urban overheating effect was more pronounced during the HWs when compared to nighttime. The advective flux was found as the most important interaction between urban overheating and HWs, in addition to the sensible and latent heat fluxes.

Urban overheating has become a growing concern in the Northern Territory of Australia, where residents are suffering from excessive heat and frequent heatwaves. The characteristics of the local climate of Alice Springs and the impact of mitigation strategies are investigated in this study. Experimental campaigns were performed to determine the characteristics of urban overheating. Advanced microclimate simulations were performed to develop mitigation scenarios. Further, ambient temperature measurements have been carried out for 11 months to assess the magnitude and characteristics of the urban heat island. During the night, the city was warmer than the surrounding desert environment with an average close to 4.1 °C, while it presented cooler temperatures by 2.7 °C during morning hours. Microclimate models developed to assess the influence of the proposed mitigation strategies found a possibility to decrease the maximum ambient temperature of Alice Springs up to approximately 1.1 °C using the combination of mitigation strategies.