Low Solar Altitudes Research Articles

Daylight Comfort Performance of a Vertical Fin Shading System: Annual Simulation and Experimental Testing of a Prototype

This study aims to develop and evaluate a vertically rotated fin shading system for an energy-efficient, user-friendly office space. The system was designed to protect a 4 × 8 m office room with a south-facing facade from excessive solar radiation and glare. The shading system was modelled and simulated using Rhino/Ladybug 1.6.0 software with Radiance engine, based on real-weather data (*.epw file) for Wrocław, Poland at 51° lat. The simulation calculated the useful daylight illuminance (UDI) for 300–3000 lux and the daylight glare probability (DGP) for ten static and four kinetic variants of the system. The optimal angle of the fin rotation for the static variant was found to be α = 40°. The kinetic variants were activated when the work plane illuminance exceeded 3000 lux, as detected by an internal sensor “A”. The simulation results show that the kinetic system improved the daylight uniformity in the office room, achieving UDI300–3000 values above 80% for more than 40% of the room area. A prototype of the system in a 1:20 scale was built and tested on a testbed at Wrocław University of Science and Technology, using TESTO THL 160 data loggers. The measurements were conducted for a week in early November 2023, and three clear days were selected for analysis. The measurement results indicate that the low solar altitude on clear days causes high illuminance peaks (15–18 Klux) and significant contrast in the room, leading to unsatisfactory DGP values consistent with the simulation outcomes. Therefore, the study concludes that the proposed system may need an additional shading device to prevent glare during periods of low solar altitudes.

Analysis of the Ranging Capability of a Space Debris Laser Ranging System Based on the Maximum Detection Distance Model

Based on the radar equation and system noise characteristics, the maximum detection range model of a space debris laser ranging system at a 1064 nm wavelength is established, taking into account the factors of atmospheric transmission and sky background radiance. Through theoretical analysis and simulation experiments, the influencing factors of atmospheric transmission and sky background radiance are studied, and the influencing factors are normalized into the maximum detection range model by polynomial fitting. The results indicate that a high atmospheric transmission comes from a high altitude and low target zenith angle; a low sky background radiance comes from a small target zenith angle and low solar altitude angle, while the angular distance has no obvious influence on the sky background radiance. The experimental results indicate that the comprehensive accuracy of the maximum detection range model of the system is 86%, and the effectiveness of the model is verified by using a 1064 nm wavelength laser ranging for the debris target with a distance of 700–1100 km and a cross section area of 4–10 m2. The model can be used to evaluate the ability of the space debris laser ranging system at a 1064 nm wavelength.

A comparison of the use of traditional glazing and a novel concentrated photovoltaic glazing (CoPVG) for building solar gain analysis using IESVE

The aim of this study is to compare the difference in solar gain for an internal space when a novel Concentrated Photovoltaic Glazing (CoPVG) unit is compared against traditional glazing modules. The CoPVG is an innovative glazing system developed by Ulster University, that takes advantage of Total Internal Reflection (TIR) to direct solar radiation into the internal space during periods of low solar altitude (around winter) harnessing the thermal contribution of solar gain and daylight. During periods of higher solar altitude (around summer), the solar radiation is mostly directed onto embedded photovoltaic cells. Previous work assessed the concept’s optical functionality, through experimental measurement and computational ray-tracing. Dynamic simulation in Matrix Laboratory (MATLAB) using a series of codes to represent the optical function of the CoPVG’s and Integrated Environmental Solutions Virtual Environment (IESVE) was validated by the experimental data. This work investigates methodologies in determining the transmissivty of the system in a dynamic simulation approach using ray tracing and Radiance in IESVE for visualisation, thereby building on the versability of this software to allow building designers and consultants to investigate energy and economic benefits of this system and systems like it in real building applications. The impact of integrating CoPVG as a replacement to traditonal glazing on a sun-facing building facade is assessed and the solar gain in the adjaciant space is compared throughout the year. During the summer months the integrated system reduces solar gain in the space by 34% but only 11% in the winter months, representing a reduction in the overall annual building energy needs. The study presents the potential economic and environmental savings provided by reduced cooling.

Numerical investigation on the effect of different types of configuration on the optical performance of solar flat plat reflecting system

The solar flat plate reflecting system (SFPRS) and its configuration significantly influence the reflection pattern of the solar radiation to the receiving surface. Present study numerically investigates the impact of square type configuration (STC) and hexagonal type configuration (HTC), on the performance of SFPRS by analysing the behaviour of beam rays and their interaction with the reflectors. The derived equations for solar radiation and fundamental equations of three-dimensional geometry were employed to develop a customized ray tracing algorithm (RTA) within the MATLAB software. The code incorporates a methodology to explore the behaviour of rays, including direct rays (DR), single reflected rays (SR), twice reflected rays (TR), three times reflected rays (THR), and rays leaving the system (LR). The results for the STC were validated with previous successful experimental outcomes. The optical performance of HTC is 15% higher than STC. Additionally, HTC demonstrates geometrical advantages over STC with an 8% increase in SR and a 13% increase in TR types of rays. Besides, STC exhibits greater participation of THRs and LRs type’s rays, resulting in lower optical efficiency. Consequently, the study concludes that the use of HTC is preferable over STC, when dealing with low solar altitude angles on multiple days.

Integrated Kinetic Fins for Western Facades in Territories with Low Solar Altitudes

Insufficient daylighting can negatively affect working quality and productivity and increase lighting energy consumption in buildings. Particularly, the western orientation has a non-uniform daylighting distribution, especially at the zone next to the window resulting from the unequal radiation distribution of sunlight. Therefore, this study presents an innovative system known as Integrated Kinetic Fins (IKF), which can respond parametrically to the sun’s movement; to enhance the daylighting distribution during the late working hours for the western façades and decrease the high illuminance daylighting spots near the windows. The study optimizes the fin parameters based on a selected territory; then, the fi angles are automatically controlled. The IKF is applicable in regions with clear skies and low solar altitudes. Finally, a comparison between a traditional kinetic system and the IKF is made, and the results are reported. The system shows an enhancement of daylight distribution during these late hours, where the contrast has been improved by 22% and uniformity has been enhanced by 10%, which consequently contributes to reducing potential glare.

Optimal design of inhomogeneous semi-transparent photovoltaic windows based on daylight performance and visual characters

This study aims to optimize the solar cell strip width (CSW) and cell coverage ratio (CCR) of inhomogeneous semi-transparent photovoltaic (IH-STPV) windows to balance the daylight performance and visual characters. The IH-STPV windows with identical CSWs and CCRs but with vertical cell (V-cell) strip layout and horizontal cell (H-cell) strip layout were investigated through comparative experiments and a subjective survey. A visual angle model was first developed to optimize the CSW to mitigate the impact of cell strips on visual characters. By using the experimentally validated daylighting model, the annual daylighting simulation in various daylight climate regions was performed based on the optimized CSW. Finally, the optimal CCRs corresponding to specific CSWs were recommended. The experimental results indicated that the daylight glare risk of the V-cell window was lower than that of the H-cell window, but the difference became less significant when the viewpoint distance increased. Besides, the subjective survey results revealed that the visual discomfort caused by the solar cell strips could be alleviated by extending the viewpoint distance, and the visual characters of the H-cell window were better. The simulation results showed that cities at higher latitudes tended to require a higher CCR due to the low solar altitude angle which causes the higher frequency to see the sun in the view field of the window.

Water surface albedo and its driving factors on the turbid lakes of Northeast China

Lake water surface albedo (LWSA) is a critical parameter for describing energy flux balance at the air–water interface. It is used to measure the capacity of lake water surface reflectance in the shortwave radiation band, which controls the energy partitioning between atmosphere and lake. LWSA and its driving factors, including solar radiation angle, water quality and meteorology, in lakes of Northeast China was analyzed in this research. Solar altitude angle emerged as the most important controlling factor of LWSA. The results showed a strong reduction in LWSA values with increase in solar altitude angle. The study also documented a strong effect of suspended matter on the radiative properties of lakes surface, leading to increased LWSA with increased in suspended matter concentration, especially at high solar altitude angles (R2: 0.76). While no significant association (R2: 0.11) was found between LWSA and chlorophyll-a concentration, LWSA was positively correlated with wind speed (R2 of 0.62 and 0.50 at high and low solar altitude angles, respectively), likely a consequence of wind-driven sediment resuspension in lake waters. Although chromophoric dissolved organic matter (CDOM) and organic particulate matter can affect energy partitioning and spectral distribution of incident solar radiation in lake waters, there was insufficient evidence of measurable effects on LWSA. Variations in LWSA recorded in this study were primarily dependent on similar solar altitude angles and backscattering properties of inorganic particulate matter suspended in the water column. Higher surface albedo was found in the turbid lakes.

Empirically testing the influence of light regime on diel activity patterns in a marine predator reveals complex interacting factors shaping behaviour

Abstract Diel cycles in marine predator diving behaviour centre around the light‐mediated diel vertical migration (DVM) of prey, and are considered critical for optimizing foraging and limiting competition across global seascapes. Yet, our understanding of predator diel behaviour is based primarily on examining relative depth usage between constant day/night cycles with no formal investigation of how varying light regimes interact with abiotic factors to shape diel activity. The extreme seasonal light regimes (midnight sun, polar night, day/night cycle) in the Arctic provide a unique natural experimental setting to empirically investigate the occurrence and intensity of diel behaviour in marine predators relative to changing light levels while concomitantly assessing interacting abiotic factors. Depth time series data from satellite‐linked tags deployed on six beluga whales (Delphinapterus leucas) for up to 12 months were used to quantify diel behaviour by calculating dissimilarity in time‐at‐depth between periods of low and high solar altitude on each day. Generalized additive mixed effects models were used to examine the influence of hours of daylight across extreme light cycles, coupled with bathymetry and sea ice concentration; focal diel patterns were further examined relative to the thermal structure of the water column. As predicted, belugas exhibited cathemerality during the midnight sun, and initiated diel behaviour with the onset of the fall day/night cycle, with a marked increase in its intensity with the progression to equal day/night length. Occurrence of diel patterns, however, was complex; ceasing in regions with seafloor depths <700 m, and occurring with greatest intensity when the water column was thermally homogeneous within the upper 150 m. Through empirical investigation, this study demonstrates that the onset of day/night light cycles and presumably associated prey DVM can modulate predator diel dive behaviour under certain circumstances, but highlights how the complex interaction of abiotic factors with light regime shape dynamic spatiotemporal patterns. These findings, building on a body of recent work, emphasize that the traditional view of the ubiquitous occurrence of diel behaviour tied to DVM at the base of the food web oversimplifies vertical predator–prey interactions, identifying the need for more structured investigation. Read the free Plain Language Summary for this article on the Journal blog.

Experimental characterization of the thermal performance of the Haines 2 solar cooker

This work presents the most exhaustive experimental characterization of the thermal performance of the Haines 2 solar cooker available to date. Two Haines 2 solar cookers were tested side-by-side in Malaga, Spain, 36.7°N, between May 2021 and December 2021. A novel test procedure using empty pots and a tilted plane with variable inclination gave useful information about the influence of the solar altitude angle on cooker performance, and allowed identification of the best range for each of the two available reflector configurations for this cooker. Some suggestions are given to improve the cooker design for low solar altitude angles. In addition, a large number of water heating tests partly based on the ASAE S580.1 standard protocol were conducted to i) determine the standardised power, ii) examine the influence of the solar altitude angle, and iii) investigate the impact of using partial loads. All these results provide a complete characterization of the performance of this cooker in a wide range of operating conditions of practical interest. It is recommended that future versions of ASAE S580.1 standard consider the influence of both solar altitude angle and partial loads.

A large-region fog detection algorithm at dawn and dusk for high-frequency Himawari-8 satellite data

ABSTRACT Satellite remote sensing provides effective methods for fog detection at large scales. At dawn or dusk, however, the separation of fog from the surface remains a great challenge because of the minor radiation difference between fog and the surface. This study develops a novel algorithm for fog detection suitable for dawn and dusk from high-frequency data of the Himawari-8 satellite. Methodologically, the area was divided into three subregions according to the distance of the terminator line. In regions at daytime that are far from the terminator line, a fog detection index of the low solar altitude angle (FDI LSAA) was built to isolate the fog through the relationship between the mid-infrared (MIR) brightness temperature (I MIR ) and its difference with the thermal infrared (TIR) brightness temperature (BTD = I MIR – I TIR , where I MIR and I TIR are the brightness temperatures at the MIR and TIR bands). In regions near the terminator line, the fog was extracted from the surface by a Gaussian mixture model (FD-GMM NTL) by the differences in MIR and TIR radiation changes. After that, the fog was further extracted from the low and mid-high clouds by the enhanced low cloud detection index (ELCDI) and by the difference in BTD and TIR characteristics. In regions at night, a BTD threshold value was adopted to detect fog. Validation results demonstrated that the algorithm in this study could precisely detect large-region radiation fog including dawn and dusk, with the overall probability of detection (POD) accuracies range from 76.3% to 89.2% at dawn and 67.3% to 77.0% at dusk. The relatively low accuracy at dusk was mainly attributed to desert in the study area, which has a similar BTD with fog after a day of solar radiation. Results of this study provide new insight for fog detection at dawn and dusk, which enhances the application of remote sensing in meteorology forecasting.

The Solar Eruption of 2017 September 10: Wavy with a Chance of Protons

Abstract High-resolution SUVI images reveal an interesting new picture of particle acceleration in powerful solar eruptions. Typically, powerful solar eruptions include a coronal wave component, as well the traditional CME and flare components. At low solar altitudes, coronal waves refract downward, toward the solar surface, because of the slower Alfvén speeds at the base of the corona. The refracted wave plus the shock wave ahead of an intense CME allow for a two-step shock acceleration process that can result in relativistic or GLE particles. This mechanism may be particularly applicable to the first-to-arrive, prompt relativistic particles measured by the Fort Smith neutron monitor during GLE # 72 on 2017 September 10.

A study on the structure of Solar/Photovoltaic Hybrid system for the purpose of preventing overheat and improving the system performance

In countries, such as Korea, where climate change is clear due to the four seasons, some of the collected energy must be released in the summer season, and these measures for heat dissipation fail to be very effective, thus causing system overload and defects frequently. In this study, we devised an overheating prevention system for the solar hot water and heating system using the variation of the shadow caused by the solar altitude angle that changes every hour, and for this purpose, a solar power generation module was placed over the solar collector. By using simulations, the system was designed in such a way that direct sunlight would be naturally blocked from reaching the solar collector due to the high solar altitude in the summer and that 100% of direct sunlight could reach the collector due to the low solar altitude in the winter. It was confirmed that the designed conditions were also satisfied in the actual test bed. In order to predict the performance of the system through simulations, the temperature of the solar thermal storage tank was calculated every hour after modifying the energy equation used in a previous study, and as a result of determining whether the system is overheated afterwards, it is expected that the degree of system overheating can be reduced. The shading did not affect the system efficiency in the season in which an actual heating and hot water load was needed.

Distribution of charged lunar dust in the south polar region of the moon

Lunar dust is one of the most threatening problems confronting the return of human beings to the moon. In this work we studied the spatial distribution behavior of charged lunar dust in the solar wind plasma environment in the south polar region of the moon and considered the influence of a mini-crater using Spacecraft Plasma Interactions Software. The distribution of dust and plasma at low solar altitude angles of 20° and 0° was studied, and the spatial density of lunar dust was ∼ 1010.4 m−3 and ∼ 1011.5 m−3, respectively. This is because a higher surface potential will result in transportation of small dust particles and photoelectrons can also neutralize positively charged lunar dust. The dust density in the plasma void region created by a mini-crater with a 5 m high wall was studied. We obtained a quasi-neutral electric environment in the plasma void region of the mini-crater, and the dust density was about a magnitude lower than that in other regions. The dust risk to a spacesuit is much lower on the nightside than on the dayside, but there is severe charged lunar dust transport in the region between light and shade, which is dominated by the difference in surface and plasma potential caused by photoelectrons.

Origami-foldable tessellated Crystalline-Si solar cell module with metal textile-based stretchable connections

The increasing demand for photovoltaic (PV) electricity has resulted in wider usage for many applications. Current dominant PV electrical sources use crystalline silicon (c-Si) solar modules. These would provide greater potential as an energy source if they could be installed to any surface with a curvature, for example integration into buildings, and would perform better under omni-directional incident light, which is not considered in the design of current modules. In this study, we propose an origami-type foldable c-Si solar cell module by introducing a tessellated module design and textile-based woven metal connections to overcome the limitations of using c-Si solar cell modules on curved surfaces and under various light conditions. For the proposed module, two main concepts are introduced: a tessellation design for rigid folding and stretchable textile-based metal connections. The flexible crease pattern and interconnection allows the modules to be folded up to 180°, and a diagonal force on the metal textile can be induced on the inter-module connections using rotating wires. These features allow solar cell modules to cover an arbitrary surface without electrical degradation. Tessellating the module allows for maximum potential using the origami design when applied to both flat and curved surfaces. The origami-type foldable tessellated modules performed better than conventional modules. Their energy production under various angles of incident light is higher per day than that of flat modules, even during periods of lower intensity sunlight from a low solar altitude. These findings demonstrate a new approach to extend the usage of c-Si solar cells. • We introduced origami-foldable solar cell module for covering arbitrary surface. • The metal textile, the connector of the module, is stretchable and flexible. • Tessellated module with origami pattern allows rigid-folding without area loss. • The 64-cell module are successfully deformed as paper along the crease lines. • The energy production is higher per day than of flat modules.

UV Index Does Not Predict Ocular Ultraviolet Exposure.

PurposeThe ultraviolet index (UVI), available online, is an international linear scale of levels from 0 to 13+ that warns about the risk of sunburn; however, it does not address the risk to eyes. Our purpose was to develop a useful instrument to warn the public against ocular ultraviolet (OUV) exposure and to serve as a tool for researching UV-induced ocular diseases.MethodsA rotating model head that included ultraviolet B (UVB) sensors documented UV irradiance at the crown and at the eyes spanning eight azimuths from sunrise to sunset under different climatic conditions in each season. The dose intensities obtained were compared with their respective UVI levels. Doses to the eyes were mathematically transformed to develop an OUV index with linear levels from 0 to 13+, similar to the UVI. Then, readings from both instruments were compared.ResultsUV exposure at the crown increases with solar culmination, whereas that to the eye is greater under low rather than maximum solar altitude. The OUV index levels were higher than recorded UVI levels in the summer under low solar altitude in the early morning and mid- to late afternoon and were markedly higher all day in winter when solar altitude remains low.ConclusionsThe UVI does not provide sufficient warning about the risks of ocular UV damage. The proposed OUV index is a useful instrument to warn the public against OUV exposure and to serve as a tool for researching UV-induced ocular diseases.Translational RelevanceThe OUV index is useful to prevent ocular UV-related diseases.

Performance evaluation and spectrum-based analysis of a wall-mounted photovoltaic system for zero-energy building

The concept of zero-energy building (ZEB) has attracted global attention in recent years as it involves offsetting the primary energy usage of a building on an annual base by the energy generated from renewable resources. The performance of wall-mounted photovoltaics (PV) for building applications has great potential for ZEB. In this study, we compared wall-mounted and common roof-mounted PV systems using a combination of experimental and theoretical studies. The wall-mounted PV system exhibited an unusual performance behavior depending on the season. Winter is a suitable season for energy production from the wall-mounted PV system because of the low solar altitude and resulting lower incident angle of the sun. However, the performance ratio (PR) had twin peaks throughout the day that could not be explained by the classical model that uses irradiance and temperature variation. In summer, there was less irradiance on the vertical wall and the PR had triple peaks that were also hard to explain using the conventional model. We established a detailed output power model of the wall-mounted PV using spectrum variation on a vertical plane. Our approach is the development of spectrum model that can be applied to all-climate and computed the performance variation according to the sun’s orientation and incident angle. Our model quantitatively explains unique seasonal and daily efficiency variations for the wall-mounted PV system (twin peaks in winter and triple peaks in summer). Our validated model can be utilized to map a suitable location for a wall-mounted PV system.

A novel method for making laser cut panel based daylight collector coupled to a tubular light guide

The work in this paper focuses on the development of a daylighting device which can increase the light output for longer lengths of hollow mirrored light pipe. The device proposed is passive, easy to build, and inexpensive. It uses the concept of total internal reflection in acrylic laser cut panels (LCPs) and extends the idea into a complete collector based on mathematical modelling. The novel method of fabricating laser cut panels with steep cutting angles and partial depth cuts has been discussed in this paper. This method has been combined with weight optimisation to make a lightweight yet efficient collector with no laser cuts exposed to the atmosphere. The simulation results of this collector have been compared with a flat acrylic plate coupled to a light pipe and experimental validation of simulation has been performed using a prototype. The simulation results for collector coupled to 80% reflective light pipe have shown up to 4.3 times the illuminance on model room floor as compared to light pipe with a flat plate on 21 December- the low solar altitude season for which the collector was primarily designed. Another simulation of a real dimension office space with multiple collectors shows that at least 175 lx of average illuminance is available on the work surface with 227 cm2 cross-section light pipes.

In-situ Measurement of the Arctic Ocean for Optical Property Analysis During 2019 Cruise

The Arctic issue has increased due to global warming. The Arctic is losing the role of cooling because reducing sea ice by warming on the Arctic, which is changing the energy balance on the Earth system. Change of Arctic ocean, atmosphere, and cryosphere influence on an ecosystem of Arctic as well. These changes are monitoring by remote sensing due to the Arctic is difficult for human access, and where is a wide area. However, a low solar altitude on the Arctic limits Ocean Color Algorithms applies to the Arctic because most ocean color algorithms are based on empirical data in the mid-latitude. Continuous data sampling on the Arctic ocean is the best way to improve and develop a suitable ocean color algorithm for the Arctic. This paper aims to report ocean observation data acquired by Ice-Breaker research vessel Araon during the summer Arctic expedition of 2019. Acquired samples are chlorophyll-a, suspended sediment concentration, in-situ measured ocean optical properties. Sampled data showed that there is a significant effect of dissolved organic matter in its inherent optical properties. We use these data for the aims of improving and develop ocean color algorithms in the Arctic.

NOx-Reduction Performance Test for TiO2 Paint.

In South Korea, the gradual increase in particulate matter generation has received significant attention from central and local governments. Exhaust gas, which contains nitrogen oxides (NOx), is one of the main sources of particulate matter. In this study, the reduction of NOx using a coating material mixed with a titanium dioxide (TiO2) photocatalyst was demonstrated. The NOx reduction performance of the TiO2 photocatalyst-infused coating was evaluated by applying the ISO 22197-1: 2007 standard. Subsequently, the performance was evaluated by changing the NO gas concentration and ultraviolet (UV)-A irradiance under standard experimental conditions. It was determined that NOx reduction can be achieved even if the NO gas concentration and UV-A irradiance are lower than those under the standard conditions when the TiO2 photocatalyst-infused coating was used. This study revealed that NOx reduction can be realized through TiO2 photocatalyst-infused coating in winter or cloudy days with a low solar altitude. It was also confirmed that compared with the UV-A irradiance, the NO gas concentration has a greater effect on the NOx reduction performance of the TiO2 photocatalyst-infused coating. These findings can be used to evaluate a variety of construction materials with TiO2 photocatalysts in the future.

Accuracy of Mean Radiant Temperature Derived from Active and Passive Radiometry

The concept of the mean radiant temperature (Tmrt) allows the study of radiative exchanges between a human and its environment. It presupposes that the radiant effects on the person of the actual environment, which is generally heterogeneous, and the virtual environment, which is defined as homogeneous, are identical. ISO 7726 specifies the required accuracy in Tmrt as input of rational thermal indices, outdoors ±5 (K). Tmrt accounts for the radiant heat absorbed by skin/clothing from the shortwave (SW) and longwave (LW) spectral bands. Most of the radiant components are isotropic. However, there are anisotropic SW components; namely the direct irradiance and under clear or partly obstructed skies a significant circumsolar fraction (fcs) in the diffuse irradiance. Both originate from the close proximity of the solar disk. This study highlights the effect of fcs on Tmrt. In the scope of human biometeorology a standing body posture is standard. For unidirectional irradiances its radiant cross-section varies dependent on the solar altitude. Active radiometry in deriving Tmrt is based on measured irradiances. One method is the Klima-Michel-Modell (KMM) that uses readily available measurements from standard meteorologically radiant observations. KMM references Fanger’s area projection factors that are derived from precise measurements of real humans. Thus, KMM serves as reference in evaluation of further methods. One is the six-directional instrument (Tmrt,r,6−Dir). Slightly simplifying a standing human, it represents a subject as a rectangular solid. Tmrt,r,6−Dir is derived based on measured irradiances incident on the vertical and horizontal planes. In passive radiometry the energy balance equation of a black globe thermometer is solved that leads to Tmrt,Tg,BG. fcs significantly impacts Tmrt with noticeably reduced values for high and increased for low solar altitudes. Hence, accounting for fcs is essential for the accuracy of Tmrt. For KMM an extension to an existing algorithm is provided in order to include fcs into the Tmrt calculation that results in Tmrt,r,KMM. For Tmrt,r,6−Dir the radiant cross-section of the solid depends to a minor extent on its azimuth relative to the solar azimuth. As a result Tmrt,r,6−Dir slightly scatters compared to Tmrt,r,KMM. However, it remains within ±2 (K). Tmrt,Tg,BG compared to Tmrt,r,KMM complies only at night with the ISO 7726 bin of ±5 K. Tmrt,Tg,BG significantly overestimates Tmrt,r,KMM during the daytime, because of its greater SW absorptance compared to skin/clothing and to a smaller extent because the standing posture is represented by a sphere. Particularly in sunny conditions, Tmrt,Tg,BG is subject to considerable variance. Thus, outdoors during the daytime, Tmrt,Tg,BG is unable to serve as an appropriate input for the calculation of rational-based thermal indices.