Incident Solar Radiation Research Articles

Evaluating the potential of persistent luminescence in counteracting urban overheating

In recent years, the use of numerical simulations to model real atmospheric conditions over cities has become increasingly popular. One of the primary objectives of these models is to assess the efficacy of various strategies for mitigating the Urban Heat Island (UHI) phenomenon. At the same time, researchers have developed and studied new adaptive materials for building applications that aim to reduce buildings’ energy consumption and improve urban microclimate conditions, while performing radiative cooling. Among the new generation of passive cooling solutions, persistent luminescent (PL) materials have emerged as a cutting-edge option for energy-saving purposes, owing to their ability to reject the incident solar radiation through both reflection and light emission. Here, the Princeton Urban Canopy Model (PUCM) is used to evaluate the potential of an advanced PL roof coating to counteract urban overheating. The phenomenon of persistent luminescence is modeled for the first time, taking advantage of experimentally obtained parameters coming from previous studies. Results demonstrate how persistent luminescence can effectively mitigate surface overheating reducing the roof’s surface temperature and net shortwave radiation up to 1.15 °C and 35 W/m2 respectively, with consequent benefits to the overall energy balance of the envelope. Such results may be further increased with the optimization of PL materials for engineering solutions.

Focused solar annealing for block copolymer fast self-assembly

Block copolymer (BCP) self-assembly has tremendous potential applications in next-generation nanolithography. It offers significant advantages, including high resolution and cost-effectiveness, effectively overcoming the limitations associated with conventional optical lithography. In this work, we demonstrate a focused solar annealing (FSA) technique that is facile, eco-friendly, and energy-efficient for fast self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films. The FSA principle involves utilizing a common biconvex lens to converge incident solar radiation into a high-temperature spot, which is directly used to drive the microphase separation of PS-b-PMMA thin films. As a result, PS-b-PMMA undergoes self-assembly, forming ordered nanostructures in a vertical orientation at seconds timescales on silicon substrates with a neutral layer. In addition, the FSA technique can be employed for grafting neutral polymer brushes onto the silicon substrate. Furthermore, the FSA's compatibility with graphoepitaxy-directed self-assembly (DSA) of BCP is also demonstrated in the patterning of contact holes. The results of contact hole shrinking show that contact hole prepatterns of ∼60.4 nm could be uniformly shrunk to ∼20.5 nm DSA hole patterns with a hole open yield (HOY) of 100 %. For contact hole multiplication, doublet DSA holes were successfully generated on elliptical templates, revealing an average DSA hole size of ∼21.3 nm. Most importantly, due to the direct use of solar energy, the FSA technique provides many significant advantages such as simplicity, environmental friendliness, solvent-free, low cost, and net-zero carbon emissions, and will open up a new direction for BCP lithography that is sustainable, pollution-free, and carbon-neutral.

Evaluation of the electrical parameters and performance of floating PV generators

This study provides evaluation of floating photovoltaics (PV) in the Brazil tropical climate and discusses the specific technical and environmental benefits and limitations. This paper develops a model simulating the annual performance of the photovoltaic generator of a floating photovoltaic plant as a function of a given conditions. The reference is a 1.2-MWp floating-PV system commissioned in 2023 near the city of Grão Mogol, Brazil, in the reservoir of the PCH Santa Marta hydropower plant. The influence of the ambient meteorological and marine parameters on the PV module temperature, current, voltage, and power were evaluated. The simulation uses a reference crystalline-Si PV module and the Engineering Equation Solver (EES). Relevant experimental data, including incident solar radiation, ambient temperature, and wind speed were used as input data for the model. The effect of these parameters on the thermal end electrical parameters was assessed. Although small variations were found throughout the year, significant hourly and daily variations were observed, depending on solar irradiation and ambient and resulting module surface temperatures. The voltage at the maximum power decreases with the increase of the solar module surface temperature. The convective heat transfer rates are higher than the radiative heat transfer rates. This study provides a first-time complete energy and exergy analysis of a floating PV system (FPVS) incorporating the various heat transfer rates, electrical and irradiance parameters, under climate and meteorological conditions for this Brazil location.

Bidirectional optical response hydrogel with adjustable human comfort temperature for smart windows.

Smart windows are effective in reducing the energy consumption of air conditioning and lighting systems, while contributing to maintaining the comfort zone of temperature in the indoor environment. Currently used smart windows mainly rely on traditional single-phase thermochromic material in which only one abrupt optical change occurs during temperature changes, and their inherent characteristics may not be suited for a practical balance of energy saving and privacy protection. Here, we developed a novel bidirectional optically responsive smart window (BSW) with unique bidirectional optical response features by introducing sodium dodecyl sulfate (SDS)/potassium tartrate (PTH) micelles into PNIPAM hydrogel to form a composite hydrogel, which was encapsulated in two glass panels. The upper critical solution temperature (UCST) and lowest critical solution temperature (LCST) of the material can be individually adjusted and are capable of matching the human comfort zone of temperature. In addition, the smart window exhibits remarkable transparency (92.5%), visible light transmission ratio (Tlum = 91.31%), and excellent solar modulation (ΔTsol,UCST = 76.34%, ΔTsol,LCST = 76.75%). Moreover, it possesses selectivity in transmitting light in the infrared band of solar radiation and can complete the "transparent-opaque" transition in a very narrow temperature range (<1 °C). When at comfortable temperatures, the highly transparent smart windows facilitate interior light and appreciation of the view. At low temperatures, SDS/PTH micelles aggregate to form large micelles, blocking the transmission of light and protecting customer privacy. At high temperatures, PNIPAM can undergo a "sol-gel" transition, thus blocking incident solar radiation. Taken together, these proposed materials with bidirectional optical response characteristics would be harnessed as a promising platform for building energy conservation, anti-counterfeiting, information encryption, and temperature monitoring.

Projections of Solar Radiation Incident on the Surface and Cloudiness for the Northeast Region of Brazil Through a Set of Climate Models

Resumo Estudos indicam a intensificação das mudanças climáticas, com aumento da temperatura do ar, alterações no padrão das chuvas e maior variabilidade para outros elementos climáticos. O setor energético renovável pode contribuir com a redução dos impactos na atmosfera. Todavia, as fontes renováveis dependem do clima e o aumento da demanda por energia exige um planejamento coerente com as novas condições. Este estudo teve como objetivo apresentar os resultados relacionados à radiação solar incidente na superfície e à nebulosidade para o Nordeste brasileiro. Utilizou-se um conjunto de modelos climáticos globais (BESM, HadGEM2-ES e CanESM2) associados ao regional Eta, para projetar dados futuros para os períodos de 2041-2069 e 2070-2099, comparando-os ao período histórico de 1961-1990, considerando os cenários RCP4.5 e RCP8.5 aplicados pelo Painel Intergovernamental sobre Mudanças Climáticas. Os resultados evidenciaram o aumento predominante da radiação solar incidente (média de 1,7% pelo HadGEM2-ES e 2,5% pelo CanESM2), exceto para o BESM (-3,5%) e redução para a nebulosidade, com valores médios entre -1,1% (BESM) e -53,4% (CanESM2). Esses resultados podem favorecer a produção de energia solar fotovoltaica nesta região, sendo assim, tem-se elevada expectativa quanto à diversificação da matriz energética brasileira, redução da dependência de combustíveis fósseis e aumento da segurança energética.

Efficiency Evaluation of Evacuated Solar Tube Collectors in Sakha Republic (Yakutia)

Calculations of solar radiation incident on an inclined surface were performed considering the installation location, local time, azimuth angle, tilt angle, atmospheric transparency coefficient and surface albedo. The calculations were based on long-term meteorological observation archives. The accuracy of the solar radiation calculations for the inclined surface was verified. A comparative analysis was conducted between the calculation results carried out for the installation location, tilt angle, and azimuth angle of the experimental setup and pyranometer measurements. Thermal energy production by evacuated solar tube collectors was also calculated. These calculations were performed on an hourly basis, taking into account the total solar radiation falling on the inclined surface and the atmospheric air temperature. The calculated values were compared with experimental data obtained from an ultrasonic heat meter. The payback period of solar heating systems for various locations was used as an efficiency indicator for the solar collectors. The article estimated the payback period for Verkhoyansk town in the Sakha Republic (Yakutia). Economic efficiency strongly depends on the installation location of the solar collector and the thermal energy tariff at the installation site.

Stepped solar tracking model with different acceptance angles for various solar concentration schemes

In the last decade, the energy industry has taken a great social, environmental and economic impact due to the exponential increase in the use of fossil fuels. World governments have come to the conclusion that it is necessary to promote research and development of renewable energy technologies for their global exploitation. The energy potential of the Sun is shown as one of the most adaptable alternatives for domestic and industrial uses. Several mathematical models of direct solar radiation have been carried out using various solar tracking strategies; The importance of these systems lies in optimizing the amount of solar radiation in any type of collector. In this research work, the mathematical analysis of incident solar radiation on a flat surface is proposed using MATLAB of various solar tracking schemes in clear sky conditions for the geographical coordinates and climatological conditions of the city of Zacatecas. When comparing the different cases of solar tracking, the following is observed: (a) More solar radiation reaches the surfaces that comply with some sun tracking scheme per month, compared to those surfaces that do not move. (b) The surface that receives the least amount of solar radiation every month is the horizontal surface. The solar irradiation per month estimated for this case is approximately 25% below the maximum calculated value corresponding to the monitoring of heliotrope-type solar collection. Regarding the comparative analysis of the data obtained, it can be seen that: The clear sky model prepared by ESRA has a behavior very close to the data from the Zacatecas_04 Solarimetric Station, having a difference with a maximum value of 0.13% for the month of January same year.

An Experimental Investigation of the Performance of a Solar Heater under Climate Conditions of South of Iraq

In general, solar water heating system can be described as a beneficial device for heating water by the utility of incident solar radiation. In the present study, an experimental solar water heater was constructed in Misan City, south of Iraq. The constructed experimental unit is a box of glass with a width of 40 cm. To measure temperatures of the experimental unit 7 K-type thermocouples were used. Three different inclination angles were investigated. The results showed that in the month of January, temperature of the solar water heater reached around 70 °C with an inclination angle of 37°. Furthermore, it was conducted that for the investigated period (January), temperatures reached the maximum at around 14 p.m. and then there was a decrease in the temperature. Moreover, it was concluded that the height of the solar water heater has a significant influence on the temperature.

МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ТЕМПА ИЗМЕНЕНИЯ ТЕМПЕРАТУРЫ ВНУТРИ СОЛНЕЧНОЙ ТЕПЛОВОЙ УСТАНОВКИ ДЛЯ ЗАМАРИВАНИЯ КОКОНОВ ТУТОВОГО ШЕЛКОПРЯДА

In view of reducing the consumption of fuel and energy resources required for immobilizing the pupa of live silkworm cocoons, a high-performance solar thermal device designed for killing the pupa of cocoons is being proposed in this work. This portable device can be transported by any vehicle and handled by a single operator, and it does not require any special qualifications. Application of this device enables the saving of 100% of fuel and energy resources consumed in existing conveyor-type cocoon drying aggregates at the premises destined for the primary processing of cocoons. Experiments to study temperature conditions inside a solar thermal device with loaded living cocoons were carried out in industrial settings. Measurements of the ambient temperature inside the solar thermal unit and the flux of total solar radiation incident on the horizontal surface of the solar device were made by means of proven tools. Based on the findings from experimental investigations, a mathematical model of the rate of change in the temperature of cocoons inside a solar thermal device has been developed and proposed, taking into account the thermal characteristics of its enclosing elements, the arrival of solar radiation, and changes in ambient temperature. This mathematical model will enable the development of a solar thermal device for a similar purpose for the required temperatures inside the device.

Experimental study of RRC-PV modules under hot summer and cold winter climate

Building-integrated photovoltaic (BIPV) and building-integrated radiative cooling (BIRC) technologies are popular methods for utilizing renewable energy to address the energy crisis. However, limited facade areas of buildings restrict the amount of renewable energy that can be harvested. The design of reversible radiative cooling-photovoltaic (RRC-PV) module was introduced to address this issue. During the day, the PV side converts part of the incident solar radiation into electricity. At night, the module can be flipped and the RC side emits infrared radiation to the cold outer space, allowing for the free cooling energy exploitation.The performance of RRC-PV modules was tested in Shenzhen with hot summer and cold winter climate, by applying them as rooftop awnings and overhang shadings. Solar power generations were similar for both experiments, with daily electrical efficiencies in the range of 11.4–13.0 %. Meanwhile, the radiative cooling performance was better in the rooftop awning experiment, with an average nocturnal cooling power of 33.7–34.5 W/m2. In contrast, the average nocturnal cooling power reduced to 4.8–4.9 W/m2 in the overhang shading experiment. The results highlighted the importance of evaluating the radiative cooling potential by assessing the sky exposure of building facades.

Projected changes in incident solar radiation in Northern Hemisphere high-latitude areas

Projected changes in incident solar radiation in Northern Hemisphere high-latitude areas

A novel stomatal resistance equation for modeling heat and mass transfer of extensive vegetative roofs

The cooling potential of vegetated roofs depends on the stomatal resistance (rs), leaf area index, and other factors. Sailor (2008) and Tabares-Velasco and Srebric (2012) are among the most cited heat and mass transfer vegetative roof models. They include different equations to estimate rs, which show large differences, and significantly overestimate rs under certain conditions. Therefore, their models offer particular opportunities for improvement to reflect the actual vegetation cooling potential. This is necessary to predict the impact of vegetative roofs more accurately on the building energy performance and the urban heat island effect. The rs of both vegetative roof heat and mass transfer models have been developed based on studies with species that are not commonly planted on vegetative roofs. It was found that both models overestimate the rs under certain conditions that could turn into the underestimation of the transpiration rates and the cooling potential. Consequently, this paper aims to develop a novel equation for rs based on field measurements in a semiarid climate. The species tested were Glandularia berterii (C3), Selliera radicans (C3), Phyla reptans (C3), Aptenia cordifolia (CAM), Sedum palmeri (CAM), and Sedum spurium (CAM). A New Linear Model (NLM) was formulated to estimate rs. The regressors of NLM are minimum stomatal resistance (rs,min), incident solar radiation (Rsh), leaf area index (LAI), substrate volumetric water content (VWC), and vapor pressure difference (VPD). The results show that rs,min and Rsh reflect 64 % of rs; the species with higher cooling potential were Selliera radicans, Sedum palmeri, and Sedum spurium due to higher LAI and lower/moderate rs,min; and, the NLM showed a better agreement with the measured rs, correcting points where Sailor (2008) and Tabares-Velasco and Srebric (2012) equations significantly overestimated rs. Finally, it was demonstrated that the developed NLM better represents the stomatal behavior and distinguishes the responses between C3 and CAM species.

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 &gt;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.

A Stochastic Bayesian Artificial Intelligence Framework to Assess Climatological Water Balance under Missing Variables for Evapotranspiration Estimates

The sustainable use of water resources is of utmost importance given climatological changes and water scarcity, alongside the many socioeconomic factors that rely on clean water availability, such as food security. In this context, developing tools to minimize water waste in irrigation is paramount for sustainable food production. The evapotranspiration estimate is a tool to evaluate the water volume required to achieve optimal crop yield with the least amount of water waste. The Penman-Monteith equation is the gold standard for this task, despite it becoming inapplicable if any of its required climatological variables are missing. In this paper, we present a stochastic Bayesian framework to model the non-linear and non-stationary time series for the evapotranspiration estimate via Bayesian regression. We also leverage Bayesian networks and Bayesian inference to provide estimates for missing climatological data. Our obtained Bayesian regression equation achieves 0.087 mm · day−1 for the RMSE metric, compared to the expected time series, with wind speed and net incident solar radiation as the main components. Lastly, we show that the evapotranspiration time series, with missing climatological data inferred by the Bayesian network, achieves an RMSE metric ranging from 0.074 to 0.286 mm · day−1.

Ground-air temperature tracking from a geothermal climate-change observatory in South India

A geothermal climate-change observatory at Choutuppal (17.29 oN, 78.92°E) in south India was put into operation in July 2009 to study the inter-relationships between subsurface, ground-surface and surface-air temperature. The observatory is the first of its kind in a low latitude region with a significant monsoon season. Subsurface temperature measurements were obtained at different times of the year in two boreholes at the observatory drilled into granite to 21 m and 210 m depths respectively; a continuous record of shallow ground temperatures was acquired at six different depths to 1.2 m next to the deeper boreholes. Meteorological parameters recorded at the same site include surface air temperature (SAT), relative humidity, precipitation, solar radiation, wind speed and direction. Analysis of ground-air temperature data for the first five years (2009–2014) reveals the following. (i) Air temperature changes diffuse into the granitic subsurface with associated attenuation of high frequency components and phase lag characteristic of conductive heat transfer. (ii) Ground temperatures measured in the 1.2 m and 21 m deep holes track the diurnal and seasonal changes in SAT respectively, (iii) The ground is warmer than air on average; the difference is not constant but varies from −2.1 to +7.6 °C with a mean of 3.4 ± 1.8 (SD) oC, (iv) Ground-air temperature difference is influenced by incoming solar radiation and monsoon precipitation. On average, the ground warms by 2.5 °C for 100 Wm−2 increase in average incident solar radiation. The study highlights the importance of long-term monitoring to test ground-air temperature tracking critical to using borehole temperatures to infer climate change.

Dynamics and variability of microclimate in an unmanaged mountain forest after a bark beetle outbreak

Forest disturbances alter hydrological, energy, and microclimatic characteristics and their extents vary with the landscape characteristics of the terrain. We evaluated changes in evapotranspiration and latent heat rate in an unmanaged, central European mountain forest (Norway spruce) after a bark beetle-induced mortality of >75 % trees, and the spatial variability in microclimate during its natural regeneration. We observed that (1) the annual mean incident solar radiation to the treeless plots was 8.2 MJ m−2 day−1 (95 W m−2), being reduced by ∼45 % compared to its theoretical flux by high average cloudiness (70.6%) and short daily sunshine (4.3 hour day−1). The observed energy input to the forest floor beneath survived canopies (1.2 MJ m−2 day−1) was an order of magnitude lower than solar radiation to the canopy surface. (2) The mean annual evapotranspiration and the average annual latent heat rate decreased by 155 mm yr−1 and 385 MJ m−2 yr−1 (12 W m−2), respectively, after tree dieback. (3) The soil and air temperatures at individual plots correlated positively with the incident solar radiation and negatively with elevation. Mean soil and air temperatures exhibited similar lapse rates of 5.9–8.0 °C km−1 during the growing season (May-October). The energy input (positive relationship) and elevation (negative relationship) explained 74–83 % of the between-plot variability in mean soil and air temperatures and 51–77 % of their daily amplitudes during the growing season. (4) On sunny days, the observed soil and air temperatures were significantly lower (by ∼50 and 15 %, respectively) than ground surface temperature based on thermal satellite data (Landsat-8). The ground surface temperature explained 80–92 % of the observed variability in the soil and air temperatures. (5) The between-plot differences in daily soil and air temperatures and their amplitudes were from 24 to 70 % explained by solar radiation (positive correlation) and relative air humidity and wind speed (negative correlations).

Comparative study of energy balance in urban and forest areas in Central Amazonia

Data from two experimental sites in central Amazonia were used, one located in a forested region and the other in an urban region. The values of the radiation and energy balance components were measured at both sites. The observed components of the radiation balance in the forest, and urban areas were quite different. The city, the radiative (albedo and emissivity) and thermal (absorptivity) parameters of the surface produced greater reflection of solar radiation and emission of longwave radiation. Urban pollution reduced the incident solar radiation and increased the longwave radiation emitted by the atmosphere. The energy balance presented marked differences in the partition between sensible and latent heat flux between forest and city. In the forest, much of the available energy is converted into latent heat flux, due to the process of evapotranspiration. Whereas, in the city, energy is equally divided into sensible and latent heat fluxes.

Study on the Photothermal Performance of a "Thermal Shielding" Coating Using Tungsten Bronze as Functional Material for Asphalt Pavement.

Asphalt pavements absorb more than 90% of the incident solar radiation, which induces not only high-temperature degradation but also the urban heat island (UHI) effect. In this study, a novel nanoscale non-stoichiometric compound containing tungsten (MxWO3) was used for the first time to prepare thermal shielding coatings to reduce the temperature of pavements and mitigate the UHI effect. Coatings with good shielding characteristics were selected for outdoor thermal insulation tests to evaluate their properties. MxWO3 (M = K, Na, Cs) exhibited significant thermal shielding, especially CsxWO3. Outdoor thermal insulation tests were performed for the CsxWO3 coatings, and it was found that the greater the doping, the more significant the thermal shielding effect. Compared with untreated pavements, the surface-coated pavement exhibited significant cooling at 5 cm and 15 cm depth-wise, which reduced the overall pavement temperature by 1-2 °C, and the coating thickness affected the cooling effect.

Photovoltaics: Panacea to Africa Sustainable Development

African countries are falling behind in attaining the sustainable development goals. They are in dire need of electricity, which had been declared the essential tool to achieve most goals, to meet their population’s utilizable energy requirement. With renewables being globally adopted energy options to save the changing climate and preserve the environment and biodiversity, photovoltaic (PV) is advocated to remedy the energy deficiency for sustainable development. All over Africa indicates viability in PV energy owing to the incident global solar radiation (Gh). Nigeria being a case study shows awareness of PV energy, which has manifested in the attitude towards its penetration and the expected benefits. With the anticipated threat of climate change on PV performances, the projected incident Gh across Nigeria has shown two epochs which are yet viable for PV energy by the year 2100. Foreseeable challenges in the PV penetration and investments have been presented as wrongdoings and whistleblowing is advocated as the policy that will ensure the PV penetration for sustainable development.

UV-A and UV-B combined with photosynthetically active radiation change plant growth, antioxidant capacity and essential oil composition of Pelargonium graveolens

BackgroundThe different wavelengths of solar radiation incident on earth [herein: Photosynthetically Active Radiation (PAR) , Ultra Violet-A (UV-A) and Ultra Violet-B (UV-B)] and their spectral balance not only have an impact on plants’ growth, morphology and physiology, but also are important for the quality and quantity of plant secondary metabolites.Material and methodsIn an outdoor study we addressed the effects of PAR intensity and UV-A and UV-B on the growth, yield, phenolic and flavonoid content, antioxidant activity and essential oil composition of Pelargonium graveolens L’Hér. The experiment was performed with split plots in a randomized complete block design with three replications. During the growth, two PAR intensities (ambient PAR and reduced PAR) and four UV treatments (ambient UV, enhanced UV-A, enhanced UV-B and enhanced UVA + B) were applied.ResultsHigh PAR intensity decreased the length and width of leaf, the height of plant and fresh weight of aerial parts, and increased the dry weight of aerial parts. Enhanced UV-B irradiation was associated with reduced plant height, leaf expansion and fresh and dry weight of aerial parts. Interestingly, the negative effect of UV-B radiation on morphology and growth of plant was largely alleviated by high PAR intensity. The amount of total phenols and flavonoids, antioxidant activity and essential oil production of P. graveolens strongly increased with the increase of UV-B irradiation and PAR. On the other hand, UV-A radiation did not significantly influence total phenol and flavonoid content, antioxidant activity and essential oil composition. Moreover, the combination of high PAR intensity and UV-B led to further increases in total flavonoid content and antioxidant capacity. Both high PAR intensity and enhanced UV-B increased the percentage of geraniol in essential oil, leading to a slight reduction of citronellol/geraniol ratio which is a marker of quality for rose geranium essential oil.ConclusionsOverall, we conclude that UV-B irradiation was associated to reduction of plant growth and yield, while, the adverse effect of UV-B irradiation on the plant was mitigated by high PAR intensity. On the other hand, both high PAR and enhanced UV-B boosted the production of phenols, flavonoids and essential oil. Considering that the lower citronellol/geraniol ratio is the most important indicator for the economic value of rose geranium essential oil, reducing citronellol/geraniol ratio under enhanced UV-B radiation and/or high PAR is likely to be favorable.