Solar Spectra Research Articles

Spectral Aerosol Optical Depth Retrievals by Ground-Based Fourier Transform Infrared Spectrometry

Aerosol Optical Depth (AOD) and the Ångström Exponent (AE) have been calculated in the near infrared (NIR) and short-wave infrared (SWIR) spectral regions over a period of one year (May 2019–May 2020) at the high-mountain Izaña Observatory (IZO) from Fourier Transform Infrared (FTIR) solar spectra. The high-resolution FTIR measurements were carried out coincidentally with Cimel CE318-T photometric observations in the framework of the Aerosol Robotic Network (AERONET). A spectral FTIR AOD was generated using two different approaches: by means of the selection of seven narrow FTIR micro-windows (centred at 1020.90, 1238.25, 1558.25, 1636.00, 2133.40, 2192.00, and 2314.20 nm) with negligible atmospheric gaseous absorption, and by using the CE318-AERONET’s response function in the near-coincident bands (1020 nm and 1640 nm) to degrade the high-resolution FTIR spectra. The FTIR system was absolutely calibrated by means of a continuous Langley–Plot analysis over the 1-year period. An important temporal drift of the calibration constant was observed as a result of the environmental exposure of the FTIR’s external optical mirrors (linear degradation rate up to 1.75% month−1). The cross-validation of AERONET-FTIR databases documents an excellent agreement between both AOD products, with mean AOD differences below 0.004 and root-mean-squared errors below 0.006. A rather similar agreement was also found between AERONET and FTIR convolved bands, corroborating the suitability of low-resolution sunphotometers to retrieve high-quality AOD data in the NIR and SWIR domains. In addition, these results demonstrate that the methodology developed here is suitable to be applied to other FTIR spectrometers, such as portable and low-resolution FTIR instruments with a potentially higher spatial coverage. The spectral AOD dependence for the seven FTIR micro-windows have been also examined, observing a spectrally flat AOD behaviour for mineral dust particles (the typical atmospheric aerosols presented at IZO). A mean AE value of 0.53 ± 0.08 for pure mineral dust in the 1020–2314 nm spectral range was retrieved in this paper. A subsequent cross-validation with the MOPSMAP (Modeled optical properties of ensembles of aerosol particles) package has ensured the reliability of the FTIR dataset, with AE values between 0.36 to 0.60 for a typical mineral dust content at IZO of 100 cm−3 and water-soluble particle (WASO) content ranging from 600 to 6000 cm−3. The new database generated in this study is believed to be the first long-term time series (1-year) of aerosol properties generated consistently in the NIR and SWIR ranges from ground-based FTIR spectrometry. As a consequence, the results presented here provide a very promising tool for the validation and subsequent improvement of satellite aerosol products as well as enhance the sensitivity to large particles of the existing databases, required to improve the estimation of the aerosols’ radiative effect on climate.

A methodology to simulate solar cells electrical response using optical-electrical mathematical models and real solar spectra

Herein we present a robust methodology to simulate the solar cells electrical response using optical-electrical finite-difference mathematical models and experimental data of solar spectrum. In this methodology, we suggest the use of mathematical PV models for three purposes: 1) to find the unknown solar cell electrical parameters from experimental J-V curves; 2) to simulate the response of solar cells under narrow-band incident radiation; and lastly 3) to simulate the short-circuit current response to experimental solar spectra. We used APE (Average Photon Energy) and SF (Spectral Factor) to assess the solar cells spectral response. We applied the method for data collected from the city of Belo Horizonte, Brazil. Both APE and SF analyses have shown that OPV presents relatively better spectral response than p-Si cells, because Belo Horizonte solar radiation is predominantly shifted to a blue-rich spectrum, compared to the AM1.5G. OPV cells show an annual average SF of 1.10, compared to the approximately 1.00 of p-Si cells. The methodology is presented in a workflow format, and we hope it will be useful for other researchers that are looking for procedures to simulate solar cells electrical response.

Size-Dependent and Enhanced Photovoltaic Performance of Solar Cells Based on Si Quantum Dots

Recently, extensive studies have focused on exploring a variety of silicon (Si) nanostructures among which Si quantum dots (Si QDs) may be applied in all Si tandem solar cells (TSCs) for the time to come. By virtue of its size tunability, the optical bandgap of Si QDs is capable of matching solar spectra in a broad range and thus improving spectral response. In the present work, size-controllable Si QDs are successfully obtained through the formation of Si QDs/SiC multilayers (MLs). According to the optical absorption measurement, the bandgap of Si QDs/SiC MLs shows a red shift to the region of long wavelength when the size of dots increases, well conforming to quantum confinement effect (QCE). Additionally, heterojunction solar cells (HSCs) based on Si QDs/SiC MLs of various sizes are presented and studied, which demonstrates the strong dependence of photovoltaic performance on the size of Si QDs. The measurement of external quantum efficiency (EQE) reveals the contribution of Si QDs to the response and absorption in the ultraviolet–visible (UV-Vis) light range. Furthermore, Si QDs/SiC MLs-based solar cell shows the best power conversion efficiency (PCE) of 10.15% by using nano-patterned Si light trapping substrates.

Intercomparison of low- and high-resolution infrared spectrometers for ground-based solar remote sensing measurements of total column concentrations of CO<sub>2</sub>, CH<sub>4</sub>, and CO

Abstract. The Total Carbon Column Observing Network (TCCON) is the baseline ground-based network of instruments that record solar absorption spectra from which accurate and precise column-averaged dry-air mole fractions of CO2 (XCO2), CH4 (XCH4), CO (XCO), and other gases are retrieved. The TCCON data have been widely used for carbon cycle science and validation of satellites measuring greenhouse gas concentrations globally. The number of stations in the network (currently about 25) is limited and has a very uneven geographical coverage: the stations in the Northern Hemisphere are distributed mostly in North America, Europe, and Japan, and only 20 % of the stations are located in the Southern Hemisphere, leaving gaps in the global coverage. A denser distribution of ground-based solar absorption measurements is needed to improve the representativeness of the measurement data for various atmospheric conditions (humid, dry, polluted, presence of aerosol), various surface conditions such as high albedo (>0.4) and very low albedo, and a larger latitudinal distribution. More stations in the Southern Hemisphere are also needed, but a further expansion of the network is limited by its costs and logistical requirements. For this reason, several groups are investigating supplemental portable low-cost instruments. The European Space Agency (ESA) funded campaign Fiducial Reference Measurements for Ground-Based Infrared Greenhouse Gas Observations (FRM4GHG) at the Sodankylä TCCON site in northern Finland aims to characterise the assessment of several low-cost portable instruments for precise solar absorption measurements of XCO2, XCH4, and XCO. The test instruments under investigation are three Fourier transform spectrometers (FTSs): a Bruker EM27/SUN, a Bruker IRcube, and a Bruker Vertex70, as well as a laser heterodyne spectroradiometer (LHR) developed by the UK Rutherford Appleton Laboratory. All four remote sensing instruments performed measurements simultaneously next to the reference TCCON instrument, a Bruker IFS 125HR, for a full year in 2017. The TCCON FTS was operated in its normal high-resolution mode (TCCON data set) and in a special low-resolution mode (HR125LR data set), similar to the portable spectrometers. The remote sensing measurements are complemented by regular AirCore launches performed from the same site. They provide in situ vertical profiles of the target gas concentrations as auxiliary reference data for the column retrievals, which are traceable to the WMO SI standards. The reference measurements performed with the Bruker IFS 125HR were found to be affected by non-linearity of the indium gallium arsenide (InGaAs) detector. Therefore, a non-linearity correction of the 125HR data was performed for the whole campaign period and compared with the test instruments and AirCore. The non-linearity-corrected data (TCCONmod data set) show a better match with the test instruments and AirCore data compared to the non-corrected reference data. The time series, the bias relative to the reference instrument and its scatter, and the seasonal and the day-to-day variations of the target gases are shown and discussed. The comparisons with the HR125LR data set gave a useful analysis of the resolution-dependent effects on the target gas retrieval. The solar zenith angle dependence of the retrievals is shown and discussed. The intercomparison results show that the LHR data have a large scatter and biases with a strong diurnal variation relative to the TCCON and other FTS instruments. The LHR is a new instrument under development, and these biases are currently being investigated and addressed. The campaign helped to characterise and identify instrumental biases and possibly retrieval biases, which are currently under investigation. Further improvements of the instrument are ongoing. The EM27/SUN, the IRcube, the modified Vertex70, and the HR125LR provided stable and precise measurements of the target gases during the campaign with quantified small biases. The bias dependence on the humidity along the measurement line of sight has been investigated and no dependence was found. These three portable low-resolution FTS instruments are suitable to be used for campaign deployment or long-term measurements from any site and offer the ability to complement the TCCON and expand the global coverage of ground-based reference measurements of the target gases.

A broadband digital receiving system with large dynamic range for solar radio observation

Solar radio spectra and their temporal evolution provide important clues to understand the energy release and electron acceleration process in the corona, and are commonly used to diagnose critical parameters such as the magnetic field strength. However, previous solar radio telescopes cannot provide high-quality data with complete frequency coverage. Aiming to develop a generalized solar radio observing system, in this study, we designed a digital receiving system that could capture solar radio bursts with a broad bandwidth and a large dynamic range. A dual-channel analog-to-digital converter (ADC) printed circuit board assembly (PCBA) with a sampling rate of 14-bit, 1.25 Giga samples per second (GSPS) cooperates with the field-programmable-gate-array (FPGA) chip XC7K410T in the design. This receiver could realize the real-time acquisition and preprocessing of high-speed data of up to 5 GB s−1, which ensures high time and spectral resolutions in observations. This receiver has been used in the solar radio spectrometer working in the frequency range of 35 to 40 GHz in Chashan Solar Observatory (CSO) established by Shandong University, and will be further developed and used in the solar radio interferometers. The full-power bandwidth of the PCBA in this receiving system could reach up to 1.5 GHz, and the performance parameters (DC–1.5 GHz) are obtained as follows: spur free dynamic range (SFDR) of 64.7–78.4 dB, signal-to-noise and distortion (SINAD) of 49.1–57.2 dB, and effective number of bits (ENOB) of > 7.86 bit. Based on the receiver that we designed, real-time solar microwave dynamic spectra have been acquired and more solar microwave bursts with fine spectral structures are hopeful to be detected in the coming solar maximum.

In the Trenches of the Solar–Stellar Connection. I. Ultraviolet and X-Ray Flux–Flux Correlations across the Activity Cycles of the Sun and Alpha Centauri AB

Abstract This study focuses on high-energy proxies of stellar magnetic activity over long-term starspot cycles of three low-activity Sun-like stars: α Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun itself. Data sets include: daily solar ultraviolet irradiance spectra and X-ray fluxes from the Solar Radiation and Climate Experiment, during recent sunspot Cycles 23 and 24; Interface Region Imaging Spectrograph long-slit stigmatic imaging of solar Mg ii h (2803 Å) and k (2796 Å) in quiet and active regions; and Hubble Space Telescope Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α Cen AB. Established stellar “flux–flux” relations, for example X-rays (T ∼ 1 MK) versus Mg ii (T ∼ 8000 K), showed increasing power-law slopes with increasing formation temperature, but these give way on the Sun to bent power laws, and surprising inversions in the activity hierarchy: Si iii is more “active” (steeper power laws) than N v, despite the latter’s four times higher formation temperature. The Sun’s flux–flux behavior, nevertheless, remarkably parallels its low-activity solar twin α Cen A. In contrast, the cooler, somewhat more active, K dwarf companion displays correlations more in line with the previous stellar paradigm. The new flux–flux relations offer a way to vet numerical spectral simulations and proxy-based irradiance models, and extrapolate solar global activity indices into regimes below or above the grasp of contemporary records, or to exoplanet hosts at the low end of the Sun-like activity ladder.

Helicity proxies from linear polarisation of solar active regions

Context. The α effect is believed to play a key role in the generation of the solar magnetic field. A fundamental test for its significance in the solar dynamo is to look for magnetic helicity of opposite signs both between the two hemispheres as well as between small and large scales. However, measuring magnetic helicity is compromised by the inability to fully infer the magnetic field vector from observations of solar spectra, caused by what is known as the π ambiguity of spectropolarimetric observations. Aims. We decompose linear polarisation into parity-even and parity-odd E and B polarisations, which are not affected by the π ambiguity. Furthermore, we study whether the correlations of spatial Fourier spectra of B and parity-even quantities such as E or temperature T are a robust proxy for magnetic helicity of solar magnetic fields. Methods. We analysed polarisation measurements of active regions observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics observatory. Theory predicts the magnetic helicity of active regions to have, statistically, opposite signs in the two hemispheres. We then computed the parity-odd EB and TB correlations and tested for a systematic preference of their sign based on the hemisphere of the active regions. Results. We find that: (i) EB and TB correlations are a reliable proxy for magnetic helicity, when computed from linear polarisation measurements away from spectral line cores; and (ii) E polarisation reverses its sign close to the line core. Our analysis reveals that Faraday rotation does not have a significant influence on the computed parity-odd correlations. Conclusions. The EB decomposition of linear polarisation appears to be a good proxy for magnetic helicity independent of the π ambiguity. This allows us to routinely infer magnetic helicity directly from polarisation measurements.

Detection of HCOOH, CH3OH, CO, HCN, and C2H6in Wildfire Plumes Transported Over Toronto Using Ground‐Based FTIR Measurements From 2002–2018

AbstractThe Fourier transform infrared (FTIR) spectrometer at the University of Toronto Atmospheric Observatory has been operational since 2002, collecting solar absorption spectra from which atmospheric trace gas profiles and columns are retrieved. The time series of total columns of CH3OH and HCOOH over Toronto are presented here for the first time, along with those for CO, HCN, and C2H6. Transport of wildfire plumes over the site results in enhanced columns of biomass burning species. Here we report the detection of biomass burning enhancement events between 2002 and 2018. Several simultaneous enhancements of CO, HCN, and C2H6were observed, and the measured columns were used to derive emission ratios and emission factors for HCN and C2H6for fire events in 2012, 2015, and 2017. From these events, which included plumes from both boreal and temperate forest fires, emission ratios with respect to CO were derived using CO lifetimes of 30 and 61 days. HCN emission ratios range between 0.0037 ± 0.0003 and 0.0057 ± 0.0008, while C2H6emission ratios vary from 0.00122 ± 0.0015 to 0.019 ± 0.001. Enhanced columns of CH3OH and HCOOH were also observed during the 2015 and 2017 events, and emission ratios were derived but have greater uncertainties due to shorter lifetimes and other sources for these gases. The FLEXPART, HYSPLIT, and GEOS‐Chem models were used for source attribution and traveltime estimation. GEOS‐Chem was run in the tagged CO simulation mode and successfully captured the CO enhancements from fires for the 2015 and 2017 events.

High-performance infrared thermal radiation suppression metamaterials enabling inhibited infrared emittance and decreased temperature simultaneously

Infrared thermal radiation suppression techniques are vital to the survival of various vehicles/targets, and low-emissivity materials are conventionally employed to reduce infrared radiant power of targets. However, infrared radiant power depends not only on infrared emittance but also heavily on the temperature according to Steven-Boltzmann law (P=εσT4). In this work, it is for the first time, a novel type of infrared stealth material based on tailoring radiative properties in an ultra-broadband ranging from 0.4 µm to 14 µm is proposed. A low emittance in atmosphere window (3–5 µm, 8–14 µm) is achieved to suppress infrared radiation, and a high emittance from 5 to 8 µm is obtained to reduce temperature via radiative cooling from metamaterial surface to the atmosphere. Meanwhile, low absorptance in the solar spectra (0.4–2.5 µm) can help to resist the solar heat. As a result, the infrared radiant power in the atmospheric window is prominently reduced benefiting from low emittance and decreased temperature. This work helps guide the design of more effective infrared stealth materials and paves the way for the applications of metamaterials in infrared stealth applications.

Impact of spectroscopic information on total column water vapor retrieval in the near-infrared spectral region

Water vapor is an important greenhouse gas. The atmospheric water vapor content is monitored by remote methods, which require accurate spectroscopic information about H2O absorption line parameters. The problems of accuracy of accounting the selective water vapor absorption in the simulation of atmospheric transfer of solar radiation are considered in this work. The atmospheric spectra are simulated using different versions of spectroscopic databases of H2O absorption line parameters and compared with the solar spectra measured by a ground-based Fourier transform spectrometer. The total column (TC) water vapor is retrieved from the solar spectra measured. The effect of the differences in absorption line parameters in modern spectroscopic databases on the results of retrieval of the TC water vapor from high-resolution spectra is estimated.

Photoelectron distribution on sunlit surface of the Moon: A formalism

An analytical formulation describing the characteristic energy distribution of photoelectrons over the sunlit regolith of the Moon has been presented. In deriving the distribution function, Fowler's approach based on fermionic lattice electrons for photoemission has been coupled with observed solar spectra, photoelectric quantum yield, and latitude dependent surface temperature. It is noticed that the dominant contribution in the photoelectron distribution function comes from extreme ultraviolet photons (3 eV–300 eV) of the solar spectra. The analysis also illustrates that the photoelectron distribution for the observed solar spectra is significantly different from the spectrum based on Planck's radiation law. In results, the photoelectron distribution is found to be a significant function of the lunar surface potential—the photoelectron distribution in the steady state considerably differs from that of the uncharged surface. In calculations, the variation in the photoelectron distribution function with the lunar latitude, quantum yield, and work function of the surface material has been parametrically analyzed, and it is found to be sensitive to the constituent parameters.

Strain-dependent electronic and optical properties of boron-phosphide and germanium-carbide hetero-bilayer: A first-principles study

Opto-electronic properties of boron phosphide–germanium carbide (BP/GeC), a new van der Walls hetero-bilayer (HBL) with all possible stacking patterns, are studied under the density functional theory originated first-principles. The dynamical and chemical stabilities of the hetero-bilayer are confirmed by phonon spectra and binding energy. Among the dynamically stable HBLs, HBL 1 has the lowest binding energy with the smallest interlayer spacing of about 3.442 Å. Both values and natures (indirect or direct) of the electronic band structure are highly responsive to the stacking patterns. We have found that HBL 1 is indirect, while HBL 2 and HBL 3 become a direct bandgap at the K high symmetry point. All HBLs show type-II band alignment. Both compressive and tensile biaxial strains on the electronic properties of HBLs have been considered. All the HBLs become a direct bandgap for the compressive strain at 4% and 6%. We have also presented the optical property calculations on the HBLs, namely, the complex dielectric function and absorption properties, showing unique optical properties with significant absorption (5 × 105 cm−1 in HBL 2) in the whole solar spectra compared with their comprising monolayers. Moreover, the strain-dependent optical absorption coefficients with varying photon wavelengths are calculated and the maximum value is attained to be about 6.5 × 105 cm−1 in HBL 2 at 4% compressive strain. Consequently, the optoelectronic properties we have explored in our proposed new hetero-bilayer systems can guide the experimental realization of the hetero-bilayers and effective use in the future photovoltaic applications.

Synthesis of CZTS without sulfurization process and its performance evaluation on n-Si substrate as ITO-free photovoltaic cell

Kesterite Cu2ZnSnS4 (CZTS) nanostructure is synthesized without the sulfurization process using a solvothermal technique. The induced effects in the optical properties of the fabricated film of this nanostructure are studied. As XRD analysis revealed the as-prepared film is polycrystalline in nature which indexed in the tetragonal Kesterite structure of the CZTS phase. Optical properties related to solar cell parameters, such as absorption coefficient, penetration depth, Urbach energy, and energy band gap are studied. The absorption coefficient of 1.5 × 105 cm−1 is observed at 1.5 eV, which matches the optimum bandgap of the solar spectra. The penetration depth as a function of photon energy for CZTS is shown. Al/Si/CZTS/Al heterojunction photovoltaic cell is fabricated. The as-prepared fabricated cell shows a low short circuit current (Isc) of 1.5 mA and a low fill factor (FF) of 27.2%. Upon the annealing at 350 °C in the N2 atmosphere without any sulfurization, the cell performance was much enhanced, where the ISC improved up to 8.9 mA and the FF up to 33.5%. In addition, dramatic improvement in the power conversion efficiency (η) was observed from 0.91% up to 6.72% for the as-prepared and annealed cell, respectively.

Energy saving analysis of a transparent radiative cooling film for buildings with roof glazing

• A transparent radiative cooling (T-RC) film has been proposed for building energy saving. • The film can be applied on glazing for reducing solar absorption and improving infrared emission. • A maximum indoor temperature reduction of 21.6 °C can be achieved with the T-RC film. • Annual air conditioning energy consumption can be reduced by 40.9–63.4%. A transparent radiative cooling (T-RC) film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window (8–13 μm) is applied on roof glazing for building energy saving. To evaluate the performance of the T-RC film, two identical model boxes (1.0 m × 0.6 m × 1.2 m, L × W × H ) were constructed and the inside air temperatures were measured in August in Ningbo, China. Results show that the maximum temperature difference between the two model boxes with and without the T-RC film was 21.6 °C during the experiment. A whole building model was built in EnergyPlus for the model box. With a good agreement achieved between the calculation results and the measured temperature data, the experimentally validated EnergyPlus model was then extended to an 815.1 m 2 exhibition building with roof glazing to analyze the annual air conditioning (AC) energy consumption. The results show that by incorporating both the T-RC film's cooling benefit in summer and heating penalty in winter, the annual AC energy consumption of the exhibition building can be reduced by 40.9–63.4%, varying with different climate conditions.

Martian Atmospheric Spectral Radiance Used as Model for Water Vapor Correction of Terrestrial Carbon Dioxide Absorption Profile Around 2 μm

Proper recovery of the depth and the shape of the carbon dioxide (CO2) absorption profile around 2 $\mu \text{m}$ on the solar radiance spectra of earth’s atmosphere calls for a correction due to water vapor (H2O) absorption at the adjacent wavelengths. This work proposes a method for such correction by comparison with the spectral radiance of Mars’ atmosphere where CO2 is the major component. It compares the radiance spectra derived from the images of the Airborne Visible Infrared Spectrometer—Next Generation (AVIRIS-NG) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) with the MODTRAN-simulated synthetic spectra and establishes that the truncation of CO2 absorption depth due to H2O absorption can be rectified by a proportionality constant. This method is easy and is expected to be suitable for all-purpose imaging spectrometers with medium spectral resolution.

Evaluating Radiometric Responsivity Degradations of TANSO-FTS/GOSAT Using Principal Component Analysis

AbstractThe short-wavelength infrared bands of the Thermal and Near-Infrared Sensor for Carbon Observation (TANSO)–Fourier transform spectrometer (FTS) instrument on board theGreenhouse Gas Observing Satellite(GOSAT) have degraded, which affects the retrieval of data for CO2and CH4. Herein, a new algorithm that uses principal component analysis (PCA) to evaluate these degradations from on-orbit solar calibration spectra has been developed. The datasets of the spectra were decomposed using PCA, and the temporal variations of their components were fitted using the appropriate functions. Our results show that PCA is effective to construct a suitable degradation model for TANSO-FTS. Comparisons of CO2data retrieved using the new degradation model with that using the ground-based FTS indicate that the new model improves the measurement biases.

Germanate glass layer containing Eu3+ ions and gold nanoparticles for enhanced silicon solar cell performance

Efficiency enhancement of solar cells is a goal of the photovoltaic industry, and different approaches can be used to achieve this objective. For example, the modification of the incident solar spectra using down shift spectral converters covering the solar cell represents an alternative that has been reported in the literature. In this case, there is an interplay between the gain in the efficiency due to the modification of the incident solar spectra and the losses attributed to absorption and reflection of these layers. In order to mitigate this problem, an immersion oil between the solar cell and the luminescent layer can be used to match the differences between the linear refractive indices. Besides, the luminescence of rare earths in the visible spectra can be enhanced by metallic nanoparticles. Employing these strategies, we present results of germanate glasses with rare earth ions and gold nanoparticles to enhance silicon solar cell performance when used as cover layer. Efficiency increase of about 18.42% is demonstrated for silicon solar cells covered with GeO2-PbO glasses doped with Eu3+ ions and containing spherical gold nanoparticles with average size around 8 nm.

Calculating the Energy Yield of Si-Based Solar Cells for Belgium and Vietnam Regions at Arbitrary Tilt and Orientation under Actual Weather Conditions

Predicting actual energy harvesting of a photovoltaic (PV) installation as per site-specific conditions is essential, from the customer’s point of view, to choose suitable PV technologies as well as orientations, since most PVs usually have been designed and evaluated under standard illumination. Hence, the tendency lives in the PV community to evaluate the performance on the energy yield and not purely on the efficiency. The major drawback is that weather conditions play an important role, and recording solar spectra in different orientations is an expensive and time-consuming business. We, therefore, present a model to calculate the daily, monthly and annual energy yield of Si-based PV installations included in commercial panels as well as tandem solar cells. This methodology will be used to evaluate the benefit of potential new technologies for domestic and building integrated applications. The first advantage of such a numerical model is that the orientation of solar panels and their properties can be easily varied without extra experiments. The second advantage is that this method can be transferred to other locations since it is based on a minimum of input parameters. In this paper, the energy yield of PV installations for different regions in Belgium and Vietnam will be calculated.

Spectrally robust series/parallel-connected triple-junction photovoltaic cells used for artificial photosynthesis

We have overcome two drawbacks involved in series-connected double-junction (S-2J) and triple-junction (S-3J) photovoltaic cells to compose monolithic modules of artificial photosynthesis consisting of directly connected photovoltaic cells and electrolyzers of the same size. One is current mismatching among the subcells under solar spectrum variation. The other is inefficient utilization of high-energy photons that can generate sufficiently high voltage to promote the target reaction, caused by consumption of two or three photons for extracting a single electron regardless of the photon energies. This arises from the predetermined operating voltage, contrasting to no restriction of the output voltage for solar cells combined with power conditioners. In a series/parallel-connected triple-junction (S/P-3J) photovoltaic cell, the series-connected middle and bottom cells are connected with the top cell in parallel. High-energy photons absorbed in the top cell are efficiently utilized because the photoexcited electrons are directly extracted. Although relative intensities of high-energy photons in the measured solar spectra changes remarkably, the top cell is free from the current matching restriction. On the other hand, current matching between the middle and bottom cells approximately holds, because solar spectrum in the relevant range changes only slightly. Consequently, the S/P-3J significantly improves solar-to-chemical conversion efficiency (ηSTC) and is more advantageous on overcast days owing to the spectral robustness. Using the state-of-the-art electrolyzers, ηSTC = 32%−26% of H2 production by water splitting is estimated on fine and overcast days. CO2 reduction to CO proceeds with ηSTC = 30%−25%. These values are higher than those for the S-2J by 3%−9%.

Fourier transform infrared time series of tropospheric HCN in eastern China: seasonality, interannual variability, and source attribution

Abstract. We analyzed seasonality and interannual variability of tropospheric hydrogen cyanide (HCN) columns in densely populated eastern China for the first time. The results were derived from solar absorption spectra recorded with a ground-based high-spectral-resolution Fourier transform infrared (FTIR) spectrometer in Hefei (31∘54′ N, 117∘10′ E) between 2015 and 2018. The tropospheric HCN columns over Hefei, China, showed significant seasonal variations with three monthly mean peaks throughout the year. The magnitude of the tropospheric HCN column peaked in May, September, and December. The tropospheric HCN column reached a maximum monthly mean of (9.8±0.78)×1015 molecules cm−2 in May and a minimum monthly mean of (7.16±0.75)×1015 molecules cm−2 in November. In most cases, the tropospheric HCN columns in Hefei (32∘ N) are higher than the FTIR observations in Ny-Ålesund (79∘ N), Kiruna (68∘ N), Bremen (53∘ N), Jungfraujoch (47∘ N), Toronto (44∘ N), Rikubetsu (43∘ N), Izana (28∘ N), Mauna Loa (20∘ N), La Reunion Maido (21∘ S), Lauder (45∘ S), and Arrival Heights (78∘ S) that are affiliated with the Network for Detection of Atmospheric Composition Change (NDACC). Enhancements of tropospheric HCN column were observed between September 2015 and July 2016 compared to the same period of measurements in other years. The magnitude of the enhancement ranges from 5 % to 46 % with an average of 22 %. Enhancement of tropospheric HCN (ΔHCN) is correlated with the concurrent enhancement of tropospheric CO (ΔCO), indicating that enhancements of tropospheric CO and HCN were due to the same sources. The GEOS-Chem tagged CO simulation, the global fire maps, and the potential source contribution function (PSCF) values calculated using back trajectories revealed that the seasonal maxima in May are largely due to the influence of biomass burning in Southeast Asia (SEAS) (41±13.1 %), Europe and boreal Asia (EUBA) (21±9.3 %), and Africa (AF) (22±4.7 %). The seasonal maxima in September are largely due to the influence of biomass burnings in EUBA (38±11.3 %), AF (26±6.7 %), SEAS (14±3.3 %), and North America (NA) (13.8±8.4 %). For the seasonal maxima in December, dominant contributions are from AF (36±7.1 %), EUBA (21±5.2 %), and NA (18.7±5.2 %). The tropospheric HCN enhancement between September 2015 and July 2016 at Hefei (32∘ N) was attributed to an elevated influence of biomass burnings in SEAS, EUBA, and Oceania (OCE) in this period. In particular, an elevated number of fires in OCE in the second half of 2015 dominated the tropospheric HCN enhancement between September and December 2015. An elevated number of fires in SEAS in the first half of 2016 dominated the tropospheric HCN enhancement between January and July 2016.