Solar Input Research Articles

Discriminant Analysis of the Solar Input on the Danube’s Discharge in the Lower Basin

This paper presents the extent to which the combination of extra-atmospheric and hydroclimatic factors can be deciphered to record their contribution to the evolution and forecasting of the Danube discharge (Q) in the lower basin. A combination of methods such as wavelet filtering and deep learning (DL) constitutes the basic method for discriminating the external factors (solar activity through Wolf numbers) that significantly contribute to the evolution and prediction of the lower Danube discharge. An ensemble of some of the most important factors, namely, those representing the atmospheric components, i.e., the Greenland-Balkan Oscillation Index (GBOI) and the North Atlantic Oscillation Index (NAOI); the hydroclimatic indicator, the Palmer Hydrological Drought Index (PHDI); and the extra-atmospheric factor, constitutes the set of predictors by means of which the predictand, Q, in the summer season, is estimated. The external factor has to be discriminated in the Schwabe and Hale spectra to make its convolutional contribution to the Q estimation in the lower Danube basin. An interesting finding is that adding two solar predictors (associated with the Schwabe and Hale cycles) to the terrestrial ones give a better estimation of the Danube discharge in summer, compared to using only terrestrial predictors. Based on the Nash–Sutcliffe (NS) index, a measure of performance given by the extreme learning machine (ELM), it is shown that, in association with certain terrestrial predictors, the contribution of the Hale cycle is more significant than the contribution of the Schwabe cycle to the estimation of the Danube discharge in the lower basin.

Solar‐Driven Redox Splitting of CO2 Using 3D‐Printed Hierarchically Channeled Ceria Structures

AbstractFuel produced from CO2 and H2O using solar energy can contribute to making aviation more sustainable. Particularly attractive is the thermochemical production pathway via a ceria‐based redox cycle, which uses the entire solar spectrum as the source of high‐temperature process heat to directly produce a syngas mixture suitable for synthetizing kerosene. However, its solar‐to‐fuel energy efficiency is hindered by the inadequate isotropic topology of the ceria porous structure, which fails to absorb the incident concentrated solar radiation within its entire volume. This study presents the design and 3D‐print of hierarchically channeled structures of pure ceria by direct ink writing (DIW) to enable volumetric radiative absorption while maintaining high effective densities required for maximizing the fuel yield. The complex interplay between radiative heat transfer and thermochemical reaction is investigated in a solar thermogravimetric analyzer with samples exposed to high‐flux irradiation, mimicking realistic operation of solar reactors. Channeled structures with a stepwise optical thickness achieve a higher and more uniform temperature profile compared to that of state‐of‐art isotropic structures, doubling the volume‐specific fuel yield for the same solar flux input. Thermomechanical stability of the ceria graded structures, DIW‐printed using a novel ink formulation with optimal rheological behavior, is validated by performing 100 consecutive redox cycles.

Topological Analysis and Solar Grid-Tied Integration of Level Building Network Based Extendable High Power Multilevel Converter

This paper presents a new solar multilevel converter (SMLC) with closed-loop control to integrate solar PV arrays with medium voltage 3.3 kV grid. This multilevel converter produces higher number of levels in the output voltage with less usage of semiconductor switches. This solar converter utilizes only ten switches and three PV sources with equal voltage to have seven levels in the output voltage. The main motive is to have minimum switches, which reduces the count of driver circuits for a power converter. Moreover, a reduced switch converter requires less space in terms of installing the power and auxiliary components. This solar power converter comprises a solar photovoltaic (SPV) array fed level building network (LBN) nested within the six switches connected in a rectangular arrangement. The converter has two PV sources at its upper and lower ends. This solar converter is also ideal for asymmetric configurations. Moreover, the increase in solar input power is possible with more count of the LBNs. The converter switching states and operating path demonstrate the working operation of the new solar PV system. A comparison of the proposed solar converter is made with existing multilevel topologies. The system is modeled and executed in closed-loop control to showcase its effectiveness for solar power conversion. The solar converter transfers the power in varying solar conditions successfully.

Boosting interfacial solar steam generation by three-dimensional bilayer cellulose aerogels

Interfacial solar steam generation (ISSG) provides a sustainable approach of clean water production through desalination and water purification. It is still needed to pursue a fast evaporation rate, high-quality freshwater production, and low-cost evaporators. Herein, a three-dimensional (3D) bilayer aerogel was fabricated using cellulose nanofiber (CNF) as a skeleton filled with polyvinyl alcohol phosphate ester (PVAP), and carbon nanotubes (CNT) as a light absorbing material in the top layer. The CNF/PVAP/CNT aerogel (CPC) had broadband light absorption ability and exhibited an ultrafast water transfer rate. The lower thermal conductivity of CPC effectively confined the convert heat in the top surface and minimized heat loss. Additionally, a large amount of intermediate water caused by water activation decreased the evaporation enthalpy. Under 1 sun irradiation, the CPC-3 (3.0 cm height of CPC) achieved a high evaporation rate of 4.02 kg m−2 h−1 with an energy conversion efficiency of 125.1%. The additional convective flow and environmental energy made CPC achieve an ultrahigh evaporation rate of 11.37 kg m−2 h−1, surpassing 673% of the solar input energy. More importantly, the continuous solar desalination and higher evaporation rate (10.70 kg m−2 h−1) in seawater revealed that CPC was a promising candidate for practical desalination. Outdoor cumulative evaporation was up to 73.2 kg m−2 d−1 in weak sunlight and lower temperature, which would meet the daily drinking water demands of 20 people. The excellent cost-effectiveness of 1.085 L h−1 $−1 presented its potential for a wide range of practical applications, such as solar desalination, wastewater treatment, and metal extractions.

Symmetry in Hillslope Steepness and Saprolite Thickness Between Hillslopes With Opposing Aspects

AbstractThe structure of the critical zone (CZ) is a product of feedbacks among hydrologic, climatic, biotic, and chemical processes. Past research within snow‐dominated systems has shown that aspect‐dependent solar radiation inputs can produce striking differences in vegetation composition, topography, and soil depth between opposing hillslopes. However, far fewer studies have evaluated the role of microclimates on CZ development within rain‐dominated systems, especially below the soil and into weathered bedrock. To address this need, we characterized the CZ of a north‐facing and south‐facing slope within a first‐order headwater catchment located in central coast California. We combined terrain analysis of vegetation distribution and topography with soil pit characterization, geophysical surveys and hydrologic measurements between slope‐aspects. We documented denser vegetation and higher shallow soil moisture on north facing slopes, which matched previously documented observations in snow‐dominated sites. However, average topographic gradients were 24° and saprolite thickness was approximately 6 m across both hillslopes, which did not match common observations from the literature that showed widespread asymmetry in snow‐dominated systems. These results suggest that dominant processes for CZ evolution are not necessarily transferable across regions. Thus, there is a continued need to expand CZ research, especially in rain‐dominated and water‐limited systems. Here, we present two non‐exclusive mechanistic hypotheses that may explain these unexpected similarities in slope and saprolite thickness between hillslopes with opposing aspects.

Parametric analysis for exergetic optimisation of a solar shell-and-tube latent heat storage unit for agricultural applications

Thermal energy storage by employing phase change materials (PCMs) has gained huge attention in many fields but despite great potential, a broader implementation in agricultural processes is yet to be achieved. Therefore, a standalone system for solar thermal energy storage using a Scheffler concentrator was developed for variety of agricultural applications. This study is aimed at the exergetic optimisation of the system by assessing the impact of various intensities of solar thermal input and flow rates on the exergetic performance and exergetic distribution inside an inversely arranged shell and tube heat storage unit. The experimental setup consisted of a cylindrical heat receiver, an inversely arranged shell and tube PCM tank and a flat plate resistive electric heater for solar irradiation simulation. The tank filled with 4 kg of RT70HC PCM was subject to various charging cycles under 2.5 LPM, 5 LPM, 7.5 LPM and 10 LPM flow rates and 450 W/m2, 575 W/m2, 700 W/m2 and 825 W/m2 of simulated solar intensities. The results indicate that increasing the mass flow rate enhances the heating uniformity within the tank but also leads to higher total exergy losses. However, the difference in the rate of exergy stored in the PCM was mostly negligible. Conversely, increasing the exergetic thermal input had a significantly positive impact on the rate of exergy stored in the PCM.. The exergetic efficiency of the PCM tank varied from 17.5% to 9.2%, with its peak value recorded at a 2.5 LPM flow rate and 1070 W of exergetic input.

Thermo-economic analysis and multi-objective optimization of solar aided pumped thermal electricity storage system

The concept of solar energy aided pumped thermal electricity storage (Solar-PTES) was proposed to improve the round-trip efficiency, as well as the solar energy utilization efficiency. The thermodynamic model was developed for such Solar-PTES system with the nominal electricity input of 5 MW and the nominal storage capacity of 6 equivalent hours. Taking the round-trip efficiency, energy density and levelized cost of storage as indicators for system performance, the effects of main design parameters were investigated, including that of main components performance parameters and cycle state parameters. The multi-objective optimization algorithm was applied for optimizing three performance metrics and the trade-off analysis was performed. The results indicates that the round-trip efficiency drops with the growing energy density, while the levelized cost of storage firstly decreases as the round-trip efficiency drops and then slightly rises. The minimum case of levelized cost of storage is selected for investigation. In that case, solar heat input is 5.05 MW and solar energy utilization efficiency of Solar-PTES system is 35.7 %. The nitrogen mass flow rate is 27.54 kg/s. The round-trip efficiency, energy density and levelized cost of storage for Solar-PTES system are 68.1 %, 16.63 kWh/m3 and 0.143 ± 0.023 $/kWh, respectively.

Low-temperature solar thermal-power systems for residential electricity supply under various seasonal and climate conditions

In this work, the performance of low-temperature (<100 °C) solar thermal-power systems to satisfy residential electric loads was analyzed. The solar-driven system was designed to provide a fraction of the total electricity demand in a complementary operation with the electric grid. The analysis was conducted for an coperation during seven days each season, considering real solar and climate variables and residential loads at different climate zones in the United States. The efficiency of the system strongly depends on the solar radiation profile and the ambient temperature. Maximum efficiencies of around 9.5% were obtained in the cold and marine climate zones due to the high solar energy input and low heat dissipation temperatures. In these two zones, the system could supply more than 98% of the electricity demand all seasons. At mixed-humid and hot-humid regions, the system supplied around 50% of the electric load in three of the four seasons, but it only supplies about 27% of the electricity needs in the mixed-humid zone during summer and hot-humid zone during winter. The effect of the solar collector field area and the tank volume was also analyzed. In general, larger solar fields positively impact the efficiency. However, the impact of the tank volume varies depending on the solar radiation profile and the load requirements. Average efficiencies for the seven-day operation can be larger than 6% with a proper selection of the solar collector area and tank volume for an Organic Rankine Cycle with a capacity of about 2.6 kW. Finally, an economic analysis of the system was conducted, and the results were compared with a solar PV + battery system of similar capacity. It is expected that the cost for the analyzed solar-thermal system decreases in the coming years with the increased interest on low temperature applications.

Empirical assessment of the role of the Sun in climate change using balanced multi-proxy solar records

The role of the Sun in climate change is hotly debated. Some studies suggest its impact is significant, while others suggest it is minimal. The Intergovernmental Panel on Climate Change (IPCC) supports the latter view and suggests that nearly 100% of the observed surface warming from 1850–1900 to 2020 is due to anthropogenic emissions. However, the IPCC’s conclusions are based solely on computer simulations made with global climate models (GCMs) forced with a total solar irradiance (TSI) record showing a low multi-decadal and secular variability. The same models also assume that the Sun affects the climate system only through radiative forcing – such as TSI – even though the climate could also be affected by other solar processes. In this paper I propose three “balanced” multi-proxy models of total solar activity (TSA) that consider all main solar proxies proposed in scientific literature. Their optimal signature on global and sea surface temperature records is assessed together with those produced by the anthropogenic and volcanic radiative forcing functions adopted by the CMIP6 GCMs. This is done by using a basic energy balance model calibrated with a differential multi-linear regression methodology, which allows the climate system to respond to the solar input differently than to radiative forcings alone, and to evaluate the climate’s characteristic time-response as well. The proposed methodology reproduces the results of the CMIP6 GCMs when their original forcing functions are applied under similar physical conditions, indicating that, in such a scenario, the likely range of the equilibrium climate sensitivity (ECS) could be 1.4 °C to 2.8 °C, with a mean of 2.1 °C (using the HadCRUT5 temperature record), which is compatible with the low-ECS CMIP6 GCM group. However, if the proposed solar records are used as TSA proxies and the climatic sensitivity to them is allowed to differ from the climatic sensitivity to radiative forcings, a much greater solar impact on climate change is found, along with a significantly reduced radiative effect. In this case, the ECS is found to be 0.9–1.8 °C, with a mean of around 1.3 °C. Lower ECS ranges (up to 20%) are found using HadSST4, HadCRUT4, and HadSST3. The result also suggests that at least about 80% of the solar influence on the climate may not be induced by TSI forcing alone, but rather by other Sun-climate processes (e.g., by a solar magnetic modulation of cosmic ray and other particle fluxes, and/or others), which must be thoroughly investigated and physically understood before trustworthy GCMs can be created. This result explains why empirical studies often found that the solar contribution to climate changes throughout the Holocene has been significant, whereas GCM-based studies, which only adopt radiative forcings, suggest that the Sun plays a relatively modest role.

Iceberg-inspired solar water generator for enhanced thermoelectricity–freshwater synergistic production

Interfacial solar steam generation has emerged as a promising eco-friendly and low-carbon emission technology to address the global water scarcity. So far, the majority of attention is paid to the improvement of the evaporation rate while the efficient vapor collection sector remains broadly unexploited. Herein, an inverted iceberg-inspired solar water generator (ISWG), consisting of a thermoelectric generator coated by a photothermal agent, a bilayer all-fiber nonwoven fabric and a passive cooling vapor condenser, is constructed. Inspired by the shape of an iceberg, the majority of the ISWG system is underneath the bulk water, leaving only the evaporation section floating on the water. This ISWG system not only avoids the vapor condensation induced solar input loss, but also transfers the heat to the surrounding bulk water, resulting in passive cooled and enhanced vapor collection. Moreover, a thermoelectric generator, which utilizes the temperature difference between the photothermal layer and evaporation layer, is sandwiched for thermal conduction in place of the traditional metal plate. The ISWG can achieve a high vapor collection rate of 1.02 kg m-2 h−1 and extra output electricity with a power of 0.47 W m−2 under sunlight with the ambient temperature at about 42 ℃. This work may pave the way for the development of an efficient solar-induced water-electricity co-generation system in tropical islands.

Investigating Potential Causes for the Prediction of Spurious Magnetopause Crossings at Geosynchronous Orbit in MHD Simulations

AbstractDuring intense geomagnetic storms, the magnetopause can move in as far as geosynchronous orbit, leaving the satellites in that orbit out in the magnetosheath. Spacecraft operators turn to numerical models to predict the response of the magnetopause to solar wind conditions, but the predictions of the models are not always accurate. This study investigates four storms with a magnetopause crossing by at least one GOES satellite, using four magnetohydrodynamic models at NASA's Community Coordinated Modeling Center to simulate the events, and analyzes the results to investigate the reasons for errors in the predictions. Two main reasons can explain most of the erroneous predictions. First, the solar wind input to the simulations often contains features measured near the L1 point that did not eventually arrive at Earth; incorrect predictions during such periods are due to the solar wind input rather than to the models themselves. Second, while the models do well when the primary driver of magnetopause motion is a variation in the solar wind density, they tend to overpredict or underpredict the integrated Birkeland currents and their effects during times of strong negative interplanetary magnetic field (IMF) Bz, leading to poorer prediction capability. Coupling the MHD codes to a ring current model, when such a coupling is available, generally will improve the predictions but will not always entirely correct them. More work is needed to fully characterize the response of each code under strong southward IMF conditions as it relates to prediction of magnetopause location.

Optical Modelling of a Fresnel Mirror Field for the Development of a Spectral Splitting CPVT Collector

Concentrating photovoltaic thermal (CPVT) collectors could contribute to supply renewable mid-temperature heat and electricity simultaneously, e.g. for applications in the industrial sector. Although CPVT can be still seen as a niche technology, it has a high potential for the future. One of the technological challenges of CPVT are the contradictory temperature requirements within the receiver, as the thermal part should provide temperatures as high as possible, while the electrical part consisting of conventional PV cells shows best efficiency at low temperature. Therefore, this research work focuses on the development of a CPVT collector with integrated Spectral Splitting, which is an approach to overcome the discrepancy of internal temperature demands. The basis for the developed CPVT collector is a Fresnel mirror field consisting of 28 mirror stripes and providing a gross area of 13.34 m². The presented paper describes the optical modelling of this Fresnel mirror field, which was necessary before working on the receiver design in order to yield the dimensions of expected focus image on the receiver input plane. Furthermore, the resulting concentrated irradiance is a major parameter for calculating thermal and electrical efficiencies of the system, thus, this was another target for the modelling work. The optical model for the Fresnel mirror field was developed in MATLAB™ in a general way, as the number of mirrors and all geometric parameters are set as input variables. This makes it possible to use it not only for the available mirror field, but also for the design and optimisation of any other Fresnel mirror system. The model calculates the single mirror angles depending on the sun position and considers all four mechanisms of internal shading that are typical for such concentrators. Furthermore, the cosine losses in transversal and longitudinal direction are calculated. The results of the modelling are satisfying, as the experimental validation on the present mirror field was successful. The model provides comprehensive outcomes like the geometric efficiency depending on the sun´s elevation angle, the mean geometric efficiency at varying geometric parameters, local and mean irradiance in the receiver input plane, as well as mean irradiance and total solar input depending on time.

Advanced Design of High‐Performance Moist‐Electric Generators

AbstractIn recent years, a rapidly growing demand is witnessed for energy‐conversion technologies. The moisture‐electric generators (MEGs) which can generate electricity without need of mechanical, thermal, or solar energy input have great potential in meeting the demand. Compared with carbon materials, hydrogels and other materials like vitrimers have been rapidly developed for MEGs over the last two years, leading to significant breakthrough in MEG's performance such as much wider working range of humidity, remarkably higher output, and longer duration. Designs of MEGs have also been advanced with elaborated consideration of active material and device structures. Though some reviews present the recent development from their unique aspects, reviews in the view of advanced design for MEGs are few. Here, the newest development is systematically reviewed in the field of MEG devices, reflecting advanced design for moist‐induced power generating systems. First, background and mechanisms are briefed, and then most important considerations for active material design are illustrated together with solutions to the shortcomings of materials. Next, strategies are summarized to obtain MEG devices with high output performance by taking the whole power generating process into consideration, after which, the design thought for future MEGs is proposed. Finally, some perspectives are put forward.

Tracing the Snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics

Abstract. The instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth's history, most notably because of the slowly increasing solar luminosity. Quantifying this critical CO2 concentration is not only interesting from a climate dynamics perspective but also constitutes an important prerequisite for understanding past Snowball Earth episodes, as well as the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth's entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons and the identification of secular changes difficult. Here, we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth's history in one consistent model framework. We find that the critical CO2 concentration decreased more or less logarithmically with increasing solar luminosity until about 1 billion years ago but dropped faster in more recent times. Furthermore, there was a fundamental shift in the dynamics of the critical state about 1.2 billion years ago (unrelated to the downturn in critical CO2 values), driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance: for critical states at low solar luminosities, the ice line lies in the Ferrel cell, stabilised by the poleward winds despite moderate meridional temperature gradients under strong greenhouse warming. For critical states at high solar luminosities, on the other hand, the ice line rests at the Hadley cell boundary, stabilised against the equatorward winds by steep meridional temperature gradients resulting from the increased solar energy input at lower latitudes and stronger Ekman transport in the ocean.

Energy analysis of novel hybrid solar and natural gas combined cycle plants

The integration of renewable energy sources into standard energy systems is a fundamental step in the energy transition. The purpose of the paper is to investigate the integration of solar energy into a traditional natural gas-fired combined cycle power plant, while also evaluating the impact of intercooling, in terms of energy efficiency and CO2 emissions. Solar energy is integrated into the gas turbine topping cycle through parabolic trough collectors, with the aim of preheating the air leaving the compressor. Two additional configurations have been compared, based on one- and two-stage intercooled compression. The goal is to find the optimal hybrid configuration. To this purpose, a thermodynamic analysis of the overall plant has been performed, and a numerical model has been specifically developed to simulate the solar field. The model has been integrated into Thermoflex™ to simulate the overall combined cycle. Solar-to-electric conversion efficiency, based on solar energy input alone, has received specific attention to make relevant comparisons with conventional concentrated solar based power plants. Furthermore, net electric efficiency, electrical power share due to solar energy integration, natural gas savings, and CO2 emissions have been investigated. The solar-to-electric conversion efficiency has been shown to increase with the compression ratio while the net electric efficiency decreases. To achieve a trade-off between the need for high net electric efficiency and high solar integration, an optimization based on the Pareto front was carried out. The selected configuration consists of one intercooling stage and a compression ratio of 17.9, resulting in a solar conversion efficiency of 33%, which is much better than traditional solar-only power plants. Additionally, the net electric efficiency is 69.5%. To test this configuration under actual operating conditions, a one-year simulation was carried out in two cities with different climates: Messina and Torino. An average annual solar-to-electric efficiency of around 32% can be achieved in both cities, with natural gas savings of 7.7% and 5.8% per year for Messina and Torino, respectively.

A Review of Hybrid Floating Solar Plant Designs

Abstract: The demand for power will have doubled by the year 2050. Solar energy currently meets a small percentage of the world's demand, despite its enormous potential as an eco-friendly method for producing electricity. Utilizing land resources sustainably is one of the challenges. As an alternative, floating PV (FPV) plants on bodies of water, such as a dam, reservoir, canal, etc., are gaining popularity worldwide. This project aims to design a hybrid floating solar system that can produce renewable energy in light of the above. Among the hybrid technologies addressed are FPV &amp; hydro systems, FPV &amp; pumped hydro, FPV &amp; wave energy converter, FPV &amp; solar tree, FPV &amp; tracking, FPV &amp; conventional power, and FPV &amp; hydrogen. The review also summarises the main benefits and drawbacks of hybrid floating solar PV (FPV) systems. The hybrid FPV technologies with hydro and solar energy input were some of the most promising ones for producing power efficiently. The important ideas in this paper advance understanding and could serve as a catalyst for the creation of environmentally friendly, sustainable hybrid floating installations

The predictive power of magnetospheric models for estimating ground magnetic field variation in the United Kingdom

Space weather events can have damaging effects on ground-based infrastructure. Geomagnetically induced currents (GIC) caused by rapid magnetic field fluctuations during geomagnetic storms can negatively affect power networks, railways as well as navigation systems. To reduce such negative impacts, good forecasting capability is essential. In this study we assess the performance of contemporary magnetohydrodynamic (MHD) models in predicting the external-only ground magnetic field perturbations at three United Kingdom observatories during two severe space weather events: September 2017 and March 2015. Simulated magnetic data were acquired via Community Coordinated Modeling Center (CCMC), using the following models: Space Weather Modeling Framework (SWMF), Open Geospace General Circulation Model (Open GGCM) and Lyon–Fedder–Mobarry (LFM) combined with the Rice Convection Model (RCM). All simulations use spacecraft measurements at L1 as their solar wind input in calculating ground perturbations. Qualitative and quantitative comparison between measured and modelled values suggest that the performance of MHD models vary with latitude, the magnetic component and the characteristics of the storm analysed. Most models tend to exaggerate the magnitude of disturbances at lower latitudes but better capture the fluctuations at the highest latitude. For the two storms investigated, the addition of RCM tends to result in overestimation of the amplitude of ground perturbations. The observed data-model discrepancies most likely arise due to the many approximations required in MHD modelling, such as simplified solar wind input or shift in location of the electrojets in the simulated magnetospheric and ionospheric currents. It was found that no model performs consistently better than any other, implying that each simulation forecasts different aspects of ground perturbations with varying level of accuracy. Ultimately, the decision of which model is most suitable depends on specific needs of the potential end user.

Energetics of Shock-triggered Supersubstorms (SML < −2500 nT)

The solar wind energy input and dissipation in the magnetospheric–ionospheric systems of 17 supersubstorms (SSSs: SML < −2500 nT) triggered by interplanetary shocks during solar cycles 23 and 24 are studied in detail. The SSS events had durations ranging from ∼42 minutes to ∼6 hr, and SML intensities ranging from −2522 nT to −4143 nT. Shock compression greatly strengthens the upstream interplanetary magnetic field southward component (B s), and thus, through magnetic reconnection at the Earth’s dayside magnetopause, greatly enhances the solar wind energy input into the magnetosphere and ionosphere during the SSS events studied. The additional solar wind magnetic reconnection energy input supplements the ∼1.5 hr precursor (growth-phase) energy input and both supply the necessary energy for the high-intensity, long-duration SSS events. Some of the solar wind energy is immediately deposited in the magnetosphere/ionosphere system, and some is stored in the magnetosphere/magnetotail system. During the SSS events, the major part of the solar wind input energy is dissipated into Joule heating (∼30%), with substantially less energy dissipation in auroral precipitation (∼3%) and ring current energy (∼2%). The remainder of the solar wind energy input is probably lost down the magnetotail. It is found that during the SSS events, the dayside Joule heating is comparable to that of the nightside Joule heating, giving a picture of the global energy dissipation in the magnetospheric/ionospheric system, not simply a nightside-sector substorm effect. Several cases are shown where an SSS is the only substorm that occurs during a magnetic storm, essentially equating the two phenomena for these cases.

Interaction between the turbulent solar wind and a planetary magnetosphere: A 2D comet example

Context. Using the newly developed code Menura, we present the first global picture of the interaction between a turbulent solar wind and a planetary obstacle in our solar system, namely a comet. Aims. This first publication sheds light on the macroscopic effect of the upstream solar wind turbulence on the induced magnetosphere of a comet. Methods. Using a hybrid particle-in-cell simulation code, we modelled a medium activity comet using turbulent and laminar solar wind input, for a direct comparison between the two regimes. Results. We show how the turbulent characteristics of the solar wind lead to a smaller obstacle size. We then present how the upstream turbulent structures, traced by the perpendicular magnetic field fluctuations absent in the laminar case, self-consistently drape and pile up around the denser inner coma, forming intense plasmoids downstream of the nucleus, pulling away dense cometary ion bubbles. This pseudo-periodic erosion phenomenon re-channels the global cometary ion escape; as a result, the innermost coma is found to be on average 45% less dense in the turbulent case than predicted by simulating a laminar upstream flow.

Effects of Solar Resource Sampling Rate and Averaging Interval on Hourly Modeling Errors

Solar energy modeling errors due to time-averaged hourly inputs are significant where solar resource variability and inverter loading ratio are both high. However, predictions of photovoltaic (PV) system performance are most frequently made with hourly solar resource inputs, typically computed from satellite data obtained every 15 or 30 min. Therefore, we studied the effects of solar resource sampling rate and time-averaging interval on hourly modeling errors by using high-frequency measurements from eight different locations across the United States. When we selected minute-average measurements at various sampling rates and averaged them to hourly data, we observed increasing modeling errors for sampling rates 30 min or shorter. At a 30-min sampling rate averaged hourly, we observed an error that was 50% of 1-min samples averaged hourly. As sampling rate approached 60 min, modeling errors decreased, partially canceling out due to the randomness of the low-frequency sampled data. We examined PV systems with dc–ac ratios <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 1.3 and observed that clipping errors dominated modeling errors from other sources like transposition to plane-of-array irradiance at sites with greater solar variability. Based on our analysis, we recommend that an hourly modeling correction be applied whenever hourly inputs are used, especially at sites with high solar variability and dc–ac ratios greater than one.