Recent simulations and observations suggest that clouds interact with offshore wind farms, yet the physical mechanisms governing this interaction remain unclear. Here, we investigate these processes using large-eddy simulations of stratocumulus-topped boundary layers, systematically removing key forcings to isolate their physical effects. We consider three progressively simplified scenarios: (i) a fully developed marine stratocumulus boundary layer, (ii) a case without radiative forcing, which weakens both cloud-top longwave cooling and entrainment, and (iii) a clear-sky case in which both radiative forcing and liquid water are removed. The presence of cloud-top radiative cooling increases entrainment, leading to a less stable and deeper boundary layer that promotes vertical transport of momentum and energy toward the turbines. This leads to a faster wake recovery, with direct implications for the performance of neighboring wind farms. Overall, our results demonstrate that radiatively driven cloud-top entrainment is a key mechanism linking cloud dynamics to the performance of large wind farms and underscore the need for wind-energy models that explicitly represent interactions among wind farms, the atmosphere, and cloud processes.

Although 43% of Africa’s population (amounting to about 600 million people) have no access to electricity, Africa still has 40% of the global potential for solar power. In 2022, Africa produced 12 641 MW of electricity from solar energy, amounting to 1.2% of the global production of solar electricity. Of this, 11 516 MW was from solar photovoltaic (PV) cells. The massive deployment of solar PV technology in Africa to address energy access also poses a challenge of lack of skilled manpower in the sector. What factors drive and influence Africa’s solar sector manpower provision and in what ways are African stakeholders addressing this? Using mixed-method research, interviews (individual and focus group), and published literature and policy documents, we considered Nigeria, Ghana, and Uganda as our focus countries of study. Our study revealed (1) the complexity of the existing regulatory and governance frameworks and how they impact solar skills training, (2) the challenges of greening solar technical and vocational education and training in Africa, and (3) best practices in solar technical education delivery within the African continent that other stakeholders could learn from. We conclude by highlighting how addressing the identified challenges can lead Africa toward a more sustainable energy transition path.

In photosymbiotic giant clams, vertical columns of single-celled algae absorb sunlight that has first been forward scattered from a superficial layer of light-scattering cells called iridocytes. In principle, this arrangement could lead to a highly efficient system but it has been unclear how to calculate a productivity denominator to normalize the performance of the system. Inspired by the geometry observed in the clam, we have created an analytical model that calculates the idealized performance of a system with a geometry similar to the clam. In our model, photosynthesis-irradiance behavior obeys that of algal cells isolated from clams. Using a standard rate of eight photons of photosynthetically active radiation required to create one molecule of $\mathrm{O}$${}_2$, we find that a fixed geometry of the “light-dilution” strategy employed by the clams can reach a quantum efficiency of 43% relative to the solar resource in intense tropical sunlight. In comparing the performance of the model to published photosynthesis-irradiance relations of living clams, we have observed that the living system easily exceeds the performance of the static model. Therefore, we have next considered a model in which the system geometry changes dynamically to optimize the quantum efficiency as a function of the solar irradiance. In this scenario, with changes in irradiance typical of a sunny tropical day, the performance of the model was consistent with that of large mature living clams and had a quantum efficiency of 67%. We also show that a similar dynamic modulation of the clam-tissue geometry could plausibly occur in the living animals. We have considered the possibility that efficiency gains in the living system could also occur via further optimization of per-cell absorbance of multiply scattered light within the highly absorbing system. However, a numerical model of radiative transfer within clam tissue that captures realistic multiple scattering has not located efficiency gains relative to the simpler single-pass analytical model. Therefore, we infer that additional resource efficiency over the dynamic, large-clam-like model would require nontrivial organization among cells at small length scales. We also observe that boreal spruce forests coupled to atmospheric haze may realize the same scale-invariant scattering-and-absorbance strategy as the clams but at a different, larger, length scale. Given these results, our model may demonstrate the maximum realizable light-use efficiency of a large photosynthetic system relative to the solar resource. The general principles here also readily generalize to any photosynthetic cell type or organic photoconversion material and solar-irradiance regime. They could therefore provide inspiration both for engineering novel efficient photoconversion processes and materials and inform optimal land-use estimates for efficient industrial biomass production.

Selenium is experiencing renewed interest as a promising candidate for the wide bandgap photoabsorber in tandem solar cells. However, despite the potential of selenium-based tandems to surpass the theoretical efficiency limit of single-junction devices, such a device has never been demonstrated. In this study, we present the first monolithically integrated selenium/silicon tandem solar cell. Guided by device simulations, we investigate various carrier-selective contact materials and achieve encouraging results, including an open-circuit voltage of $V_{\mathrm{oc}}=1.68\mathrm{V}$ from suns-$V_{\mathrm{oc}}$ measurements. The high open-circuit voltage positions selenium/silicon tandem solar cells as serious contenders to the industrially dominant single-junction technologies. Furthermore, we quantify a pseudo fill factor of more than 80% using injection-level-dependent open-circuit voltage measurements, indicating that a significant fraction of the photovoltaic losses can be attributed to parasitic series resistance. This work provides valuable insights into the key challenges that need to be addressed for realizing higher efficiency selenium/silicon tandem solar cells.

Oxides containing metals or metalloids from the $p$ block of the periodic table (e.g., $\mathrm{In}$, $\mathrm{Sn}$, $\mathrm{Sb}$, $\mathrm{Pb}$, and $\mathrm{Bi}$) are of technological interest as transparent conductors and light absorbers for solar-energy conversion due to the tunability of their electronic conductivity and optical absorption. Comparatively, these oxides have found limited applications in hydrogen photoelectrolysis, primarily due to their high electronegativity, which impedes electron transfer for reducing protons into hydrogen. We have shown recently that inserting $s$-block cations into $p$-block metal oxides is effective at lowering electronegativities while affording further control of band gaps. Here, we explain the origins of this dual tunability by demonstrating the mediator role of $s$-block cations in modulating orbital hybridization while not contributing to frontier electronic states. From this result, we carry out a comprehensive computational study of 109 ternary oxides of $s$- and $p$-block metal elements as candidate photocatalysts for solar hydrogen generation. We down-select the most desirable materials using band gaps and band edges obtained from Hubbard-corrected density-functional theory, with Hubbard parameters computed entirely from first principles, evaluate the stability of these oxides in aqueous conditions, and characterize experimentally four of the remaining materials, synthesized with high phase uniformity, to validate and further develop the computational models. We thus propose nine oxide semiconductors, including $\mathrm{Cs}\mathrm{In}$${}_3$$\mathrm{O}$${}_5$, $\mathrm{Sr}$${}_2$$\mathrm{In}$${}_2$$\mathrm{O}$${}_5$, and $\mathrm{KSbO}$${}_2$, which, to the extent of our literature review, have not been previously considered as water-splitting photocatalysts.

Layered nickel-rich lithium transition-metal oxides (${\mathrm{Li}\mathrm{Ni}}_x{\mathrm{Mn}}_y{\mathrm{Co}}_{1-x-y}{\mathrm{O}}_2$; where x ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density $\mathrm{Li}$-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline $\mathrm{Ni}$-rich cathodes using operando x-ray methods in uncompromised machine-manufactured industrylike full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house operando x-ray studies of pilot-line-built ${\mathrm{Li}\mathrm{Ni}}_{0.8}{\mathrm{Mn}}_{0.1}{\mathrm{Co}}_{0.1}{\mathrm{O}}_2$–graphite A7 pouch cells, it is shown that their electrochemical-capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at a C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock-salt) phase that impedes the ${\mathrm{Li}}^{+}$ kinetics and increases cell impedance. Postmortem electron and x-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial $\mathrm{Li}$-ion cells with surface-modified single-crystalline $\mathrm{Ni}$-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline $\mathrm{Ni}$-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of $\mathrm{Li}$-ion cells and presents a methodology for achieving this.

Recent studies on the flow phenomena in stratified thermal-energy-storage (TES) systems have shown that heat conduction from the hot upper fluid layer through the vertical tank sidewall into the lower cold fluid layer leads to counterdirected wall jets adjacent to the vertical sidewalls. It was shown that these phenomena destroyed half of the total exergy content in less than a tenth of the storage time constant of a $2$-${\mathrm{m}}^3$ stratified TES system. This paper investigates short-term fluctuations of the wall jets since these fluctuations can potentially mix the hot and cold zones of the thermal stratification that are separated by the thermocline region. Using particle-image velocimetry measurements in two regions of a TES model experiment (near-wall region and far-field region) and analyzing the frequency content of the velocity fields revealed characteristic oscillations for different regions. In the near-wall region, observed fluctuations agreed well with an adjusted boundary layer frequency from the literature, showing that the wall jet is transitioning from laminar to turbulent flow. In the far-field region, the oscillations are related to the Brunt-Väisälä frequency. It is shown that the fluctuations from the boundaries of the thermocline region are most dominant and propagate into deeper regions of the thermocline. A comparison to data from the large-scale test facility for thermal energy storage in molten salt at the German Aerospace Center in Cologne showed good agreement. The consensus between the two experiments proves firstly that a small-scale model experiment with water as a storage liquid can be used to analyze the physical phenomena of large-scale molten salt storage facilities and secondly that these fluctuations are relevant for exergy destruction in real-scale TES.

The blending of hydrogen generated using clean energy into natural gas pipeline networks is proposed in order to utilize existing energy systems for their planned lifetimes while reducing their reliance on fossil fuels. We formulate a system of partial differential equations (PDEs) that govern the flow dynamics of mixtures of gases in pipeline networks under the influence of time-varying compressor and regulator control actions. The formulation is derived for general gas networks that can inject or withdraw arbitrary time-varying mixtures of gases into or from the network at arbitrarily specified nodes. The PDE formulation is discretized in space to form a nonlinear control system that is used to prove that homogeneous mixtures are well behaved and that heterogeneous mixtures may be ill behaved in the sense of monotone ordering of solutions. We use numerical simulations to compute interfaces in the parameter region of sinusoidal boundary conditions that delimit monotonic, periodic, and chaotic system responses. The interfaces suggest that any solution in the monotonic response region is not chaotic and will eventually approach a periodic orbit. The results are demonstrated using examples for a single pipeline and a small test network.

A forced oscillation event in power grids refers to a state where malfunctioning or abnormally operating equipment causes persisting periodic disturbances in the system. While power grids are designed to damp most perturbations during standard operations, some of them can excite normal modes of the system and cause significant energy transfers across the system, creating large oscillations thousands of miles away from the source. Localization of the source of such disturbances remains an outstanding challenge due to a limited knowledge of the system parameters outside of the zone of responsibility of system operators. Here, we propose a new method for locating the source of forced oscillations that addresses this challenge by performing a simultaneous dynamic model identification using a principled maximum likelihood approach. We illustrate the validity of the algorithm on a variety of examples where forcing leads to resonance conditions in the system dynamics. Our results establish that an accurate knowledge of system parameters is not required for a successful inference of the source and frequency of a forced oscillation. We anticipate that our method will find a broader application in general dynamical systems that can be well described by their linearized dynamics over short periods of time.

The development of a highly selective, membrane-based ion separation technology could significantly improve the sustainability and energy efficiency of water treatment technologies and emerging applications, such as electrochemical ${\mathrm{CO}}_2$ reduction, extraction of valuable metals from seawater, and battery recycling. In this work, we show through computational modeling that an electronic flashing ratchet mechanism can be used for high-precision ion separation. The suggested ratchet-based ion pumps utilize a unique feature of electronic ratchets, frequency-dependent current reversal, to drive ions with the same charge, but different diffusion coefficient, in opposite directions. The model shows that ions whose diffusion coefficients differ by as little as 1% can be separated by driving them in opposite directions with a velocity difference as high as 1.2 mm/s. Since the pumping properties of the ratchet are determined by a time-varying electric input signal, the proposed ion pumps could be instrumental in realizing an efficient, large-scale, and fit-for-purpose system for selective ion separation. Examples of ratchet-driven systems for lithium extraction from seawater, lead removal from drinking water, and water desalination are discussed and analyzed.

Emerging quantum technologies, such as quantum computations and precise sensing, provide new opportunities in the fields of science and engineering. While energy consumption is a major concern for modern industry and society, it is rarely taken into consideration for quantum technologies. Especially, the potential of quantum technologies directly powered by renewable energy has long been neglected. The initialization, manipulation, and readout of quantum systems generally require high-power-consuming equipment, such as a dilution refrigerator, a microwave-power amplifier, and a high-power laser. Here, we discover a direct utilization path for solar energy to steer the quantum states of negatively charged nitrogen-vacancy centers in diamond, which is one of the most promising solid-state quantum systems in the past decades. Following this method, we demonstrate sunlight-driven quantum magnetometry. The initialization and readout of this quantum magnetometry are achieved directly by sunlight, and conventional microwave manipulation can be removed by using a microwave-free scheme. By utilizing ambient energy directly, our method brings potential solutions to the energy-consumption issue of quantum technologies. This technique can be further extended to multiple quantum systems, and thus opens the door to environmentally sustainable quantum technologies and self-powered quantum sensing in the future.

Baroclinicity, which leads to height-dependent driving pressure gradients, occurs in various situations such as the flow transition between land and sea, and sloping terrain. It has been shown that baroclinicity modifies the structure of the atmospheric boundary layer. For example, negative shear baroclinicity creates additional turbulence at higher elevations, which might influence the energy entrainment into large wind farms. Here, we use large-eddy simulations to study the effect of baroclinicity-induced negative shear on the wind farm power production and energy entrainment into a large wind farm. In agreement with the literature, our simulations show that negative geostrophic wind shear significantly modifies the mean wind velocity in the atmospheric boundary layer. Specifically, for the cases considered in the study, the negative geostrophic shear causes a change in the mean velocity up to 2.3 m/s at hub height, which greatly alters the wind farm power production. Additionally, we demonstrate with an energy budget analysis that a wind farm does not necessarily benefit from the additional turbulence created by the negative geostrophic wind shear. The reason for this is that the baroclinicity-induced negative shear alters the height and strength of the low-level jet and creates an upward flux above the jet, limiting the energy entrainment into the wind farm. Our results show that wind resources are altered in the boundary layer due to negative geostrophic wind shear and should be considered in wind farm modeling and power forecasts.

${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ is a highly efficient photocatalyst for the overall water splitting reaction under UV irradiation. However, an atomic-level understanding of the active surface sites responsible for the oxidation and reduction reactions is still lacking. Here we present a unified experimental and computational account of the photocatalytic activity at the SrO and ${\mathrm{Ti}\mathrm{O}}_2$ terminations of aqueous solvated [001] ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$. Our experimental findings show that the overall water-splitting reaction proceeds on the ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ surface only when the two terminations are simultaneously exposed to water. Our simulations explain this, showing that the photogenerated hole-driven oxidation primarily occurs at SrO surfaces in a sequence of four single hole transfer reactions, while the ${\mathrm{Ti}\mathrm{O}}_2$ termination effects the crucial band alignment of the photocatalyst relative to the water oxidation potential. The present work elucidates the interdependence of the two chemical terminations of ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ surfaces, and has consequent implications for maximizing sustainable solar-driven water splitting.

Despite being capable of very fast charging, the pseudocapacitive properties of electrochemical capacitors still require significant research to attain energy densities comparable to that of batteries. Herein we discuss and theoretically benchmark the physics of quantized capacitance as a Faradaic charge storage mechanism, providing near “ideal” pseudocapacitive properties in the context of batterylike energy storage. Through careful electrolyte and reactant engineering, our physical analysis suggests that this less explored “pseudocapacitive battery” mechanism could provide power densities of approximately ${10}^4$ W/L combined with volumetric energy densities in the range of 100 Wh/L (or potentially greater). These benchmarks are arrived at though a comprehensive analysis of two-dimensional (2D) graphitic nanoparticles considering the impact of solvation, electron-electron interactions, and electron transfer processes. In general, our findings indicate that 2D nanomaterials exhibiting quantized capacitance provide a promising and underexplored physical axis within electrochemical capacitors towards realizing very fast charging at energy densities comparable to that of batteries.

The atmospheric concentration of methane has more than doubled since the start of the Industrial Revolution. Methane is the second-most-abundant greenhouse gas created by human activities and a major driver of climate change. This APS-Optica report provides a technical assessment of the current state of monitoring U.S. methane emissions from oil and gas operations, which accounts for roughly 30% of U.S. anthropogenic methane emissions. The report identifies current technological and policy gaps and makes recommendations for the federal government in three key areas: methane emissions detection, reliable and systematized data and models to support mitigation measures, and effective regulation.

The large variability of renewable power sources is a central challenge in the transition to a sustainable energy system. Electricity markets are central for the coordination of electric power generation. These markets rely evermore on short-term trading to facilitate the balancing of power generation and demand and to enable systems integration of small producers. Electricity prices in these spot markets show pronounced fluctuations, featuring extreme peaks as well as occasional negative prices. In this article, we analyze electricity price time series from the European Power Exchange market, in particular the hourly day-ahead, hourly intraday, and 15-min intraday market prices. We quantify the fluctuations, correlations, and extreme events and reveal different time scales in the dynamics of the market. The short-term fluctuations show remarkably different characteristics for time scales below and above 12 h. Fluctuations are strongly correlated and persistent below 12 h, which contributes to extreme price events and a strong multifractal behavior. On longer time scales, they get anticorrelated and price time series revert to their mean, witnessed by a stark decrease of the Hurst coefficient after 12 h. The long-term behavior is strongly influenced by the evolution of a large-scale weather pattern with a typical time scale of four days. We elucidate this dependence in detail using a classification into circulation weather types. The separation in time scales enables a superstatistical treatment, which confirms the characteristic time scale of four days, and motivates the use of $q$-Gaussian distributions as the best fit to the empiric distribution of electricity prices.