Traditionally, for the planning and assessment of solar energy systems, the amount of solar radiation (sunlight) incident on the Earth’s surface is assumed to be constant over the years. However, with changing climate and air pollution levels, solar resources may no longer be stable over time and undergo substantial decadal changes. Observational records covering the past decades confirm long-term changes in this quantity. Here we examine how the latest generation of climate models used for the 5th IPCC report projects potential changes in surface solar radiation over the coming decades, and how this may affect, in combination with the expected greenhouse warming, solar power output from photovoltaic (PV) systems. For this purpose, projections up to the mid 21st century from 39 state of the art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analysed globally and for selected key regions with major solar power production capacity. The large model ensemble allows to assess the degree of consistency of their projections. Models are largely consistent in the sign of the projected changes in solar radiation under cloud-free conditions as well as surface temperatures over most of the globe, while still reasonably consistent over a considerable part of the globe in the sign of changes in cloudiness and associated changes in solar radiation. A first order estimate of the impact of solar radiation and temperature changes on energy yields of PV systems under the RPC8.5 scenario indicates statistically significant decreases in PV outputs in large parts of the world, but notable exceptions with positive trends in large parts of Europe, South-East of North America and the South-East of China. Projected changes between 2006 and 2049 under the RCP8.5 scenario overall are on the order of 1%/decade for horizontal planes, but may be larger for tilted or tracked planes as well as on shorter (decadal) timescales

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SUMMARY We introduce a new method for the numerical integration over curved surfaces and volumes defined by a level set function. The method is based on the solution of a small linear system based on a simplified variant of the moment‐fitting equations. Numerical experiments suggest that the accuracy of the resulting quadrature rules exceeds the accuracy of traditional methods by orders of magnitude. Using moments up to an order of p, the measured experimental orders of convergence exceed hp. Consequently, their construction is very efficient because only coarse computational grids are required. The conceptual simplicity allows for the application on very general grid types, which is demonstrated by numerical experiments on quadrilateral, triangular and hexahedral grids. Copyright © 2013 John Wiley & Sons, Ltd.

We present a higher order discretization scheme for the compressible Euler and Navier-Stokes equations with immersed boundaries. Our approach makes use of a discontinuous Galerkin discretization in a domain that is implicitly defined by means of a level set function. The zero iso-contour of this level set function is considered as an additional domain boundary where we weakly enforce boundary conditions in the same manner as in boundary-fitted cells. In order to retain the full order of convergence of the scheme, it is crucial to perform volume and surface integrals in boundary cells with high accuracy. This is achieved using a linear moment-fitting strategy. Moreover, we apply a non-intrusive cell-agglomeration technique that averts problems with very small and ill-shaped cuts. The robustness, accuracy, and convergence properties of the scheme are assessed in several two-dimensional test cases for the steady compressible Euler and Navier-Stokes equations. Approximation orders range from 0 to 4, even though the approach directly generalizes to even higher orders. In all test cases with a sufficiently smooth solution, the experimental order of convergence matches the expected rate for discontinuous Galerkin schemes. 4 B. MÜLLER ET AL.intersected by the immersed boundary, which allows us to avoid integration sub-cells and, as a result, to extend the scheme to higher approximation orders. Second, we do not require any reformulation of the boundary conditions, which allows us to evade the limitation to adiabatic slip walls. Finally, we have extended the approach to the compressible Navier-Stokes equations. State of the artMethods in the spirit of the original IBM by Peskin [1] have drawn much interest ever since their introduction in 1972 [2]. Within the present work, the term IBM is used in the general sense of methods making use of computational domains that do not conform with the problem domain, hence separating the aspects of discretization and geometry representation to a large extent. This idea is the core of many modern developments in the context of the finite element method such as the extended finite element method (XFEM) [5], the finite cell method [6], Nitsche-type methods [7], and even the finite difference method [8]. In the following, we will focus on numerical methods of the finite element type that are able to deliver higher order convergence rates in the presence of curved immersed problem geometries.First efforts in this direction using XFEM/Nitsche-type approaches have been presented in [9,10] in the context of linear elasticity and in [11] in the context of Stokes flow. Both approaches rely on planar surface triangulations for the numerical integration of the weak forms, which renders the introduction of quadrature sub-cells inevitable if higher order convergence of the scheme is desired. An interesting alternative has been proposed in [12] where special enrichment functions for common features such as circular sections or corners are introduced. Unfortunately, the presented scheme appears to be...

During the past years, much research work has been focused on efficiently harvesting solar energy with black silicon (b-Si). However, semiconductor Si can only utilize solar energy with wavelength smaller than λ = 1110 nm (bandgap E g = 1.12 eV) for photovoltaic applications or photoelectrochemical conversions. Light with wavelength beyond the band edge (above λ = 1110 nm) cannot be used. Here, we prepared highly conductive b-Si without an apparent optical bandgap by a reactive ion etching process, which can largely absorb light with a wide range wavelength and even far into the near-infrared region (∼2500 nm). The optimized b-Si with surface texture shows the specular reflection rate lower than 0.1% and the average total reflection (specular reflectance + diffuse reflectance) is about 1.1%. Additionally, we briefly introduce the mechanism and reflection principle of surface nanostructured b-Si. By using b-Si structured material, we successfully convert the solar energy to electric power via photo-thermoelectric conversion, especially solar energy exceeding 1110 nm wavelength can also be efficiently used. The excellent light trapping of sunlight shows great potential for photothermal applications, such as photothermal imaging, seawater desalination, and further applications.