Sanderse B.,Energy Research Center of the Netherlands
Journal of Computational Physics | Year: 2013
Energy-conserving methods have recently gained popularity for the spatial discretization of the incompressible Navier-Stokes equations. In this paper implicit Runge-Kutta methods are investigated which keep this property when integrating in time. Firstly, a number of energy-conserving Runge-Kutta methods based on Gauss, Radau and Lobatto quadrature are constructed. These methods are suitable for convection-dominated problems (such as turbulent flows), because they do not introduce artificial diffusion and are stable for any time step. Secondly, to obtain robust time-integration methods that work also for stiff problems, the energy-conserving methods are extended to a new class of additive Runge-Kutta methods, which combine energy conservation with L-stability. In this class, the Radau IIA/B method has the best properties. Results for a number of test cases on two-stage methods indicate that for pure convection problems the additive Radau IIA/B method is competitive with the Gauss methods. However, for stiff problems, such as convectiondominated flows with thin boundary layers, both the higher order Gauss and Radau IIA/B method suffer from order reduction. Overall, the Gauss methods are the preferred method for energy-conserving time integration of the incompressible Navier-Stokes equations. © 2012 Elsevier Inc.
Coletti G.,Energy Research Center of the Netherlands
Progress in Photovoltaics: Research and Applications | Year: 2013
For the first time, the sensitivity to impurities of the solar cell conversion efficiency is reported for a state-of-the-art (i.e., 18%) and advanced device architecture (i.e., 23%). The data are based on the experimental results obtained in the CrystalClear project for the state-of-the-art cell process and extrapolated to a device with excellent front and rear surface passivation. Both device structures are not assumed to work in low injection level as several studies assumed before, but real operating conditions are considered. This is a fundamental difference with the past and required for modeling future high efficiency devices. The impurity with highest impact is Ti, followed by Cu, Cr, Ni and Fe, which form together a group two order of magnitude less sensitive than the former. In high efficiency devices, a large reduction of the impurity impact is visible for impurities with large capture cross-section ratio like Fe, which reduces its relative difference in comparison with, for example, Cr, which has a small capture cross-section ratio. In general, advanced devices will be more sensitive to the impurity content than the state-of-the-art cell design. This effect is partly compensated by a reduction of the substrate thickness. The impurity sensitivity as function of the substrate thickness is reported. Copyright © 2012 John Wiley & Sons, Ltd. For the first time, the sensitivity to impurities of the solar cell conversion efficiency is reported for a state-of-the-art (i.e., 18%) and advanced device architecture (i.e., 23%). Both device structures are not assumed to work in low injection level. This is a fundamental difference with the past and required for modeling future high efficiency devices. In general, advanced devices will be more sensitive to the impurity content than the state-of-the-art cell design. The effect of the substrate thickness is also taken in consideration in the study. Copyright © 2012 John Wiley & Sons, Ltd.
Boonekamp P.G.M.,Energy Research Center of the Netherlands
Energy Efficiency | Year: 2011
The Energy Service Directive (ESD) of the European Union (EU) stipulates that member states realize 9% energy savings for the period 2008-2016. A harmonized calculation approach, consisting of a combination of top-down and bottom-up methods, will be developed to determine the savings of energy efficiency improvement measures. However, it is unclear which part of all realized energy savings is eligible in meeting the ESD target. One can argue that not all savings, especially the autonomous efficiency gains, should be accounted for, but only savings due to (new) policy. An analysis is made of the way the methods can be applied, how baseline choices define the savings and whether these represent policy-induced savings. It is shown that the given target could be met with total energy savings that equal 1.0% of ESD energy use per year, hardly more than realized at present. With other choices, the target is met with total savings of 1.6% per year. The savings found are made comparable with the 2.4% yearly savings derived from the 20% savings target for 2020 formulated by the EU. Given the large gap between ESD savings and the savings target, it is concluded that the methods and baselines used should be chosen such that the ESD target leads to realized savings after 2008 at the upper side of the margin. © 2010 Springer Science+Business Media B.V.
Van Lare M.,FOM Institute for Atomic and Molecular Physics |
Lenzmann F.,Energy Research Center of the Netherlands |
Polman A.,FOM Institute for Atomic and Molecular Physics
Optics Express | Year: 2013
We experimentally compare the light trapping efficiency of dielectric and metallic backscattering patterns in thin-film a-Si:H solar cells. We compare devices with randomly patterned Ag back contacts that are covered with either flat or patterned aluminum-doped ZnO (AZO) buffer layers and find the nanostructure at the AZO/a-Si:H interface is key to achieve efficient light trapping. Simulations show that purely dielectric scattering patterns with flat Ag and a patterned AZO/a-Si:H interface can outperform geometries in which the Ag is also patterned. The scattering from the dielectric patterns is due to geometrical Mie resonances in the AZO nanostructures. The optimized dielectric geometries avoid parasitic Ohmic losses due to plasmon resonances in the Ag, and open the way to a large number of new light trapping designs based on purely dielectric resonant light scattering. © 2010 Optical Society of America.
De Coninck H.,Energy Research Center of the Netherlands |
Backstrand K.,Lund University
Global Environmental Change | Year: 2011
With the publication of the IPCC Special Report on Carbon dioxide Capture and Storage (CCS), CCS has emerged as a focal issue in international climate diplomacy and energy collaboration. This paper has two goals. The first goal is to map CCS activities in and among various types of intergovernmental organisations; the second goal is to apply International Relations (IR) theories to explain the growing diversity, overlap and fragmentation of international organisations dealing with CCS. Which international organisations embrace CCS, and which refrain from discussing it at all? What role do these institutions play in bringing CCS forward? Why is international collaboration on CCS so fragmented and weak? We utilise realism, liberal institutionalism and constructivism to provide three different interpretations of the complex global landscape of CCS governance in the context of the similarly complicated architecture of global climate policy. A realist account of CCS's fragmented international politics is power driven. International fossil fuel and energy organisations, dominated by major emitter states, take an active role in CCS. An interest-based approach, such as liberal institutionalism, claims that CCS is part of a "regime complex" rather than an integrated, hierarchical, comprehensive and international regime. Such a regime complex is exemplified by the plethora of international organisations with a role in CCS. Finally, constructivism moves beyond material and interest-based interpretations of the evolution of the institutionally fragmented architecture of global CCS governance. The 2005 IPCC Special Report on CCS demonstrates the pivotal role that ideas, norms and scientific knowledge have played in transforming the preferences of the international climate-change policy community. © 2011 Elsevier Ltd.