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[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] India has committed to Paris Agreement to generate 30 per cent of its total electricity from renewable Sources by 2030. Roof top solar system will help it to some extent. It is also expected that the distribute; generation (roof top solar PV) at the consumer end will compensate to the acute power shortage in several states. (author)
[en] Grid connected solar system is an emerging technology to harvest solar incident radiation for production of electricity which can be fed to the grid directly. As part of the energy conservation activities as well as considering the importance the Government of India has given to harness Solar Energy, IGCAR has initiated projects in this line. To start with, a pilot plant of 30 kWp grid connected solar plant is installed and commissioned on 14th August 2015. On an average, this system, produces 120 to 150 units of electricity per day. On days with good solar insolation the production clocked 175 units. This is the largest solar system installed at Kalpakkam so far. All the operations are automatic and no manual intervention is envisaged for normal operation. It is not provided with any battery backup as the electricity generated is transferred to the gird on real time basis and no storage is necessary. This arrangement will ensure better efficiency at a lesser capital and maintenance cost
[en] France is aiming to reduce the share of nuclear power in the country's electricity mix, and increase the share of wind and solar power. However, given the intermittency of these renewable energy sources, massive storage systems are required when their share exceeds a certain threshold. That generates additional costs on top of the subsidies already granted to these energies. This article attempts to quantify that additional cost, which varies between 6.3 Euros and 31.6 billion Euros depending on various scenarios. In fact, the cost of renewables storage varies according to our calculations between 108.3 Euros and 251.4 Euros per MWh. That additional cost could be reduced if storage yields were improved. One of the lessons to be drawn from this analysis is that it would be preferable to finance R and D in storage technologies rather than using costly feed-in tariffs or feed-in premiums to finance an increase in renewables. The greatest challenge lies with respect to inter-seasonal storage rather than very short-term battery-based storage. The prospects for power-to-gas and gas-to-power are also promising, but have yet to be proven in practice. (authors)
[en] In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks.
[en] The issue of power quality is largely absent from discussions on energy, including those related to multi-annual energy programming, where the focus remains on security of supply, admittedly of critical importance. Clearly, blackouts or power outages, such as those that crippled Paris' Montparnasse railway station and its surrounds in late July 2018, tend to make the headlines. And a deep dive into this subject rapidly leads to complex considerations on the physics of electricity and network codes that the non-specialist may find daunting. Nevertheless, the growing dependence of our economies on digital technology and the emergence of intermittent renewable energies in the electricity mix are creating new challenges, with the question of power quality being a prime example. (authors)
[en] We present the results of a detailed study of the first accurate 3D ground state interaction potential energy surface (PES) of the Ne–Li2 system by quantum calculations using the coupled-cluster singles and doubles excitation approach with perturbative treatment of triple excitations [CCSD(T)]. The calculations were carried out for the frozen molecular equilibrium geometries and for an extensive range of the remaining two Jacobi coordinates, R and θ, for which a total of about 1976 points is generated for the surface. Mixed basis sets, aug-cc-pVTZ for the Ne atom and cc-pCVTZ for the Li atom, with an additional (3s3p2d2f1g) set of midbond functions are used. The ab initio points on the PES are fitted to a 96-parameter algebraic form with an average absolute error of 0.00000255% and a maximum error less than 0.00888%. The experimental results are compared with our ab initio potential surface calculations. Our PES gives more accurate results along with the experimental data.
[en] Highlights: • The study focussed on the techno-economic assessment of thermal energy storage systems. • Data-intensive bottom-up models for each storage systems were developed. • Costs for sensible, thermo-chemical, and latent heat storage systems were developed. • The electricity cost from using these thermal energy storage systems is $0.02–$1.19/kWh. - Abstract: In this paper, a data-intensive cost model was developed for sensible heat, latent heat and thermochemical storage systems. In order to evaluate the economic feasibility of storage systems, five scenarios were developed depending on the method of storage. The five scenarios considered were indirect sensible heat, direct sensible heat using two tanks, direct sensible heat using one tank, latent heat and thermochemical storage. A Monte Carlo simulation was performed for all the scenarios to examine the uncertainty in the levelized cost of electricity when parameters such as solar multiple, plant capacity, storage duration, capacity factor, and discount rate are changed. The levelized cost of electricity ranges for individual scenarios are; 0.08–0.59 $/kWh for indirect sensible heat, 0.03–0.22 $/kWh for direct sensible heat using two tank, 0.02–0.16 $/kWh for direct sensible heat using one tank, 0.06–0.43 $/kWh for latent heat, and 0.22–1.19 $/kWh for thermochemical storage. The results indicate that when uncertainty is taken into account, the investment cost for thermochemical storage is clearly higher than other scenarios. This study will provide key information for industry and policy makers in decision making and in determining the economic viability of thermal energy storage systems.
[en] Biodiversity is threatened by the expansion of human activities. In this context, the nuclear industry, which is essentially concentrated in terms of material flows and industrial sites, has a number of advantages over wind and solar energy: much lower consumption of land and raw materials, and the ability to recycle. In de-carbonised energy scenarios, these differences argue in favour of maintaining a significant part of nuclear power rather than 100% renewable energy production
[fr]La biodiversite est menacee par l'expansion des activites humaines. Dans ce contexte, la filiere nucleaire, concentree par essence en termes de flux de matieres et de sites industriels, presente quelques avantages en comparaison des energies eolienne et solaire: consommations bien plus faibles de surfaces et de matieres premieres, aptitude au recyclage. Dans les scenarios d'energie decarbonee, ces differences plaident pour le maintien d'une part significative de nucleaire plutot qu'une production assuree a 100 % par les energies renouvelables
[en] Highlights: • Heat transfer for PCHE in TEG was investigated in detail by 3D CFD analysis. • Experimental data for a 200-W TEG implemented with PCHEs are newly presented. • Power density of the TEG was sufficiently high at low temperature. • Reduction of TEG flow rate requirements from use of PCHEs is estimated. - Abstract: Printed circuit heat exchangers (PCHEs) are employed to improve the compactness of a thermoelectric generator (TEG). PCHEs allows miniaturization of the heat exchanger without excessive additional cost, and permit high temperature and pressure (up to 1100 K and 600 bar) of working fluid, which enable high thermoelectric conversion efficiency. To investigate the pressure loss and thermal resistance of a PCHE in detail, three-dimensional computational fluid dynamic (CFD) analysis is conducted. Experimental results of the proposed TEG with PCHEs are newly presented. The TEG provides power density of 233.1 kW/m3 at inlet temperatures of 448.15 K (hot side) and 293.15 K (cold side), which is the highest value in literature for a low-temperature TEG (<505.15 K hot side). Based on the models of friction and heat transfer in a PCHE validated by the experiment, it is noted that the flow rate required for the heat exchangers in a TEG producing a given amount of electrical power can be reduced by adaption of PCHEs. Such novel results on the TEG with PCHEs might be helpful for more compact design and expands the applicability of TEGs for waste heat recovery.