Controlling Volatility of Wind-Solar Power In Germany

The main advantage of wind-solar power is the electric power production free of CO2. Its main disadvantage is the huge volatility of the system [national electric energy consumption powered by wind-solar power]. In fact, if this power production, averaged over one year, corresponds to the averaged electric consumption and is intended to replace all other electric power generating devices, then controlling the volatility of this system by using storage alone requires huge capacities of about 30TWh, capacities not available in Germany. However, based on German power data over the last six years (2015 till 2020) we show that the required storage capacity is decisively reduced, provided i) a surplus of wind-solar power is supplied, ii) smart meters are installed, iii) a different kind of wind turbines and solar panels is partially used, iv) a novel function describing this volatile system, is introduced. The new function, in turn, depends on three characteristic numbers, which means, that the volatility of this system is characterized by those numbers. When applying our schemes the results suggest that all the present electric energy in Germany can be obtained from controlled wind-solar power. And our results indicate that controlled wind-solar power can produce the energy for transportation, warm water, space heating and in part for process heating, requirering an increase of the electric energy production by a factor of 5. Then, however, a huge number of wind turbines and solar panels is required changing the appearance of German landscapes fundamentally.

Fallback Accretion Halted by R-process Heating in Neutron Star Mergers and Gamma-Ray Bursts

The gravitational wave event GW170817 with a macronova/kilonova shows that a merger of two neutron stars ejects matter with radioactivity including r-process nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering long-lasting activities of a short gamma-ray burst (sGRB), such as extended and plateau emissions. We investigate fallback accretion with r-process heating by performing one-dimensional hydrodynamic simulations and developing a semi-analytical model. We show that the usual fallback rate dM/dt ∝ t −5/3 is halted by the heating because pressure gradients accelerate ejecta beyond an escape velocity. The suppression is steeper than Chevalier’s power-law model through Bondi accretion within a turn-around radius. The characteristic halting timescale is ∼104–108 s for the GW170817-like r-process heating, which is longer than the typical timescale of the long-lasting emission of sGRBs. The halting timescale is sensitive to the uncertainty of the r-process. Future observations of fallback halting could constrain the r-process heating on the scale of a year.

Design of a contactless powered and piezoelectric-actuated tool for non-resonant low-frequency vibration-assisted machining of brittle-hard materials

Ultrasonic-assisted grinding (UAG) is the state-of-the-art process for machining of brittle-hard materials. In comparison to conventional processes, the main advantages lie in the reduction of tool wear and process forces. Such a vibration system is based on a resonant actuator and a power supply unit generating the alternating current. Both units are interconnected by a contactless energy transfer (CET) system. This system configuration shows one optimal working point at the resonant frequency with maximum amplitude, which is significantly depending on the tool shape. In this work, a piezo-activated tool system is designed to realize non-resonant low-frequency vibrations. Major emphasis is put on the thermal behavior of the piezo drive, particularly on the in-process heating depending on the working frequency. In addition, focus lays on the theoretical and numerical design of the radial operating transducer CET system for a previously set actuator design. As a result, this system configuration offers a fully variable adjustment of the amplitude from under 1 to over 50 μm at frequency range. Outside this range, higher amplitudes can be achieved for short periods to the detriment of the fatigue strength according to FKM.

Analysis of the Potential for Reducing Life Cycle Greenhouse Gas Emissions from Motor Fuels

The assessment of life cycle greenhouse gas emissions of motor fuels is important due to the legal obligations and corporate social responsibility of the petroleum industry. Combining the Life-Cycle Assessment with optimization methods can provide valuable support in the decision-making process. In this paper, a mathematical model of a refinery was developed to analyze the impact of process optimization on GHG emissions at the fuel production stage. The model included ten major refinery units. Fuel production costs were minimized by taking into account the number of constraints. The analysis was performed in two steps. First, the model was run for the reference case of fuels composition. Then, more than twelve thousand model runs were performed. In each model, the fuel composition was changed. This change represented the exogenous pressures and resulted in different flows of mass, energy and GHG emission at the refinery. The most favorable results in terms of GHG emissions were then identified and analyzed. Additionally, the impact of using low-carbon fuels for process heating was evaluated. The study showed that fuel blending management could lead to the reduction of GHG emissions by 0.4 gCO2-eq/MJ while the use of low-carbon fuel for process heating results in a reduction of GHG emissions by 2 ca. gCO2-eq/MJ.

Numerical Performance Investigation of Parabolic Dish Solar-Assisted Cogeneration Plant Using Different Heat Transfer Fluids

Parabolic dish solar collectors gain higher solar to thermal conversion efficiency due to their maximum concentration ratio. The present research focuses by integrating the parabolic dish solar collector to the steam cycle producing power and rate of process heating. Pressurized water, therminol VP1, and supercritical carbon dioxide are the examined working fluids in the parabolic dish solar collector. The aim of the current research is to observe the optimal operating conditions for each heat transfer fluid by varying inlet temperature and flow rate of the working fluid in the parabolic dish solar collector, and combination of these parameters is predicted to lead to the maximum energy and exergy efficiencies of the collector. The operating parameters are varied to investigate the overall system efficiencies, work output, and process heating rate. Findings of the study declare that water is an efficient heat transfer fluid at low temperature levels, whereas therminol VP1 is effective for a higher temperature range. The integrated system efficiencies are higher at maximum flow rates and low inlet temperatures. The efficiency map of solar collector is located at the end of study, and it shows that maximum exergy efficiency gains at inlet temperature of 750 K and it is observed to be 37.75%.

Techno-Economic evaluation of an evacuated tube solar air collector with inserted baffles

Evacuated tube solar collectors exhibit excellent performance even in poor insolation periods and are highly preferred for low as well as for medium temperature applications. In this study, an evacuated tube with inserted baffle solar air collector (ETIBSAC) was developed to investigate the effect of mass flow rate of air on energy, exergy, enviro-economic characteristics. The results revealed that the maximum outlet air temperature was observed during the peak irradiance period as 80.5 °C and the system is capable of delivering hot air above 50 °C between 9:30 am to 4:00 pm in clear sky days at the mass flow rate 100 kg/h. The maximum thermal efficiency of 55.4% was achieved at the mass flow rate of 500 kg/h. The highest exergy efficiency of 2.7% was recorded at 100 kg/h and diminishes with increasing mass flow rate of air due to more exergy destruction. The cost per kWh to deliver the hot air in the range of 60 to 70 °C is estimated as 0.00027 $(0.02 INR) at the mass flow rate of 100 kg/h. It is concluded that the developed air collector can be efficiently used for process heating applications.