Energie · Gebäude · Umwelt (EGU)
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The global salinity gradient power (SGP) potential is between 1650 - 2000 TWH/a and can be converted by mixing two solutions with different salinities. The harnessing of SGP for conversion into power can be accomplished by means of pressure retarded osmosis (PRO) and reverse electrodialysis (RED). PRO and RED are membrane-based technologies and have different working principles. PRO uses a semipermeable membrane to seperate a concentrated salt solution from a diluted solution. The diluted solution flows through the semipermeable membrane towards the concentrated solution, which increases the pressure within the concentrated solution chamber. The pressure is balanced by a turbine and electricity is generated. RED uses the transport of ions through cation and anion exchange membranes. The chambers between the membranes are alternately filled with a concentrated and diluted solution. The salinity gradient difference is the driving force in transporting ions that results in an electric potential, which is then converted to electricity. The comparison shows that there are two different fields of application for PRO and RED. PRO is especially suitable at extracting salinity energy from large concentration differences. In contrast, RED are not effect by increasing concentration differences. So PRO are supposed to focus on applications with brines or waste water and RED on applications with river water and seawater. Moreover, just a few measured values from processes under real conditions are available, which makes it difficult to compare PRO and RED.
Assessment of noise mitigation measures during pile driving of larger offshore wind foundations
(2021)
Wind energy is an important source of electricity generation, but the construction of offshore wind foundations causes high underwater sound pressure, harming marine life. In this context limiting values for underwater noise emissions were set to protect the marine flora and fauna. Therefore, noise mitigation measures during pile driving are mandatory to comply with these limits. Current development in the wind industry lead to increasing wind turbine sizes, requiring a larger pile diameter, which leads to higher underwater noise emissions. As a result, the state of the art noise mitigation systems might not be sufficient and a combination of different technologies is necessary. This article focuses on the issue of noise mitigation during pile driving with respect to large pile sizes. First, the most tested and proven noise mitigation techniques (big bubble curtain, hydro sound damper, and IHC-noise mitigation system) are described, following an analysis of noise reduction measurements in applications at different offshore wind farm projects. In the end the suitability of current noise mitigation systems for large monopiles is evaluated, regarding their effectiveness and practicability.
Originally this article was supposed to be a comparison between the technological differences of bottom-fixed offshore wind turbines (BOWT) and floating offshore wind turbines (FOWT). However, several authors already contributed to this topic and came to the conclusion that the higher levelized costs of energy (LCOE) prevent FOWTs from successfully entering the energy market. Multiple sources seem to agree on this conclusion but often do not provide the reader with further information regarding the LCOE. This is the reason why this article understands itself as an in depth cost comparison between BOWTs and FOWTs. For this purpose, individual LCOE are calculated for the upcoming FOWT technologies such as spar-buoy (SPAR), tension-leg platform (TLP) and semi-submersible platform (semi-sub) as well as conventional BOWTs using the wind turbines hours of full utilization (HOFU). The resulting functions are visualized graphically in order to determine break-even points between BOWTs and FOWTs. Finally, a sensitivity analysis is carried out to determine the influence of the weighted average costs of capital (WACC).
Despite their important role in our energy system, common wind turbines have some disadvantages. Mainly, those disadvantages are connected to the intermediate conversion of wind energy in rotational energy. The resulting effects include maintenance costs and social acceptance problems. There are different technological approaches, that convert wind energy to electrical energy without its conversion to kinetic energy. As one of those technologies, the electrostatic wind energy conversion is to be discussed in this article. For this discussion, the historical development of this technology is presented. There are three important projects which will be presented to explain the technology and its different technological approaches. Those projects are the WPG, the EWICON and the SWET. Furthermore the results of those different experimental projects are collected and analyzed. On the basis of this analysis it is discussed, whether or not the electrostatic wind energy conversion could be of importance in a future energy system. Therefore the technology is set in relation to modern wind turbines. Also, important factors that influence the efficiency and energy output of those systems are outlined for further research. Due to different technological approaches a suggestion is made for the most promising system setting.
With floating offshore wind turbines, new sources of wind energy can be used, which cannot be tapped into by bottom-fixed wind turbine systems. However, due to their design, they experience additional motion caused by wind and wave loads. The motions that are induced into the system have an oscillating course. This affects the aerodynamic properties of the wind turbine and leads to changes in the thrust force and power output of floating wind turbines compared to bottom-fixed wind turbines. Furthermore, the motions lead to an earlier breakdown of the helical wake structure behind the wind turbine and moreover lead to a decreased reliability of the rotor blades. Differences in the effects of wind and wave loads on the aerodynamic performance of floating offshore wind turbines supported by different platform systems were found.
The effects of different unsteady ventilation strategies on flow-structures in a room are investigated and compared to steady ventilation with the same mean exchange rate. For this, whole-field optical flow measurements were executed by means of a particle image velocimetry system (PIV) in a Reynolds-scaled room model in water. In a first series of experiments, sinusoidal varied supply flows with different frequencies were analysed; two equally supplied simple nozzles in the ceiling were used as inlets. The setup was validated by comparing jet velocities with literature values.
Typically, room airflows are investigated with punctual measurement techniques (e.g.
anemometers), which have an impact on the flow field, or with smoke gas experiments. By using PIV, the flow can be analysed without any influence of sensors or stands/traverses and whole-field measurement data with high spatial resolution and detailed information on the flow field can be collected.
Local and time-averaged velocities and standard deviations were calculated for all scenarios. Unsteady conditions were created by a sinusoidal variation of the supply flow rate with frequencies between 0.025 1/s and 0.050 1/s, an offset of about 1.1 m3/h and an amplitude of about ±1.0 m3/h, which leads to a mean exchange rate of 3.5 1/h. Although averaged velocity fields only show slight differences between steady and unsteady conditions, single pictures vary widely. First effects of unsteady ventilation on flow structures can be recognized. Steady structures are destroyed, and velocities change rapidly.
The inlets will be changed to small-scale ceiling-diffusors in future experiments to create more realistic room ventilation conditions. Other types of unsteady supply flows will be implemented, and parameters will be varied. The results of the PIV-measurements can be used to validate CFD simulations and to derive dimensioning rules and application recommendations.
There are many hydropower turbines for low heads or low flows on a small scale. Many technologies are unsuitable for developing countries because equipment or materials are limited, high-tech machines are to expensive or spare parts are not readily available. This review combines currently available technologies with the requirements of developing countries in small, micro and pico hydropower. In small hydropower a propeller turbine from Thailand has a high efficiency of 70 to 80 percent at calculated production costs of around $ 513 per kW. Pumps as turbines are suitable for developing countries in micro hydropower due to readily availability, low price and an large number of standard sizes. In pico-scale, a low-cost Turgo wheel can be made of spoons for $ 48 and yields acceptable values in comparison to a 3D printed Pelton wheel for $ 822. While the Turgo wheel is suitable for high heads, a homemade siphon turbine can be used for low heads. The siphon turbine generates up to 200 W, is made of materials that are available anywhere in the world, and costs less than $ 50.
Because of the rapid expansion and widespread application of wind energy the overall environmental impacts of wind power plants have increased as well. For the further development of wind power, methods to lessen the adverse effects wind power has on avian populations have to be implemented. This review aims to find effective methods to reduce avian collision rates with wind turbines and that therefore can reduce bird fatality rates.
For the assessment the different mitigation methods, for which concrete data was found, are compared with each other regarding the hypothetical effort of implementation and effectiveness in reducing avian collision rates with wind turbines.
These methods are:
(a) Coloring of rotor blades
(b) Coloring of the tower base
(c) Ultraviolet/violet lightning
(d) Temporary shut-down of wind turbines
(e) Auditory warning signals
(f) Repowering
All of the mentioned methods report influence on reducing avian collision rates or at least the behavior of birds in flight.
This review found the following three methods to be most effective:
(a) Coloring of rotor blades
(b) Temporary shut-downs of wind turbines
(c) Repowering
The most effective method to reduce avian collision rates at horizontal axis wind turbines is to paint one of the rotor blades black and consequently increasing the visibility of the rotor blades. The presented study reports 71,9 percent reduction of found carcasses of birds at the treated turbines. For this method the effort of implementation is low while the effectiveness is high.
The effectiveness of the found mitigation methods has been proven and they are suited for application. The method of using lightning or sound fields require more testing to determine their effectiveness. Another topic for research could be how different mitigation methods interact with each other. Is there a significant advantage to be had if multiple mitigation methods are applied at the same wind power plant or turbine? Furthermore the environmental impacts of wind turbines are not limited to birds. Other animals like bats are affected too and might require different methods of mitigation.
About 75% of the world's energy consumption takes place in cities. Although their large energy consumption attracts a large number of research projects, only a small fraction of them deal with approaches to model energy systems of city districts. These are particularly complex due to the existence of multiple energy sectors (multi-energy systems, MES), different consumption sectors (mixed-use), and different stakeholders who have many different interests.
This contribution is a review of the characteristics of energy system models and existing modeling tools. It evaluates current studies and identifies typical characteristics of models designed to optimize MES in mixed-use districts. These models operate at a temporal resolution of at least 1 h, follow either bottom-up or hybrid analytical approaches and make use of mixed-integer programming, linear or dynamic.
These characteristics were then used to analyze minimum requirements for existing modeling tools. Thirteen of 145 tools included in the study turned out to be suitable for optimizing MES in mixed-use districts. Other tools where either created for other fields of application (12), do not include any methodology of optimization (39), are not suitable to cover city districts as a geographical domain (44), do not include enough energy or demand sectors (20), or operate at a too coarse temporal resolution (17). If additional requirements are imposed, e.g. the applicability of non-financial assessment criteria and open source availability, only two tools remain.
Overall it can be stated that there are very few modeling tools suitable for the optimization of MES in mixed-use districts.
Wind energy has steadily gained importance in the generation of renewable energy over the last 25 years. A wind turbine has an average life expectancy of about 25 years. After that, thermoplastic composite materials from the rotors, among other things, accumulate and have to be recycled. Previous methods, such as landfilling, incineration and pyrolysis, have not yet proven to be effective in terms of the circular economy because the recycled material cannot be reused for equivalent products. The use of thermoplastic materials can be a sensible alternative, as thermoplastic resins can be recycled almost without loss of value due to their properties. Recycling of fibreglass is also possible with less loss of stiffness. In the future, it will be crucial to scale up thermoplastic rotor blades and create a market for the recycled material.