@techreport{Tillenburg2021,
  author    = {Tillenburg, Dennis},
  title     = {Technical challenges of floating offshore wind turbines - An overview},
  doi       = {10.25974/ren_rev_2021_03},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136770},
  pages     = {13-18},
  year      = {2021},
  abstract  = {Floating offshore wind (FOW) holds the key to 80 \% of the total offshore wind resources, located in waters of 60 m and deeper in European seas, where traditional bottom-fixed offshore wind (BFOW) is not economically attractive. Many problems affecting floating offshore wind turbines (FOWT) were quickly overcome based on previous experience with floating oil rigs and bottom-fixed offshore wind. However, this technology is still young and there are still many challenges to overcome. This paper shows that electrical failures are amongst the most significant errors of FOWT. The most common cause was corrosion. It is also stated that the control system is most often affected, and that the Generator is frequently involved. Material corrosion is also the key factor when it comes to the most common overall reason for failures. A particular attention must be paid to mooring line fracture. Mooring lines are especially vulnerable to extreme sea conditions and the resulting fatigue, corrosion, impact damage, and further risks. It must be stated that the primary challenge is that of economics. Over time technological costs will decline making FOW more competitive and hence attractive for greater depth.},
  language  = {en}
}
@techreport{Wagenknecht2021,
  author    = {Wagenknecht, Fiona},
  title     = {Assessment of noise mitigation measures during pile driving of larger offshore wind foundations},
  doi       = {10.25974/ren_rev_2021_04},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136786},
  pages     = {19-23},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@techreport{Tchorz2021,
  author    = {Tchorz, Enno},
  title     = {Sensorless maximum power point tracking systems in wind energy conversion systems - A review},
  doi       = {10.25974/ren_rev_2021_05},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136791},
  pages     = {24-29},
  year      = {2021},
  abstract  = {Wind energy conversion systems have attracted considerable attention as a renewable energy source due to depleting fossil fuel reserves and environmental concerns as a direct consequence of using fossil fuel and nuclear energy sources. The increasing number of wind turbines increases the interest in efficient systems. The power output of a wind energy conversion system depends on the accuracy of the maximum power tracking system, as wind speed changes constantly throughout the day. Maximum power point tracking systems that do not require mechanical sensors to measure the wind speed offer several advantages over systems using mechanical sensors. In this paper four different approaches that do not use mechanical sensors to measure the wind speed will be presented; the assets and drawbacks of these systems are highlighted, and afterwards the examined algorithms will be compared based on different characteristics. Finally, based on the analysis, an evaluation is made as to which of the presented algorithms is the most promising.},
  language  = {en}
}
@techreport{Steinigeweg2021,
  author    = {Steinigeweg, Joshua},
  title     = {Review of the suitability of thermoplastic rotor blades in terms of the circular economy},
  doi       = {10.25974/ren_rev_2021_06},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136809},
  pages     = {30-34},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@techreport{Haener2021,
  author    = {H{\"a}ner, Jurek},
  title     = {Technologisches Lernen im Bereich Windenergie an Land},
  doi       = {10.25974/ren_rev_2021_07},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136814},
  pages     = {35-41},
  year      = {2021},
  abstract  = {Diese Arbeit befasst sich mit Kostentrends in Zusammenhang mit technologischem Lernen von Windenergie an Land in den USA, in Deutschland und weltweit. Ziel dieser Arbeit ist es, eine Lernkurve f{\"u}r Windenergie an Land zu bestimmen. Daf{\"u}r wurden Daten zu Stromgestehungskosten (LCOE) und Kosten f{\"u}r die Installation (COP) von Windenergieanlagen (WEA) im Zeitraum von 1983 bis einschließlich 2020 gesammelt, grafisch dargestellt und weitergehend ausgewertet. Die grafische Darstellung der Datenlage verdeutlicht die zeitliche Entwicklung der Technologie. Zur Beschreibung dieser Lernkurven wurden die Progress Ratio (PR) und Learning Rate (LR) in f{\"u}nf unterschiedlichen Modellen bestimmt. Anhand derer sich in Kombination mit der zuk{\"u}nftig installierten Leistung von WEA eine Prognose {\"u}ber zuk{\"u}nftige Kosten ableiten l{\"a}sst. Die ermittelten LR bewegen sich zwischen 13 \% und 28 \%, woraus sich LCOE im Jahr 2030 zwischen 44,03 US\$/MWh und 61 US\$/MWh ergeben.},
  language  = {de}
}
@techreport{Hoge2021,
  author    = {Hoge, Alexander},
  title     = {Measures for mitigating avian collision rates with wind turbines - Determining an effective technique regarding effort and effect},
  doi       = {10.25974/ren_rev_2021_08},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136826},
  pages     = {42-47},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@techreport{Wittor2021,
  author    = {Wittor, Yannick},
  title     = {Harvesting wind energy through electrostatic wind energy conversion - Comparison with common wind turbines and future possibilities},
  doi       = {10.25974/ren_rev_2021_09},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136832},
  pages     = {48-52},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@techreport{Speller2021,
  author    = {Speller, Julian},
  title     = {Self-build small wind turbines - A review},
  doi       = {10.25974/ren_rev_2021_10},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136845},
  pages     = {53-56},
  year      = {2021},
  abstract  = {Self-build small wind turbines are used for rural electrification in the developed and developing world as well as for educational purposes. To give an overview about self-build small wind turbines a systematic literature review was conducted. The identified literature deals with two different vertical and horizontal axis turbine designs. The vertical axis turbines are both prototypes while one of the horizontal axis designs, the design by Piggott is widely used in rural electrification projects. Different papers dealing with the optimization of the Piggott design exist. In retrospect the conduction of a holistic review was not possible due to limited resources and length of this review. Nevertheless it can give a quick overview and a starting point for further research.},
  language  = {en}
}
@techreport{Scheffler2021,
  author    = {Scheffler, Mark},
  title     = {Low-Cost Hydropower Turbines for Developing Countries},
  doi       = {10.25974/ren_rev_2021_11},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136858},
  pages     = {57-62},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}
@techreport{Hinse2021,
  author    = {Hinse, Michael},
  title     = {The Wells turbine: state of the art},
  doi       = {10.25974/ren_rev_2021_12},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-136861},
  pages     = {63-66},
  year      = {2021},
  abstract  = {The first oscillating water column was invented in 1940. In the past decades the need of wave energy systems has significantly increased. This article quickly describes the Wells turbine and possibilities to enhance its performance and should answer the question: what are the design parameters that can be optimized? Furthermore it gives a small outlook about the history of oscillating Water Columns.},
  language  = {en}
}