There has been a big increase in production and investments in wind turbines and wind farms in last 20 years. New generation of wind turbines is more reliable than from 1980’s are, which necessary condition is energy production is to play an important role among renewable energy sources. Over the last 30 years, the size of wind turbines increased 7 times, as nominal power increased nearly 14 times. At present, turbines capable of producing over 10 MW of power are being developed. The main reason for continued growth of turbines sizes is to minimize the energy cost per kilowatt-hour. However, it is worth remembering that according to the „square-cube law”, there is a maximum size after the surpassing of witch the cost of ever-larger turbines would grow faster than financial gain from the increased size. In this article, authors present energy storage methods and devices for wind power plants and cost-effectiveness of the individual energy storage methods. Authors also present data about energy storage efficiency and groups of energy storage devices for wind power plants such as: compressed-air power stations + gas turbine (CAES), utilizing underground wells, pumped storage power plants, rechargeable batteries (lithium-ion, lead-acid, sodium sulphur, VRB, zinc-flow, zinc-air, zinc-air), flywheels, hydrogen production and storage systems, superconducting magnetic energy storage (SMES), electrostatic storage – electrolytic capacitors.
Brakes are one of the most important safety features in every mechanical vehicle starting from bikes and finishing on airplanes. Brakes have to be designed in order to meet safety, reliability, efficiency and economical requirements. One has to remember that not only design of brake is important but also friction material used in its construction. Without proper materials, brakes are not able to generate proper braking moment. The braking moment is the most important parameter of brake from operation point of view. It is directly connected with braking distance as well with amount of force needed to achieve assumed braking parameters for the mechanical vehicle. Stability of braking moment is important in order to get optimized characteristics of the braking process itself. Most of the brake characteristics and efficiency calculations base on assumption that braking moment should be stable during braking process. During years of tests made on full scale brakes and friction material sample tests, author observed that real braking moment curve is not stable during braking process. This phenomenon is likely to affect braking efficiency and in result slightly change braking distance. In this paper author would like to address this issue by showing brake moment curves made for different brakes and friction materials. Tests, which were author's base for paper contents, were made using full scale brake testing and friction material sample testing. All of the tests described in the paper were performed in Landing Gear Laboratory of Warsaw Institute of Aviation in which author works on daily basis.
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