The friction velocity, k the von Kármán constant (0.41), ∆Z the zero-plane displacement and Z 0 the roughness height. The horizontal wind speed is determined by the surface roughness as given in the Equation (1), where Z is the vertical coordinate,
Flow in built areas is highly turbulent and complex. The renewed interest on these turbines is attributed to nano and micro grid development together with the rapid advancements in the energy storage technologies. The small-scale wind turbines play a key role in decentralized power generation. The collective findings will add profound knowledge to the VAWT community and will aid in the development of efficient VAWTs in the future. The current study explores each configuration in detail with an emphasis on their structural arrangements shedding light on the aerodynamic behaviours in low wind speed. Power capacity above 500 kW is termed as large or utility-scale wind turbines. Turbines of power capacities less than 50 kW are small scale wind turbines, whereas medium scale wind turbines have their power capacities in the range of 50 kW to 500 kW. The evaluation of wind turbines is categorized into three, based on their power capacities. Due to early failures and limited funding compared to HAWT, various innovative concepts have not been fully explored or not commercialized. As the research on VAWT gained momentum during early 1980s numerous configurations have been conceived and put to test. Though Darrieus built smaller models to establish his invention, a 7-kW power generation model was built in 1950 by Morel. Darrieus, a French aeronautical engineer in 1925 and subsequently obtained a U.S. Lift based Darrieus turbine was invented by G.J.M. Later, it was realized that the lift force is more efficient than drag and in order to achieve sufficient lift, the blade shape has to be different on the top and bottom side. The early VAWTs are in construction based on the aerodynamic drag simply, whereas the reverse drag is eliminated by covering the advancing blade to generate net torque. The IEA roadmap anticipated that 18% of the global energy demand will be met by wind energy by the end of 2050. Today, wind energy is one of the major sources of renewable energy with the total installed capacity of 600 GW as of 2018. The need for alternative energy, other than fossil fuels and the exponential growth in the energy demand has sprouted interest in the development of wind turbines in the past years. Despite notable innovations do happen afterwards, it was not until 1970, wind turbines are recognized for power generation during the energy crisis. History of wind turbines dates back to 7th century in Afghanistan, 9th century in Persia followed by the introduction of HAWT around 12th century in Europe.
This review is envisioned as an information hub for the major developments in VAWT and its technical advancements so far. This paper is a modest attempt to highlight the state-of-the-art information on the ongoing developments focusing on decentralized power generation. Innovative concepts and the feasibility to scale up for megawatt electricity generation, especially in offshore environments are investigated. Various configurations of VAWT have been assessed in terms of reliability, components and low wind speed performance.
The reason for the technical challenges and past failures are discussed. The current study aims to summarize the development of VAWT, in particular, Darrieus turbine from the past to the project that is underway. Though the Horizontal Axis Wind Turbines (HAWT) is preferred for multi-megawatt power generation, Vertical Axis Wind Turbines (VAWT) is as competitive as HAWT. Wind energy witnessed tremendous growth in the past decade and emerged as the most sought renewable energy source after solar energy.