Energy generation for miniature wind turbines boosted with super-efficient blades
Specially designed blades for small residential wind turbines have been created by a Spanish engineering consultancy in a bid to boost their energy efficiency.
The blades are wider than on other small wind turbines and the tips are designed to improve aerodynamic performance which also helps to reduce noise and vibrations.
More than 940,000 small wind turbines were in use around the world by the end of 2014 and based on current rates of growth, estimates suggest this number could grow by 20 per cent by 2020.
“The project aims to lower costs and increase the power generated by the small and medium wind turbines,” said Fernando Aznar at Solute, which helped to design the blades
To optimise performance the blades have also been designed in tandem with a new pitch control system. This adjusts the blades so that they sit at the best angle to the wind, to maximise efficiency.
“This system has to be pushed by the blades,” Aznar explained. “The passive pitch system was created and configured in order to decrease the total cost of the wind turbine and protect the machine.”
Airflow around the new blades was studied using computer modelling techniques which allowed the researchers to estimate power production, as well as pitch torque and thrust, to aid the design of the pitch control system.
“Air flow near to the tip of the blades has a significant impact on the efficiency and the noise from the wind turbine as well as the aerodynamic force on the blade,” said Lin Ma, a mechanical engineer at the University of Sheffield in the UK, who carried out the computer modelling.
“The new blade design takes consideration of the performance, noise, aesthetic aspect, the cost of manufacturing of the turbine and the long term operational and maintenance costs.”
Small wind turbines (like the one pictured above) are often installed in urban and semi-urban areas. However, these locations are challenging as they require turbines that work at variable, often low, wind speeds while running smoothly and producing little noise. These conditions directly affect the technical requirements for wind turbine generators.
Spanish renewable energy company 4fores also developed lighter weight electricity generators to be paired with the new blades.
“The challenge was to obtain a permanent magnet synchronous generator which operates at lower rotational speeds than currently used generators, while maintaining benchmark size, power and efficiency, and keeping cost at a low level,” said Jorge Herrero Ciudad with 4fores.
When being turned at low speeds, generators often suffer from jerkiness. This undesirable characteristic is caused by an issue known as cogging torque.
By focusing on reducing cogging torque, the researchers managed to produce a generator that vibrates less, reducing noise and improving reliability, and can start producing energy at lower wind speeds.
When combined with new power conversion electronics developed by the project, it is estimated that this will improve energy harvesting by up to 20 per cent at the most common wind conditions in urban environments.
The new generators are also 50 per cent lighter than conventional generators. “This has been achieved using cutting edge design methods and cutting edge materials,” Ciudad said. “For instance, the structure of the generator uses aerospace-grade aluminium when typically steel is used.”
A lower weight generator reduces turbine costs in two ways. The generators are cheaper as they use less material and the other parts of the turbine, such as the tower, can be smaller as they have less weight to support.
Turbines featuring the new blades and generators are being tested at three different sites, representing three different usage scenarios: energy efficient buildings, shore-lines and industrial areas.