Small Wind Turbines

Designed for Urban/Rural Utility by NAL-National Aerospace Laboratories, Bangalore

Unfortunately, most of the wind resources currently available have been designed for larger, rural-mounted turbines; thus, they are not well suited for India's nascent market. A consequence of this is that many potential urban small wind turbine owners over-predict their local wind resource, which is both costly and inefficient.

National Aerospace Laboratories (NAL) is a high technology oriented institution concentrating on advanced topics in the aerospace and related disciplines, based in Bangalore, INDIA. NAL employs a staff of about 1,300 with about 350 full-fledged R&D professionals. NAL is equipped with facilities such as the Nilakantan Wind tunnel Centre and a computerised fatigue test facility. NAL also has facilities for investigating failures and accidents in aerospace.

Wind energy related activities had been initiated at NAL by the first director Dr P Nilakantan in 1959 and later valuable contributions were made through the wind resource assessment leading to the discovery of major windy sites in the southern India during the 70's energy crisis. In the past few years, NAL had ventured into the design and development of wind turbines in order to create the indigenous technology base within the country. With its rich multi-disciplinary experience in the niche area of design of aircraft wings and helicopter rotors, an indigenous development of a 1 kW wind turbine rotor for low wind conditions was taken up and successfully completed.

Operating range of Wind turbine

Careful choice of aerodynamic profiles of the rotor blade are the key requirements of ensuring low cut in and better energy yield from the turbine. This was addressed by carefully studying the performance of airfoils at low Reynolds number of the order of 105, which is the operating regime of Small wind turbines. About 14 airfoils were considered. Individual evaluation of each one of them was done so as to assess the performance of the wind turbine in terms of the power curve. Based on the requirement of low cut in, optimal energy generation in low wind condition and smooth aerodynamic stalling, NACA 4412 profile was chosen. Blade shape was subsequently designed for a 4 bladed rotor configuration.

The rotor design methodology that has been evolved includes design, analysis, manufacturing and testing.

Structural Design & Analysis

Conventionally the blades are made of glass composites (GFRP) that leave behind large ecological footprints. In this context, the carbon fibre composite (CFRP) was chosen as the blade material. The CFRP offered a light weight blade due to its inherent higher specific stiffness and strength properties on one hand, while being amenable to a relatively ecofriendly disposal as compared to GFRP on the other. With its decades of experience, NAL tuned the in-house established Aerospace grade composite materials technology for wind turbine application to cater to the need of a light weight material. This ensured less rotor inertia and low the cut-in. Finite Element analysis was carried out using the commercially available codes such as HyperMesh & Nastran for optimization of the composite layup scheme, and henceforth, the blade weight for the defined design and off-design loads. FE analysis results are shown in figure above. The lay up sequence and ply drops to resist the inplane and out-of-plane loadings were judiciously arrived at after a thorough FE analysis. The required design data on CFRP was generated in-house. A single CFRP blade weighs about 600 grams and further weight optimization exercise is being pursued.

The blades were fabricated with the wet lay-up technique. Composite tools with modular features were specially developed for this purpose to facilitate incorporation of modifications in the future with ease and less time. Blades were developed as a sandwich structures. Polyurethane foam (PUF) core was casted into the required shape of the inner contour of the blade and moulded in-situ with the carbon fibre reinforcement, thereby imparting rigidity to the blade shell. The quality check on this PUF core carbon epoxy blade was carried out using a cost effective tap test non-destructive technique

PMG has partnered with NAL to jointly manufacture and market 1 kW wind turbines. For more information on price and after sales service, contact us....

Download Brochure....