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One of the most asked questions prior to building homemade wind turbines is the number of blades to be used. For the last 50 years, wind energy system manufacturers have used two to three blades. However, the third blade was not much of an option if the priority is to increase aerodynamic efficiency.
During tests, it is found out that increasing the number of blades from one to two increases aerodynamic efficiency by 6%. However, when two blades are increase to three, there is only a 3% increase of efficiency. Minimal improvements are yielded from additional blades. Furthermore, as the number of blades increases, the thinner the blade gets, sacrificing blade stiffness and power generation.
The cost is also affected by the number of wind turbine blades. In general, fewer blades mean less manufacturing and material cost. A wind turbine with fewer blades is also able to build up higher rotational speed with reduced peak torques, allowing lower generator and gearbox costs.
Number of blade concepts
1-bladed concept
It may look pretty unbalanced and strange but a one-blade wind turbine save an entire cost of a rotor blade. Although more economical with regards to manufacturing costs, one-blade wind turbines suffer from aesthetic and noise problems. A counterweight on the other side of the hub needs to be placed to balance the rotor and keep it from rotating.
Teetering or 2-bladed concept
Some wind turbines have only two rotors to save up on the cost of a third blade. However, 2-blade wind turbines are being overtaken by 3-blade wind systems due to aesthetic and noise issues. Rotational speeds also generate less energy, making it a poor second to third-bladed wind turbines.
3-bladed Danish concept
Modern homemade wind turbines have three-bladed designs, also referred to as the Danish concept. This design provides a smoother operation during turbine yaw due to symmetrically balanced cyclic loads. While two-bladed concepts allow less manufacturing, materials, and maintenance costs, three-bladed wind turbines are considered by some people to be more balanced and pleasant to look at compared to one or two bladed turbines.
Old and modern wind turbines differ in speed and materials use. Modern small wind turbine blades are mostly made from aluminum because of its low density and resistance to corrosion. When combined with composite materials, it allows the blades to gain speed as the winds pick up. Commercial wind turbines use a variety of materials that require composite fabrication techniques to ensure the durability and longevity of the blades.
If you are building homemade wind turbines, consider a two-blade concept for easy installation and construction. However, if you want a quieter wind turbine operation, higher efficiency, and do not mind spending for an additional rotor, go for three-bladed wind turbines. Residential wind turbine blades do not have to be made from expensive materials. Look for lightweight glass-enforced plastic or even laminated wood to reduce material costs. If budget is not an issue, use graphite-fiber in epoxy for specific load-bearing parts of the rotor blades.