A reader says:

I have got land with a wind density of 140 watts/sq. meter at 50 m up. I’m thinking of installing a 100-kW generator, but using 14-m blades (These were used on 250-kW turbines where wind density is 354 watts/sq. meter) I can get a good capacity factor. However, the strength of the blades can be just 40% of blades used for 250-kW turbines.

But I do not know the weight of 14-m long fiberglass blades for either the 250 kW and for 100 kW turbines. I know the weight of each 100-m long blade (Ed note: Mahesh may mean a 50-m blade) for a 1-MW turbine is about 50 tons (Ed. Note: maybe for the entire rotor), and that the weight of the blade is not linearly proportional, but rises with some exponential function. A 9-m blade weighs about 547 kg and a 14-m version, about 760 kg.

If I want to use a different material for the blade, I do not know the relation between strength, length, and weight of a blade for particular power capacity.

Can your readers provide a generalized formula for calculating blade weight for particular length to produce a required power? I know strength to weight ratios of different materials but I do not know how to calculate required strength. Or, can you suggest a good article or book to study this?

Thank you.

-Mahesh Chavan

Readers can add comments below. –PD

M.SAJID says

aslam o alikum.i determined the mass of blade by aboe formula it is almost 20 kg for 5 kw HAWT .is it right? (material fiber glass)

and now how i find the mass of tower and height?

M.SAJID says

sir.i want to desig a 5kw winnd turbine as a class project…all other calculation i have done but i have no information how i calculate the mass of tower and blade…..guide me,. thank you

Paul Dvorak says

Thanks for the update, Mr. Chavan.

To be clear, the baseline equation, for example, reads Mass = 0.1452 x R x 2.9158 NOT Mass = 0.1452 x R to the 2.9158 power.

Paul

Mahesh Chavan says

Dear Sir,

Regarding weight of blades, I have got a good document:

The link is :

http://www.google.co.in/url?q=http://www.phillipselectric.com/pdf/WTG_NREL-Wind-Turbine-Design-Costs-Model-2005.pdf&sa=U&ei=-bWWUIKhGI2srAeiioHYDA&ved=0CBQQFjAB&usg=AFQjCNHuRRW47Z7plTBNdF0eaYEchz52nA

On page 15 of the said document the relationship given for fiber glass blades is :

Figure 1. Blade mass scaling relationship.

Baseline: mass = 0.1452 * R2.9158 per blade

Advanced: mass = 0.4948 * R2.53 per blade

where R = rotor radius

So, at least for fiber glass blades, now I have some hint.

I hope to get relationship between strength of materials and blade length at the earliest.

Thanking you.

-Mahesh Chavan

Mahesh Chavan says

Dear Sir,

Thanks a lot for putting my question regarding blade strength, length and weight,

In this regard I have myself found some information which I feel will interest the readers.

There is one 250 KW WES-30 which uses two blades of entire carbon fiber, each weighing 315 kg. Now from one study on internet regarding sera-8 blade study, I came to know that entire carbon fiber blades are 2.4 times costlier than entire fiber glass blades, but their weight is mere 22 %. Based on this data I can extrapolate weight of entire fiber glass blades as (315 * 2 / 22 ) * 100 = 2863.63 Kg

Now, Mr. Paul Dvorak has kindly told me that weight of he blade changes as cube of the length. This meant, when length of the blade doubles, weight increases by the power of 3 where as power increases only by square of the length.

Interestingly, for First two NASA wind turbines of 100 KW and 200 Kw capacity they had used steel blades weighing 2090 kg for both. In another model NASA had used two aluminum blades each weighing 909 kg. for 100 KW turbines. However Putnam’s 1.25 MW wind turbine used steel blades weighing 16 tons.

Readers are requested to submit data of actual blade length, material of the blade and blade weight and off course wind generator power in this forum. So that above formula can be verified.

Scott Battles says

I posted a couple links to some good materials below. In short there is not a simple answer to complex question. It is amazing to look at theses blades and understand the complexity of these seemingly simple blades. The blade or airfoil needs to have smooth contours as much as possible. Any noise is air resistance and any sharp edge will allow harmonics to build up or cause stress points. Harmonics obviously destroy the drive train. A good blade design is crucial. Send me your contact information through the below NWTO and I have some other good reading material.

Best Regards Scott Battles Wind Instructor, Pinnacle Career Institute

National Wind Technician Organization, Midwest Operations Mgr.

http://www.aseanenergy.info/abstract/31029154.pdf

http://www.mech.utah.edu/senior_design/05/uploads/WindTurbine/twist_couple5.pdf