## Power Coefficient

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Moderator: Bonnie.Jonkman

Sina.Ameli
Posts: 75
Joined: Mon Oct 15, 2018 11:23 am
Organization: FSU
Location: Florida

### Power Coefficient

Dear Dr. Jonkman,
In wind turbines, is it possible that CP (Power Coefficient) becomes negative sometimes in region 3?
Thanks,
Best regards,
Sina

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

### Re: Power Coefficient

Dear Sina,

I would normally except the time-averaged value of Cp to remain positive in Region 3, but I could imagine situations where the instantaneous value of Cp goes negative temporarily.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Sina.Ameli
Posts: 75
Joined: Mon Oct 15, 2018 11:23 am
Organization: FSU
Location: Florida

### Re: Power Coefficient

Dear Dr. Jonkman,

Thanks for your prompt response. In what situations CP is negative? For instance, is it possible when we have a sudden drop in the wind speed creating a negative torque and finally a negative power coefficient, i.e the wind turbine behaves like a motor (propeller)?

Thanks,
Best regards,
Sina

Jason.Jonkman
Posts: 5738
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

### Re: Power Coefficient

Dear Sina,

I'm not sure, but the instantaneous values of Cp certain fluctuate when simulating in turbulence. Again, I wouldn't look at that much, focusing instead on the time-averaged Cp values.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov