Thanks for the very precise feedback; the last paragraph seemed more understandable to me than the above physics. I am aware of most of that but was questioning towards the behaviors of the wind turbine in a battery-charging applications.
A few more bullet points on my project, that also answers TomW quest, I am just designing a turbine for low wind regime and that's also a part of my academic interest. I need to be able to answer the most miniature questions, even not-thought of technical points, so that I could avail my masters. Anything that comes across my mind or from my fellow colleagues, juniors or seniors, I attempt to put that in a sensible format for comments from the board members. Does that answer your question, TomW.
My design a 48V~5 KW turbine with a 3-bladed rotor diameter of 6.3m (20-feet), that I availed from a local fiberglass firm -professionally built as per the airfoil patterns, which has a unique drive train design of turning two PMAs, one 3KW(rated 400 rpm -Asian origin) and the second 2KW (rated 300rpm-also Asian product), which are connected to the rotor shaft with a 1 to 3.5 rpm gearing . I am supposing that the turbine would achieve a rating of 5KW at only 100 rotor rpm (at around 7.5 m/s) AND up to 8KW at 9m/s when the rotor is turning at 150 rpm.
As you say that the rotor speed stays constant after the cutin, then why do we see a battery charger turbine's speed increase and decrease so frequently? It doesn't stay the same and keeps on increasing and decreasing smoothly.
My understanding is that beyond the cutin rpm ( I would name it as an overhead rpm value - any ideas on calculating that) , the rpm is directly proportional to the wind speed.
Regarding the information on my turbine, do you see any sensibility in the ratings? If these don't tele much, then how would you rate or imagine my turbine in terms of rotor rpm, cut-in wind speed, general idea of gearing (if its right), battery cutin rotor rpm etc...I know there is a lot more information needed on the PMAs and the blade profile etc...but generally any reference or presumptions would help.
Generally a 3-bladed 20-footer commercial battery charger turbine would be rated at 7 to 9-KW in 12 m/s winds, I am driving my 5KW @ 7.5 to 8m/s -calculations or (more appropriately) presumptions by comparing is to commercially available turbines.
Any ideas, suggestions and recommendation would help.
Thanks.