I'll make some comments. Som eof the questions are a bit tricky for a trial and error fellow like me but...
"As a newbie, I am also interested in this subject. I've seen a few designs so far and you guys have a pretty good handle on designing but the steps seem to be confusing."
Starting from scratch is sort of tricky and I think some trial and error is necessary. I tend to get a pretty good handle on teh sort of power I can expect at any given rpm from an alternator though by looking at past projects. Starting from scratch - I would build the magnet rotors, and test a coil in there. It gives a starting point anyhow.
"As an example, suppose I wanted to build a generator with 4 foot blades. I can get a fair indication of the power I'll be able to make from the swept area. But what's next? Do I need to pick a tip speed ratio (TSR) next and design the generator from there to work at the expected average RPM I'll get from the average wind velocity here?"
Yes, and build it powerful enough so that it won't burn up in higher winds - in other words, keep resistance low enough so that it's efficient enough so that too much heat doesn't build up.
" How do I pick the right TSR? Am I going about this from the wrong end? Is the TSR selected first and the generator designed around that or is the TSR selected based on the generator which is designed first?"
I think about any reasonable machine you woud plan for TSR between 5 and 7 'average'. In practice, TSR will vary depending on the wind speed because the alternator will not track the cubic power curve of the wind (without an electronic MPPT controller of some sort anyhow). I usually like to think we'll be running TSR around 6 in 'average' winds. At 'cutin' you have to figure the TSR will be extra high because there is no load on the machine below cutin, so I usually figure TSR of 8 or so at cutin, and then it drops off from there hopefully. I expect my 20' machine runs at TSR of 4 or so in high winds and cuts in at TSR around 8.
I usually start out planning the diameter of the machine - build an alternator that's suitable for that sort of power at those speeds and then test it. Often times the alternator does not do exactly what I'd expect so then the plans for blades might change a bit from there.
A good safe way to go in my opinion - if it's a new design, is build your alternator on the heavy side (too powerful) and get the cutin speed right or too low.. not in an extreme way but it's good to lean on too powerful. From there - if its too slow you can open the airgap - if resistance is too low and it stalls the blades you can add resistance downstream. For a 'new' machine it's not the worst way to go - a bit more cost and weight but it's better to come out on the 'too powerful' side of things and have to detune the machine than it is to come out on the 'not powerful enough' side and burn out or have a machine that runs very fast/makes noise etc.
