Re-posted and updated from OSEE google group:
I've been looking into electrical requirements for the ducted HAWT that I'm working on, and I am a bit concerned about getting blade speeds and amperage ratings right so that I don't end up with a giant fireball on the end of a pole.
I'd like to have a purely drag-oriented (blades always downwind of the tower) wind turbine since
this simplifies construction and strength concerns when there are high-speed gusts, as a shroud won't have to deal with potential vibrations from furling side-on to the wind, however at the same time it raises potential heat-dissipation issues if the alternator is capable of harnessing much of the power from high wind speeds. I know it can be done because it has been field-tested a few times in Japan, for instance this system at Kyushu University, where this open paper notes that this prototype had a 2.5m rotor diameter and was rated to 5000W, while an earlier prototype in the paper with a 0.7m rotor diameter and a (proportionately) much larger duct was apparently rated at 500W.

So far I've been taking most of my electrical and rotor-blade advice from Hugh Piggott's "Wind Turbine Recipe Book" (2009 version), where he put forward a set of scalable plans for un-ducted turbines with rotor diameters ranging from 1.2m to 4.2m with alternators rated from 200W to 1000W respectively (he vaguely rates anything over 3.6m as 1kW), with a design Tip Speed Ratio (air velocity past blade tips in relation to free-stream wind speed) of 5 to 7 respectively.
In that book, 9-coil 24V stator windings for 1.8m and 2.4m turbines (rated 350W and 700W respectively) are suggested as 110 turns and 45 doubled-up turns of 1.5mm diameter copper wire (the latter being equivalent to 90 turns of 2mm, suggested to 'double up' in order to avoid 'clumsy wire sizes'). I want to make a similar 24V stator for a 0.9m diameter ducted prototype, but with the coil mounting more squashed in diameter (and so possibly slightly less efficient). I have drawn up a rough representation here of how I think stator coils could be mounted, using an ABS casing pressed against an aluminium plate as a heat-sink - cut with small parts poking out into the passing airflow to help dissipate heat.
My question to any electrical engineers is: what sort of current rating might be safely achievable in such a setting if I were to use something like 2mm diameter wire? I ask because I was checking this handbook-sourced guide on AWG ratings, and the quoted 'conservative' maximum ratings sound a bit confusing. I just got hold of a big cheap pack of N35 20x3mm neodymium disk magnets to test this with, after reading that lower-flux ones have greater thermal and mechanical stability. These things are still strong and difficult to handle though.

This is especially important where I want to test out a wind turbine because here on the north coast of Scotland we occasionally get storms blow across that can bring wind speeds up to around 50mph (80.45km/h, 22.35m/s) and gusts over 60mph (96.54km/h, 26.82 m/s). If you run a calculation on theoretical kinetic energy in that wind, P = (density/2)*area*(windspeed^3), then this turns out as max theoretical power = (1.2kg/m^3)/2 * ( (3.14*0.45^2)m^2 * (26.82m/s)^3) = 7360W.