Please understand I appreciate all of the hard work you do to provide this forum, and at the end of the day it is YOUR forum and you need to do what you think is best; no arguments from me on that. It just seemed to me like Windy Nation was getting an unusual reception for what looked to me like pretty good test videos. I do understand being leery of people with commercial interests and spammers in general, but this hobby really does need some people who can provide kits and bits to those who want to play but do not have a full shop at their disposal. Sorting out the scammers from the honest ones is a difficult task, and I have no first hand knowledge of Windy Nation either way. I simply thought the act of sharing some of his prototype testing was refreshing, particularly for someone with commercial interests.
7.7ft diameter. If your output is ~500W @ 27mph this implies an overall cp of ~0.113. This is perhaps the most "honest" cp I have ever seen associated with a commercial interest small scale wind turbine. If the cp is constant (which it NEVER is) this implies 85W @ 15mph and 13W @ 8mph. On the list of tests you might consider is plotting your overall cp at numerous wind speeds from cut-in to furl and work on maximizing the cp in the 12mph-18mph range. If you could get the overall cp up to ~0.25 @ 15mph you should see ~189W from 7.7ft diam blades. Even if your cp drops linearly from 0.25 @15mph to 0.05 @ 27mph you would be gaining a great deal of actual Wh in areas that simply do not have sustained 27mph winds (most of the world). Improving the overall cp is a tricky thing, as I am certain you are aware, but sacrificing high-wind performance for a higher output at more reasonable wind speeds is really worth spending some time on.
Following is a table of RPM for various TSRs / Wind Speeds:
Radius 8 12 15 20 30 50 80
TSR Feet MPH MPH MPH MPH MPH MPH MPH
8 7.7 116 175 218 291 436 727 1164
7 7.7 102 153 191 255 382 636 1018
6 7.7 87 131 164 218 327 545 873
5 7.7 73 109 136 182 273 455 727
4 7.7 58 87 109 145 218 364 582
3 7.7 44 65 82 109 164 273 436
2 7.7 29 44 55 73 109 182 291
1 7.7 15 22 27 36 55 91 145
Obviously real-world TSRs are NOT constant across variable wind speeds, and are ultimately greatly affected by loading, but a bit of blade testing should give you some clues to the TSR range at a given wind speed. In order to get "peak" output at a certain wind speed, you need to determine the most efficient TSR loading at that wind speed, then design your alternator to reach its peak efficiency @ that RPM. For a hobbyist this "recursive approach" to a final design is typically too much work, but for someone with commercial interests, this methodical approach will yield a far superior product. You might even consider offering two or more alternator configurations for any given set of blades. Obviously you might need to offer different furling options as well.
Most commercially available turbine bits/kits tout their specs @ 10m/s-15m/s (22mph-33mph) wind speeds while most people live in areas with typical wind speeds in the 5m/s-9m/s (12mph to 20mph) range with only occasional 25mph to 35mph winds. While 500W to 5kW claims are rampant in marketing literature, there are very few places windy enough to ever see these outputs. Getting 200W from a more typical 15mph wind with furling occurring in 25mph to 30mph range would serve people much better. Designing an alternator to reach peak performance in the 100rpm to 300rpm range is a bit more challenging than designing an alternator to reach peak performance @ 600rpm to 1200rpm, but the investment in time will greatly improve the total realized power from the turbine. Of the two methods to maximize alternator performance in the 100rpm to 300rpm range (gearing, increased magnet count), increasing the magnet count is the more efficient (IMHO), but you should consider both methods.
Anyway, I look forward to reading more about your tests, and hope that others here will help you on your way to turning prototype into product.