Power available from the wind:
P = .5 * rho * A * v^3 * Cp * Ng
P = 10.000 W (their "rated value")
rho = 1.225 kg/m^3 (assuming standard atmosphere)
A = 12 m^2 (FULL frontal area...)
v = 12.4 m/s (28 mph, their "rated value")
Cp= coefficient of performance (should be < Betz=0.59)
Ng = generator efficiency; set to Ng=1 here
With these figures, solving for Cp, I get Cp=0.71)
Which means they get 71% of the energy of the wind from what's actually available.
So they beat Betz.
Now, this Cp was calculated using a frontal area of 12 m^2, assuming that the entire frontal (projected) area of the turbine generates power. Which it doesn't. I think half of the area is more closer to it, but I know too little of VAWTs to make a better guess. Smaller area means their (implicitly) claimed Cp gets even higher.
This was assuming that Ng, generator efficiency, was 1 (100%). I usually calculate my gennies for Ng = 0.70-0.75
If one would take these corrections in account, they would achieve overunity.
They either deserve a Nobel prize for physics or prosecution for fraud/misleading advertising.
I don't think they'll get either though.
Not only that, I notice two different diameters for their 'delta-II':
In this file it says dia = 158"(4 m) (http://pacwind.net/download-pdf/Delta_II7-23-07.pdf)
In here, it says dia = 96" (http://pacwind.net/):
"Physical Specifications:
Cage Height 120 inches
Cage Diameter 96 inches"
(I originally calculated using the 96" value and arrived at a Cp=1.15 instead of .71, wondering where my error was as I verified the calculations. Seems they give two entirely different diameters for the same product in different places).
Whatever way, even calculated 'in their advantage', they beat Betz. Depending on some other (realistic) assumptions, they even achieve overunity.
But I'm not even sure which data is the right one for their product. 96" diameter ? 158 " ?
Caveat emptor.