Your VAWT center shaft is destroying the air passing to the rear blade to add power to it.
Remove most of the shaft, to just not more than about 15 % eight, make another disk and firmly attach the upper ends of the VAWT.
To see what type of RPM multiplier you need, try to read the RPM and the wind velocity, divide the RPM by 2 to give the working RPM ( close enough), then see what is the generator Volts/RPM to calculate the multiplier gear.
Example: no load RPM = 110 RPM ; loaded RPM = 110 /2 = 55
Generator 15v /400 RPM =
Multiplier = 400 /55 = 7.27 :1 multiplier, make around 7 to 7.9 ratio.
Your wind mill looks ( estimating) like it is 3 inch X 12 inch or 36 square inches, then you have additional losses due to the loading of the opposite half side giving braking effects, plus the shaft destroying the wind passage to the opposite half.
I made one, several decades before, I am retired now, using 2 - 55 gallon containers cut in half and placed one on top of each other with plywood for the bottom the middle and the top.
The bottom plywood was utilized to produce the gear ratio for the generator ( I do not recall the generator pulley diameter).
The wind mill produced around 50 - 80 watts ( I do not recall exactly).
Nando
