It is alittle difficult to be certain from those photos, but the blades seem to have the correct (flat) side facing the wind. It looks like the blades turn clockwise-- is that correct?
In that last photo you showed, you see the 'straight' side of the blade pointing toward the wind. It should be leaning forward a bit at the tip(s) like this symbol between the quotation marks: " / " < < < WIND direction < < <
Thats as if I'm standing on the LEFT side of the mill looking at the tip angle of a blade.(with the blades turning clockwise)
Of course it don't need to be leaning THAT much forward though. But if the blade tips are simply straight up and down instead of leaning forward, they could be stalling or even air braking.(I believe)
It is too hard to tell from those photos to see the angles of the blades on each side. They almost look flat from BOTH sides.
You had said that one time the blades DID speed up some. Did you see any AMPS showing on the ammeter?
If the blades do in fact turn clockwise, you might try putting a STEEL WASHER under each blade's UPPER mounting bolt, (toward the 'leading edge' side of blade) in order to raise the angle outward more at the tip of each blade, just to see what happens.
It sure has me baffled as to what could be wrong.
That DC motor of yours probably has about the same cogging as the DC motor I am using. The numbers are about the same as mine. My DC motor mill is doing very good in all winds and starts up VERY easy. My blades are just PVC but are the same diameter as yours are. Those blades of yours are much wider and should be much better (all around) than PVC blades as DanB said. Even though there is signifant cogging with such a DC motor, those diameter blades should easily start-up like mine does and take off and generate nice even in a 10mph wind.
Of course having the mill that close to the house and trees is going to hinder the winds quite a bit, but you should still get some better results than you are getting for sure.
Did you get any instructions that came with the blades, like which direction they are suppose to turn? You should email the supplier and ask some questions.
YOu will figure it out.
Wish I could help more.