A 7-12 mph start up sounds really good until you look at the curve.

A 400 watt wind generator @27 mph only produces 25 watts per hour @ 12 mph. Not worth turning on the inverter.

I doubt you could mount a wind generator on a chimney. The vibration would crack your mortar.

in the US your competition is Bergey Windpower and SouthWest Windpower so see what they are doing…..

there are also alOT of small wind generators made for small yachts that put out 70-100w..look at agood chandlers catalouge to see what available…….Rutland makes a small ABSOLUTELY SILENT w/t…….

and as was said, 300 watts aint much…..

and look carefully at your output power curve…..a lot of turbines are rated at xyz watts…turns out thats for an unrealistic wind speed…….yes indeed 7 m/s or 12 mph is what you need to aim at…….

It’s not primarily about the cost. One of your examples has an area of 4 square metres and is rated at 240W in a 33mph wind. That’s not a lot of power, it’s a big machine (on a domestic scale) and I rarely get winds anything like that speed. I doubt if many chimneys would stand this structural load. I am very interested in the technology but economically it’s a non starter.

I would need a machine that was optimized for a wind speed of about 7m/s. And it would have to have high efficiency to keep the size down. Inevitably this would mean a high tip-speed ratio and therefore noise; it is a difficult balance.

All the same I wish you well, these machines will suit some applications.

300 watts isn’t enough power to make it worth the effort.