Current shipping systems cut-in wind speed is between 5 and 6 mph. The RoofMill™ is fully Hybrid and it's output at any wind speed is a combination of wind and solar hybrid power. So power at start-up speed cannot ignore that there is substantial solar power in every RoofMill™ as well. Wind power is a great thing but it is irradic and variable over time. That is why the RoofMill™ is fully hybrid, only hybrid. The RoofMill™ is not a turbine, it's a complete energy system. So, comparing it to any of these wind only systems out there is no comparison at all.
A wind only home energy system is what I started with myself. I have had solar only energy systems. As I developed hybrid power systems I decided that I would never want a wind only system, not a solar only system. I find both to be needing the other and they belong together and are complimentary. Day by day, season by season, wind and solar work great together.
EXAMPLES: On a windy night, a solar only home system is useless. On a still sunny day, a wind turbine is useless. Seasonally winter is better wind, summer is better solar. The RoofMill™ is a decidedly hybrid system and I decided that since I would never own a wind only or solar only system for my home, I would not want to sell them either. So, back to the question, cut-in speed is where there is not much wind, not much wind power in any wind only system. It's the exact scenario of why this system is hybrid. No wind system is making much power at cut-in speed. Let's hope that a person has a well designed hybrid for that scenario. The 4.2kW RoofMill™ is the same system I run on my own home every day. So, as people compare things like cut-in speed also look at the solar, if that system compared is not solar hybrid, forget it, it's not as good and well featured home energy system as the RoofMill™. No wind only system is as good as a hybrid power system.. period. No Solar only system is as good as a hybrid power system.. period.