Andy Kruse

Depends on what you want to spend. If you are a hobbyist and want to play around, any turbine that follows the basic design, upwind, horizontal axis, three blades with passive pitch and yaw is fine. If you invest more than $5K, then certification is critical. Above that, make sure it's a design that can be financed. Stay away from "breakthrough" designs.

There were almost as many designs of wind turbines as there are automobile brands in the world. I have been part of this industry for over 40 years and recall the '80s and 90's as the industry experimented with horizontal, vertical, up-wind, down-wind, 1, 2, 3, 4, and more blades, active yaw, passive yaw, active pitch, passive pitch... Southern California was at once time littered with every possible contraption. The successful companies focused on LCOE and settled on one common design we all see today - horizontal axis, upwind with three blades, and active yaw and pitch. period. Even small wind but the yaw and pitch are generally passive. And, towers - Every design was thought of and all settled on mono-pole.

There are several factors that affect efficiency - Blade design, alternator efficiency, gearbox or direct drive, power electronics. Every step from kinetic to usable electricity includes losses. Then, the turbine is properly sighted. Sighting is not directly part of efficiency, but it has a significant impact on performance, which is tied to the true measurement - LCOE.

Efficiency does not matter. LCOE is what matters. Efficiency has a direct impact on LCOE but that is not the full story. The blade on a vertical Axis Wind Turbine can approach the Betz limit. This is the conversion of kinetic energy into mechanical energy. However, siting a VAWT and the reliability of a VAWT would have a significant impact on its LCOE. Furthermore, to suggest installing on a rooftop "could" be efficient, but EVERY site is different, and advanced modeling would be required to determine if that is a suitable site. Most sites would not be appropriate.

You want to begin with understanding your goals. Generally, economics is a big one. Many technologies could be used in the project. Solar, Wind, Storage, CHP, fuel cell, etc. You also want to understand the application and the location. Is this to offset more expensive onsite generation? Will the microgrid be used as primary power or backup? That helps you know what you can consider and what to leave out. The easiest way is to use an optimization software like HOMER. It can consider all these, including O/M, depreciation, interest rates, etc. The software can run many scenarios to help narrow down your research. It's also critical to understand your load, hour by hour.