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Active vs Passive Variable Geometry in small wind turbines: everything you need to know

In the dynamic landscape of small wind turbines, the choice between active and passive variable geometry holds profound implications for efficiency, sustainability, and energy consumption. These two technologies represent distinct approaches to harnessing the power of the wind, each with its unique set of advantages and considerations. In this article, we explore the characteristics of active and passive variable geometry, shedding light on their differences and the impact they have on the small wind energy sector.

Before we dive in, it is essential to understand what exactly do we mean when we talk about variable geometry in small wind turbines. The best way to do so is by thinking about the wings of an airplane: some parts of the wings are moved by the pilot in order to alter their aerodynamic properties, so that the change in wing shape can allow the plane to take off, switch direction, or slow down before landing.
The same principle applies to vertical-axis variable-geometry wind turbines: in order to make the most out of every gust of wind, the blades of the turbine can be moved to change their orientation and produce more energy. And here is where today’s topic comes into play.

Image 1 - variable geometry in the wing of an aierplane
Image 2 - variable geometry in a (windcity) wind turbine

Now, back to the difference between active and passive variable geometry.

“Passive” is a word of profound meaning, and not one of easy understanding as “Active”, therefore some etymology is needed to appreciate the deep matter substantiating a passive approach in deep tech. 
Passive originates from latin passivus, a late form of passu, past participle from the verb patior of the same greek and indoeuropean root of pathos (passion): 

patior (present infinitive patī, perfect active passus sum) 
(transitive) I suffer, endure, tolerate.  
(transitive) I allow, acquiesce, permit, submit.  
“Patere lēgem quam ipse fēcistī / tulistī.” 
Submit to the law which you yourself made / proposed. 
(intransitive) I exist, live 
“Pati sine regno”. 
To live without a king. 

A passive deep tech therefore has to do with the strive to obtain a benefit from an equilibrium with the forces of Nature just by allowing, and so suffering, enduring, reacting to its actions. 

Now that we have defined the meaning of ‘passive’, when talking small wind turbines, the key distinction lies in how variable geometry adjusts to find the optimal position for maximum wind energy production. In this regard, passive variable geometry simply relies on the power of wind to adjust the position of the blades of the small wind turbines: in order to produce energy, the blades are built with a specific mechanic that allows the turbine to self-adjust according to wind flows. In contrast, active variable geometry involves the consumption of energy ー either some of the energy produced, or the energy supplied by a secondary source ーto adjust system components for optimal wind energy production through the use of sensors, actuators, servo-motors, etc. This usually consists of an AI powered system operating all the time, that collects data and sends signals to the turbine, electronically changing the position of the blades. Moreover, to be real-time, active controls can hardly be wireless, thus requiring a rotating contacts box: yet another source of uncertainty for operating conditions, and mechanical complication for system integration. In short, while this approach provides precision and control over turbine positioning, it comes at the expense of utilizing a portion of the energy generated or to be dependent on external energy sources to fine-tune their positioning, introducing an element of complexity and energy dependency.

It is then clear how the prowess of passive variable geometry becomes even more pronounced when considering the potential for complete off-grid use and optimal energy production. This distinctive feature allows systems to operate independently, producing the maximum possible energy without external dependencies. The ability to function off-grid is a pivotal attribute, particularly in situations of necessity, where self-sufficiency becomes paramount. In these scenarios, the passive variable geometry not only maximizes energy production but also ensures a reliable and sustainable power source, reinforcing its role as an innovative technology in the small wind energy sector.

Windcity proudly stands as a pioneer in implementing passive variable geometry within the wind power sector. We patented and produce a purely mechanical technology which allows our turbines to harmonize with every gust of wind without consuming additional energy. Our commitment to innovation and our passive philosophy of “letting the wind take the lead” places us at the forefront of small wind energy, setting new standards for eco-friendly and efficient solutions, and opening the field to true, functional, off-grid applications.