DISCOVER OUR INNOVATIVE TECHNOLOGY
The technical challenges
Wind, like all renewable sources, is not a homogeneous resource and the different types of flows cannot be exploited in the same way.
The theoretical limit of energy that can be extracted from a turbine is about 59% of the total kinetic energy that hits it; this is called the Betz limit, but in practice only a few very large turbines reach values close to 48%. This parameter, which on turbines is called the power coefficient (Cp), indicates how much of that kinetic energy that was available in the air, I can actually capture. It is not uncommon to find products online that fraudulently ignore this parameter and declare powers that would be real only in the middle of a hurricane.
The turbines currently available on the market are divided into two macro-categories based on the position of the axis: the horizontal axis turbines (HAWT) that we all know, and the vertical axis turbines or VAWT , like the one we propose in our project.
Although horizontal-axis turbines perform better on average in terms of Cp, they dramatically lose their advantage in the presence of turbulent wind, since they must be continuously oriented towards the direction of its origin.
Vertical-axis turbines, on the other hand, capture air flows from any direction, a great advantage in urban settings.
However, they do present some challenges: their higher inertia compared to horizontal-axis turbines often makes them unsuitable for chasing the typical gusts of wind in cities. This problem is partially mitigated by the use of composite materials for the blades, which are not always recyclable, sometimes provide the necessary resistance to fatigue cycles and increase the overall cost of the rotor.
Our goal is to overcome these limitations, making urban turbines more efficient, safe and sustainable; in general a valid alternative or support to photovoltaics where space, exposure or shading do not allow the installation of a system or its expansion.
The urban challenges
Extracting energy from wind in cities is a complex challenge. Wind flows, rather than being laminar and constant, are confused, swirling, sudden and change direction easily. These conditions reduce the wind speed near the ground, decreasing the available power density , or the amount of energy that passes through the blades of a turbine per square meter.
The power density of a given location is a parameter that indicates how rich in wind it is per square meter: at 10 meters above the ground, the entire Italian territory has an average capacity of 140 Watts per square meter, while a third of the country has at least 300 W/m² available .
In urban areas, the challenge is further amplified by gusts, which accelerate the turbine rotors intermittently, with periods of a few minutes for hundreds of times a day. To exploit them effectively, the rotors must be light, with low inertia, or a high capacity to accelerate under the thrust of the wind .
Imagine having to push a shopping cart. If it is empty, with a short push, the burst, you can easily get it going and gain speed. But if the cart is full of heavy bottles, the same short push is not enough: it remains almost stationary due to its high inertia, requiring more force or a longer impulse to start moving.
Wind turbines with high inertia behave like a full trolley : short gusts of wind in urban areas, which act as intermittent pushes, struggle to get the rotor moving. Reducing inertia becomes essential to capture energy even from these unstable and irregular air flows.
The safety of components, noise, vibrations transmitted to buildings, integration into urban aesthetics, environmental sustainability throughout the entire life cycle, electromagnetic interference and safety for avifauna, are other challenges we are working on to create a product that can finally integrate where energy is increasingly required, the urban environment .
Cumulative distribution of average power density at 10 meters height on Italian soil. 10% of the territory has an average power density of 615 W/m²
Urban wind resource measured on a rooftop showing a period with high fluctuations; data averaged at 1 Hz (1 data point per second, dotted lines) and at 0.1 Hz (1 data point every 10 seconds, solid lines). Note the amount and intensity of fluctuations in just over 3 minutes.
The innovation
Our turbine addresses technical and urban challenges with an innovative patented solution . To reduce inertia, which varies exponentially with the square of the distance, we have designed a system that changes the diameter of the turbine only when there is an actual need to accelerate the rotor. This can become even more efficient thanks to an artificial intelligence algorithm that learns to predict gusts and positions the blades at the optimal diameter, allowing it to be in tune with the intermittent flows of the urban environment.
So it is possible to have a turbine that can vary the inertia and keep the wind capture area large , depending on the weather conditions, but can also give us extra energy stored in the form of inertia if the load calls for a "boost".
We have also integrated into the same system a second blade pitch variation mechanism that allows for fine adjustment to reduce the forces on the turbine, limit the rotation speed, ensure self-start and reduce fatigue cycles, increasing the useful life of the turbine.
These features lead to an improvement in environmental sustainability by allowing for an increase in the energy produced and to a greater economic return over time for the buyer, compensating for the purchase investment in fewer years.
The advantages can then be extended to a wide range of users who need portable electricity, such as recreational boating or campers; in these cases we would have the possibility of providing an efficient product that can be folded up on itself with a button before leaving for the next destination.
Let's do the math
Data is essential to evaluate the potential of micro-wind. Wind power increases with the cube of the wind speed: a doubling of the speed generates eight times more energy. For this reason, installations are recommended in areas with an average annual wind speed of at least 4 m/s (about 14 km/h).
However, saying that a turbine is 3 kW means nothing if you do not specify at what wind speed it reaches that power. Generally, this value is obtained between 10 and 12 m/s (36-43 km/h).
Our analysis shows that, with the same blades compared to two competitors, we are able to reduce inertia by between 120% and 270%. This translates into greater energy harvested during gusts, up to 300 per day in cities, and halving the turbine start-up speed.
Thanks to these solutions, we could use a wide range of recyclable materials up to 7 kg heavier per blade without compromising performance, benefiting the environment and costs.
In Italy, 20% of the territory is affected by an average wind speed of 4.3 m/s, sufficient for a 10 m² turbine to produce approximately 8000 kWh per year, generating an economic value of approximately €2000 at the current cost of energy.
Graph between the cumulative probabilistic distribution of wind speed of Lecce and the energy produced by a VAWT turbine without geometry variation against the variable geometry turbine of IKARIA. Note in light blue, the amount of additional energy expressed in kWh that can be recovered with this system.
Graph between the cumulative probabilistic distribution of wind speed of Trieste and the energy produced by a VAWT turbine without geometry variation versus the variable geometry turbine of IKARIA.
To this energy must then be added the additional energy that can be recovered thanks to our technology by extending or contracting the radius of the turbine to ensure that it captures the maximum amount of wind within its structural limits, obtaining a gain between 17% and 38% more than a fixed geometry turbine, even when the others stop!
​