Below is a “Technology Note” prepared by Carl Baker at Pacific Northwest National Laboratory (PNNL), offering an independent look at our Pterofin oscillating-wing concept. In this note, he highlights key considerations and potential approaches for harnessing wind and water energy using our technology, touching on areas such as mechanical design, fluid flow alignment, and practical applications in diverse settings. His observations reinforce the adaptability of Pterofin in different environments—particularly where infrastructure constraints or resource limitations may favor simple, serviceable systems. We appreciate PNNL’s perspective and believe it helps illuminate both the promise and the engineering challenges of Pterofin technology. By sharing insights from experts beyond our own team, we hope to encourage open discussion and continued innovation in renewable energy solutions.
Pterofin Technology Note (from Pacific Northwest National Laboratory)
This technology note summarizes recommendations and observations about the Pterofin wind- (or water-) generation technology (visible on-line at pterofin.com). This device employs one (or more) variable-pitch blades (or wings) arranged along a driven shaft (or set of coaxial shafts). Each blade is pitch-controlled in a way that produces rotary oscillatory motion in the driven shaft. As each blade reaches its limit of travel in one direction, the blade pitch is reversed and the blade consequently reverses direction and drives the shaft in the opposite direction.
The design concept is effective in capturing energy from any moving fluid – wind or water are the most widely available candidates. The comments below focus on the use of wind power, but a water-based application may be more advantageous for the device.
The questions and issues regarding the technology at the time of request included the following:
1. Electrical Power Generation
The device presents some challenges as the prime mover for an electrical power generation system. The displacement executed by the wings varies in both amplitude and frequency according to the impinging wind speed. Any mechanically simple drive mechanism connecting a Pterofin device to an electrical generator will result in electrical power that likewise varies in frequency and amplitude (voltage). This poses significant power utilization challenges for applications that require stable alternating current (household use or grid power generation). These challenges could be addressed mechanically via the use of a number of different types of devices. Some examples would include:
An alternate approach to electrical power generation would be to use an extremely simple coil-and-magnet type of generator such as is used in a “shake” type flashlight (http://en.wikipedia.org/wiki/Mechanically_powered_flashlight#Shake_type_design). This type of generator relies on a rectifier to convert the irregular alternating current (AC) produced by the generator into unidirectional current that can be used to charge a battery. The simplest way to drive this type of generator system is probably to arrange the driven shaft of the Pterofin device so that it has an offset crank driving a connecting rod, which in turn carries a magnet back and forth (or up and down) past the generator coil.
A similar arrangement to the above could be used instead to operate a piston pump for lifting water.
2. Flow Alignment
Alignment of the device with the impinging fluid flow direction poses a challenge. Since the device oscillates in an asymmetric way, it is difficult to devise a method to cancel out the torques generated by oscillation so that a passive method (such as a tail fin or simple drag) can be used to align the device. In many water-driven implementations, the direction of the water flow is relatively stable and predictable. In this instance, the device can simply be carefully aligned with the flow and fixed in place.
A dual-wing design configured not unlike a bird, with the pitch axes of the two wings in a co-planar configuration would cancel out the asymmetric torques if the wings could be coupled so that they traveled in equal-and-opposite oscillations. This arrangement might passively self-align with no tail fin if the wings were down-wind of the (vertical) alignment axis. This arrangement necessarily limits the travel of the two wings – at most they could dip to horizontal and rise to vertical, but the physical size of the wing would limit the range of motion to significantly less than 90 degrees.
Another approach to addressing the flow alignment issue is to adjust the device design so that the axis about which it oscillates is perpendicular to (rather than parallel with) the flow direction. If this arrangement can be obtained, the axis of oscillation can be placed “after” or “downwind” of the axis of alignment and the device becomes self-aligning. A device similar to this (http://www.wind-power-innovations.com/) could be made self-aligning.
3. Applications
Since wind is highly variable, wind energy applications are generally constrained to applications where opportunistic energy collection can be exploited. A grid-based power system can most easily exploit wind if existing load-following sources can manage the transient supply from the wind-based source. An off-grid power system can most easily exploit wind if the power can easily be stored for later use.
Water-based applications are more stable and predictable, so load-following sources do not need to be as robust. However, opportunities for grid-scale hydro-power are limited since most existing viable large-scale sites have been developed or are protected.
One design advantage of the Pterofin device is that the mechanical portion of the device can be installed at or near ground-level, where it can be more easily serviced. This benefit is most advantageous in applications where large towers are not practical. There could be aesthetic reasons for this, or it could be that the local industrial infrastructure does not have the necessary resources to construct and maintain the towers themselves or to easily deliver workers and tools to the top of the tower for routine servicing of the system. One such circumstance is in developing economies.
With the difficulties of power generation and the characteristics of the device itself, a very attractive application of the Pterofin technology may be in developing economies. If a kit consisting of a very few simple and inexpensive parts (and some plans or general directions) could be provided to individuals, they could construct a micro-scale generator system using mostly locally-obtained materials. A very small generator system would provide sufficient power to recharge a cell phone or LED flashlight over the course of a day. Making these devices available to low-income people in developing economies could provide a considerable improvement in quality of life at a very low cost.
The design concept is effective in capturing energy from any moving fluid – wind or water are the most widely available candidates. The comments below focus on the use of wind power, but a water-based application may be more advantageous for the device.
The questions and issues regarding the technology at the time of request included the following:
- Difficulties with gearing and other mechanisms to drive electrical power generation
- Steering the device into the wind (for a wind-powered application)
- Potential applications (developing economies vs. developed economies, individual users vs. utility-owned grid generation)
1. Electrical Power Generation
The device presents some challenges as the prime mover for an electrical power generation system. The displacement executed by the wings varies in both amplitude and frequency according to the impinging wind speed. Any mechanically simple drive mechanism connecting a Pterofin device to an electrical generator will result in electrical power that likewise varies in frequency and amplitude (voltage). This poses significant power utilization challenges for applications that require stable alternating current (household use or grid power generation). These challenges could be addressed mechanically via the use of a number of different types of devices. Some examples would include:
- A continuously variable transmission (CVT) with an automated revers-er
- A pair of ratcheting (or clockwork-winding) mechanisms could be used – one to be driven in each direction of oscillation. Energy could be stored in one or two springs or flywheels or by lifting a weight or weights against gravity to generate potential energy. A secondary drive system would then be used to convert the potential energy into electrical power.
An alternate approach to electrical power generation would be to use an extremely simple coil-and-magnet type of generator such as is used in a “shake” type flashlight (http://en.wikipedia.org/wiki/Mechanically_powered_flashlight#Shake_type_design). This type of generator relies on a rectifier to convert the irregular alternating current (AC) produced by the generator into unidirectional current that can be used to charge a battery. The simplest way to drive this type of generator system is probably to arrange the driven shaft of the Pterofin device so that it has an offset crank driving a connecting rod, which in turn carries a magnet back and forth (or up and down) past the generator coil.
A similar arrangement to the above could be used instead to operate a piston pump for lifting water.
2. Flow Alignment
Alignment of the device with the impinging fluid flow direction poses a challenge. Since the device oscillates in an asymmetric way, it is difficult to devise a method to cancel out the torques generated by oscillation so that a passive method (such as a tail fin or simple drag) can be used to align the device. In many water-driven implementations, the direction of the water flow is relatively stable and predictable. In this instance, the device can simply be carefully aligned with the flow and fixed in place.
A dual-wing design configured not unlike a bird, with the pitch axes of the two wings in a co-planar configuration would cancel out the asymmetric torques if the wings could be coupled so that they traveled in equal-and-opposite oscillations. This arrangement might passively self-align with no tail fin if the wings were down-wind of the (vertical) alignment axis. This arrangement necessarily limits the travel of the two wings – at most they could dip to horizontal and rise to vertical, but the physical size of the wing would limit the range of motion to significantly less than 90 degrees.
Another approach to addressing the flow alignment issue is to adjust the device design so that the axis about which it oscillates is perpendicular to (rather than parallel with) the flow direction. If this arrangement can be obtained, the axis of oscillation can be placed “after” or “downwind” of the axis of alignment and the device becomes self-aligning. A device similar to this (http://www.wind-power-innovations.com/) could be made self-aligning.
3. Applications
Since wind is highly variable, wind energy applications are generally constrained to applications where opportunistic energy collection can be exploited. A grid-based power system can most easily exploit wind if existing load-following sources can manage the transient supply from the wind-based source. An off-grid power system can most easily exploit wind if the power can easily be stored for later use.
Water-based applications are more stable and predictable, so load-following sources do not need to be as robust. However, opportunities for grid-scale hydro-power are limited since most existing viable large-scale sites have been developed or are protected.
One design advantage of the Pterofin device is that the mechanical portion of the device can be installed at or near ground-level, where it can be more easily serviced. This benefit is most advantageous in applications where large towers are not practical. There could be aesthetic reasons for this, or it could be that the local industrial infrastructure does not have the necessary resources to construct and maintain the towers themselves or to easily deliver workers and tools to the top of the tower for routine servicing of the system. One such circumstance is in developing economies.
With the difficulties of power generation and the characteristics of the device itself, a very attractive application of the Pterofin technology may be in developing economies. If a kit consisting of a very few simple and inexpensive parts (and some plans or general directions) could be provided to individuals, they could construct a micro-scale generator system using mostly locally-obtained materials. A very small generator system would provide sufficient power to recharge a cell phone or LED flashlight over the course of a day. Making these devices available to low-income people in developing economies could provide a considerable improvement in quality of life at a very low cost.
