Michael Fallwell's projects:
Glider powered windmill
A km³ (0.216 Mile³) of air has a mass of about 1 million Tons and even a wind of 2.5 m/s (5.6 mph) is a large amount of energy. Coupling to such a difuse mass is not a trivial matter
Horizontal Axis Wind Turbines (HAWT) are approaching 100 m and are becoming the largest aerodynamic devices ever built. At this level, they can produce 2-3 MW at high energy wind sites.
It is well understood that there is a size horizon out there at about 5-10 MW where growth becomes uneconomic.
1 MW may sound like a lot of power, but it is actually just a bit over 1000 horse power.
So to impact energy usage in a significant way continued growth is essential.
Future wind turbines will need to be much larger than the largest proposed today, in order to pick up even 20% of consumption.
The HAWT is structually a group of cantilever beams. The system we are proposing is instead mostly a tensile structure. As a result, it can be many times as efficient and will have different scale limits. For instance, our 6 m (20 ft) model can economically operate at a height of about 300 m (1000 ft) - well above the height of the largest HAWT. Large HAWTs can generate a bit more than 2 W/kg (1 W/lb) . The 6 m (20 ft) model should put out nearly 100 times as much.
The wind comes from the direction of the camera. The glider crosses the wind and drags the cable through pulleys on the ground. These are coupled to generators. With a wind of 15 km/h (12 mph) the glider speed is 160 km/h (100 mph). For 6 m (20 ft) span, the lift is 200 kg (4000 lbs) and thrust is about 200 kg (400 lbs), giving an output of about 50 KW. The combined length of the kevlar cable is 1 km (0.6 miles) and for a strength of 4500 kg (10000 lbs), the weight of the cable would be approximately 150 kg (300 lbs). The many new degrees of freedom opened by the design allow it to be scaled up considerably.
At the end of the run, the glider reverses direction to begin a new cycle.
Advantages of a Nonaxial windturbine
Low Speed Wind Energy Systems
The goal of this project is to demonstrate the utility of a wind system based on tensile structures and begin to determine its scale limits and cost per KWH. Existing wind systems cost about a dollar a watt and have capacity factors of less than 5%. Tensile based wind systems should prove to be much more economical.
A schematic model of the load paths in a horizontal axis wind turbine (HAWT) is complex because of vibration and flutter. If we ignore these and look at the primary loads we see a number of small wings only 15% of the radius long moving at about 10 times among speed.
An extensive search at the library at New Mexico State University and the internet has revealed little work in this vein.
While there is some prior art for tethered wind energy systems, there seem to be none with well defined hard surfaced air foils or that move across the wind. There are a number of patented designs using fabric, balloons or sails that use a single line that is paid out down wind to generate electricity, which then are reeled in with a motor to complete the cycle. They all fail to take advantage of the increased coupling available to a wing when tacking across the wind. This is a significant factor as loading will be hundreds of times greater, under these conditions.
Loads of this magnitude, call for a very robust wing and cable structures. Power output will be hundreds of times greater, for the same wing area, than for a single cable system. This is because it is extracting energy from a much larger air mass.
Low wind speed turbines have been identified as key elements of the national renewable energy plan for future growth of wind energy.
Primary project tasks will include development of a marketable 5kW wind system for off the grid users and will demonstrate a prototype 100kW system, with high capacity factors. Another innovation to be tested will be a virtual variable span wing. This technology will allow the system to maintain full output as wind speeds decline.
Together these technologies may allow NREL to meet its goal of 0.03 $/kWh with short lead times and reduced capital cost. The technology should be attractive to many small farmers near cities. It will create many manufacturing and export jobs in this country.
Clearance from the FAA, would be needed to operate high output systems that could be deployed at altitudes in excess of 1000 feet. The problem of hazards to small aircraft could be addressed, by installation of a receiver designed to detect and locate aircraft by their transponder signals, thus causing the gliders to dive away to avoid collisions.
Most systems less than 1MW will operate at altitudes low enough to avoid the need for special clearances unless they are in high traffic areas, but even for small systems these detectors may be economic, as it should help to reduce the cost of insurance.
The drag produced even by faired cables may limit output so the advantages of high lift air foils will be included in this investigation.
The interruption of power at the end of each cycle as the glider turns back can be avoided by phasing multiple systems to smooth the flow of power.
Initial cost is expected to be $200/kW, falling over time to about $50/kW The integration of this type system with existing wind farms may improve output by forcing air down from higher altitudes.
Should the cable break, control of the glider is not lost, even though damage to the glider will likely result. The risk to persons and property is reduced by the smaller mass and speed compared to horizontal axis wind turbines. The cable length will generally define the danger zone. The most significant hazard identified is the whip of the broken cable. The low mass and stretch of Kevlar cable and the energy absorbing properties of chain link fencing will reduce this. Testing the life and failure modes of the cable will be a big priority. So as experience is gained, loads can be gradually increased and safety margins adjusted to a design lifetime. Maintenance and security will be real economic issues for autonomous distributed wind energy. Real time diagnostic and security systems will be connected to the web to allow a timely response to problems as they arise.
Visual profile can be reduced by hangering the glider while not in use. This further reduces environmental impact.
Offshore and agricultural applications are also being studied.
A virtual variable span of any desired length is achieved by the close formation flight of a number of gliders. Since the reaction mass is equal to the square of the span this allows much better coupling to a low speed air mass and will result in capacity factors rarely experienced with HAWTs.
A first prototype of the glider.
Advantages to California
Being the first mover in the market should help California’s manufacturing and export markets nationally and internationally.
Wide availability of low speed wind resource would place a premium on land near existing transmission systems and substations, thereby reducing infrastructure costs. Desert land east of Los Angeles would become a significant wind resource.
If capital cost of this system proves out to $200,000/MW at the high capacity factors predicted, this technique will need little pump priming to achieve market penetration. Global penetration may effect moderation in fossil fuel prices generally, and give small farmers an alternative income, freeing them to take a longer term view of resource management. Availability of excess power for water pumping should benefit water quality issues.
At these prices many hydro electric systems will need to be revaluated.
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