Mothra-Tech Wind Power Calculation for FAA provisionally-defined Stream-Tube
- Keywords- Mothra-Tech, Dense-Arrays, Super-Density-Operations (SDO), Crosswind-Anchors, Airspace Streamtube Efficiency (ASE), Land Footprint Efficiency (LFE), Kite Arch
Premise- Single-Anchor AWES units do not maximize airspace streamtube efficiency nor land footprint efficiency and so are poorly scalable. Crosswind anchors, such as are used for kite arches, do maximize spacial efficiency. Mothra-tech is rope-loadpath kite arch based, for superior space efficiency and scalability.
Estimated power for a Mothra-based AWES unit within FAA specified airspace came from the Wind Power Calculator at-
The basic equations for calculating turbine performance for a given wind are presented on the Calculator page, which fortunately accepted high-altitude numbers. To determine the input numbers, the provisional FAA AWES ceiling of 2000ft was rounded down to 600m, with a 1200m crosswind extent selected to define a representative airspace "stream tube".
With the inputs below for the model kite unit, a power output was calculated-
Efficiency (%) 10
Wind density (watt/sq.m) 3000
Rated height (meters) 500
Turbine height (meters) 500
Rotor area (sq.m) 360,000
Power (watt) 108MW
-------------- Notes ----------------
- A low most-probable wind velocity was chosen from the Calculator table, rather than typical high-velocity rated windspeed:
From the Calculator table-
Class 3 50 m (164 ft)
Wind Power Density (W/m2) 300-400
Average Air Speed m/s (mph) 6.4-7.0 (14.3-15.7)
- This rule-of thumb- a doubling of wind velocity per fivefold increase in altitude- was used to derive an approximate wind density at altitude (rather than the provided power-law).
- 10% WECS efficiency was chosen conservatively. A wide variety of WECS can operate suspended under arches. A reasonable 20% eventual efficiency would double power-out.
- 360,000m2 of WECS "rotor" area is half of the 720,000m2 total area (600x1200m2). Solidity would vary according to specific WECS design.
- Kite arch frontal projected area would be about 100,000m2. This wing would shroud the upper margin of the airspace, and generate the lift to hold up the WECS underneath. Lift is enhanced by wing-in-ground-effect geometry and quasi-tetherless arch characteristic.
- The land footprint assumption is comparable to a current 7MW HAWT (which are rated to a higher wind velocity than most-probable-wind).
- Compare with Makani M5, at only 5MW in the same airspace and footprint. Mothra-tech is true SDO, most compatible with congested airspace. Makani is asked to inform GoogleX of this competitive reality.
- A rough consensus of AWES experts see 3-5000ft as the sweet-spot for the most power at reasonable altitude. The FAA 2000ft AWES ceiling is therefore a 1/2 scale evolutionary stage. Full scale is true gigawatt AWES unit scale.
- Mothra1 is a 1/20 scale version of this AWES unit model. Rod Read's models nicely evoke the megascale. Dr. Beaujean's concept and the KiteGen Carousel are comparable by airspace utilization. Mothra-techis proposed to be more practical at lower capital-cost (based on classic kiting). Some images of Mothra1-
- Please direct questions, corrections, and comments to AWES Forum.