Kite Electricity: From Chaos to 60 Hz

Ordinary wind is actual momentum decay direct from the Big Bang. Its not easy, but wind can be harvested in chaotic bursts by kites and converted to synchronous 60 Hz electricity matched to fluctuating loads on regional grids.

A kite is a glorified rag on a string- a tethered foil. It is already a massively parallel nano-electrical system, bound together by opposed charges & operating in gaseous flows of repellent charges. A kite has the profound power of lower dimensions acting in our higher dimensional space. Quasi single-dimensional string & two-dimensional cloth has astounding properties in our four-dimensional space-time. A membrane of negligible thickness and mass is able to dam large pressure fields and process powerful flows. Mere sewing thread traveling at 200 mph can carry about a horsepower, a tangible relativistic effect in real life. Thread traveling at a thermal limit of about Mach 1.5  could carry several horsepower to an electrical generator.

A high performance tethered foil has a vast output range. Often the foil loiters weakly, then suddenly "ignites" in a gust by surging across its window. Greater than 20-to-1 power variation from cut-in to cut-out is usual. A farm of arrayed kites averages these wild random inputs, smoothing aggregated output. Networked electrical generators also level outputs, even driving laggards.

If too many or not enough wings fire or don't fire at once, things fry. A kite farm of properly designed (coupled) oscillators can self-synchronize in poly-phase to a master beat, as a phased array.  It helps if every link of the energy harvesting chain wants to oscillate at some factor of 60 (1,2,3,4,5,6,10,12,15,20,30) so that harmonic frequency hopping is natural (but watch out for massive rogue synchrony!). Kite arrays can fire in traveling waves where the wings move much like centipede legs; a beautiful spectacle.

Recent KiteLab experiments show these ideas are workable. A current design has six FlipWing membrane wing-mills in various synchronous modes driving a single generator shaft via sprags (freewheel clutches) with reasonable smoothness, for the generator and other rotating parts have a lot of flywheel mass. As desired, added flywheel mass further smoothes output. The latest AWE (Airborne Wind Energy) Base Unit, with an improved crosswind geometry, recently suggested by Joe Faust, consists of two orthogonal pendulum/freewheels whose wild dance is damped by a cable driving an electric generator. It is a classical chaotic double pendulum, run mostly backwards, chaos into order, how cool is that? But such a beating heart needs a bit of control.

Chaotic Control (chaos control) began decades ago by sending under-actuated interplanetary space probes to unstable orbital locations where the right tiny nudge then set the craft on a desired trajectory, an engineered Butterfly Effect. There are many places to introduce small anti-chaotic trim inputs into an AWE energy chain. Generally every other power link or so can add a bit of passive or active tuning toward a final clean power signature. There need not be complex centralized control, just the regional grid's master synch AC signal and each phased array unit provided with a global state and phase assignment. 

Wind aloft is tunable by finding an altitude where the wings fire at a desired synch factor (while avoiding turbulent boundaries). Membrane wing-mills are frequency tunable by varying tension (catenary) on the halyard &/or sheet winch; tighter means faster. Never mind that some wings fire out of phase due to turbulence & phase/frequency transitions. Just as a few ruffled feathers hardly affect a bird; misfiring elements are negligible, if enough of an array is behaving.

The latest generation of generator/motor use smart controllers to adapt to a wide range of conditions, eliminating most gearing or ponied units. Direct current (DC) and asynchronous alternating current (AC) is practical for unsynched generation if standard rectifier/inverter stages are inserted in the loop. Old fashioned circuit breakers/relays can provide gross control of kite farm output. Net-metering, the selling back of extra power to a grid by small consumer-producers, has matured. The new smart super-grids will be rich in distributed generation points like kite farms.

The almost unavoidable sudden crashes (even cascaded crashes) of extreme-scale aerobatic airborne generators, as proposed by Makani Power and also by Sky WindPower, will tend to crash grids. Advanced flywheel generators, developed as hospital and data-center UPS, can catch a crashing grid, but they are overpriced for utility baseload scales. Bulk ultra-capacitors are still unavailable and will be pricey. The fail-soft qualities of large arrays of cheap simple semi-captive passively-controlled AWE elements are favored for a long time to come.

It is also important that the inflow wind field to an AWE array be predicted in realtime to assist power conditioning and reliability. As Wayne German envisioned, a cheap veil of sensor kites upwind might serve until SODAR is cheap and perfected. A key is to be able to reconstruct a high dimensional field from low dimensional sensor traces.  

Surplus generation must divert to bonus-loads or storage. Stored power bridges calm winds and help meet peak grid demands.    Kite-driven pumping around a hydroelectric dam is a promising technique. Hydrogen (H2) electrolysis loops, large-and-small, can feed back capacity.  KiteLab has introduced crude HHO production into its AWE loops (a limitation to cheap bulk electrolysis is that vapor bubbles increasingly isolate the electrodes as currents increases). Dave Lang's recent white paper to NIST (via Drachen) describes an H2 Assisted Economy (HAE) with a strong role for kite-derived H2. WindLift has been tracking bulk air compression for short term power storage during wind lulls.

To conclude: Kite Electricity has unique advantages in a diversified energy grid. With the lowest capital cost and capital-cost intensity, the fastest set-up, etc., kites will fill many gaps in energy production. Disaster relief might be kite powered. Co-generation hybrids will be attractive--like coal-to-kite transitions and tar-sand kite processing, as well as superior HHO and H2 schemes. Hurray for rags on strings!

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Thanks to John Borsheim for a refresher course in AC generation and net-metering, to Christopher Carlin for pointing out key issues in grid-synchronous alternative energy, to Vijay Davar of KLD Energy Technologies, and to Steve Edley of Active Power for sharing new electrical power generation concepts.

Dave Santos
KiteLab
Ilwaco, WA
Austin, TX