Because it has been documented that today’s technology could replace all or most fossil fuel consumption with renewable sources[1], the most important focus for writing on technical solutions to the climate crisis is what can be done today. There is too much yammering about “innovation”, and not enough attention paid to mature conservation, efficiency and renewable technology we already know how to build, and simply need to deploy. But that does not mean potential technical breakthroughs are unimportant. While conservation and efficiency that save energy are cheaper than today’s fossil fuels, renewable sources of heat and electricity are mostly more expensive. Any technology that would let us generate renewable electricity at a cost comparable to the price of saving energy would boost renewable deployment.

Not a silver bullet: we fail to deploy many efficiency techniques today that can save energy far more cheaply than the fossil fuels they could save. But truly cheap renewable electricity would greatly improve our chances of being able to phase out fossil fuels, nonetheless.

There is a nascent industry that may be on the verge of generating inexpensive, and most importantly reliable, electricity from renewable sources – requiring comparatively small amounts of public funding to push through to success.

An untapped wind resource

Grist thanks its sponsors. Become one.

Wind power on commercially developable sites could supply 72 Terawatts, many times the power the world consumes today[2]. U.S wind resources are among the world’s richest.[3]. But much of this potential is far from where electricity is consumed, requiring expensive new transmission to become usable. Further, because wind power at an individual site is variable, to ensure availability of wind power when wanted requires even more transmission, so that wind from one site can be used when no power is available from another. Even more expensive are requirements for storage and backup, to provide power when no wind site happens to be generating. None of these requirements are impossible to meet. The additional expense of a system including such stabilizers could be more than paid for if the slightly more expensive electricity generated was used more efficiently than we use power at present.

But if wind power could be generated less expensively, and generated in a way that required less transmission, less storage and less backup that would be extremely useful. It happens that there is a source of stronger more reliable wind.

Grist thanks its sponsors. Become one.

The wind resources mentioned are at 100 meters of height or under. The higher the altitude, the faster the wind blows. Other factors being equal, the power available from wind is the cube of its speed. Wind at 1 kilometer can generate a bit less than twice the energy of a turbine at 100 meters. A turbine at ten kilometers can generate eight or more times the energy of a turbine at 100 meters.. Estimated high altitude energy potential is about 100 times all energy human civilization currently consumes.

At first glance, the potential of high altitude wind power appears tantalizingly out of reach. While we could probably build one kilometer wind towers, the cost of towers that size are unlikely to ever be low enough that doubling generation will come close to paying for them. And if a one kilometer tower is impractical, a ten kilometer tower seems even less plausible.

Fortunately, giant towers are not the only means we have to reach high altitudes. Kites have been used for millennia, balloons for centuries, motorized planes and helicopters for more than 100 years. Put turbines on an automated kite, plane, balloon or helicopter with no human pilot. Run a tether to transmit the electricity to the ground, and in (in many cases) to provide power for the initial launch. The result is a flying energy generator, a wind turbine or turbines on a flying platform that can provide higher energy density and higher energy reliability and capacity factor than ground based wind turbines at a lower cost. Many developers claim that such flying energy generators (FEGs) could produce electricity with a life cycle cost of less than 2 cents per kWh with a capacity factor of 70% and above (comparable to the capacity factor of coal plants.) This is not merely an idea. A number of companies have working prototypes. It has been proven possible, though not yet practical. The only way to determine practicality will be for someone (either the government or venture capitalists) to fund the transition from proof of concept prototypes to quarter scale commercial prototypes and finally to full scale commercial prototypes. Any one of the companies working on this could probably be fully funded for the cost of the stationary budget of the Department of Energy.

Frequently Asked Questions

Q) Pie in the sky! Impossible!

A) Several companies have produced working prototypes. If it has been done, it is possible. The energy that is being tapped is high altitude winds. Those winds blow whether turbines capture or not. That energy exists regardless of whether we turn it to human purposes. All the flying turbines do is let us reach it, just as towers let us reach to wind at 100 meters to tap that.

Q) Planes and Helicopters crash! This can’t be safe!

A) Flying energy generators differ from conventional planes and helicopters in important ways. They are designed to stay in one spot rather than travel; thus they optimize for safety and stability in ways a traveling flying platform cannot. In some cases, that includes using gyroscopes in ways they could never be deployed in passenger vehicles that travel miles rather than feet. Also Flying Energy Generators (FEGs) stay in the air most of the time, unlike conventional flying platforms that take off and land daily. Takeoffs and landings are the most dangerous times for all aircraft.

Q) So are FEGS (Flying Energy Generators) perfectly safe?

A) No energy source is perfectly safe. There is no Kilowatt fairy, no BTU bunny. If we build enough Flying Energy Generators sooner or later someone will die in an accident that involves one. What we won’t see are major accidents along the lines oft the BP spill or the Massey coal mines. For that matter, we are unlikely to see accident rates comparable to current coal or natural gas generation facilities, even before fuel cycles are considered. To minimize accidents, site for FEGs of 100 KW scale and higher probably won’t be located in major urban areas, but in the low population rural communities closest to urban areas.

Q) Do you really think you can build a tether a kilometer long, let alone ten kilometers? That is one long string!

A) To name an old fashioned technology, Kevlar-Aluminum composites are more than strong enough to hold up at ten kilometers, and conductive enough to get electricity back to the ground. Such a long run of aluminum will result in 20% power losses, but that has already been taken into account in estimates that generation costs for FEGS will be less than 2 cents per kWh. And we have far better material for tethers than Kevlar-Aluminum composites these days. For that matter, U.S. law enforcement already uses tethered balloons of up to 15,000 feet to monitor illegal flights by drug smugglers.

Q) So why would this be less expensive than conventional wind turbines?

A) The cost of comparably sized rotors is higher for FEGs than for conventional turbines, but since they turn faster the cost per MW is much lower. And the flying turbines run more often which lowers the cost per unit of electricity produced even more than the cost per amount of peak generating capacity. In industry jargon capacity utilization is higher. (Capacity utilization is electricity produced compared to what could be produced if t
he turbine ran at maximum capacity 24/7.) FEGs run at 70% to 90% capacity utilization. This is similar to coal and nuclear power plants, rather than to tower based turbines that run at 35% to 40% capacity. Further, tethers are less expensive than towers.

Q) If capacity utilization is comparable to that of coal, does that mean that flying wind generators can provide baseload power the way coal does?

A) Without storage and backup, probably not. Although FEGs utilize 70% and even 90% or 95% of capacity, unlike coal and nuclear, we can’t control WHEN the outage happens. The wind dies down, and the turbine generates less (or zero) power, just as with ground based turbines. Whereas, most shutdowns or curtailments in coal and nuclear facilities are planned in advance, or at least have plenty of notice.

However, the higher capacity means that reductions in production happen less often, and for shorter periods. So it becomes easier to combine small amounts of hydro, small amounts of storage, and natural gas to serve as backup during long term wind shortages. That would probably raise the cost of a reliable wind grind to 5 cents per kWh, which is still cheaper than power from a new coal plant. Some analysts think that if we stuck to the best sites, where capacity utilization was around 90% or more, that FEGs combined with existing hydro would constitute a reliable grid, which lowers the cost to close to the original 2 cents estimate.

Another savings is in grid upgrades. While any increase in renewable use will require some grid improvements, flying wind generators can generally be located fairly close to where power is used, simply being kept away from densely populated regions as a precaution. That means that while FEGS are still stranded wind, and need some new transmission, they don’t require long distance lines running hundreds or thousands of miles.

FEGS also lower environmental costs. While conventional wind gets dinged unfairly for threats to birds and bats, because a zero harm requirement is imposed on it that is not imposed on coal, natural gas, hydro or nuclear generation, FEGS, especially the ones running at close to 10 kilometers, would greatly lower the threat to birds and bats. Even the lower altitude FEGS run where fewer birds and bats can be found then ground level turbines. There are even fewer if FEGS are flown at a height of ten kilometers. Also FEGs are much less fussy about location. They can avoid ridges and bat and bird migration paths. Also, while I’m not an ornithologist or a bat ecologist, I would guess that large hovering or slowly circling flying platforms would at the least not attract birds or bats the way turbines on towers do, nor tempt them to fly close. I would further speculate, as someone who is not informed in this area of biology, that such platforms might even be mistaken for predators and avoided. I would welcome correction from actual experts in these areas.

Q) Won’t this interfere with air traffic?

A) Not in any way we don’t know how to deal with. Aviation would have to be excluded from locations where FEGs flew at 5 or 10 kilometers. But a quarter of a percent of U.S. land has to exclude aviation for various reasons today. There are special databases pilots check to avoid such excluded zones, which change from day to day. FEGs that flew at 600 to 1,000 meters would be considered obstacles in many cases, which would make regulatory compliance much easier than in the cases of higher altitude systems.

Q) You mentioned differing technologies. So the industry has not settled on one approach?

A) No. Differing companies are aiming at varying markets. And even those aiming at the same market have differing methods. Some of companies are building small units, aimed at farmers and villagers in poor nations – basically providing expensive power that is still cheaper than diesel electricity, cheaper than extending the grid a long distance to serve a small number of people, and cheaper than solar cells. Others are aiming for economies of scale to try and bring the cost of wind power below 2 cents per kWh.

Among the latter some are trying to build systems that fly low to simplify regulatory compliance. If a system stays below 1,000 meters in many locations, and below 600 meters in others the FAA will consider them an obstacle to air traffic rather than actual air traffic. Licensing requirements for obstacles are much simpler than requirements for air traffic. The downside is that at height, you only get power production sufficient to justify the more expensive rotors at sites that already produce pretty good wind. The rule of thumb is that the capacity factor at 1,000 meters is a bit less than double that at 100 meters. So a site that has 40% capacity at 100 meters (a surprisingly large percent of available sites) will have around 75% capacity utilization at 1,000 meters.

Flying higher can give extremely high capacity factors in areas where you would never build ground turbines. For example, there are not many places you would locate wind turbines on the ground in the greater San Diego area (not zero, but not many), but at 10 kilometers altitude you could get 70% capacity utilization from a turbine anywhere within it, including fairly distant suburbs and rural areas.

Most of the large scale systems are either flying wing or helicopter like. Most of the balloon and kite based systems are smaller scale and aimed at lower end markets with the important exception of Makani.

Q) You said companies are already building prototypes. Can you name some?

A) I can list a number, but it is worth noting that all of the systems are proof-of-concept rather than true commercial prototypes.

Sky Wind Power has built a number of “tethered helicopter” systems that fly at a low altitude, though any commercial system will have to fly much higher to generate enough power to provide true economy of scale and the low costs they aim for.

Joby Energy has a flying wing concept that is designed to generate power at under 1,000 meters in sites with good ground based wind, while still being able to fly at much higher altitudes if it can overcome regulatory barriers to doing so. It has flown a proof of concept prototype.

Makani Power is a kite system where electricity is generated on the kite and transmitted to the ground via the tether. Again, it has demonstrated a proof-of-concept prototype and is still working on the steering.

Megenn Power is a ballon based system. Basically it is intended to substitute for all or part of diesel power in off-grid and micro-grid applications. A 4 KW prototype has been tested.

WindLift is a kite based system for pumping and other small scale applications that has not yet (as far as I know) demonstrated a working prototype.


[1] Mark Z. Jacobson and Mark A. Delucchi, “A Path to Sustainable Energy by 2030: A Plan to Power 100 Percent of the Planet with Renewables,” Scientific American 301, no. 5 (Nov-2009): 58-65.

[[2] Cristina L. Archer and Mark Z. Jacobson, “Evaluation of Global Wind Power,”. Journal of Geophysical Research – Atmospheres 110, no. D12 30-Jun 2005, American Geophysical Union, 20-Jan-2008

Xi Lua, Michael B. McElroy, and Juha Kiviluomac; “Global potential for wind-generated electricity”; Proceedings of the National Academy
of Sciences of the United States of America
; June 22, 2009

[3] DOE Energy Efficiency and Renewable Energy – Wind Powering America: Wind Maps and Wind Resource Potential Estimates, (accessed April 8, 2010).

DOE Energy Efficiency and Renewable Energy – Wind Powering America: Estimates of Windy Land Area and Wind Energy Potential by State for Areas .GTE. 40% Capacity Factor at 80m, (Accessed April 8, 2010).