Do We Need Flying Wind Turbines? (Spoiler: Absolutely!)

Posted on
April 19, 2021

Solar-photovoltaics (PV), wind turbines, and Lithium-type batteries became so cheap over the past years and decades and are expected to drop further in costs in the coming years. This is mainly caused by Wright’s law and associated learning curves: with every piece produced we learn how to make it better. Particularly impressive is that today PV is 10x cheaper than it was a decade ago. Such a steep cost reduction causes more PV projects to be built which in turn fuels this virtuous cycle (positive feedback loop) of further cost reductions as companies learn to make things better with every PV project implemented. The same counts for wind turbines and even stronger for Lithium batteries due to the massively expanding production capacities for electric vehicles. These technologies have become very reliable and arguably simple: A PV plant and Lithium battery storage may have no single moving part and can be cost-effective at small-scale and at large-scale. This is amazing news as we desperately need these technologies to stop climate change. PV just became one of the least costly electricity sources in some regions, so it will be deployed further massively, phasing out more costly and dirty fossil alternatives.

Based on these exciting developments, one may ask the question: Do we need anything else? Do we need other (green) electricity generation technologies? Do we need flying wind turbines? In this blog post, we address exactly those questions.

Conventional wind turbines generate cheap electricity only at large-scale.

The first question we address is, how conventional wind turbines drove down the cost of electricity, or in other words, how have the steep learning curves been achieved? There have certainly been strong improvements in manufacturing, supply chain, planning, or modeling and predicting. But one of the strongest drivers for the reduction of the cost of electricity has been and tends to continue to be that wind turbines got bigger and bigger: The rotor diameters and accordingly tower heights have doubled from around 60m rotor diameter in 2010 to 120m in 2020. A taller wind turbine reaches stronger winds and the average energy output is increased significantly: As power scales with the wind speed cubed, a doubling of the annual energy generation is achieved already with only a 26% increase of the average wind speed. And there are further aspects of technological and economical efficiency increases for building bigger.

Nacelle of the GE Haliade-X 12MW Prototype. Source: GE.

A large tower-based conventional wind turbine obviously has a number of disadvantages. As reductions of electricity costs have been achieved mainly by upscaling, only MW-scale conventional wind turbines and wind projects with at least around 10MW are economic and implemented today—this means virtually zero wind projects below that size are implemented e.g. in microgrids, industrial power supply applications, or small free areas (too small for at least ~three MW-scale wind turbines), as those could not reach the required low cost to be competitive with other alternatives like fossil fuels. Wind turbine manufacturers may not even offer wind turbines at low-digit MW- or below MW-scale and orders of one to three (only bulk orders). In numbers, small wind turbines in the 1kW to ~100kW range have costs in the order of $3 per W capacity (the smaller the more) while reaching much lower hub heights than MW-scale turbines which cost in the order of $1 per W capacity.

Logistics of large turbines is increasingly becoming a challenge and there is often public opposition as such large wind turbines shape the visual landscape. Massive foundations or floaters and costly specialized installation vessels and cranes are required for offshore deployments. This moves wind turbine manufacturers to build even larger turbines with outputs projected to be soon in the 15 to 20MW range for a single unit. It should be noted that wind turbine manufacturers are forced to build turbines larger to unlock further reductions in cost of electricity (and it is a good thing that they have been able to achieve that, so that more wind energy generators are deployed right now). For economic viability, very high quality and long lifetime of the turbines are required: If a 20MW turbine cannot run because of a fault, the financial loss is significant, in particular if bad weather like strong winds and waves, which is actually good for power production, prevent service teams in vessels or helicopters to fix the problem quickly. A financial and logistic nightmare unfolds if an unintended replacement of large parts like gearboxes or blades is required.

Flying wind turbines generate cheap electricity already at small-scale.

These are all points, where flying wind turbines like Kitekraft systems have significant advantages: We expect that already our 100kW product costs only about $1 per W capacity which is as cheap as MW-scale conventional wind turbines. As our flying wind turbine — well, flies — it reaches similar altitudes as a MW-scale conventional wind turbine and therefore generates electricity at a similarly low cost. We intend to scale up our technology to several 100kW and multi-MW as well to unlock further cost reductions related to upscaling, but the first 100kW series product is already as cheap as a MW-scale conventional wind turbine in terms of $/W. Here the kite has only 10m wingspan and can therefore be transported in standard shipping containers. The ground station is a rather small steel assembly and only a small foundation is required if any at all (depending on the ground). No crane is planned to be required to set it up. So, logistics is infinitely easier than for a conventional wind turbine.

The visual effect of a flying wind turbine is also much lower. It is hard to spot the kite and tether if you do not know where to look.

Kitekraft flying wind turbine: almost invisible. (Quarter-scale technology demonstrator.)

Unlike conventional wind turbines, it is already economic to have more smaller units in a wind project of certain MW-size using kites, say e.g. 100MW total wind project with 20x 5MW kites, as opposed to having 7x 14MW conventional wind turbines. — One should note here that the land use is not necessarily higher for the kites in this example as they can be placed closer together than wind turbines because wake effects for kites are much smaller than for conventional wind turbines. — This has several advantages: First, with already rather small kites in terms of MW-capacity and absolute dimensions we can have competitive wind farms. Second, if a kite has downtime for some reason, only 5MW is not available instead of 14MW. On top of that, maintenance can be done close to ground level and downtime can be minimized. In the worst case, a faulty kite or even the entire system with ground station/floater could be simply swapped by a replacement kite and the faulty kite could be repaired in a specialized facility. Worth noting here is that a kite costs less than a ground station, even in our Kitekraft concept with onboard power generation. Additionally, at Kitekraft , our engineering philosophy is to design the kite and ground station as simple as possible (any sensor/actuator that can be avoided is gold) and rugged (e.g., direct drive BLDC generators) to minimize having unscheduled maintenance and downtimes in the first place.

All in all, flying wind turbines can provide electricity at similarly low cost as MW-scale conventional wind turbines already at much smaller unit- and project sizes. Over time, cost will decrease further as the unit size is increased and the flying wind turbine technology undergoes its own learning curves (Wright’s law). By being almost as scalable as PV and batteries, any wind project smaller than 10MW or any location otherwise infeasible for conventional wind turbines can be served already by our 100kW Kitekraft flying wind turbines. In this market vacuum we provide a solution which is easy to transport, deploy, and maintain on ground level.

We need wind energy generators even if we have cheap PV and batteries.

PV is never available at night, batteries have losses, and both will never be for free and require significant resources to be built. Due to seasonal effects, PV is less available during winter than during summer. To get to 100% renewables or in total to get net-zero greenhouse gas emissions — which is what we need to accomplish in the next few decades — a massive over-sizing of PV and batteries would be required if these were the only sources of electricity. As wind is often available during nighttime and more in the winter, a much cheaper and less resource intensive power system can be realized with wind energy generators. In particular, our 100kW Kitekraft flying wind turbines will enable wind power generation at many projects globally with less than 10MW capacity and soon after scaling to much larger unit sizes and projects sizes.

Construction material requirements to generate one TWh of electricity from various sources, but excluding fuel for Coal, Biomass, Nuclear, and Natural Gas. Kitekraft data is based on internal models for the 100kW product. Source of data other than Kitekraft : US Department of Energy, “Quadrennial Technology Review”, 2015, Table 10.4 “Range of materials requirements (fuel excluded) for various electricity generation technologies”.

To decarbonize the entire global economy, massive amounts of clean electricity are required. Flying wind turbines can provide a unit of energy with very low effort. We already pointed out the very low carbon footprint of flying wind turbines. The graphic above compares how much construction material in tons is required to generate one terawatt hour (TWh) of electricity from different sources. As visible, Kitekraft flying wind turbines require 10x less construction material than conventional wind turbines, which brings flying wind turbines among fossil and nuclear sources (while, obviously, a Kitekraft flying wind turbine neither produces toxic waste during power generation nor poses a nuclear safety risk). As the numbers for biomass, fossil, and nuclear do not include fuel supply, a flying wind turbine requires the least material demand to generate a unit of electricity. Depending on the solar and wind resources of a location, the inclusion of Kitekraft systems next to PV and batteries can reduce the capacity demand for PV by ~2x and for batteries by ~10x while generating the same amount of clean energy, and on top while reducing overall system costs by up to 2x.

I came across the material demand in tons per TWh of electricity generated in Bill Gates’ new book “How to avoid a climate disaster. The solutions we have and breakthroughs we need”. In the graphic above, the original source data is used and the data of our projected Kitekraft flying wind turbine 100kW product is added.

There may be materials required for PV, conventional wind, and Lithium batteries which are rare globally or at the location where it is needed (e.g. sand in the required quality, Cement, Lithium, Cobalt), so that the amount of capacity that can be built is limited, increases costs, or requires innovations. But for simplicity’s sake we do not dig into that topic. It would highlight the case even more for flying wind turbines.

If hydrogen takes off, even more clean power is needed.

Large hydrogen offensives have been reported in the news. Hydrogen can be used as fuel for large trucks, mining vehicles, and other large vehicles possibly also ships and airplanes, or as seasonal energy storage. This is also the point with Hydrogen: It is not a (clean) energy source, but only a storage medium. As of today, almost all hydrogen on the market, around 96 %, is produced by using fossil fuels. That is why it is called grey hydrogen. The CO2 emitted during production is sometimes captured and stored, resulting in what is called blue hydrogen. However, this triples the price. Green hydrogen is produced by separating water into Hydrogen and Oxygen by using renewable energy. No CO2 is emitted during this process, making it the cleanest hydrogen possible. Today, this is still quite expensive, around eight times as expensive as grey hydrogen. As this process requires clean electricity, we need even more of the clean renewable energy generators if a hydrogen economy indeed takes off!

If this price decreases in the coming years and decades, which is in part enabled by low-cost renewable energy generation, it can help to decarbonize huge industries like aviation, shipping, and at least in part steel and concrete production. For that, massive and massive amounts of renewable energy generators are required on top of those supplying us with electricity because the global electricity demand is only a fraction of the current primary energy demand. As discussed previously, flying wind turbines can help to provide that with several advantages compared to other sources.

Other renewable energies are not as scalable as PV and wind.

One may now also ask: “Ok, but what about hydro power, wave power, biomass, geothermal, or nuclear fusion?” Those can and should be used wherever it is possible, if their costs can also be reduced far enough, or in case of the latter as soon as it is available. For example, we already ran out of hydro power resources in most of Europe and North America. Wave power is only available at sea. Biomass faces the land use competition with agriculture for food production, among other issues. Geothermal needs deep bore holes and could cause mini-earthquakes. Nuclear fusion is still at least 1–2 decades away from commercialization, and it is based on steam turbine energy conversation and therefore likely cannot ramp up and down power quickly, like today’s coal and nuclear fission power plants.

On the other hand, clean energy technologies which are scalable for global deployment are PV and wind, and soon also Kitekraft flying wind turbines for the latter.

So, do we need flying wind turbines?

It is not intended to be negative about PV, wind, batteries or other renewable sources — all are very positive and have their advantages. The intend of this blog post is to highlight the potentials that can be unlocked by flying wind turbines. All in all, besides that we believe flying wind turbines will become the cheapest source of electricity at many locations, it will be the most construction material efficient one, and by far if comparing to other renewable energy sources. It will also be better scalable and easier transportable, enabling new locations infeasible for conventional wind turbines. Deployment and maintenance is much easier compared to a conventional wind turbine. One picture that one should have in mind when thinking about a Kitekraft flying wind turbine system: it is basically an oversized multicopter drone with wings tethered to the ground. With that picture in mind, it is also not nearly as complex as to design, qualify/certify, and manufacture an airplane. — Once the design is optimized and the software programmed, thousands of systems can be produced every year in relatively simple and small factories. — All those advantages of flying wind turbines, why they are needed, is not only what we think, but what our customers say and thus what the market wants. Those customers include utilities, microgrid developers and operators, as well as renewable energy projects- and hydrogen projects developers.

Update: In the initial version was a mistake in the material demand calculation for lithium batteries.

Posted on
April 19, 2021

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