Air HES

Frequently asked questions

If you have any additional questions, please contact us.

Other places for discussion:

English original
Airborne Wind Energy Forum
H2bidblog
http://www.renewableenergyworld.com/rea/blog/post/2012/06/air-hes
http://www.linkedin.com: Global Solar, Hydro, PV & Wind Energy Consortium
http://www.linkedin.com: Hydroelectric Power
http://www.linkedin.com: Water Technologies
Presentation in English

Russian original
http://habrahabr.ru/post/143099/
http://www.diforum.ru/index.php?showtopic=27185
http://www.membrana.ru/particle/18019
http://www.kiting.org.ua/forum/index.php/t/1655/
https://www.facebook.com/groups/fansofdirigibles/488928084477948
http://forum.israelinfo.ru/viewtopic.php?f=1&t=49408
http://ammo1.livejournal.com/389665.html
http://i-future.livejournal.com/673424.html
Solaris project
Presentation in Russian

What kind of pipe could be used?

Dear Andrew,
all answers you could found in Russian discussions by proper links, but... :)

Obviously that we have and can get this potential water energy, the question is how?

There are some options, for example:
1. standard pressure pipe - 30 mm, 200 ATM in bottom (your variant) -> Kevlar tube/tether, expensive + 1.5 t of water
2. gravity pipe (waterfall) - variable profile by continuity equation, no pressure (my variant) -> cheap, possible big energy losing
3. aerial lift (practically also replaces the turbine) -> middle price, but complicated

Any variant principally can be used, but demands:
1. bigger balloon - 1500-2000 m3 here - to keep additional water weight
2. R&D for stabilization of flow
3. constructive investigations

Please, ask for details.
SY, AK

Dear Andrew,

I have been thinking about your AirHES concept, having seen your comments on:
http://www.renewableenergyworld.com/rea/news/article/2012/08/obama-spars-with-romney-on-energy-in-swing-state-pitches?cmpid=WNL-Friday-August17-2012

The fog harvesting idea looks really interesting - I just can't see how the energy generation works.

The key issue seems to be the pipe. I think I understand your numbers regarding the water generation and power ratings, but I am concerned about the penstock design. For the turbine to work, the potential energy from the water needs to be converted to kinetic energy at the nozzle outlet. As you say, for a 23 kW design (1.16 l/s, 2000 m head), the flow rate through a 3 mm nozzle is 200 m/s. Your 50-100 kg mass of the water in the pipe seems consistent with extending the 3 mm diameter pipe right up to the balloon. But the friction from a 3 mm pipe would surely not allow water to travel at 200 m/s along it?

An alternative would be to use a larger pipe diameter and maintain it in closed channel flow. If you accepted 10% head loss in the pipe, then you would need a pipe of diameter 30 mm (see http://www.calculatoredge.com/mech/pipe%20friction.htm  data entered with 2000 m length, HDPE, 1.16 litre/s, diameter 30 mm). A full pipe of this dimension would carry water at a more reasonable 1.6 m/s, but hold a tube full of 1413 kg of water, breaking the limit on the balloon's carrying capacity.

Have I missed something here?

Best regards,
Andrew Urquhart.
Student at Loughborough University

How could a gravity pipe work?

Dear Andrew,

Imagine that you have just a waterfall. Obviously, if you allow it to break up into drops of rain, almost all of the potential energy will be spent on the frontal resistance, and there is the usual rain. But if you are able to stabilize the jet, no frontal resistance will be. For sufficiently large jet can also be neglected and the resistance of the air (or the wall) on the side of the border. Then almost all of the potential energy of the fall will be converted into the kinetic energy of the jet. Jet will be narrow and accelerate.

There are several ways to stabilize the jet. For example, if a stream flowing around and along the wire. You can also spin the flow in the pipe, to prevent him disintegrate into droplets. Unfortunately, science does not give the computational model for such free flows. Therefore, more research is needed.

This jet has no pressure. Moreover, it has no weight. Therefore, no matter how much water it was not the weight will be only on the resistance on the lateral boundary...
SY, AK

Dear Andrew,

I will think about your option 2 some more, but my intuitive feeling is that, if you have low pressure in the pipe near the ground, this implies that all of the potential energy from the head has been lost due to pipe ftiction.

By Bernoulli's equation, the sum of the potential, pressure and kinetic energy is a constant along the pipe. At the top of the pipe, all of the energy is potential. At the nozzle, discharging at atmospheric pressure onto the Pelton wheel, we want all the energy to be kinetic. Just before the nozzle, the velocity is low to keep the friction losses down, and at ground level there is no potential energy, so the energy is all in the form of pressure.

If the pressure and potential are both low at the ground end of the pipe, does this not mean that the kinetic energy leaving the nozzle will also be low?

Best regards,
Andrew Urquhart

What real measurement data do you have regarding water yield per square meter of collector area? (e.g., liters per m² per day under real atmospheric conditions)

The idea for the AirHES was initially conceived purely theoretically, based on physical concepts for energy purposes. When I began studying the deposition of water droplets on various surfaces, I unexpectedly learned that such systems already exist, called fog collection systems. They have been known since the 1980s and are used in several countries. There is extensive literature on these systems, including both experimental data and theoretical studies. For example, here are the data provided on the FogQuest website:

“One large fog collector, with a 40 m2 collecting surface, will typically produce an average of 200 liters per day throughout the year. On some days, no water is produced. On other days, as much as 1000 liters will be generated. The variability depends on the site. Choosing an appropriate site is of utmost importance. There are day-to-day variations in fog-water production, as well as seasonal variations, as is the case with rainfall.”

These real-world fog collection system inputs and physical assessments (based on liquid water content, wind speed, and mesh efficiency) formed the basis for the preliminary feasibility study.

I also conducted my own theoretical research based on MIT work and computer modeling to optimize potential meshes or sails, which allowed me to make approximations for developing a complex model of the AirHES.

Our own real-world measurements so far provide only indirect estimates (see the Experiments section on site). A test launch of a balloon in 2013 resulted in a break, so we can only estimate the water intake based on the change in the rope angle during testing: approximately 5 l/m²/hour, or 120 l/m²/day, which is consistent with our estimates in the feasibility study. Kite launches in 2015-2016 also yielded no direct results, as the altitudes were limited (~500 m) and the kite rarely flew inside the clouds. Laboratory (garage) tests allowed us to roughly estimate the efficiency of the kite models' meshes and sails, reaching up to 60%, which is consistent with my computer modeling calculations (see the link in the text.pdf file in each folder).

Under which atmospheric conditions do your collectors operate most effectively? (e.g., wind speed, liquid water content, temperature)

No special atmospheric conditions are required. As stated in the patent, receiving surfaces (e.g., mesh) must be located near or above the dew point, i.e., physically within the cloud (above the condensation line on the sounding (aerological) diagram or the cloud base). Obviously, depending on the cloud type, it makes sense to select the cloud zone with the highest liquid water content (LWC) value. For example, for cumulus clouds, such a zone is located approximately 1 km above the cloud base. Although the droplet moisture in the cloud remains liquid down to approximately -10°C, it is advisable not to raise the collector above 0°C, as precipitated droplet moisture can lead to icing. Also, the precipitating water flow typically increases linearly with wind speed, but specific design considerations should be taken into account, such as the automatic reduction of the receiving area for free-hanging collectors (see the complex model of AirHES).

What are the minimum meteorological conditions required for the system to generate energy?

Minimum conditions: some cloud cover, non-zero wind speed, and positive temperature in the working area. We can assume that even in the absence of clouds, dew may form on the mesh, but the expected rate of surface condensation (dew formation) is much less than the purely mechanical collection of fog or cloud droplets during volumetric condensation. However, at operating altitudes, the wind required for droplet deposition on the meshes or wind-blown fabrics (wind penetrated sails) is almost always present.

What collector surface area would be required to produce a continuous water flow of approximately 1–2 liters per second?

The AirHES cannot provide a continuous water flow regardless of the collector area, as it is a weather-dependent system. However, water (unlike electricity) is an additive (accumulative) resource, meaning it is necessary to ensure a sufficient strategic water reserve in case of adverse weather. Statistical satellite and climate data can be obtained for any location on the planet to roughly calculate the average annual performance of an optimized AirHES using a complex model. For example, for Ashdod, Israel, calculations yield an estimated average flow of ~4.5 L/m²/day, meaning a collector area of ​​ 19,200-38,400 m² would be required to achieve the target flow rate of 1-2 liters per second. However, the price of water would be only ~$0.10/m³, which is 20 times less than the current price of municipal water in Ashdod.

What altitude do you currently consider the most realistic operational height for the system?

This depends on the primary optimization objective of the AirHES (water or energy) and the accuracy of our satellite and climate data on the altitude distribution of LWC and wind speed (see table LWC.xlsx). LWC generally follows the barometric law, so the maximum horizontal drip flow is typically observed at an altitude of 1-2 km. On the other hand, the energy maximum can shift to higher altitudes (up to 5 km). However, given that the most expensive components in the AirHES design are typically the UHMWPE hoses and ropes, the optimization program automatically attempts to reduce the operating altitude to approximately 1 km. Further research is needed, as real-world cloud cover is often observed above 1 km.

What wind speed data or atmospheric models were used to estimate conditions at this altitude?

The algorithm for obtaining and processing all the necessary data is described in detail in the corresponding article. It is based on statistical satellite data from the NASA CloudSat project and climate data from the NASA MERRA-2 retrospective analysis program. Historically, this article arose from an analysis of a German paper and correspondence on a NASA forum. All averaged data for the locations examined are presented in the LWC.xlsx table.

How does the system respond to strong turbulence or vertical air currents?

Our limited experience testing the systems showed that both the aerostat and kite-based versions perform quite reliably over many hours of in-flight testing. The system is designed to utilize only lightweight, flexible, tension-based components, which should facilitate automatic stabilization, adaptability, and stability in turbulent conditions. Aerostat systems have historically proven exceptionally stable. For kites, only a sharp drop in wind speed has been critical, leading to wing geometry distortion and collapse. Clearly, introducing additional stiffening elements could solve this problem. Another option is to use "sleeping" drones, which can stabilize the surfaces in such situations. In any case, even a kite parachuting to the ground in dead calm is not considered an accident, as it does not result in structural failure or damage on the ground. When the wind resumes, the system can be easily relaunched, possibly even automatically.

What maximum wind speed can the structure withstand safely?

Obviously, the very concept of the AirHES presupposes a large windage area for the structure and, consequently, significant wind loads and displacements. At the same time, the AirHES is a hydroelectric power station, not a wind power station, and therefore can be optimized to avoid critical wind loads in every possible way. Therefore, I first wrote a paper in which I performed calculations for extreme wind speeds and displacements. Indeed, it turned out that by controlling the angle of attack of the receiving surfaces, we can avoid critical stresses up to hurricane-force winds of 55 m/s.

Further work on mesh optimization allowed us to calculate approximations for the aerodynamic coefficients of the meshes and kite sails, which made it possible to computer model and optimize the entire AirHES using the Rayleigh wind distribution and three load-reduction methods: free suspension, angle-of-attack control, and sail active area adjustment. Thus, the AirHES model automatically selects the appropriate combination of options when optimizing for a specified objective function (for example, payback time).

How does the system technically manage the hydrostatic pressure created by a several-kilometer water column?

This problem only applies to the power applications of the AirHES, and even then, hydrostatics can be avoided. Calculations show that the idea will be primarily used for water supply systems, which provide relatively high profitability and demand in areas experiencing water shortages, especially far from the sea.

Nevertheless, modern materials such as UHMWPE can easily withstand such hydrostatic loads. Optimization calculations using the AirHES model show that hydraulic loads are typically several times smaller than aerodynamic loads. Furthermore, they are distributed: hydraulic loads are greatest at the ground, while aerodynamic loads are greatest near the hose or rope attachment to the collector or rigging of the balloon/kite. For example, the calculation for Ashdod gives a hose wall thickness (D 18 mm) for hydraulics of only 0.17 mm (with a fivefold safety factor), while for longitudinal stresses from maximum wind loads (24 m/s) it is 0.81 mm (with a twofold safety factor).

What materials or pipeline technologies are planned to withstand this pressure?

There's a whole class of modern polymer materials (Kevlar, Dyneema, Zylon, Carbon fiber) that boast a strength-to-weight ratio significantly superior to steel and other traditional materials. We used UHMWPE (Dyneema) in our calculations because it's the lightest of them (0.97 g/cm³). Commercially available ropes and pipes are made from this material, but we envisioned using a flexible hose braided from these threads with a sealing sheath on the inside and UV protection on the outside. Such a hose could withstand both hydrostatic pressure and longitudinal aerodynamic loads. However, for water supply applications, we could simplify the design and use a commercially available rope, through which water could flow freely, either without a sheath at all (due to capillary action) or within a lightweight PE outer sheath (as a channel waterfall).

How will the system prevent pressure shocks or water hammer effects?

Water hammer is a pressure surge typically caused by a sudden stop or restart of flow. We believe this phenomenon is uncommon at AirHES, as the flow enters the hose from above in a free flow and exits through the nozzle below onto the Pelton turbine without any restrictions.

What pressure levels do you expect at the bottom of the pipeline at heights between 2000 and 5000 meters?

If we consider the energy application of an AirHES with a pressure pipeline (hose), the pressure will correspond to the normal hydrostatic pressure for such an altitude (200-500 atm) minus the hydraulic losses in the hose, which the optimization program typically sets at 10%. If the AirHES is used solely for water supply, the program calculates a free-flow flow with a pressure loss of 100%, meaning the pressure at the bottom will be close to atmospheric.

What calculations have been performed regarding friction losses in a pipeline several kilometers long?

The AirHES model uses the standard Darcy-Weisbach formula with a hydraulic loss coefficient of 0.00762 for a smooth plastic hose. These calculations were also verified using specialized hydraulic calculation programs, such as these. The calculation program typically automatically selects the optimal loss level based on technical and economic criteria.

What minimum inner diameter would the pipeline require to avoid excessive energy losses?

The AirHES model and optimization program do not have this limitation. The program uses the Monte Carlo method to vary various optimization parameters (including the hydraulic loss level used to calculate the hose's internal diameter) to achieve the best result (usually a technical and economic indicator) through millions of iterations.

How does the system performance change when realistic friction losses are included?

Water productivity remains virtually unchanged, as it depends only on collector efficiency and external meteorological factors (LWC, wind speed). Energy productivity also changes slightly, as the optimization program typically selects hydraulic loss levels within a narrow range (~10%).

What is the total estimated weight of the following components: collector structure, pipeline, water inside the pipeline, structural supports?

After the requested number of iterations has been exhausted, the optimization program displays the final solution, which presents all the key design, load, and technical and economic data. For example, for Ashdod, for a balloon-based solution with a collector (single-layer mesh) with an area of ​​10000 m² (100 x 100 m), we see this table on page 3:

• Collector structure: 1000 kg (Wc) - $2500 (Cc)

• Pipeline (hose): 42.42 kg (Wh) - $4242 (Ch)

• Water in hose: 243 kg (Ww)

• Structural supports: balloon shell 95.7 kg (Ws) - $1851 (Cs), supporting kite 12 kg (Wk) - $303 (Ck)

What lifting capacity must the aerostat or kite system provide to support these loads continuously?

The AirHES model assumes a force balance at the most stressed point—the hose/rope attachment point to the flight deck (see page 9). It shows that taking all forces into account (with some acceptable simplifications) yields a quadratic equation, the solution to which allows us to obtain maximum loads (for maximum wind speed) with engineering precision and, accordingly, calculate the required structural dimensions for a given safety factor.

For our example (Ashdod, aerostat), these forces are also shown on page 3, and we can calculate the required lift force of the aerostat, 14128.6 N (T0y), which ensures that the AirHES remains aloft even in complete calm. A verification calculation shows that the error in our engineering calculation is only 2% (Err).

Similarly, for the example on page 4 (Ashdod, kite), we can calculate the balance of forces so that the kite sail creates the minimum necessary lift force of 50 N (Tcyr) to keep the AirHES in the air even at a minimum calculated wind speed of 1 m/s (Vr).

What safety margins are included in case of water accumulation or icing?

In addition to the standard safety factors (aerodynamic AMS and hydrostatic HMS), the AirHES model includes additional BVF and CWF factors, which can be used to refine the model's behavior and align it with empirical data.

CWF specifies the net or sail material's weight due to moisture accumulation, as well as additional rigging and drainage. It is used to calculate the mesh or sail's weight and also affects the angle of attack when the mesh is freely suspended. It is currently assumed to be 2 in calculations.

BVF specifies the excess aerostatic lift compared to the aerostatic balance, which is equal to 1. This excess aerostatic lift can be used to optimize the aerodynamic lift to ensure the required moisture intake height and optimize the head and power of the AirHES.

Although the patent indicated that the AirHES is resistant to ice formation and accumulation, automatically descending into warmer layers of the atmosphere, such operating modes should nevertheless be avoided.

What protection measures are planned against: icing, lightning, hail, extreme temperatures?

When creating adverse weather conditions, the same principles that have been used for centuries, for example, for sailing ships, apply in most cases to the AirHES: going into harbor (parachuting to the ground), furling the sails (reducing the collector's windage), and turning the bow into the wave (reducing the angle of attack).

• Icing: Although the droplet moisture in the cloud remains liquid down to approximately -10°C, it is advisable not to raise the collector above 0°C, as the precipitated droplet moisture can lead to icing. Although the AirHES is resistant to ice formation and accumulation, automatically descending into warmer layers of the atmosphere, such operating modes should nevertheless be avoided. Various altitude control methods can be used for this, such as accumulating water in the upper reservoir, controlling the sail's angle of attack, changing the kite's area, and other active and passive (physics-based) methods.

• Lightning: The AirHES contains virtually no conductive elements unless it is specifically designed for area protection as a lightning rod. Even cloud water is practically a distillate, i.e., an insulator. Using hydrogen in a balloon can also be safe if the content of penetrating air is automatically controlled, for example, by a palladium catalyst.

• Hail: Not tested, but should likely be avoided, for example, by parachuting to the ground.

• Extreme temperatures: The AirHES operates in a cloud within a very narrow range of positive temperatures close to zero.

Have you studied how ice formation could affect the weight and aerodynamics of the system?

No, no such studies have been conducted. Although the water droplets in the cloud remain liquid down to approximately -10°C, it is advisable not to raise the collector above 0°C, as the settled water droplets can cause icing. Although the AirHES is resistant to ice formation and accumulation, automatically descending into warmer layers of the atmosphere, such operating conditions should nevertheless be avoided.

What turbine types have been considered or tested for this system?

For any high-pressure hydroelectric power plant, Pelton turbines are definitely used, as they are the simplest and have very high efficiency (up to 95%). However, for low flow rates, a reversible screw hydraulic motor can also be used. This issue was discussed in detail by Professor A.S. Baibikov, Doctor of Engineering, in his calculation example for the AirHES. We have not tested such systems, but this is a well-developed area of ​​hydraulics with numerous applications.

For which pressure and flow ranges is the turbine designed?

The Pelton turbine can be used with any water pressure and flow rate, as it is essentially a nozzle that converts the potential energy of the water column into the kinetic energy of the jet according to Bernoulli's equation. There is no pressure on the turbine runner itself, making it very simple and easy to regulate and operate. Furthermore, turbine efficiency can reach 95%.

What total system efficiency do you realistically expect? (collector → pipeline → turbine → generator)

The calculations for the AirHES model assumed a 90% energy efficiency for the conversion section (turbine → generator), and the optimization program typically selects a pressure loss in the hose of ~10%, resulting in an energy efficiency (pipeline → turbine → generator) of ~80%. For comparison, the similar efficiency at one of the largest high-pressure hydroelectric power plants (1869 m) is ~92.23%. Clearly, with energy optimization of the AirHES, this efficiency can be increased to ~90% or more.

As for the water-based collector efficiency, for our example (Ashdod), it is 22.75% for the balloon (X, p. 3), and 27.94% for the kite (X, p. 4). In the work on mesh optimization, it was shown that the efficiency of collecting drops with a single-layer collector can reach 50-60% (X, p. 7), and considering that the collector can be made multi-layer, then almost 100%, but this was not optimized in this version of the program.

How stable is the energy production when water flow varies significantly?

Clearly, both energy and water production are determined by cloud cover. According to NASA, clouds cover 67% of the Earth's surface on average, and in terms of natural factors, the uniformity of AirHES generation is even better than that of other renewable energy sources, with a typical capacity factor of ~20-40%. However, cloud cover can be very unevenly distributed at altitude, significantly reducing actual stability.

I have written a special paper on possible energy storage methods applicable specifically to AirHES:

- local hydro storage (HS) -- water storage in the upper reservoir and hose,

- cascade HS -- water storage in artificial pumped storage power plants powered by the AirHES water,

- induced (surface condensation on mesh) in the absence of clouds -- testing is needed,

- hydrogen storage (and possibly transportation) in AirHES balloons (600 times greater than the local PS).

The latter method ensures stable energy production, but requires an increase in the cost of the installation due to the addition of reversible fuel cells.

Are there buffer systems or storage mechanisms to stabilize energy production?

I wrote a special paper on possible energy storage methods applicable specifically to AirHES. Two of these methods can be used as buffer systems to stabilize energy production:

- Cascade pumped storage. As is well known, one of the best solutions to the problem of uneven power generation for any renewable energy source is currently the use of pumped storage hydroelectric power plants. To achieve this, a reversible hydroelectric power plant is built using suitable elevated ground, operating alternately in pumping and generating modes. The cascade-type AirHES elegantly solves this problem, simultaneously addressing its dependence on weather conditions. If there is a suitable elevated ground, but no river flows from it, AirHES can easily create this "river" and an intermediate upper pool, discharging its water in a natural (weather-dependent) manner not to the lower pool, but to this intermediate upper pool of the cascade hydroelectric power plant. Then, this lower hydroelectric power station will act as a hydraulic accumulator, and the coordinated operation of the AirHES itself and this cascaded conventional hydroelectric power station will completely eliminate weather dependency.

- Hydrogen storage. The AirHES has both energy and ideal fresh water (distilled water) in abundance. Moreover, the AirHES, technologically and structurally, can naturally store hydrogen in its aerostats or even transport the accumulated hydrogen in such aerostats to the consumer. This can be accomplished by using additional aerostats, which will not only support the AirHES components but also store a reserve of hydrogen. Thus, during periods of energy overproduction, by pumping hydrogen produced by electrolysis and balancing the discharge of water, it is always possible to ensure the necessary amount of water in the upstream pool and a reserve of hydrogen in the aerostats. This ensures that, when energy is needed, it can be recycled back into energy in the same balanced manner in the fuel cells (from hydrogen) and the turbogenerator (from water).

How can the collector or pipeline be serviced or replaced when the system operates several kilometers above ground?

The AirHES does not have to remain in the air continuously. The flight section can be lowered to the ground using specialized means (such as winches like any aerostat) or by independently controlled parachuting by adjusting the balance of aerostatic and aerodynamic forces (for example, by filling the upper tank with water, changing the angle of attack, and adjusting the sail area). All necessary maintenance can be performed on the ground.

Which components do you expect to be the most frequent points of failure?

Based on experience with test launches of balloons and kites, the majority of failures were due to rope breakage, most often at the most stressed point, near the attachment to the flight part. This was caused by impact loads from strong gusts of wind. Therefore, special damping devices should be installed in this area.

What physical prototypes have been built and tested so far?

The entire history of my prototypes can be tracked in the Experiments section (see each folder for a link to the description in the text.pdf file). I built and tested the first scientific prototype based on a balloon in 2013. The prototype remained airborne for several hours before the rope broke. Thus, the prototype was lost, and no direct measurements of the water intake rate were made. However, based on indirect observations (by changing the rope angle during testing), it was approximately ~5 l/m²/hour, i.e. ~120 l/m²/day), which corresponds to my estimates in the feasibility study. Subsequent prototypes based on kites and kytoons were tested in 2015-2016, but also did not yield direct results, as the altitudes were limited (~500 m) and the kite rarely flew into the clouds. At the same time, laboratory (garage) tests were conducted on scaled-down models, which allowed me to roughly estimate the efficiency of the meshes and kite models' sails, which reached up to 60%, consistent with my computer modeling calculations. After that, due to lack of funds, I only conducted theoretical research.

What actual performance results were measured during these tests?

No direct indicators were obtained during the tests. Indirect estimates were obtained that were consistent with the theoretical estimates in the feasibility study. Laboratory experiments also yielded data consistent with the results of computer modeling of collector efficiency.

How do the measured results compare with your theoretical calculations?

Since no direct data was obtained during testing, the indirect estimates are entirely consistent with the theoretical estimates in the feasibility study, which were obtained through direct testing of high-altitude fog collection systems and physical approximations. At the same time, laboratory experiments yielded direct data consistent with the results of computer modeling of collector efficiency.

What maximum power output do you consider technically realistic for a single installation?

Frankly, I don't think megaprojects are suitable for the AirHES. Rather, the ideal application for the AirHES is distributed municipal water supply for small towns and villages, with associated power generation.

Nevertheless, the feasibility study article examined hypothetical AirHES options with a mesh size of ~1 km². Within the design constraints specified there, a capacity of ~20 MW is most likely. On the other hand, the use of the AirHES with maximum design assumptions under ideal equatorial weather conditions was discussed in a controversial comparison post with solar power plants, where it could have a capacity of up to 1 GW with fantastic technical and economic indicators (~$1/kW at 1 kW/m² of mesh!). Formally, there are no restrictions on building larger AirHES.

What technical limits do you foresee when scaling the system to larger capacities?

These technical limitations were outlined in the feasibility study paper (pp. 5-6):

«In principle, the same pattern can be calculated and for the next generation - high power module with a network of ~1 km2. However, we already reach the limit values for the size of balloons and kites. To go to this power, we should change the design solutions. For example, we can use the meshes themselves as kites to support the basic weight of the produced water in the hose, and to use the balloon only to support meshes and empty hose in complete calm. This will demand the creation of an appropriate control system (preferably by using a natural physical feedback), which will monitor wind speed and emergency dumping or spraying water from the hose under the threat of falling. This also should include the need to develop a system of the automatic and interconnected accumulation of the water storage upstream and the hydrogen in ballonet balloons that will significantly reduce meteo-dependence of AirHES without using external storage (which dramatically increase the cost of wind and solar plants).»

From your perspective, what are currently the three biggest technical challenges that must be solved to build a fully operational AirHES system?

In principle, the AirHES is a synergistic combination of three well-known technologies: high-pressure hydroelectric power plants, aerostats/kites, and high-altitude fog/cloud harvesting. In this sense, it simply inherits technical solutions that are already widely used. However, the practical application of these systems in flight conditions creates a new area of ​​technical solutions. I would highlight the following three key challenges:

- aerodynamic stability of the structure in turbulence, gusts, and adverse weather conditions;

- wear resistance of the main components (cable, hose, nets, sails) from wind loads and ultraviolet radiation;

- development of damping devices, automatic control systems, and safety systems.