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).

Experiments and R&D in Russia are limited to a short summer period of 2-3 months. Actual launches are only possible a few times, as favorable weather with stable winds and low cloud cover is required. The surrounding forests present an additional challenge, as a balloon or kite failure typically results in the loss of equipment, which must be rebuilt. Experiments typically lasted several hours, but actual cloud time was measured in minutes due to altitude limitations. Furthermore, we were unable to observe the moisture accumulation process due to the lack of appropriate video equipment at the time. These issues could now be easily resolved (with R&D funding) to obtain real-world data on water accumulation. For example, drones, which are not dependent on weather and have fewer altitude and aviation safety restrictions, could be used in experiments instead of balloons and kites.

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.

The aforementioned initial feasibility study was based on generalized planetary data, assuming average cloud liquid water content and coverage (67% of the planet's surface). Subsequently, a complex AirHES model was developed, which allowed for the optimization of the design parameters of a specific installation based on feasibility criteria (usually payback period) using specific satellite and climate data for the specified location. An analysis of several locations was presented in the article, where typical values ​​are typically more than an order of magnitude lower than the corresponding tariffs, with a payback period of six months to a year.

Cloud Power & Water for different locations

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.

What causes a cloud to release water onto a mesh?

A cloud is a collection of microscopic droplets (~5-10 µm) of already condensed water. Entrained by wind and updrafts, these microdroplets can mechanically deposit on fibers of similar characteristic sizes as they pass through meshes or blown-through fabrics. This is described and modeled in detail in my work on mesh optimization, which in turn is based on the work of MIT. This mechanism is well known and has been studied in fog collectors. Another possible mechanism involves induced surface condensation and precipitation of water from vapor near the dew point, which is analogous to dew formation even in the absence of clouds. However, surface condensation is usually quantitatively inferior to bulk condensation in the cloud.

How can you eliminate the hazard to aircraft?

"Airspace regulation" is a truly complex issue, but it's important to keep in mind that long-haul aircraft fly at significantly higher altitudes. Small aircraft also don't fly just anywhere, but usually along designated corridors (just as cars typically travel along roads). Furthermore, many areas on the ground have "closed" skies (military bases, nuclear power plants, etc.), so there are special maps where such zones are designated. I personally used special notifications sent to the air traffic control service for testing the AirHES. These special notifications are called NOTAM (Notice to Air Missions / Notice to Airmen). However, they can only be used temporarily, for experimental purposes. The procedure for issuing permanent permits depends on the laws of the individual country. In any case, this is better than occupying the same space on the ground (for example, for nuclear power plants, solar power plants, and wind power plants).

A comparative analysis positioning AirHES against currently deployed technologies — passive fog nets, solar-powered boreholes, atmospheric water generation (AWG) + mini-grid solar, and trucked water supply — for the same community-scale use case.

AirHES uses the same water production principles as fog collection systems. However, the overall performance of the AirHES should significantly exceed that of fog collection systems for the following reasons:

1.       Fog is a relatively rare phenomenon compared to clouds.

2.       Fog is localized, not global like clouds.

3.       The water content of fog and wind speed near the ground are significantly lower than in clouds, so the theoretical performance of fog collectors is 1-2 orders of magnitude lower than that of the AirHES.

4.       Fog collectors are passive systems that cannot track changes in wind direction, which further reduces performance, while the AirHES is an active system that automatically rotates into the wind.

5.       Fog collectors cannot optimize altitude for maximum performance, while the AirHES can.

6.       Theoretically, the water from the AirHES should be significantly cleaner, since atmospheric pollution is concentrated near the ground.

7.       The AI ​​estimates the price of fog water at $0.25-0.60/m³, while for the AirHES, the estimates start at $0.07/m³.

8.       Finally, the AirHES can produce not only water but also hydroelectric power.

For boreholes with solar panels, the price of water can be comparable or even lower than that from AirHES. We can compare, for example, with Israel. The AI ​​estimates the price of borehole water for farming (20-100 m³/day) in Israel to be $0.22-0.45/m³, with government tariffs for agriculture at $0.70-0.90/m³. This is still approximately twice as high as the estimated price of water from AirHES (46 m³/day) of $0.10/m³.

For India, the AI ​​estimates significantly lower prices for farming (40-100 m³/day) at $0.015-0.025/m³, which could be significantly more cost-effective than using AirHES. However, borehole water for drinking may require additional treatment, which will increase its price. By combining an AirHES (which operates in cloudy weather) with a solar power plant (which operates in clear weather), a virtually uninterrupted water and energy supply can be achieved.

From AI: "The cost of water obtained from atmospheric water generators (AWG) powered by mini solar power plants (SPPs) averages $0.06 to $0.28 per liter (or $60-280/m³) when calculated over the entire system lifecycle. Unlike boreholes, atmospheric generators require a colossal amount of electricity (approximately 0.30-0.45 kWh per liter of water). Because of this, autonomous operation requires a powerful mini solar power plant with an expensive battery pack, which dramatically increases the price of each cubic meter." This is 2-3 orders of magnitude more expensive than water from an AirHES.

Water delivery by truck clearly depends heavily on location. The AI estimates this price for India of $3.5-7/m³, 35-70 times higher than the price of water from AirHES.

Technology Readiness Level (TRL) assessment at the component and integrated system level.

The TRL system is currently at the R&D stage. Many components (aerostats, kites, tethers, ascent and descent systems, and ground anchors) have been tested, refined, and verified in scientific experiments, but the integrated system has not yet been launched. Specifically, the tether damping systems, aerodynamic control, angle-of-attack and sail area control, Dyneema hoses (which are not even yet in mass production), as well as the turbine and generator for the power system, still need to be developed and tested.

We propose that this task be addressed in stages, meaning that initially, we need to ensure water production (without power) using simple kites, which could solve the problem of emergency or permanent water supplies in remote villages or islands. Only then can we move on to the full functionality of the AirHES.

Any engagement to date with governments, utilities, development finance institutions, or NGOs, including outcomes.

All my theoretical work, patenting, and experiments with the AirHES were done on my own initiative and with my own money (~$35k). I repeatedly tried to interest government agencies (the Ministry of Natural Resources, Skolkovo, etc.), corporations (RusHydro, RosAtom, etc.), scientific institutes related to meteorology, climate, energy, etc., investment funds in Russia and Israel, etc., crowdfunding platforms (Indiegogo, Planeta.ru, etc.), and social media groups (Facebook, LinkedIn, etc.), but all without success. All links can be found in my correspondence and blog on LiveJournal (https://bari-x-andrew.livejournal.com/).

Can you share the specific experimental results from the July 2013 Seliger test and the June 2015 kite test?

Everything is described in the Experiments section. For example, open the first folder, bal_130730 (i.e., balloon 2013/07/30). It contains a large number of photographs (including a diagram of the experiment with captions in English, AirHES_1_prototype.jpg, and an aerological diagram, Screenshot.png, describing the state of the atmosphere). There's also a text.pdf folder with links to the experiment description, for example, https://bari-x-andrew.livejournal.com/5896.html?thread=67080#t67080 – my comment on my LiveJournal:

“We inflated the balloon with three helium cylinders (meaning the actual volume was less than the stated 26 m³). We attached a net of approximately 0.9 m². For the first launch, we decided not to use a cambric (water pipe) and simply tied a 5-liter canister to it. During launch, the aerostatic lift was measured with an electronic dynamometer at approximately 7 kg. We released the balloon. As soon as it rose above the trees, the aerodynamic lift increased sharply. The pull on the rope increased to approximately 50 kg or more. We realized that we couldn't hold the balloon with our hands (it would simply cut off our fingers). A winch (a garden hose reel) was crashed. We constructed a mooring bollard from two helium cylinders and began to raise it slowly, tying three EKA flags at intervals of approximately 300-400 meters. We raised it to approximately 1.5 km (the cloud base according to the current aerological diagram), and the cable extended for approximately 1.7-1.8 km. The balloon began to disappear into the clouds. They left it there for about an hour. During this time, the canister apparently partially filled, the aerostatic lift decreased to 2-3 kg, and the shift increased significantly (as was evident from the angle).

We went to seek help from the Ministry of Emergency Situations. Mountaineers arrived, grabbed the cable with pulleys, and began to lower the balloon by dragging it between two horizontal points. After lowering the balloon by about a third (two of the three flags were removed), the cable broke due to chafing near the bollard. After 5-10 minutes, Presumably, the balloon was shot down by an anti-aircraft missile (a distinctive sound and a trail in the sky were heard in the direction the balloon flew).

Thus, based on indirect evidence, the presence of water in the cloud was confirmed, but scientific measurements (for which the experiment was intended) were not fulfilled."

And so on for any folder...

What water yield did your test installations actually achieve, and under what atmospheric conditions (cloud base height, liquid water content, wind speed)?

I did not obtain any significant volume of water in my experiments. Perhaps I was simply unlucky. However, more likely, I could not have been, as I lacked the resources. I worked alone on my modest savings, while this would have required serious, collaborative R&D work with a substantial budget. However, even similar projects with multi-million-dollar budgets often fail to produce results. See, for example, https://www.omnidea.net/hawe/concept.html .

What is the longest continuous operational period any AirHES configuration has been maintained? Has any configuration generated measurable electrical output — even at micro-scale — from the turbine component?

The maximum duration of the experiments was several hours. Since it failed to obtain a significant amount of water, it also failed to generate hydroelectric power or electricity. Moreover, such a goal was not set, since the AirHES (like any hydroelectric power plant) can only generate energy if there is a water flow. Therefore, the power equipment (the Pelton turbine and electric generator) were not even purchased or installed. On the other hand, generating hydroelectric power and electricity with a water flow and enormous pressure is a trivial task that is solved automatically, like any other hydroelectric power plant.

Have any of the component integrations (aerostat + fog mesh + penstock + turbine) been tested simultaneously, or have they only been tested as separate elements? If the latter, what is the plan and timeline for integrated system testing?

The sum aerostat, mesh, and water hose were tested only in beginning. However, after the first few experiments, the water hose was no longer used; a container (canister) was simply attached to the mesh or kite to measure the incoming water. In laboratory (garage) experiments on mesh and kite models, the water hose was used, but only to collect water and determine the efficiency of the nets or kite models.

What are the failure modes that have been observed or modelled — icing, mesh fouling, tether fatigue, condensation vs. actual cloud LWC dependency, turbine cavitation at low head? How are these addressed in the current design?

All that has been observed is the kite collapsing when the wind is lost, or, conversely, the rope breaking in strong gusts of wind (usually near the attachment point of the flight section). Accordingly, the kite's aerodynamics need to be improved (by adding stiffeners to the leading edge) and installing rope damper near the attachment point.

Your feasibility study for Ashdod, Israel cites a water cost of $0.105/m³ and electricity cost of $0.007/kWh. What are the specific assumptions underlying these figures — mesh area, balloon volume, aerostat altitude, local cloud frequency (hours/year), LWC, wind speed, turbine efficiency, capital cost per component, and assumed operational life?

There are no assumptions other than the initial data of the AirHES mathematical model (https://doi.org/10.13140/RG.2.2.20766.61765), satellite and climate data for one year for a given location, and automatic design optimization for the minimum payback period (https://doi.org/10.13140/RG.2.2.36466.82885). Read these articles; they provide the rationale for each figure. Moreover, all the codes are publicly available; you can recalculate or "play" with the initial data yourself. Examples of such calculations with the breakdown of all design, weight, and cost parameters for different locations can be found (https://doi.org/10.13140/RG.2.2.23032.92168).

For a community-scale installation serving 500 people in a highland African or South Asian location (cloud base ~1,500–2,500m ASL, cloud frequency ~150–200 days/year), what is your modelled: (a) capital cost, (b) levelised cost of water (LCOW) in USD/m³, (c) levelised cost of energy (LCOE) in USD/kWh, and (d) simple payback period?

To calculate data for the AirHES model, I need to know the required average annual daily water demand (the size of the mesh or kite is selected based on this), the location coordinates (to obtain satellite and climate data for the specified year), and the current local water and electricity tariffs (these are used to optimize the return on investment). Based on the optimization results, you will receive your calculated a, b, c, and d values.

The $10,000 village-of-100 estimate on the AirHES website assumes $0.5/m² mesh. What is the realistic procurement cost of the mesh at small quantities (under 5,000 m²), and what certified commercial suppliers exist for fog collection mesh suitable for AirHES?

These were the very first estimates, where the data of a two-layer (Chilean) mesh based on data from fog collectors was taken as a basis. In most cases of optimization calculations, a single-layer mesh at $0.25/m² is now automatically selected. However, the price of the mesh has little effect on the total cost, usually it is only 10-15% of the total cost. You can see an example of the calculation in (https://doi.org/10.13140/RG.2.2.23032.92168), p.3. I bought a similar mesh in much smaller quantities here in Russia, and it was quite cheap, so I do not even remember at what price per m². The AI ​​says: “The cost of agricultural polyethylene (PE/HDPE) mesh in India varies between $0.20–0.85/m², depending on density, percentage of shading (from 35% to 90%) and type of weave.”

What are the recurring operational costs — aerostat maintenance, hydrogen replenishment (if helium is not used), mesh replacement cycle, turbine servicing — expressed as a percentage of capital cost per annum?

Operating costs are currently not included in the calculations, as the estimated payback period (usually less than one year) is significantly shorter than the expected lifespan of the installation (approximately 10 years). It is assumed that replacement is easier than repair. It is also assumed that the hydrogen is produced by the AirHES itself, so only the initial inflation of the balloon is taken into account. Of course, some repairs may be required, but I expect these to be only several percentages of the capital expenditures per year.

Using the standard Technology Readiness Level (TRL) scale (1–9), where do you assess AirHES today — and at the component level (aerostat, mesh, penstock, turbine-generator, integrated system)?

Until we have a single working device, this level is meaningless. The AirHES has been thoroughly researched theoretically, but for 10 years now, there has not even been a prototype for experiments where we could fine-tune the design of both the components and the entire system. Estimate the TRL of a fusion reactor, which has cost hundreds of billions of dollars worldwide for 70 years, if not a single reactor is operational yet?

What is the minimum viable prototype specification — mesh area, aerostat volume, altitude, turbine size — that would constitute a credible demonstration for a development finance investor or government agency? What funding quantum and timeline does that require?

For a convincing demonstration (IMHO), it would be sufficient to simply lift a 1 m² piece of mesh or wind-penetrated fabric into the cloud using a standard drone and measure the accumulated water over an hour. Another option would be to conduct such measurements directly from the ground in the orographic cloud layer on the top of a mountain (incidentally, such measurements are abundant in articles on high-altitude fog collectors). Several such experiments (with different cloud water content, wind speeds, angles of attack, and "sail" materials) would allow me to confirm or refute my theoretical calculations, refine the model, and, consequently, begin the gradual creation of AirHES prototypes. Initially, in the form of $350 kites (100 m²) with a yeld of ~500 liters per day. Then, if successful, balloon-based AirHES for $20,000 (10,000 m²) with a capacity of ~50 m³/day. Then, fully-fledged energy-producing AirHES. I am even willing to start solo, but a group of 3-5 people is better. You just need a warm location year-round or an uninhabited island with sufficient cloud cover, no airplanes, but with internet, a sewing machine, and the ability to deliver the necessary materials. I think I could build a kite version even on my own in a year with about $20,000 in funding.

You have stated the patents are now free and the project is open. This is admirable but raises a question investors will ask: what is the defensible competitive moat for a commercialization partner? Is it the integrated system design, the operational know-how, the cloud-resource mapping methodology, or something else?

Well, I launched the very expensive international patent process back then because I was convinced investors needed it to protect their investments. Unfortunately, the investors never showed up, and I wasted what was, for me, a huge amount of money that I could have used for experimentation. Now, in any case, all the patents have expired. However, the know-how and the desire to make two billion people happy remain.

What are the aviation regulatory requirements for operating an aerostat at 2–3 km altitude in various jurisdictions? Have you engaged with any national civil aviation authorities (CAA), and what is the permitting pathway and timeline in a typical African or South Asian country?

Honestly, I do not know; these are questions for local lawyers, and highly specialized ones at that. I answered this here: https://airhes.com/faq/#How_can_you_eliminate . We have people in our group who work with airships and aerostats, but they mostly work on military or police contracts, for whom these restrictions do not apply. On the other hand, I understand that this is clearly a solvable issue — if AirHES is needed for water and energy supply, small aircraft may be able to restrict in this area (for example, permanent no-fly zones are established for nuclear power plants).