Airborne solar wind energy systems (ASWES)

I think this discussion is less productive. Because; the cloud cover is changing all the time and is obviously very dependent on location and season. Saying 6 km may be an ok starting point and for sure a detailed look at thia would be interesting the further one goes into the rabbit hole.

Also, the altitude is not a strict limit. The higher you go, the higher capacity factor. But its most certainly a question of dimminishing returns.

I think for a very early discussion like this having 6 km is ok, though I expect we all understand reality would be more intricate

Of course the weight of the DCDC to get to 2 kV will have a weight. It must also be in close proximity to the panels. This will be quite difficult in a soft kite scenario.

I found this, 1200 V DCDC capable of 250 kW peak at 30 kg. Expect a weight for a optimized unit for 1 MW to be around 200-300 kg. [guesstimate]. Much lighter than the cable

How about using the electricity generated to power fans which will augment airflow over a lifter kite so it can provide more lifting force at higher tether angles.

I am sure the lifter kite in an industrial system will be equipped with a KCU which will control the meanderings. Using a cable drive with crosswind action may be problematic.

The moment you add fans you may as well use them to steer the kite.

The higher the voltage, the more interesting it becomes I think, but the higher the voltage the more insulation you need IIRC. Perhaps you could only insulate the bit at the beginning and end, letting the air around the cable be the insulator for the rest, and only send electricity through the cable while it is fully reeled out. You’d have some load at altitude to absorb electricity for when the cable is not fully reeled out.

I think this could be applicable to any system that has a fixed point at altitude, so excluding the Makani design.

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Neutrally or positively buoyant, probably due to hydrogen ballonets, crosswind kytoons, attached to any system you like. It’s a neat idea because of the positive instead of negative cube scaling effect, it’s not a neat idea because of the increased surface area and so on. No comment on the practicality. You’d perhaps consider this after you already had an air filled crosswind kytoon.

For the rest of your comment, from memory, but it goes something like this: one condition for something to be accepted for publication is that all or relevant claims should be supported with evidence. In this case evidence would be observational data. A peer or interested reader should be able to verify all claims made by reading the text itself or the sources given.

@tallakt , your comment provides some interesting information.

Could you please specify the reason? Is it because of the lack of rigidity of a flexible support such as a flexible kite, and its incessant deformations? Thanks.

Indeed Jason Deign raises some drawbacks. I will quote some points for discussion:

“This technology is definitely in the realm of looking great in theory, but implementation will require overcoming major commercialization hurdles,” said Ravi Manghani, a senior analyst for energy storage at GTM Research.

​“Even if we assume this product passes the hurdle of technology feasibility, it will surely be hard to finance such projects in the very near term,” he said.

One potential challenge for the concept is that “hydrogen as a carrier gas for balloons is not allowed in many places,” he admitted.

Manghani highlighted at least three other potential stumbling blocks. The first, he said, is that hydrogen fuel cells have been tough to commercialize. "There are certain operational limitations that require frequent operations and maintenance stoppages.”

This is an economic challenge for fuel-cell systems on land, he said, and “servicing these systems at high altitude can be an order of magnitude tougher.”

A second problem is that “adding storage will add to the weight of the device, making it costlier to maintain afloat.”

One way to avoid this might be to position the fuel cell at the base of the tether, although that would presumably complicate the design by requiring a hydrogen pipeline to run from the balloon to the earth’s surface.

Finally, said Manghani: “The schematic shows energy harvesting and storage devices, but to connect to existing grids, there will be need to power conditioning as well as monitoring and controls. Again, adding those can increase costs.”

Utility-scale solar systems typically have balance-of-system components that aggregate and reduce the need for individual pieces of equipment, Manghani said. “Adding those components for individual balloon systems will drive up the costs as well.”

Even if all these issues can be overcome, the economic case for balloon-based solar might be extremely marginal outside cloudy climates, according to Oliver Soper, founding director of the renewable energy technical consultancy OST Energy.

Unlike wind, where power is a function of the cube of the air speed, PV output has a direct relationship with solar intensity, he said.

Thus, while it might make sense to harvest stronger winds using airborne turbines, the potential returns for high-altitude solar are likely more modest.

Soper noted that existing PV technology can already achieve yields of three times the northern European average in sunny locations such as Chile or South Africa.

“You would have to look at the round-trip efficiency of converting solar to hydrogen and back to electricity on the ground,” he said.

If the losses are greater than the extra energy you can generate at height, “then this concept is not going to work.”

I put in bold an element I evoked in a previous comment:

On the topic of cable voltage and insulation. I made this interactive tether designer when we considered the possibilities with flygen systems. Should be applicable to ASWES :slight_smile: Hello World!

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Thank you @aokholm : great work!

I will say I was half joking when I started “advocating” airborne solar. Not totally joking, mind you, but by the time we’re talking about how many tons of tether you need, and people are adding flying electrolyzers etc., it all starts getting pretty improbable, considering how straightforward it is to mount solar at ground level, rooftops, parking shade structures, etc.
Especially here in the Mojave Desert, it is almost never cloudy and we’re already at 3600 feet elevation. :slight_smile:

BTW, I’m pretty sure, if anyone truly wants to know the frequency of clouds and their heights, by time of year, at various locations, that data must be available.

So let me expand on my thinking about placing the DCDC high voltage power supply/transformer.

First of all I foresee that the only way this could work would be by having super lightweight membrane kites covered by film solar panels. This dictates somewhat the shape of the kites to a sheet, possibly with air pockets here and there, then a bridle ending at a single point where the main tether starts.

For such a design, you could not just put a 400 kg unit on the cloth itself, it would cause a dent in the shape, probably ruining any chance of fair aerodynamic properties of the kite.

Rather, the DCDC would have to reside at the tether attachment point or in close proximity.

This raises the question; how to transmit energy from the kite cloth to the tether attachment point?

One could have a conductive bridle. But as solar panels generate a fairly low voltage, the weight of such a bridle might be excessive. So maybe each panel should have a separate lightweight DCDC bringing the voltage to something more manageable without adding much weight. Or maybe have many tiny high voltage DCDC converters so lightweight they would not dent the kite membrane.

Anyways, these are real issues that could not be ignored.

I was giving more thought to the landing of such a huge kite. Maybe it would be beneficial if an area equal to the kite was allocated on ground, possibly elevated from any farming area or similar.

This way the plant could land during lulls and high winds and still produce some power.

All this being said, handling a soft 5k m2 kite in high winds, without ruining a solar panel film glued to the cloth, seems a bit scifi to me and does not seem to compare well with current wind or solar alternatives.

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Hello Tallak: Might it be possible to connect the solar panels in series to achieve high voltage DC without a converter or transformer?

I think it could be possible except I believe (not at all an expert) each panel runs best at its own voltage/current. So if they differ even slightly in current and they are connected in series, one of them would get a higher voltage. But maybe something that could be fixed either in the panels themselves or some added electronics.

Oh at last, I feel I can add one more layer of complexity
we need to launch it from the sea to not tear it while the material is spread out

How could they have different currents if the same current is flowing through them all in series? Isn’t that like saying a single water pipe could have a different amount of water going in at one end than is coming out at the other end? Maybe I’m missing something - current leakage? What I’m thinking is the total current would be the same amount of amps for the whole string as for any one panel. It’s just the total voltage that would climb. But the voltage difference for any one panel would be the same as for a single panel. One problem I would be looking for is how many “panels” you could run in series before the total amount of voltage is too much to handle in some way.
I’m not well-versed in solar, which keeps changing, as to how much voltage you can safely “series” up to. Especially when we’re talking about thin film (new) here. I know 300-400 Volts is not a problem, I think up to 600 Volts is OK, but not so sure beyond that, although I would guess a few thousand Volts would be workable.

As I said I dont know enough about this, but let me at least make my statements clearer:

As each panel will have their own optimal current/voltage setting, it may not be easy to connect them in series, because that optimum current will not match the common current, and also the voltage leading from having a common current may damage the panels.

As far as I can tell panels are connected in parallel. Anyways I am not bothered to investigate this as its not too important at this stage. My points still hold some truth though, that the weight of electronics, stiffness of the wing, weight of cabling and the topology of cabling and voltage together are important considerations.

From the illustration of CNRS and JFG’s solar balloon project I sketched (see below) a wind energy system (WES) part, including isotropic kites (to face any wind changes) and an airborne wind turbine.

As the initial balloon seems to be able to orient everywhere to face sun due to its apparent or supposed two axes of orientation, adding wind energy seems possible and would provide some additional and significant electricity production, as well as stabilization of the set in spite of strong winds.

I think adding the WES below the balloon looks to be easier, but above could perhaps be studied, by using the two horizontal axes on either side of the balloon.

That said such an installation raises challenges at the limit of what is possible. It is the reason why I suggested untethered solar thermic and photovoltaic systems (U-SES), for uses that are certainly more limited, although they can become more important, but whose implementation seems much easier and simpler.

Suddenly I’m reminded of the perennial announcements of resurrecting the airship and blimp industry, by showing a rendering of some very large airship pr airship/blimp, filled with details of how fast it will go, how much cargo it will handle, how wonderful it will be, then it never happens. :slight_smile: