Can this satisfy the world's energy needs? High-altitude wind power.

[joema]

Although I agree in principle, not completely. First note that the efficiency of the gasoline engine wasn't considered. The actual energy demand is about 18% of that indicated. Also, this is for a full tank of gasoline, so a few days isn't so bad.

Also, I keep seeing 50% as the practical number for electrolysis efficiency.

Thanks for catching that. However it doesn't make a huge difference, when you factor in a few other items I omitted:

The energy in a 15 gal tank of gas is about 545000 watt hrs. A modern internal combustion engine is about 25% efficient, so it can actually convert 25% * 545000 watt hrs to mechanical energy.

The question is how long would a residential-roof-size solar PV array take to produce sufficient hydrogen for equivalent mechanical energy from a fuel cell vehicle.

Let me repeat the numbers, with a few changes:

Hydrogen electrolysis efficiency: 70% (maybe optimistic, but based on actual electrolyzers available today)
Hydrogen storage efficiency: 80% (unlike gasoline there's boil off loss)
Hydrogen liquefaction efficiency: About 70% (I omitted that before -- you have to either compress or liquefy it for storage in a car).
Real-world fuel cell vehicle efficiency: About 40%. See http://www.evworld.com/view.cfm?section=article&storyid=730

Now, the fuel cell vehicle is more efficient -- about 40% vs about 25% thermodynamic efficiency. So you don't need 545000 watt hrs in the tank, but about 60% of this or 327,000 watt hrs of hydrogen.

How long does a residential roof full of PV cells take to produce this much hydrogen in a form the car can use?

327,000 watt hrs needed / (49,950 watt hours per day * 70% electrolysis efficiency * 80% storage efficiency * 70% liquefaction efficiency)

= 16.7 days for useable energy equivalent to one 15 gallon tank of gasoline.

If you're satisfied with about 1/2 the range of your gasoline car, you could fill up your hydrogen car from your home's solar array in about 1 week, assuming it's not cloudy and you dedicate 100% of your solar array output for that task.

 

[Ivan Seeking]

The energy in a 15 gal tank of gas is about 545000 watt hrs. A modern internal combustion engine is about 25% efficient, so it can actually convert 25% * 545000 watt hrs to mechanical energy.

However, there are additional losses through the drive train, but I was coming back to up that number a bit as the one that I used is an average, and a Honda Accord is obviously a more efficient choice. Also, I'm not sure how much drive train is avoided in a typical electric car today.

The question is how long would a residential-roof-size solar PV array take to produce sufficient hydrogen for equivalent mechanical energy from a fuel cell vehicle.

Let me repeat the numbers, with a few changes:

Hydrogen electrolysis efficiency: 70% (maybe optimistic, but based on actual electrolyzers available today)
Hydrogen storage efficiency: 80% (unlike gasoline there's boil off loss)
Hydrogen liquefaction efficiency: About 70% (I omitted that before -- you have to either compress or liquefy it for storage in a car).
Real-world fuel cell vehicle efficiency: About 40%. See http://www.evworld.com/view.cfm?section=article&storyid=730

Now, the fuel cell vehicle is more efficient -- about 40% vs about 25% thermodynamic efficiency. So you don't need 545000 watt hrs in the tank, but about 60% of this or 327,000 watt hrs of hydrogen.

How long does a residential roof full of PV cells take to produce this much hydrogen in a form the car can use?

327,000 watt hrs needed / (49,950 watt hours per day * 70% electrolysis efficiency * 80% storage efficiency * 70% liquefaction efficiency)

= 16.7 days for useable energy equivalent to one 15 gallon tank of gasoline.

If you're satisfied with about 1/2 the range of your gasoline car, you could fill up your hydrogen car from your home's solar array in about 1 week, assuming it's not cloudy and you dedicate 100% of your solar array output for that task.

According the the Sci Am article "Questions about a Hydrogen Economy"from May 2004, for a grid electric hydrogen fuel cell powered auto, the fuel chain efficiency is about 22% [from your solar/hydrogen example we get 39%], the vehicle is about 38% efficient, and the total efficiency is about 8%.

Edit: The most efficient option of all is steam reforming - hydrogen from methane using steam - and a H2 fuel cell powered auto. This has a "well to wheels" total efficiency of about 22%.

 

[Ivan Seeking]

Not that this applies to the home brew solar hydrogen idea since you have included the fuel chain losses in considering the cycle times, but if looking at the big picture we need to include that the fuel chain efficiency for gasoline is about 81%. So the well-to-wheels efficiency of the gasoline internal combustion engine is about 13%-14%, on the average. Petro-Diesel does a little better at about 18%.

 

[civil_dude]

Here is a very interesting article about lunar helium 3 isotopes that one shuttle payload could fuel the U.S. for a year.

http://www.space.com/scienceastronomy/helium3_000630.html

 

[turbo]

Here is a very interesting article about lunar helium 3 isotopes that one shuttle payload could fuel the U.S. for a year.

http://www.space.com/scienceastronomy/helium3_000630.html

Lunar soil has been returned to Earth, and presumably, some of it has been hemetically sealed until it can be used to test some theories about the moon's composition. Where is the He³?

Edit: For instance, do we really know deep the He³ deposition layer is? What is the concentration for a given soil type and at what depths? I don't get the impression that we know that critical information yet, except from surface samples and shallow excavations. After all, you can't just start strip-mining any place on Earth and expect to find gold, uranium ore, or coal. And how are we going to get the equipment to the Moon to strip-mine it, process the He³, compress it, and return that shuttle-load of the gas to Earth? It's not like we can go shovel a shuttle-load of lunar soil and be done with it. All of the excavating equipment, the transporters, the furnaces, extraction, compression and storage facilities would have to be located on the Moon, with crews, living quarters, food, air water and other supplies for operators. Compare this to what we have managed to put in LEO over the past few decades. I think (hope, anyway!) that we will have viable, sustainable sources of energy right here on Earth long before we develop the capability of putting heavy industry on the Moon.

 

[Francis M]

However, there are additional losses through the drive train, but I was coming back to up that number a bit as the one that I used is an average, and a Honda Accord is obviously a more efficient choice. Also, I'm not sure how much drive train is avoided in a typical electric car today.


That's difficult to say becasue there aren't any "typical electric cars" that I've seen.
I looked on the web for research on electric cars because I was curious as to what was out there from car manufacturers, kits, conversions, etc...
From car manufacturers there's hybrids but you don't avoid the drive train at all.
Kits and conversions could go either way I suppose, but I haven't seen too many direct drive electrics out there. It's been done to save weight/space for more battery banks (increase range?)and reduce drive train maintenence/complexity.
AS hit upon in another thread though, most of the electric "car" kits I've seen don't fall under the definition of a passanger car a far as DOT and NTSB specs, they're more of an enclosed two passenger trike (and don't look as if they'd hold up well in an accident even at 30MPH on the back roads that they're primarily designed to travel).

 

[Ivan Seeking]

I have been investigating the options to produce biodiesel from algae. As I had suspected, the good information is all proprietary. This comes from one of the leaders in the field.

As we and others are still developing the technology, and having to do so under intellectual property protection (since we're relying on funding from private companies, as there's no government funding for this), we're having to keep everything confidential. So, for now, you likely won't be able to find much information on the technical side of doing this. We anticipate it will be perhaps another 2 years before we have our systems ready for commercialization.

 

[denni89627]

Interesting idea. How about this. Getting your generators in the air using dirigibles. You can anchor it to a ship directly below, lift any amount of weight you want to any altitude (within reason). Than imagine another tether forming a hypotenuse with the sea and vertical anchor tether which can help hold it in position and steer it into the wind.

 

[denni89627]

correction. you would have to be able to be able to rotate the inlet for the moving air on the balloon and maybe have 4 tethers forming a square in the ocean to hold it in place. With the collection facility directly below the balloon.

 

[Ivan Seeking]

...Biofuels, long a cornerstone of the quest for greener energy, may sometimes produce more harmful emissions than the fossil fuels they replace, scientific studies are finding.

As a result, politicians in many countries are rethinking the billions of dollars in subsidies that have indiscriminately supported the spread of all of these supposedly "eco-friendly" fuels, for use in power vehicles and factories. The 2003 European Union Biofuels Directive, which demands that all member states aim to have 5.75 percent of transportation fueled by biofuel in 2010, is now under review.

"If you make biofuels properly, you will reduce greenhouse emissions," said Peder Jensen, of the European Environment Agency in Copenhagen. "But that depends very much on the types of plants and how they're grown and processed. You can end up with a 90 percent reduction compared to fossil fuels — or a 20 percent increase." [continued]

http://www.iht.com/articles/2007/01/30/business/biofuel.php

 

[Ivan Seeking]

...The first rigorous, worldwide study of high-altitude wind power estimates that there is enough wind energy at altitudes of about 1,600 to 40,000 feet to meet global electricity demand a hundred times over.

The very best ground-based wind sites have a wind-power density of less than 1 kilowatt per square meter of area swept. Up near the jet stream above New York, the wind power density can reach 16 kilowatts per square meter. The air up there is a vast potential reservoir of energy, if its intermittency can be overcome.

Even better, the best high-altitude wind-power resources match up with highly populated areas including North America’s Eastern Seaboard and China’s coastline.

“The resource is really, really phenomenal,” said Cristina Archer of Cal State University-Chico, who co-authored a paper on the work published in the open-access journal Energies.”There is a lot of energy up there, but it’s not as steady as we thought. It’s not going to be the silver bullet that will solve all of our energy problems, but it will have a role...”

http://www.wired.com/wiredscience/2009/06/highaltitudewindpower/

 

[ray b]

what % loss does tesla air system suffer vs microwave vs powerlines for high volt ac

H or He balloon shaped wings?

balloons every 1000m to hold up the cables?

jet streams shift around
could a railroad based system follow the shifts

 

[Topher925]

How is it that I missed this thread? I used to work on the skywindpower project (now called Baseload Energy).

what % loss does tesla air system suffer vs microwave vs powerlines for high volt ac

Tesla and microwave power transmission techs both have ridiculously poor efficiencies. Also, all HAWG concepts require a tether to either hold the HAWG in place or have something to pull on to drive the winch.

The Magenn concept uses helium.

Jet streams do shift around but their capacity factor is still extremely high when compared to terrestrial based winds so extracting power from them still makes sense. Maybe not financial sense, but makes sense in some ways.

 

[Ivan Seeking]

Jet streams do shift around but their capacity factor is still extremely high when compared to terrestrial based winds so extracting power from them still makes sense. Maybe not financial sense, but makes sense in some ways.

What are the major problems? Do you mean that it becomes cost prohibitive because of the changing jet streams?

 

[Topher925]

What are the major problems? Do you mean that it becomes cost prohibitive because of the changing jet streams?

No, I mean that operating a wind turbine of any type at 15,000+ feet may not make financial sense when compared to other alternatives such as nuclear. The technology proposed by all of the HAWG companies is still in its very early stages of development so its difficult to gauge what kind of capital and maintenance costs high altitude wind generation would have. However, all of the designs require exotic components such as cables or tension members which will have extremely high costs and low MTBFs, which may make high altitude wind generation not financially competitive to other alternatives.

I have yet to see any in depth cost analysis in terms of $/kWh from any of these venture capital companies, only empty promises.

 

[Ivan Seeking]

No, I mean that operating a wind turbine of any type at 15,000+ feet may not make financial sense when compared to other alternatives such as nuclear. The technology proposed by all of the HAWG companies is still in its very early stages of development so its difficult to gauge what kind of capital and maintenance costs high altitude wind generation would have. However, all of the designs require exotic components such as cables or tension members which will have extremely high costs and low MTBFs, which may make high altitude wind generation not financially competitive to other alternatives.

I have yet to see any in depth cost analysis in terms of $/kWh from any of these venture capital companies, only empty promises.

Going way back to the beginning of the thread, even back-of-the-napkin calculations make it clear that the tether is a key challenge. But it did appear to be doable using commercial products. It was looking like the power transfer was an issue as well, but with off-the-shelf 500KV generators now available, the power wire could be relatively small and light.

It seems to be a bit like tidal power: It is fairly easy to do in principle but challenging from a practical point of view. However, the energy density is hard to ignore.