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

[joema]

Well, we can guess at numbers all day, but you are ignoring the factor of three for the increased wind velocity, for a given weight to power expectation at high atltudes..

I didn't totally ignore it -- I factored in a factor of two improvement.

I agree any reasonable alternative energy source should be closely examined. However unless the technology is economically scalable to a gigantic industrial level within a meaningful timeframe, it will make no real difference. E.g, does hydrogen via solar or wind work? yes. Can you scale it to provide a large % of transportation energy consumption within two decades. No -- totally impossible. If Ralph Nader was absolute dictator over the entire globe it wouldn't be possible.

There are two discrete energy problems:

(1) Transportation energy (primarily currently petroleum). This will be significantly exhausted within 20 yrs, and possibly peak oil will hit within 10 yrs, if not sooner. This is by far the most time critical need. Working on a utility energy solution won't address this more immediate problem.

(2) Utility/industrial/residential energy (power, heating, etc). This comprises about 75% of all energy consumption, but there's sufficient conventional sources for at least 100 years. It may not be clean or desirable, but at least the lights won't go out. Much sooner transportation could grind to a stop, or oil prices disrupt world economy beyond anything yet seen.

If FEGs can be made to work -- fine, use them. Unfortunately too little is known about the viability, especially if used on a huge scale.

I mentioned biodiesel from algae mainly because it's one of the few solutions that (1) uses the existing distribution infrastructure (2) uses existing vehicle/engine technology, (3) solves most of the emission problems, inc'l CO2, and (4) fits within available real estate. Yes there are still unknowns that could preclude its use, but those are UNKNOWNS. By contrast most other alternative technologies have KNOWN problems (even at this early stage) limiting their huge industrial deployment.

We often hear of promising new energy sources. However it's important to separate what's technically feasible on a small scale, vs what can be deployed on the required vast industrial scale. We can't say "somebody will figure that part out" -- that IS a limiting factor even more than the technology itself.

 

[Ivan Seeking]

Dunno if I missed some discussion on this, but...
Because of that, I don't see why you would want to have a wing at all. If you're flying it like a kite, part of the turbine's drag is the lift you need to keep it aloft.

Are you concerned about not having the turbine perpendicular to the wind? I wouldn't be, because as you said, a turbine and wing would steal from each other and the net effect would be the same as not having the wing (actually, probably a little worse with the wing) .

In principle it seems to make sense to avoid [design around] sacrificing power for lift.

 

[Ivan Seeking]

I didn't totally ignore it -- I factored in a factor of two improvement.

Well, it turns out that 120 tons plus the generator and wing is not a lot of weight on the scale that we are discussing, and we haven't even tried to reduce weight in a proper turbine or generator design made specifically for this application. So it seems that double that number is more likely where we start hitting limits. And we have only been talking about a tinker toy approach - a worst case - as a basis. It is hardly fair to compare this to something that has a few years of actual testing.

As for the rest, I am thinking beyond just the US transportation problem. There is a real movement towards nuclear power again, and this has nothing to do with transportation energy.

 

[Ivan Seeking]

Btw, we might also run bio-diesel in fuel cells. In fact Bush has already pushed for the idea of petroleum powered fuel cells.

So this could help to make the transition to electric cars while still solving the immediate need for oil.

Oh yes, traditionally, diesel cars really suck, which is why we drive gasoline powered cars.

 

[joema]

Btw, we might also run bio-diesel in fuel cells. In fact Bush has already pushed for the idea of petroleum powered fuel cells.

So this could help to make the transition to electric cars while still solving the immediate need for oil.

Oh yes, traditionally, diesel cars really suck, which is why we drive gasoline powered cars.

That may be true historically, but newer diesels (e.g. VW PDI) are almost like gasoline engines -- very little of the old characteristics.

Re "dirty", newer diesels burning low sulfur fuel can be very clean. Biodiesel largely solves the CO2 problem -- it mostly only emits what the plants absorbed during growth.

While current SULEV and PZEV gasoline engines have reduced traditional emissions (SOx, NOx, etc) to incredibly low levels, you can't greatly reduce CO2 emissions from those. CO2 is the natural by-product of perfect, clean hydrocarbon combustion. That's where biodiesel has a big advantage, plus it's manufactured vs draining a non-renewable resource.

If biodiesel can work in fuel cells that's great, but new technology diesels are already approaching current real world fuel cell overall efficiency, and they're here today and can be immediately manufactured in vast quantities.

 

[Ivan Seeking]

Well, I must admit that this all sounds very promising. Do you have any idea what the cost of these new engines will be as compared to traditional diesel engines? Also, HP to weight ratios, lifespan, maintenance, etc, do we know how they compare in these areas yet?

Would US cities smell like french fries? I know that the veggy oil crowd drive cars that smell like fries. Hydrogen would leave us with cities that smell like clean laundry. In fact it is officially dubbed as the "clean laundry smell".

There is another huge advantage to going diesel over gasoline, I think... IIRC, diesel is much less volatile than gasoline. I don't recall the numbers, but simply filling the tank is one of the larger sources of air pollution. Many states require the vapor return line on the dispensing nozzle, but I see people defeat these all the time.

 

[joema]

Well, I must admit that this all sounds very promising. Do you have any idea what the cost of these new engines will be as compared to traditional diesel engines? Also, HP to weight ratios, lifespan, maintenance, etc, do we know how they compare in these areas yet?

The new PD diesels are already in production starting with the 2004 model year for VW and Audi. HP, hp-to-weight, etc. are generally equal or better. Lifespan and maintenance are probably equal or better than older diesels, but time will tell.

http://www.canadiandriver.com/articles/rr/04jettatdi.htm

The VW PD diesel is just one example of new-tech refinements. Other manufacturers are working on similar technology. Even cleaner, more efficient diesels than these are readily attainable.

There's a tendency to discount existing engine technology in favor of new concepts -- a few decades ago piston engines were thought obsolete and soon to be replaced by Wankels, turbines, flywheels, etc. However continuing technical refinement has produced piston engines with very low emissions, and very good power, drivability and reliability.

Would US cities smell like french fries? I know that the veggy oil crowd drive cars that smell like fries.

I don't really know how it would smell. Although biodiesel from waste vegetable oil gets a lot of press, it can't have a major influence on the energy situation -- there's just not enough of it.

...I don't recall the numbers, but simply filling the tank is one of the larger sources of air pollution. Many states require the vapor return line on the dispensing nozzle, but I see people defeat these all the time.

Yes, in fact a key difference between SULEV (Super Ultra Low Emissions Vehicles) and PZEV (Partial Zero Emissions Vehicles) is the PZEVs have lower evaporative emissions. When tailpipe emissions get this clean, the evaporative emission component becomes a greater factor.

 

[Ivan Seeking]

Now are you going to tell me that we have diesel lawn mowers coming?

Turns out that lawn mowers and weed eaters are huge offenders in the cities; so much so that some cities have begun to ban gasoline powered yard equipment.

 

[Cliff_J]

Until the US finishes its switch from diesel with the highest sulfur content to the lowest, a clean diesel is going to have the extra premium added to it. And the price has yet to really stabilize on regular diesel fuel post-katrina, so the oil companies may even step this up higher if the refining costs are higher to remove the sulfur.

The veggie oil crowd fail to mention that the unprocessed oil has a lot of containiments in it that are harmful for the components needed to make the injection system in a diesel engine work. That's one of the big reasons to run it through the transestification process into biodiesel, is to remove the glycerine that would leave behind deposits in the engine and add particulate matter in the exhaust.

In the 80s GM took their 5.7L gas engine and converted it to run on diesel. It was a pretty good seller in the heartland because farmers could purchase diesel fuel without paying road tax (for farm use and as a business expense) and drive their vehicles with it (practice has since been regulated). Here was an educated customer base, they use diesel in their tractors, yet GM ended up with a bad reputation for the motor as it aged. It would commonly break a head bolt or two and the cause was excess moisture in the fuel system that would cause an injection timing issue. Similar problems exist with biodiesel since its more prone to moisture.

To add insult to injury, the diesel fuel stations, used to only filling up trucks that have oversized fuel filtration systems, vary in quality. I've read some anecdotes of VW drivers who complain about the lack of refueling stations and having to pull their little car in next to giant trucks, and then also having to take them in for filter changes after a bad fill-up on a trip.

Even the new pickup truck diesels from GM/Ford have stepped up in usability, they are very quiet and aside from the RPM range drive similar to a gasoline engine. However, they are a $5000 premium over the gasoline engine, and how much of that is profit or additional cost is a big question. It seems in Europe the small 4cyl fuel-miser diesel is produced in large enough quantities that its price is comparable to the larger gas engine with performance of the smaller gas engine. It could happen stateside, but as joema pointed out the distribution infrastructure is going to be a problem.

And repeating my second point in this post, diesel's premium price would require a large shift in mileage to offset its higher cost for the economic viability to work out. Otherwise the US is stuck in a chicken-egg problem and political whims aren't going to change that.

 

[Ivan Seeking]

Regarding the solar farm linked earlier, I come up with an average peak output of just less than 20 watts per sq meter.

This off-the-shelf panel
http://www.kyocerasolar.com/pdf/specsheets/kc125g.pdf
is 0.9 sq meters and is rated as having a 125 watt peak output.

 

[joema]

Regarding the solar farm linked earlier, I come up with an average peak output of just less than 20 watts per sq meter.

This off-the-shelf panel
http://www.kyocerasolar.com/pdf/specsheets/kc125g.pdf
is 0.9 sq meters and is rated as having a 125 watt peak output.

That panel is crystaline, which works for small applications but can't be scaled to thousands of square miles -- the manufacturing process is similar to a semiconductor wafer. You'd need to use amorphous or some totally new technology capable of industrial scale production, which are typically much less efficient. Amorphous cells are about 6% efficient.

You also can't count peak power, but only average power (solar insolation) based on the climate. In southern Arizona, you have about 6000 watt hrs per square meter per day: http://www.windsun.com/Solar_Basics/Solar_maps.htm#Map1

Even your above crystaline solar panel won't produce 15% efficiency unless it's brand new and the sun is straight overhead. Unlike the AC output of a conventional power plant, solar cell output must be buffered or converted to AC, which costs more efficiency.

All things considered, you're lucky to get over 10% efficiency using crystaline cells, and probably 4% efficiency from amorphous cells.

10% efficiency is about 600 watt hrs per square meter per day in southern Arizona, and 4% is is about 240 watt hrs per square meter per day. In any other climate output will be much lower.

On top of the above losses, if you convert it to hydrogen via water electrolysis, you take another 50% hit (at least) in conversion and transport losses.

 

[Ivan Seeking]

You also can't count peak power, but only average power (solar insolation) based on the climate. In southern Arizona, you have about 6000 watt hrs per square meter per day: http://www.windsun.com/Solar_Basics/Solar_maps.htm#Map1

Not true. If I can show a panel with six times the peak power as compared to the peak power for the panels used, then we would expect a much higher average total power value accordingly. I was comparing peak power to peak power.

Even your above crystaline solar panel won't produce 15% efficiency unless it's brand new and the sun is straight overhead. Unlike the AC output of a conventional power plant, solar cell output must be buffered or converted to AC, which costs more efficiency.

Obviously. You seem to be going out of your way to shoot down a perfectly fair comparison. This was just one example of the improvements made in solar technology. And we haven't even looked at the truly new technology coming such as paint-on solar panels.

 

[Ivan Seeking]

Modern switching technology [power transformation] runs as high as ninety-five percent efficient.

 

[turbo]

Here's a page of links that might keep you busy for a while.

http://peswiki.com/index.php/Directory:Solar_Hydrogen

 

[joema]

Regarding the solar farm linked earlier, I come up with an average peak output of just less than 20 watts per sq meter.

This off-the-shelf panel
http://www.kyocerasolar.com/pdf/specsheets/kc125g.pdf
is 0.9 sq meters and is rated as having a 125 watt peak output.

...If I can show a panel with six times the peak power as compared to the peak power for the panels used, then we would expect a much higher average total power value accordingly. I was comparing peak power to peak power.

Your above two statements illustrate the difference between a real world output figure and a laboratory figure. A small crystalline solar array can be 15% efficient (if new). However that's meaningless since you CANNOT manufacture hundreds of square miles of crystalline semiconductors. It's physically impossible, and will always remain so because of how they're made.

To cover hundreds of square miles you must use much lower efficiency technology such as amorphous cells, or even lower efficiency paint-on cells (assuming it's ever debugged sufficiently for mass deployment).

Re peak power, what counts is the actual delivered power over a period of time. That in turn depends on climate, location, cell technology, cell aging characteristics, etc.

You seem to be going out of your way to shoot down a perfectly fair comparison. This was just one example of the improvements made in solar technology...

As stated above, it's not an illustration of solar technology improvement. The large solar farm has lower areal efficiency NOT because the technology was less advanced -- it's because you MUST use lower efficiency technology to cover large areas. You cannot cover a large area with high efficiency crystalline cells -- they are manufactured in semiconductor plants like integrated circuits are.

 

[Ivan Seeking]

I had a talk with a thirty year or so commercial aviation insider - with a world class company - and the idea of a flying wing was well received.

Hey buddy, that's a lot of wings!

 

[Ivan Seeking]

joema, if you're still around, I'm convinced.

Biodiesel, and bio from algae seem to offer a practical solutions to our energy demand today. Current petro prices makes it price competitive, which seems to have been the biggest issue. When it costs a buck or two more per gallon than regular diesel, forget it. But now I have seen it selling cheaper than regular diesel; at the pump, and right around here. Also, it looks like diesel hybrids are ready to market in the US. This is exciting stuff!

Prices for crude may drop for a time, but the demand from India and China for oil can only mean one thing.

 

[Ivan Seeking]

One thing that I don't like [in the long run anyway] is the application of photobioreactors for biodiesel production to industry, to reduce CO2 emissions. This only delays the emissions. It does reduce CO2 emission to the extent that it replaces fossil fuel usage in autos, but if autos are already using alternative fuels, it gets industry off the hook while still allowing the emissions though through a more convoluted path. Instead, ideally, carbon from industry [not produced by biofuel usage] should be trapped for long term storage. Maybe algae bioreactors can be used to mediate this process?

For example, does anyone know if plant oils can be used to make plastics?

edit: photobioreactor appears to be the proper name

 

[Ivan Seeking]

By chance, in the news...

AUDI MAKES HISTORY AS DIESEL-POWERED R10 TDI WINS MOBIL 1 TWELVE HOURS OF SEBRING

Audi is the first diesel-powered car to win a race in the American Le Mans Series.

Sebring, Fla. - Audi Sport North America made history Saturday as the diesel-powered Audi R10 TDI of Tom Kristensen, Allan McNish and Rinaldo Capello won the Mobil 1 Twelve Hours of Sebring. The new prototype is the first diesel car in the world to win a major sports car race. [continued]

http://www.americanlemans.com/News/Article.aspx?ID=1872

The guy who told me about it still hadn't stopped laughing in disbelief.

 

[Astronuc]

Solar power energizing rural China
http://marketplace.publicradio.org/shows/2006/06/19/PM200606195.html

With 20 million people waiting to get on the electrical grid in China, officials in Beijing have launched a campaign to make sure the newest energy consumers will use renewable sources instead. Rob Schmitz reports.

KAI RYSSDAL: Coal is the energy source of choice in China. A billion and a half tons of it were burned there last year to generate electricity. That's three times more than in the U.S., India, and Russia combined. There are about 120 million people in China living off the power grid. So Beijing is trying to get new electricity consumers to use renewable sources. From the Marketplace Sustainability Desk, Rob Schmitz reports.

-----------------------------------------------------------------------
ROB SCHMITZ: A sheep, a yurt, a pasture, and a forest. That once summed up Gulinar Sitkan's world here in Sorbastow, a tiny village in the remote mountains of northwestern China, near the border with Kazakhstan. Last year, her world suddenly expanded.

Through a gauze of static interference, Sitkan now sees important-looking officials shaking hands. Soldiers in a foreign war. A beautiful woman holding a soft drink can to her face. The images on her new television change almost too quickly to take it all in, and they're much more stimulating than watching her sheep.

GULINAR SITKAN [voice of interpreter]: My favorite program is the international news, because I can find out what's happening now. Before, it would take months for us to find out about news.​

Sitkan is one of the many Ethnic Kazakhs in this area who, up to a year ago, didn't have electricity. The Chinese government has provided her and hundreds of thousands of others with solar panels.

This is part of China's plan to use more renewable energy. By 2020, China plans to get 15 percent of its electricity from renewable sources. That'll add up to 120,000 megawatts, more than two times the amount of energy the state of California generates.

Douglas Ogden is vice president of the San Francisco-based Energy Foundation. He's working with Chinese officials to help them fulfill that promise.

DOUGLAS OGDEN: You know, you look around globally, there isn't another country that has set that degree of ambitious renewable energy target.​

Gulinar Sitkan adds wood to her potbelly stove. The pink scarf she wears around her head blends in with the bright red carpets that line the walls of this tiny log cabin. A rooftop solar panel provides enough power for her small television and a couple of light bulbs.

The panel was designed and supplied by one of the world's giant oil companies. You heard right. An oil company. Specifically, Shell Oil's subsidiary, Shell Solar, has supplied 40,000 of these panels to ethnic minorities throughout China's Xinjiang province as part of a project that's funded by the Dutch and Chinese governments. Shell Solar's Bo Xiao Yuan says the portability of the panels is ideal for the ethnic minorities who live in China's most remote regions.

BO XIAO YUAN: In these areas, for nomad, they keep moving all year round, so the grid power cannot be available everywhere. It's too expensive.​

After government subsidies, nomads in this area can buy a portable solar panel for around 60 US dollars. That's equal to about a tenth of what a typical nomad here makes from selling sheep's wool and meat in a year.

In a cabin in the next valley over, newlyweds Kowante and Sandokash Rahmat have finished up a day of shearing sheep. Kowante takes his dombra, a Kazakh guitar, from where it hangs on the wall, and unwinds with a song.

It's a traditional Kazakh song about two lovers who meet near an alpine lake. Kowante and Sandokash have a solar panel, too. It was a wedding present from their parents. The first appliance they bought was a tape player, which is loaded with the newest Kazakh pop songs.

They're expecting their first child this summer. Not only will this child know the latest Kazakh hits, but he or she might have a television, and, says Kowante, a computer, too. And with all of this, access to a world they could have only imagined a year ago.

In Sarbastow, northwestern China, I'm Rob Schmitz for Marketplace.

http://www.efchina.org/home.cfm

In March 1999, after a series of meetings and consultations with scientists, policy-makers, business leaders, and analysts in China and the United States, the staff and boards of The David and Lucile Packard Foundation and The Energy Foundation launched the China Sustainable Energy Program. The William and Flora Hewlett Foundation joined as a funding partner in 2002.

The China Sustainable Energy Program (CSEP) supports China's policy efforts to increase energy efficiency and renewable energy. The program emphasizes both national policy and regional implementation. The program strives to build capacity in China to analyze energy savings and renewable energy opportunities, and to develop policies to capture those opportunities. The program helps Chinese agencies, experts, and entrepreneurs solve energy challenges for themselves. At the request of Chinese non-governmental organizations (NGOs), the program supports capacity building and technology policy transfer through linking Chinese experts with "best practices" expertise from around the world. When it determines there is an unmet need in the field, the program may convene workshops, commission papers, or take other direct initiatives, in addition to its primary role as a grant-maker.

 

[Astronuc]

Interesting article from Purdue Engineering -

The Energy Challenge for Our Generation’s Engineers
https://engineering.purdue.edu/Impact/Energy/

Modern civilization has coasted on fossil fuels, but Earth's supply will peak—then decline. We need a sustainable energy future. Purdue Engineering with support from its partners is taking solving this predicament to heart.

-----------------------------------------------------------------
Somewhat related:

Purdue part of new $21 million fluid power energy research center
http://news.uns.purdue.edu/html3month/2006/060519.Ivantys.ERC.html

WEST LAFAYETTE, Ind. — Discovering ways to reduce fuel consumption, developing devices for people with mobility impairments and designing state-of-the-art rescue robots are just three of the goals of a new multimillion-dollar research center involving the Discovery Park Energy Center, Department of Agricultural and Biological Engineering and School of Mechanical Engineering at Purdue University.

The National Science Foundation announced a $15 million, five-year grant to support the new Engineering Research Center for Compact and Efficient Fluid Power. Industry partners will augment the funding with $3 million, and seven universities involved in the center will contribute an additional $3 million. The center will be based at the University of Minnesota Twin Cities campus, and Purdue will house one of the center's research labs in its MAHA Fluid Power Laboratory.

"This center will advance fundamental knowledge, providing a platform for technology that will spawn new industries," said Lynn Preston, leader of the Engineering Research Centers Program at NSF. "We are impressed with the ambitious goals of the center for research and education and the strong partnership with industry."

Fluid power is a $33 billion industry worldwide. Industry areas include aerospace, agriculture, construction, health care, manufacturing, mining and transportation. Fluid-power technology encompasses most applications that use liquids or gases to transmit power in the form of pressurized fluid. The complexity of these systems ranges from a simple hydraulic jack used to lift a car when replacing a tire to sophisticated airplane flight control actuators that rely on high-pressure hydraulic systems.

 

[Astronuc]

Let's not forget Russ's thread - YOU!: Fix the US Energy Crisis

https://www.physicsforums.com/showthread.php?t=42564

It probably should be stickied as should this thread.

 

[Ivan Seeking]

New Zealand Company Produces World’s First Sample Of Bio-Diesel From Algae

New Zealand-based Aquaflow Bionomic Corporation announced today that it had produced its first sample of home-grown bio-diesel fuel with algae sourced from local sewerage ponds.

“We believe this is the world’s first commercial production of bio-diesel from algae outside the laboratory, in ‘wild’ conditions. To date, bio-diesel from algae has only been tested under controlled laboratory conditions with specially selected and grown algae crops,” explains Aquaflow spokesperson Barrie Leay. [continued]

http://www.dieselforecast.com/WireReportDetails.php?wireID=142

 

[Ivan Seeking]

And, a story indirectly related to the FEGs concept:

... Multimax is one of several defense companies pouncing on the military's renewed interest in using high-flying, unmanned, helium-filled balloons -- sometimes tied to the ground with a long rope -- as possible weapons. Lockheed Martin Corp. is developing a blimp that it says will reach an altitude of 65,000 feet, while Raytheon Co. is developing one designed to reach 10,000 feet and be tethered to the ground. Blackwater USA, better known as one of the largest security contractors in Iraq, expects to finish its prototype, which aims to reach an altitude of 5,000 feet to 15,000 feet, in December.[continued]

http://www.washingtonpost.com/wp-dyn/content/article/2006/08/06/AR2006080600499.html

 

[dansydney]

I think there are many viable clean power solutions out there its just a matter of people willing to build and fund the required plants, machines etc. I think its much harder fighting the greed and politics associated with world energy usage than the actual making/finding etc of a clean energy source.

 

[Ivan Seeking]

Last night on a re-broadcast of Scientific American Frontiers, they did a spot on the Algae project at MIT.
http://www.pbs.org/saf/1506/segments/1506-3.htm
http://www.pbs.org/saf/1506/

Note that at the top of the page [under "Hydrogen Hopes"] is the option to watch online.

 

[turbo]

Great link, Ivan! I love it. I have wondered for the past few years if photovoltaic technology would ever allow the production of hydrogen on small (my house and personal vehicles) scales so that we could free ourselves from the petro industry. This gives me some hope. Sure, people in apartments and in the city might have to use commercial retail sources, but what if I could buy or build my own hydrogen generator and supply my own enegy. Right now the only thing that the south-facing side of my roof does is keep out the rain and reflect the Sun's energy. What if it could provide enough energy to keep the house cool in the summer and supplement the heating requirements in the winter?

 

[joema]

...I have wondered for the past few years if photovoltaic technology would ever allow the production of hydrogen on small (my house and personal vehicles) scales so that we could free ourselves from the petro industry...the only thing that the south-facing side of my roof does is keep out the rain and reflect the Sun's energy...

Average solar insolation for much of the US population area is 4-5 kilowatt hrs per square meter per day: http://www.windsun.com/Solar_Basics/Solar_maps.htm

Normally you wouldn't convert to hydrogen for local household use -- that would add considerable conversion loss. You'd just use the electricity directly.

How much solar cell roof area and how many hours would it take to produce enough hydrogen to refuel a fuel cell vehicle with comparable performance to a Honda Accord?

Hydrogen electrolysis is about 70% efficient, vehicle/depot storage about 80% efficient, fuel cells about 70% efficient, electric motors about 92% efficient, for total end-to-end efficiency of about 42%.

A 15-gal tank of gasoline holds 1.86E6 BTUs or 545000 watt hours of energy.

Assume your solar-useful roof collecting area is 20 by 40 feet (74 square meters). Note you can't count the whole roof area, just that portion that receives direct sun.

Your roof receives (74 m^2 * 4500 watt hr / m^2 / day) or 333,000 watt hours per day, on average. At 15% solar cell efficiency, it produces 49,950 watt hours per day. Running it through the hydrogen/fuel cell cycle, the delivered hydrogen energy is 42% of this, or about 21,000 watt hrs per day. So it would take 545000 watt hrs per tank /21000 watt hrs per day or 25 days to fill up your hydrogen car with equivalent energy to a tank of gasoline.

If you live in Yuma, Arizona, you have about a 2x advantage in solar insolation, which lowers the time required to about 12 days.

It appears the solar/hydrogen/fuel cell vehicle refueled by your solar roof panels isn't practical.

I enjoyed the Scientific American Frontiers videos, but such programs never do the above pragmatic math, so constantly leave viewers with unrealistic impressions. Then years go by and people wonder why hydrogen cars aren't here yet. The reason isn't a conspiracy, but the physics work against you, and these items are rarely adequately explained by programs like this.

 

[turbo]

Thank you very much joema for keeping practicality at the forefront.

 

[Ivan Seeking]

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.

 

[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.