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Here is the most interesting thing I have seen in the area of biodiesel: algae that is about 50% oil by weight, can grow in brackish water and eats human and industrial waste...

Well, algae ponds should be pretty good for that. Some folks from UNH are saying that you can yield biodiesel from algae at a rate that would imply, by my math, efficiencies of 13 to 26 percent.

And while it's plausible to grow algae ponds over thousands of square miles, it's less plausible to stick chips of difficult to manufacture, energy-intensive silicon over that same area. Not to mention that the energy comes out in an easy-to-use form that our current transportation infrastructure can make use of.

Although the Stirling solar looks quite promising. We'll see how the installation in California comes out.

Particulate emissions is a big problem with diesel, but not nessessarily biodiesel. The Diesel that we run on in our country has sulfur added to it as a lubricant, and sooty sulfur compounds are a result. Biodiesel doesn't need to have sulfur added as it is naturally lubricating. Most pollutants that are high in diesel is significantly reduced as a result of running straight biodiesel as compared to diesel, with the exception of NOx (which is slightly increased but can be compensated for by advancing the timing on the engine). But to get this reduction you would need to not run a blend with diesel. My old DOT bookmark is broken, but this site has numbers that were similar. Please take with grain of salt: http://www.geocities.com/medicalmarijuana2003/fact 29.htm

As far as the other folks' concerns on having enough crop space. Try checking out this Government funded study which concludes that much of the needed biodiesel can be harvested from algae (which can be up to 50% oil) that is grown in places like the Sonoran desert. We can also use municipal waste runoff to fertilize it. http://www.unh.edu/p2/biodiesel/article_alge.html

Not a problem if we use algae as the feedstock. We can use non-arable land, salt water, and sewage to grow the algae. And since it has a conversion efficiency several times higher than soybeans, it becomes feasible to supply *ALL* of the vehicular energy needs of the US using biodiesel.

http://www.unh.edu/p2/biodiesel/article_alge.html

Making soybean biodiesel cheaper won't solve the problem because the limited supply will only meet so much of the required energy needs. It might even cause more problems by creating economic pressure to convert food oils into fuels.

However, it's not as simple as that; the technology hasn't been developed to actually farm the stuff on a commercial scale, but there are people working on that. The first test deployments are by these guys, who are using the exhaust systems from conventionally-fired power to provide nutrients for the algae and prevent the release of CO2 and NOx into the atmosphere.

But yes, in the future you might well be able to grow all the fuel for your car in your backyard.

large amounts of concrete also recycle well into the sand and gravel used to make new concrete. Concrete recycling is generally only done on the scale of contruction/demolitions. How can you tell that recycling these materials saves energy? Recycling centers will PAY to take them.

Uhm, I haven't heard about this. Years ago for a few years I worked for a concrete/masonery contractor and what was said then was that using recycled concrete could be hazardous. Things may of changed since though.

I think it's generally just the sand and gravel that's reused, and new cement has to be added. And it may be limited in its uses. Hmm... come to think of it contractors usually have to pay to drop off their old concrete. Just that the fence company I worked for had a deal with the local company cause we put up their fence for a good deal. But it's probably cheaper than having the large bulk taken to a landfill.

After a little research it appears that the aggregate is mainly used for lining roads and the like before the final surface (concrete or asphalt) is poured. There is apparantly research that is making recycled aggregate useful in making up some of the bulk in general concrete usage, but a good portion of virgin material must be used as well. Materials testing prior to construction is strongly recommended before actual application as there are some changes in characteristics. Some pretty good information here and a thorough writeup can be found here. It also appears that one of the greatest benefits is in reconstruction, where old concrete can be processed on site for new uses eliminating the need to truck the debris out and then ship new materials in, leading to significant cost savings and greatly reduced effects on traffic patterns.

Even so, in terms of energy density, it is hard to beat hydrocarbons, and the distribution system is already in place. Since the algae consume as much CO2 as is produced by the combustion of the diesel, there is no net increase in greenhouse gasses. It is effectively solar power, with an efficient energy carrier. In addition, the OPOC diesel engine, allows for very small size and high efficiency. (it is ~1lb/HP, or ~0.6g/W ;) More details are available here.

Also, when flywheel energy storage matures a bit more, it should allow for some great improvements in electric and hybrid cars. Flywheels have extraordinary power density, and can be charged and dischared in seconds, which allows them to recapture ~80% of the energy during braking, and provide for decent acceleration. There is some information at AFS Trinity, though the site could be a bit better. The basic ideas behind this flywheel tech are fascinating in themselves, but I've already wandered far enough off topic...

I vote biodiesel from algae.

By the way, I'm in complete agreement. Nuclear fission for the backbone with solar and wind as decentralized supplements.

So how many million barrels a day can we make if we try really really hard with really really expensive oil in short supply?

Depends. How much cooking oil do McDonald's, Burger King, Wendy's, Arby's, Dairy Queen Brazier, and other major fast food chains go through? And it appears that only about ten million acres of algae ponds on desert land would be needed to replace all the diesel and petrol that motor vehicles in the United States use.

Furthermore, the electricity may not come from coal necessarily but instead can come from wind, solar, etc, or many other forms as it does in many states, not just California. The addition of even a small gasoline engine adds greatly to the total range of an electric-only vehicle. Combined with roof-top solar all across the southwest means that this is a very viable option and no one is "inflating numbers", so to speak.

Imagine if we start to use bio-diesel turbo-injected hybrid engines for our needs -- possibly hundreds and hundreds of miles per gallon. yes, the algae economic feasability tests are underway but I think at this point in our planet's history it is our money or our lives and not a great deal of money at that, either. I'm willing to pay a premium now rather than get a wrecked environment in the future (in our lifetimes!)

biofuel is great AND sustainable, and we actually don't need
to have that much more farmland to produce enough
to meet the countries energy needs!
http://www.unh.edu/p2/biodiesel/article_alge.html

hydrogen right now is just terribly inefficient. now if you new a way to separate hydrogen from water easily... I think the storage problems are less difficult to overcome. Of course the vendors of this fireplace have solved the `storage' problem provided and made an extrememly inefficient electric heater.

Personally if I have to use electric heat I just leave all my computers on. They generate enough heat to keep my basement warm :)

This fellow claims that bio-diesel made from soy or rape seed produce more energy than the amount required to produce the fuel.

"Overall Energy Balance (each unit of energy put in yields....)
3.2 units (soy)
4.3 units (rapeseed)"

This makes sense to me, as both crops are much less resource intensive than maize (corn for you americans, which requires nitrogenous fertilizers while soy fixes nitrogen), can be grown in skankier climates (rapeseed is grown in places like North Dakota and Manitoba) and require much less processing to produce fuel.

They are also working on algae based bio diesel.

Check out this article on the subject:

http://www.unh.edu/p2/biodiesel/article_alge.html

This stuff has the potential to produce 20,000 gallons of biodiesel per acre per year. And you an grow it in saltwater, or the effluent streams of wastewater treatment plants.

Micro algaes present the best option for producing biodiesel in quantities sufficient to completely replace petroleum. While traditional crops have yields of around 50-150 gallons of biodiesel per acre per year, algaes can yield 5,000-20,000 gallons per acre per year. Algaes grow best off of waste streams: agricultural, animal, or human. Some other studies have looked into designing raceway algae ponds to be fed by agricultural or animal waste. We are now pursuing funding to investigate redesigning wastewater treatment plants to use raceway algae ponds as the primary treatment phase with the dual goal of treating the waste and growing algae for biodiesel extraction. We also plan to investigate the possibility of using the algae mush (what is left after extracting the oil) as a fertilizer."

Micro algaes present the best option for producing biodiesel in quantities sufficient to completely replace petroleum. While traditional crops have yields of around 50-150 gallons of biodiesel per acre per year, algaes can yield 5,000-20,000 gallons per acre per year. Algaes grow best off of waste streams: agricultural, animal, or human. Some other studies have looked into designing raceway algae ponds to be fed by agricultural or animal waste. We are now pursuing funding to investigate redesigning wastewater treatment plants to use raceway algae ponds as the primary treatment phase with the dual goal of treating the waste and growing algae for biodiesel extraction. We also plan to investigate the possibility of using the algae mush (what is left after extracting the oil) as a fertilizer."

I'm a big supporter of Biodiesel myself. Especially the idea put forth in that link with using high-oil algae which can be grown in the ocean, eliminating land restrictions and irrigation problems.

For things you need real petrolatum oils for, you can use Thermal Depolymerization to create a light crude oil product from nearly any biological waste (offal, manure, other agricultural wastes) and scrap plastics. We already have the means to convert the resulting produce to whatever we need to manufacture lubricants, plastics etc.

Both are 100% renewable and carbon-neutral. AND it would require virtually no change in domestic energy infrastructure except getting people to buy diesel instead of gasoline engine vehicles.
=Smidge=

but if we bio-engineer algae or bacteria to produce biomatter for fuels, you might be wrong.

http://www.unh.edu/p2/biodiesel/article_alge.html

See, that's where the heart of the problem is-- specifically, transportation, especially of food.

Fuel cells developements currently come in two flavors: hydrocarbon and hydrogen. Hydrogen is an energy storage mechanism (with non-trivial engineering transport and storage problems), not an energy source. Since it's a gas at STP, hydrogen is more easily explosive than gasoline, and in liquid form has less than 1/3 the energy density per unit volume (although 3 times as much per unit weight). Economical methods for making it now are electrolysis (which wastes approximately 60-80% of the source energy), and synthesis from hydrocarbons... the depletion of which is the original problem

Most solar cells today, even Qdots, require nearly as much energy to manufacture as they generate over their useful lifetime. Ocean-wave generators have some of the NIMBY problems of nuclear, not to mention the difficulties of deploying in a corrosive environment, and working with fun things like Zebra Mussels gumming up operations. Wind power has promise (despite some avian environmental impacts), although the intermittency of load capacity makes it more suitable to generating energy for storage (EG: water storage or electrolysis of hydrogen). The losses inherent in such will increase the end price of such energy, but it may fill some premium nitches.

The best hope would be for the development of a effective crop (possibly a genetically modified algae) growable with "organic" methods (EG: no fertilizer-- those are petroproducts these days) that could serve as a biodiesel stock. An efficient solar to petroproduct energy storage method might allow a transition from current petroleum sources, both for fuel and plastics use. Redevelopment of rail cargo transport might help the energy economy as well. But I'm not convinced any of it is going to happen in a timely manner.

http://www.unh.edu/p2/biodiesel/article_alge.html

yep..
hmm.. wonder why this isn't more prevelant.

http://www.unh.edu/p2/biodiesel/article_alge.html

"Enough biodiesel to replace all petroleum transportation fuels could be grown in 15,000 square miles, or roughly 12.5 percent of the area of the Sonora desert."

Sounds promising to me. Even if biodiesel meets half the demand, at least we'll be extending the impending doom of "peak oil".

http://www.unh.edu/p2/biodiesel/article_alge.html

They're probably using the high-oil algaes investigated by the University of New Hampshire here. UNH says some algae are made of over 50% oil. algae are some of the most efficient photosynthesis machines around. once you've got the oil, it's just a matter of standard transesterification, a normal part of biodiesel production (and really, the only step necessary when you have clean oil).

Yes, but how much do you use in your lab? Most biochemistry protocols I know of use amounts measured in microcuries or even less. The University of New Hampshire requires routine urinalysis for tritium exposure for workers who handle more than 100 microcuries.

An emergency exit sign with six-inch lettering contains about 10 curies. In order to handle those quantities (or the substantially greater amount required to make a bright light saber) I wouldn't be at all surprised if there were fairly strict licensing and medical monitoring requirements.

Jesus Fucking Christ, doesn't ANYONE research details being disputed before spewing them further?

A simple search on google for 'KFC' led mainly to regional KFC corporate websites, and to a few other notable sites about this subject:

Snopes,UNH story

replacing petroleum with renewable energy sources is a pipe dream.

See above. Unless you're figuring on our running out of sewage any time in the foreseeable future.

Its particularly sad turn-off the magnetospheric spacecraft, since the magnetospheric is such a complex system and being able to collect data from mulitple spacraft is so vital to understanding the system. Though the instruments on spacecraft do degrade over time, I know that the Polar spacraft, for exaple, is still collecting useful data. it is still being used in multi-spacecraft studies, along with newer spacecraft like Cluster, to better understand the magnetosphere.

The big advantage of biofuels is that while they are growing, they absorb all the CO2 that they will emit when burned some months later. The more biofuel feedstock we grow, the more CO2 it will absorb while growing. We pay our CO2 debts in advance, and there's no net addition to atmospheric CO2. Here's a link to a paper that suggests the cultivation of agae in salt pools to make biodiesel which can be burned in unmodified diesel-from-oil engines.

with respect to waste streams... what about sewage?

With respect to arable land, who says it has to be arable? The following quote discusses the sewage into algae biomass oil research Mike Briggs is doing:

You can look at them for yourself at the University of New Hampshire site here [unh.edu] This is largely based on research successfully completed at DOE in 1998 and shelved because cheap oil looked like forever back then. You can find the DOE reports from the UNH link. Biomass algae is a more efficient biodiesel source than food grains, etc. because a single-cell organism doesn't require wasting energy and nutrients on making the rest of the plant (stalks, roots, etc.) and grows in hours, not months. The difference between food grain biomass and algae biomass is the difference between 1-3 barrel / acre / year and 91-360 barrels / acre / year. (see the UNH site for detail) Biodiesel you can burn in a car / truck / plane.

Using algae biomass as a practical energy solution requires removing a couple of process bottlenecks, one being growing the algae while capturing methane generated in its growth cheaply (the DOE solusion used open raceway ponds), and getting the oil out of the algae cheaply. You won't see much about possible solutions for a while because in order to get research funding, anybody with what he thinks are the right answers is discussing them on an NDA basis with potential investors or team members. (based on comments I've seen from researchers... and because I'm looking for money myself in this area)

With respect to solar, neither of you brought up an obvious point. What happens when the sun goes down? ,p.A homeowner on the grid can choose either battery backup (since you've priced this, you know this means REAL BIG batteries) or grid backup, buy power when the rates are low.

The choices are more limited with respect to supplying utility grade power:

• very large-scale storage
• a worldwide electrical grid
• a solar power satellite network

I favor the solar power satellite solution, since JP Aerospace appears to be on the edge of success with their blimp-to-orbit space transportation solution, which promises orders-of-magnitude reductions in the price-per-kilogram for boosting payloads into orbit to less than what NASA says on their solar power satellite project site is required to make a SPS project feasible.

With respect to solar cells themselves, I am not at all certain about whether or not the real problem in getting the cost down in this application is best done through new types of solar cells or through more economical packaging of existing devices. Wafer-scale cells with arrays of cells photolithographed onto them, automated laser testing to mask out defective cells just might reduce costs quite a bit. Or not, this is not my field and I'm not really equipped to run the numbers. But I suspect an effective 100% yield on very high production volumes certainly wouldn't hurt.

The other possibility that occurs to me for reducing the cost of a solar power satellite array is to replace NASA's rigid structure setup with solar cell array modules strung on cables combined with microwave transmitters to make very large phased-array antenna systems to ship the power back without having to carry it back to a central power nexus and separate antenna system. The central control nexus would gather the physical location of the cell arrays and instruct the array transmitters as phase-control information. Not saying this is THE answer, just suggesting that thinking outside NASA's box might be in order here.

The URLs for the NASA project, etc. are on the page in my sig.

Algae based biodiesel may have a lot more promise. I've seen it claimed that a small part of the Mojave desert could supply the US with all necessary vehicle fuel.

i think you have it almost exactly backwards!

http://www.biodiesel.org/resources/faqs/

- biodiesel reduces particulate exhaust relative to petrodiesel.
- biodiesel reduces global warming emissions (CO2, not particulate which you claim) by 78% relative to petrodiesel.
- biodiesel *is* a green solution
- someone has done the math for biodiesel using an algae feedstok: http://www.unh.edu/p2/biodiesel/article_alge.html

regarding this comment about biodiesel: ...
"I don't see how it could ever approach being even 1% of the fuel we use nationwide." ...

don't forget the algae potential. per this UNH study http://www.unh.edu/p2/biodiesel/article_alge.html about10 million acres would be required for our usage, which is ~1/40th of our current crop farming space.

Hydrogen is a Boondoggle. The energy density is so low, that we might as well use batteries if we're going to power vehicles with it. (It may be good for stationary purposes.) If we really wanted to, we could convert all US vehicles to diesel, and run them all with Algae-Derived Biodiesel using sewage as a feedstock. Because of the greater efficiency of algae, supplying all of our vehicular needs is actually feasible.

This would alleviate both the global warming problem and our dependence on Middle-Eastern petroleum. The technology is available now, and because of the high energy density, no sacrifices on the part of automotive consumers are required in terms of range and performance. (We may need to invest in research into better catalytic converters and turbocharging technology.)

Biodiesel is a great route for disposing of waste fat, make no mistake. And thermal depolymerization is going to be a wonderful system for turning organic waste into valuable products, too. But running our society on them? No, the energy we require is far too great for such inefficient pathways to supply it.

why did you bother to write two paragraphs which say "yeah, uh, corn is not a good fuel source. there's gotta be something better. dunno what it is. humm, maybe there's nothing better." next time hows about doing some reading before hitting 'submit'. i guess i wasn't blunt enough with my links, here's a good place to start: energy sufficient to fuel the entire US is available from the sun and it doesn't take radical technology and it doesn't take crazy amounts of cropland. all it takes is waste water in oversized kiddie pools, oily alge and the replacement of gasoline engines with diesel engines. (this link was in the grandparent too).

i'm told (yes, be skeptical) that the energy produced by ethanol does not equal the energy used to produce it. i'd imagine that's because we use a ton of petroleum fertilizer for corn production.

that doesn't mean a closed carbon cycle fuel is DOA, it just means we chose the wrong crop. why did we choose corn when there are hundreds of other options? see: pork barrel and ADM

did you know an automobile can run on wood? you won't drive terribly fast (yay, says the cyclist!) but it works (link and link). using crops such as willow trees (for gassification) or alge to make biodiesel is totally feasable and results in a very positive net energy gain.

From the biodiesel page at the University of New Hampshire:

Diesel fuel has an energy density of 1,058 kBtu/cu.ft. Biodiesel has an energy density of 950 kBtu/cu.ft, and hydrogen stored at 3,626 psi (250 times atmospheric pressure) only has an energy density of 68 kBtu/cu.ft.4 So, highly pressurized to 250 atmospheres, hydrogen's volumetric energy density is only 7.2% of that of biodiesel. The result being that with similar efficiencies of converting that stored chemical energy into motion (as diesel engines and fuel cells have), a hydrogen vehicle would need a fuel tank roughly 14 times as large to yield the same driving range as a biodiesel powered vehicle. To get a 1,000 mile range, a tractor trailer running on diesel needs to store 168 gallons of diesel fuel. When biodiesel's slightly lower energy density and the greater efficiency of the engine running on biodiesel are taken into account, it would need roughly 175 gallons of biodiesel for the same range. But, to run on hydrogen stored at 250 atmospheres, to get the same range would require 2,360 gallons of hydrogen. Dedicating that much space to fuel storage would drastically reduce how much cargo trucks could carry. Additionally, the cost of the high pressure, corrosion resistant storage tanks to carry that much fuel is astronomical.

For information on better energy alternatives, check the above URL or the one in my sig.

ultra low sulpher diesel is already available at many gas stations (most arco stations) in california.

maybe i'm a rouge environmentalist (or maybe i don't fit a box) -- i think diesel technology is great. the problem is the fuel. removing sulpher from petro diesel allows catalitic converters to be used while biodiesel closes the carbon cycle -- it doesn't put any more carbon into the air than was removed from the air by the organisims that created the fuel.

traditionally, biodiesel has focused on waste oils from the food industry, waste tallow from the meat industry and food oils such as canola (AKA rape seed [yes, there are differences]) and palm oil when the prices are low. the problem is that producing enough oil to fuel even a relatively efficient country would require enormous amounts of land (the entire country of england would have to be covered in rape/canola to produce enough diesel to meet their current demand). but new ideas have emerged, placing oil producing algae at the cutting edge of bio-fuel oil production. some algae are well over 50% oil. farming these algae would drastically reduce the area needed to produce oil and could be produced using waste water from sewage, crop runoff or sea water. this paper on biodiesel from algae, published at the university of new hampshire, claims that the vehicle energy requirements of the US could be met by flooding 12.5 percent of the sonora desert with sea water and producing algae (the article doesn't advocate this -- production should be distributed, it's just a measurement demonstration of the possibilities).

The Formidable Article claims that:

If produced in mass [sic], their cost is predicted to fall to $50,000 by 2010. The Stirling solar dishes are also easy to maintain...

On the other hand, an analysis of algal biodiesel ponds (and some other neat things) from here by Michael Briggs at the University of New Hampshire Physics Department mentions:

Ponds equivalent to their design could be built around the country, using wastewater streams (human, animal, and agricultural) as feed sources. We found that at NREL's yield rates, 15,000 square miles (3.85 million hectares) of algae ponds would be needed to replace all petroleum transportation fuels with biodiesel. At the cost of $80,000 per hectare, that would work out to roughly $308 billion to build the farms.

The operating costs (including power consumption, labor, chemicals, and fixed capital costs (taxes, maintenance, insurance, depreciation, and return on investment) worked out to $12,000 per hectare. That would equate to $46.2 billion per year for all the algae farms, to yield all the oil feedstock necessary for the entire country. Compare that to the $100-150 billion the US spends each year just on purchasing crude oil from foreign countries, with all of that money leaving the US economy.

So, it looks like biodiesel requires more maintenance, but could probably be started up more quickly because the algae takes care of worrying about building itself. I like the fact though that the algae consumes CO2 from the atmosphere and cleans out wastewater.

I agree that VO and biodiesel seem like a good energy alternative. The main problem with that is most people don't own diesel cars.

I'm running my '03 VW Jetta on straight vegetable oil (waste oil that's otherwise thrown out after using it in a deep fryer). There are pictures at http://vw.ourwebstop.com

Here's an interesting article regarding how we might produce all the biodiesel necessary to replace the energy we currently import. http://ww.unh.edu/p2/biodiesel/article_alge.html

All that radioactive stuff is waste. It must be stored carefully, for long periods of time. And noone has a solution that works both politically, geologically, and medically.

Energy Amplifier
or more realistically, Integral Fast Reactor.

Both reuse waste.

http://www.unh.edu/p2/biodiesel/article_alge.html

This option makes a lot more sense to me. No likelihood of glowing children, and, despite the suggestion of flooding the dessert, could be easily decentralized around the country to make it harder to take out by terrorists.

I do wonder how making the middle east irrelevant would affect world politics. Think it would be a good idea to do BEFORE their nuclear weapons programs come to full fruition.

A few days ago I read on Slashdot about biodiesel produced by a very efficient algae. One big stumbling block was that you needed CO2 in concentrations like you would get from the exhaust of a power plant to grow that algae at top rate. And looky here, today Slashdot is discussing a bunch of power plants putting out CO2 and they don't know what to do with it.

I think this paints a complete picture of the future of transportation: a plug-in diesel/electric hybrid running on biodiesel. The batteries are charged from zero-polution electric plants which feed the carbon dioxide to algae farms which create the oil for biodiesel. The car runs most of the day on the electricity, but switches to diesel when the battery gets low. IMHO this is a far more realistic scenario than the fuel-cell which is getting a good deal more political attention than it deserves at thsi stage.

There are bacteria that can generate small amounts of hydrogen gas. If genetic engineering can make these bacteria much better at this function, we will have very good renewable energy source.

Hydrogen is a very poor source of energy - it's energy density is very low. (it takes 1/3 of the available energy in the hydrogen just to compress it to a liquid!) It's explosive. It's very inefficient.

Better to consider alge that produces bio-diesel - much denser, more compact, no expensive compression, no equipment retrofitting... the list of benefits goes on and on....

The global warming pundits insist that they must ordinarily be constant. That's fairly unlikely; there appear (in the small amount of data we have collected over the past few decades) to be complicated cycles at work. We do not understand those cycles. Therefore we cannot claim to have altered them.

b) Even if it's not as bad as the leading climate scientists tell us, it's no reason to say "hey.. all is fine. let's waste energy and blow as much CO2 into the atmosphere as we can."

If we don't know for sure it would be a good policy to be cautious.

There are many problems with using hydrogen as a fuel. The first, and most obvious, is that hydrogen gas is extremely explosive. To store hydrogen at high pressures for as a transportation fuel, it is essential to have tanks that are constructed of rust-proof materials, so that as they age they won't rust and spring leaks. Hydrogen has to be stored at very high pressures to try to make up for its low energy density. Diesel fuel has an energy density of 1,058 kBtu/cu.ft. Biodiesel has an energy density of 950 kBtu/cu.ft, and hydrogen stored at 3,626 psi (250 times atmospheric pressure) only has an energy density of 68 kBtu/cu.ft.4 So, highly pressurized to 250 atmospheres, hydrogen's volumetric energy density is only 7.2% of that of biodiesel.

A common dream from the environmentalist community is having a solar panel on the roof of a home to electrolyze water, producing hydrogen for a fuel cell vehicle. It's a nice dream, but not particularly realistic. As a real world example, consider Honda's facility in California that requires an 8 kW solar array to produce enough hydrogen to drive one small hydrogen vehicle roughly 7,500 miles per year. Such an array could power several homes in California, but is only enough for powering one small car half the normal driving range in the US. For an average family with two vehicles that drive an average distance of 15,000 miles per year, an array of 32 kW would be needed - considerably more with larger vehicles. A 32 kW array would cost on the order of $160,000, and could not be installed just on the rooftop of a single home - it would likely require the south-facing rooftops of at least 4-8 houses to power the vehicles from one home (and that's if you live in sunny California...

Please disregard my previous message, for I clicked the 'submit' button by mistake. My apologies.

Those who wish to further hydrogen as a major fuel fail to point out its lack of energy density. According to the UNH article on algal biodiesel (linked by Engineer-Poet), gaseous hydrogen (at 250 atm [3626 psi]) has an energy density of 68 kBtu ft^-3, while petroleum diesel and biodiesel have energy densities of 1058 kBtu ft^-3 and 950 kBtu ft^-3, respectively.

Biodiesel, while requiring slightly more fuel than petroleum diesel at a given distance, requires significantly less fuel than pressurized hydrogen (UNH article). Obviously, the ubiquity of vehicles running on petrol engines presents major disadvantages; it would be impossible if not ridiculous to replace current petrol vehicles with diesel engines. Though pure biodiesel can run in diesel engines, wouldn't it still produce carbon dioxide?

I might go offtopic, so bear with me here. Not many point out the differences and similarities between conventional fuels (petrol, diesel) and alternative fuels (biodiesel, hydrogen) chemically. Those who wish to further hydrogen as a major fuel fail to point out its volatility to oxygen and its lack of energy density. According to the UNH article on algal biodiesel (linked by Engineer-Poet), highly-pressurized hydrogen must be stored in tanks that are constructed with rust-proof materials. In addition, hydrogen at 250 atm (3626 psi) has an energy density of 68 kBtu*ft^-3, while petroleum diesel has an energy density 1058 kBtu ft^-3

If you want to change the world's energy cycles you're going to need something with at least 20 times the productivity of standard farm crops, like the UNH biodiesel-from-algae thing.