Soybeans ~40 gal/acre
Corn ~60 gal/acre
Mustard ~140 gal/acre
Jatropha~160 gal/acre
PalmOil ~650 gal/acre

and
ta-da

algae 10-20000 gal/acre

Do a google on GreenFuel Technologies Corp ..
They've got a continuous bioreactor going commercial ..

The 'algae' folks claim that all motor fuels and
heating oil can be replaced with the equivalent of
500,000 acres of closed-loop algae production ..
who knows .. Ford also looked at Mustard plants as
a source of biofuel back in the day ..
--
and my answer, re hemp...

Hemp is a viable source of woody biomass, no deforestation necessary. In fact, while an acre of trees is about 60% cellulose, and acre of hemp is nearly 75%. How much hemp is necessary to meet current US energy needs? Somewhere between 10 million and 90 million acres, depending on how efficient the production is. Every year, the US government pays farmers (in cash or "kind") to not farm what they call the "soil bank", which happens to be about 90 million acres of farmland. The math is pretty simple.

Hemp seed oil is very similar to petroleum diesel fuel, and produces full engine power with reduced carbon monoxide and 75% less soot and particulates. Hemp stalk (different than the part that can make paper and textiles) can be converted into 500 gallons of methanol/acre. US energy consumption is responsible for 80% of the world's air pollution. The use of hemp biomass fuel would be a globally responsible evolution.

http://mit.edu/thistle/www/v13/2/enviro.html
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Hemp as Biomass for Energy

Tim Castleman

© Fuel and Fiber Company, 2001

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Industrial hemp can be grown in most climates and on marginal soils. It requires little or no herbicide and no pesticide, and uses less water than cotton. Measurements at Ridgetown College indicate the crop needs 300-400 mm (10-13 in.) of rainfall equivalent. Yields will vary according to local conditions and will range from 1.5 to 6 bone dry tons of biomass per acre. California's rich croplands and growing environment are expected to increase yields by 20% over Canadian results, which will average at least 3.9 bone dry tons per acre.

Hemp seed oil for BioDiesel

Production of oil

Grown for oilseed, Canadian grower's yields average 1 tonne/hectare, or about 400 lbs. per acre. Cannabis seed contains about 28% oil (112 lbs.), or about 15 gallons per acre. Production costs using these figures would be about $35 per gallon. Some varieties are reported to yield as much as 38% oil, and a record 2,000 lbs. per acre was recorded in 1999. At that rate, 760 lbs.of oil per acre would result in about 100 gallons of oil, with production costs totaling about $5.20 gallon. Sales of the remaining stalk material at $72 per ton will provide another source of income. It is estimated that a crop grown for both seed and fiber will produce about 3 tons of stalk, which is selling for about $72 per ton, resulting in a $216 per acre credit. This will reduce the cost of the oil to about $3 per gallon. Further reductions will accrue as the agronomic knowledge base is enlarged, and economies of scale are realized, lowering production costs while improving yields.

This oil could be used as-is in modified diesel engines, or be converted to biodiesel using a relatively simple, automated process. Several systems are under development worldwide designed to produce biodiesel on a small scale, such as on farms using "homegrown" oil crops.

Production of Bio-Diesel

Basically methyl esters, or biodiesel, as it is commonly called, can be made from any oil or fat, including hemp seed oil. The reaction requires only oil, an alcohol (usually methanol) and a catalyst (usually sodium hydroxide [NaOH, or drain cleaner]). The reaction produces only biodiesel and a smaller amount of glycerol or glycerin.

The costs of materials needed for the reaction are the costs associated with production of hemp seed oil, the cost of methanol and the NaOH. In the instances where waste vegetable oil, or WVO, is used, the cost for oil is of course, free. Typically methanol costs about $2 per gallon and NaOH costs about $5 per 500g or about $0.01 per gram. For a typical 17-gallon batch of biodiesel, you would start with 14 gallons of hemp seed oil; add to that 15% by volume of alcohol (or 2.1 gallons) and about 500g of NaOH. The process takes about 2 hours to complete and requires about 2000 watts of energy. That works out to about 2kw/hr or about $0.10 of energy (assuming $0.05 per kw/hr). So the total cost per gallon of biodiesel is $? (oil) + 2.1 x $2 (methanol) + $5 (NaOH) + $0.10 (energy) / 14 gallons = $0.66 per gallon, plus the cost of the oil.

Hemp Cellulose for Ethanol

Another approach will involve conversion of cellulose to ethanol, which can be done in several ways including gasification, acid hydrolysis and a technology utilizing engineered enzymes to convert cellulose to glucose, which is then fermented to make alcohol. Still another approach using enzymes will convert cellulose directly to alcohol, which leads to substantial process cost savings.

Current costs associated with these conversion processes are about $1.37 per gallon of fuel produced, plus the cost of the feedstock. Of this $1.37, enzyme costs are about $0.50 per gallon; current research efforts are directed toward reduction of this amount to $0.05 per gallon. There is a Federal tax credit of $0.54 per gallon and a number of other various incentives available. Conversion rates range from a low of 25-30 gallons per ton of biomass to 100 gallons per ton using the latest technology.

In 1998 the total California gasoline demand was 14 billion gallons. When ethanol is used to replace MTBE as an oxygenate, this will create California demand in excess of 700 million gallons per year. MTBE is to be phased out of use by 2003 according to State law.

In this case we can consider biomass production from a much broader perspective. Sources of feedstock under consideration for these processes are:

We will address these in turn and show why a dedicated energy crop holds important potential for ethanol production in California, why hemp is a good candidate as a dedicated energy crop, and how it may represent the fastest track to meeting 34% of California's upcoming ethanol market demand of at least 580-750 million gallons per year.

http://www.fuelandfiber.com/Hemp4NRG/Hemp4NRG.htm

I'm still looking for BTU figures, and petrochemical and water inputs for the various biocrops. I'm also thinking about a weed called teasel, since I'm hacking down plants taller than me in the garden. Problem is, that it is a biennial.But, in Cal,you can walk on it for a year, and then it shoots up during late winter/ early spring, right when fields get planted. Maybe in the rows?
There is currently a hemp industry bill in the Calif. lege.
Problem I have pushing hemp is everybody says "But it will seed my crop." :-)
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And, from a paper on algae,
 In the early days of the automobile, most vehicles ran on biofuels, with Henry Ford himself being a big advocate of alcohol produced from industrial hemp (not to be confused with marijuana).
http://www.energybulletin.net/2364.html