The Industrial Revolution in Britain occured when the discovery and application of coal suddenly released industry from its dependence upon the forests which had been steadily cut down since the time of the Romans.
It is difficult to imagine that a field, forest, or peat moorland entirely devoted to photosynthetic capture of solar energy will be able to provide significantly more biofuel energy than when we harvest the entire growth, dry it, and burn it for fuel.
So how much land would we need to devote to biofuels, to replace even one tenth of our petroleum consumption?
Lord Kelvin's estimate of the capacity of vegetation to capture solar energy in Britain or Germany was two tons per square metre per thousand years.
This is equal to two thousand tons per square kilometre (a million square metres) per year.
ORNL
gives
Energy content of wood fuel
(air dry, 20% moisture) =about 15 GJ/tonne (gigaJoules per thousand kilograms)
but one Kwh = 3.6 MJ (megaJoules).
and one gigawatt-year is 8760 gigawatt-hours,
so two thousand tons of vegetation, optimistically, gives perhaps 30,000 GJ,
One gigawatt-hour is a million Kwh, i.e. 3,600 GJ
one gigawatt-year is 8760x3600 = approximately 31.5 million GJ
Which comes out to the accuracy of the available figures at just more than a thousand square kilometres for a gigawatt-year of production per year.
Divide by 2.6 to convert to sq. miles: 384 sq miles, probably 390 to 400, which agrees fairly well with the estimate in the next paragraph.
It is known that coppiced willow, which produces "withes" that were traditionally used for basketmaking, is quite a good way to obtain annual harvests of wood. Ordinarily, the withes on a given tree are harvested at three year intervals. So the annual harvest is taken from one third of the entire coppice.
It is said to yield three to ten times as much woody mass per acre per year as Red Oak or Eastern Cottonwood, and 53% of the energy per pound of Red Oak. So it's probably the most productive form of cellulose/lignin biofuel.
But it has been reckoned that the entire English county of Kent would have to be covered in such coppice, in order to have an annual harvest of biofuel energy to match the single 1050 MW nuclear generator Dungeness B (Dungeness is in Kent). My own attempt, using two optimistic sources, was that it takes from 410 to 1100 square miles, to produce the equivalent of a gigawatt-year of heat energy. It has also been reckoned that if all the forests in the USA were harvested in a sustainable way for fuel, they could scarcely meet 10% of our energy demands.
Worse, even if we could convert every scrap of cellulose and lignin that grew in our energy plantations to monosaccharides, and then ferment those to ethanol, we have to sacrifice at least a third of the carbon, to feed the yeast.
C6H12O6 = 2CO2+2C2H5OH
Put it another way, how many square miles of Brazil's tropical rainforest needs to be replaced by sugar cane to replace Brazil's oil imports with E-85 motor fuel?
And, of course bio-engineering, Genetic Modification(GM) is anathema to some of the extreme "Back to Nature" wing of environmentalists.
Nature wants you to Die