A short chat on biofuels
I'm going to assume we're interested in getting off fossil fuels,
not just making a half-hearted 10% or 20% reduction in fossil fuel use.
Are biofuels part of the answer to
When discussing this question (or indeed any question to do with
energy), it's important to do the numbers.
There are three concerns about the numbers for biodiesel:
Turning plants into biofuel requires
many processing steps - spreading fertilizer, herbicide
and pesticide; ploughing;
harvesting; drying; transport; chemical transformation
- all of which require investment of energy.
How do those extra energy inputs compare to the final
If the processing steps actually require you
to put in roughly as much
energy as the final energy delivered, then surely there
would be little point in
I'll discuss the numbers below.
To make biofuels requires land to grow plants on.
Where would we grow the biofuels, how much land would be needed, and
are we sure that no-one needs to do anything else with that land?
The final concern is that biofuels are marketed like
a magic pixie-dust, transforming whatever it touches to green.
If you buy 'B20' biodiesel, for example,
then it's actually just 20% biodiesel,
and 80% normal diesel.
So if pure biodiesel is doing any good at helping get
us off fossil-fuels, B20 biodiesel is doing very little
good, because someone who uses B20 is still using 80%
normal diesel. Yet the marketers will
paint the dispenser green and tell people that they've 'done their
Amazingly, in the UK, even B5, which is just 5% biodiesel
and 95% fossil fuel, is permitted to be marketed as 'biodiesel'.
This is greenwash. Homeopathic greenwash.
Before we discuss the numbers, here are a few positive
claims made about biodiesel. ([source])
'Biodiesel burns better in a diesel engine than
conventional diesel', in that its emissions
of unburned hydrocarbons, carbon monoxide, and particulate matter
are lower, and emissions of sulfur oxides and sulfates
Biodiesel leads to 50% less ozone-forming
emissions than diesel.
We need to address the first two questions
separately for each biofuel.
The main biofuels in use today are
biodiesel and bioethanol.
made from oilseed crops:
soybeans, sunflower, canola, mustard,
palm, coconut, safflower, hemp, jatropha;
and used cooking oil from restaurants.
1. Energy costs of processing, expressed in terms of CO2
site supporting biodiesel:
A 1998 biodiesel lifecycle study by the
US Departments of Energy and Agriculture,
concluded that biodiesel reduces net CO2
emissions by 78 percent compared to petroleum diesel.
However, this study has been criticised.
'Overly optimistic assessment in US DOE Report':
'These estimates were overly optimistic, and out of line with other analyses'
For further reading see
'Biofuels for Oil Addicts
According to a lifecycle analysis from MIT (Groode and Heywood):
Ethanol made from corn -- consumes too much energy, inferior to gasoline,
unless careful use made of co-products.
Ethanol made from cellulose (eg from switchgrass or corn byproducts)
-- not yet a commercial technology -- might be energetically better than
break-even but economically unclear.
Growing switchgrass is said to be promising because its life cycle is
about 10 years, so transport costs are reduced.
Is there enough land (using current farming techniques)?
The quick answer:
For the UK to grow its own transport fuel?
For the USA to grow its own transport fuel?
(The USA has a much lower population density!)
[and a biodiesel advocate
agrees with this]
In a bit more detail, let's look at the UK.
Let's assume we take over 75% of the country and
devote it entirely to biofuel production.
The UK has an area of 4000m2 per person.
So we have 3000m2 per person devoted to
Now, bring along the sunlight. The average
power of sunlight falling on Britain is 50W/m2.
(That's 1000W/m2, the power of raw sunlight,
multiplied by a daylight factor of (1/4),
a sunniness factor of (1/3),
and a latitude factor of 0.6.)
[Correction: Actually 100 W/m2
is more accurate
for the UK.]
The best plants are roughly 1% efficient at turning
sunlight into carbohydrates [Correction:
actually 0.5% efficient is
more accurate for energy crops in the UK], so the chemical
power delivered by
the 3000m2 biofuel plantation is
3000m2 x 0.5W/m2 = 1.5kW.
Or to put it in the units your energy bills come in,
36 kWh per day.
Don't forget, that's before we allow for the energy required
in the processing steps.
How does this compare with the energy we use for
The transport consumption of
the UK averages out to 42 kWh per day per person.
For example, taking just one intercontinental trip by plane
per year requires an amount of energy equivalent to 24 kWh per day per person.
First written July 2007; updated Fri Dec 23 09:49:23 GMT 2011.
See also Sustainable Energy - without
the hot air (published December 2008).