there is sufficient net gain in energy (minimal fossil-fuel inputs for
planting, fertilizing, harvesting, processing)
There are two main reasons to go to biofuels:
energy independence (from imports), via domestic production:
they can be grown almost anywhere that the climate allows. Many areas of the US qualify
for growing field crops for biofuels (corn, sorghum, switchgrass);
these crops can go dormant or be reseeded and need not be winter-active or
even winter-hardy. Southern regions
of the US
hold promise for algae, with the limitation that the culture can't be
allowed to freeze. Heating is very
expensive and seriously reduces the net energy yield, so that siting is very important.
low potential for air pollution: coal, in contrast, is the dirtiest fuel
imaginable, as it contains mercury in significant amounts, as well as
sulfur as another major pollutant.
Biofuels contain no more than background levels of such pollutants,
so that burning them causes little impact.
Nitrogen oxides form in any combustion, but these are controllable
in vehicles with catalytic converters.
At powerplants, the picture is mixed.
of climate change: net reduction in greenhouse gas emissions. Burning any fuel emits CO2 to
the air, with attendant contributions to climate change. Regrowing the crop recaptures CO2
in a sustainable cycle. Carbon
neutrality is not guaranteed, however; see below.
concomitant problems of:
high land usage per unit of net energy produced (energy yield is on the
order of 1 to 3 W m-2 annual average, vs. the other distributed
direct solar sources, photovoltaics or solar thermal, at 35 W m-2),
or even traditional fossil-fuel extraction and processing (on the order of
kW m-2, given the spatial footprint of mines, wells, roads relative
to the very high energy density of the fuels). Heuristic calculations are given in Appendix I below.
of food crop prices from competition for land and for resource inputs
use - for irrigation, or for evapotranspiration of a good fraction of what
would have otherwise become runoff. See Appendix II
conversion at the expense of wild species that provide diverse ecosystem
services (host plants for insects and nesting sites for birds that provide
pest control; flood control; etc.)
- Pest and disease problems: for the biofuel crops
themselves (if they are extensive monocultures) or for other crops,
humans, livestock, and wild fauna and flora, if the biofuel crops are
hosts for pests and disease vectors. Appendix III below
notes some problems that could develop very rapidly.
inputs, noted earlier…and, for algal biofuels, especially biodiesel, there
is a high energy/ fossil-fuel input in fabricating the massive containment
systems. See Appendix
mining from soil - net extraction of N, P, K, micronutrients. Fortunately, in many designs these
nutrients can be returned to the soil (or tank), if the process waste
containing the nutrients is returned to the growth site. This makes the
nutrient-mining problem far more
amenable than with food crops, where the ultimate disposal is in sewage
streams that are often mixed with industrial streams that contain toxic
loads (sewage sludge never made it as a fertilizer).
organisms are grown in soil or tanks, the demand for fertilizers adds a
significant marginal expense to the product. See Appendix V
pollution from N and P fertilizer excesses carried into waterways by
runoff and deep drainage. Ordinary
food crops in the Mississippi River basin and other basins are already
responsible for massive N and P loads that lead to very large (multiple
tens of thousands of km2) coastal dead zones; the N and P
support algal blooms, which, upon death, deplete dissolved oxygen in water
to essentially zero. Biofuel
cropping has the potential to add to this problem.
A closer look at the two goals, energy
independence and GHG reduction, which are mixed together in any decision
are often projected to be indefinitely renewable (barring land
degradation from soil erosion or nutrient mining, increasing pest and
disease problems, or economic and political problems from interference
with the food crops market). The
multiple tradeoffs - economic, environmental, social
- against using depletable fossil fuels need project-specific evaluation.
are cheaper ways to go, such as using coal where it is abundant, as long
as one can continue to externalize the costs of climate change, air
pollution, and water pollution).
Of course, the cheaper ways have negative effects on GHG
emission reduction, viewed over the life cycle of the system:
qualifier: what type of land was converted to biofuel production? Several recent studies show that
conversion of some cover types (e.g., tropical forest) to biofuels
production releases massive amounts of GHG, mostly CO2, from
decay or burning of original cover, plus oxidation of soil organic
carbon. In some cases, the land
conversion emitted more than 90 times the annual C capture by the biofuel
qualifier: what fossil-fuel inputs were used, particularly in processing
the biomass? In some egregious
cases in the US,
coal was used for distilling the alcohol.
The net carbon impact was adverse, because coal generates twice
the CO2 per unit energy delivered compared to common hydrocarbons (oil or
natural gas). Why use coal for
distillation in biofuel production, vs. biomass itself, or why not use
coal for direct synthesis of liquid transportation fuels, such as by the
Fischer-Tropsch synthesis (used by South Africa
under apartheid during embargoes imposed by other nations)?
is an abundant internal resource in the US and several other
for ethanol production are largely political, and do not account for GHG
are essentially absent (research funds only) for direct coal conversion
to liquid fuels
A potential role/niche for our consulting
consortium: evaluation of biofuel options (design, operation, governmental policies) by site, region, or political entity
the full context (all the issues above);
such context is highly unlikely to be provided by potential vendors of various
biofuel production systems.
evaluation methods and quantifying all the criteria.
these to the specific system design(s): crop species, climate, soils,
economic conditions, processing methods, GHG treaties, etc.
optimization models with mixed objectives and constraints (a very
interesting area of applied mathematics, and with great promise in this
I: estimates of land use
Gutschick, GCCC director
fact: photosynthesis has a low energy efficiency. There are very good reasons for this,
including metabolism required to make organisms self-maintaining /
self-repairing and also the drop in atmospheric CO2 over
millions of years that plants themselves caused by being partly
rot-resistant and thus causing the burial of huge amounts of carbon.
green plants capture energy in light, using about 120 photons to make one
molecule of glucose sugar. The
energy in the photons is more than 4 times larger than the energy captured
in making sugar, so that the efficiency of capturing energy in sunlight is
less than 25% at best. That's in
the initial steps. The plant then
has to use part of the energy in sugars to make other things – proteins,
fats, etc., and also to remake damaged parts. The highest efficiency attained in field
crops is 6% over a season in sugar cane.
The average efficiency is more like 2%. For the globe as a whole, it is 0.3%,
because of dormant seasons, etc.
Algae are no better than land plants. However, they can be grown in contained
cultures that use high levels of CO2, such as in power-plant
exhaust (oops – that means taking up mercury and such if it's a coal-fired
plant). They might hit 6% on a
does this mean for land use? The
other consideration is that sunlight is a dilute resource. We can hit 1 kW per square meter at high
noon in clear western US
climates, but the average is about 180 W per square meter (W m-2),
accounting for day and night, winter and summer, clear and cloudy
conditions. So, at 6% efficiency in
capturing energy, algae might average 10 or 11 W m-2.
as raw biomass. They have to be
processed, and drying either is really slow (using more sun and more
land, or, worse, using some of the energy provided by the rest of the
crop). If the system hits 60%
efficiency in going from raw biomass energy to final electric or fuel
energy, we're getting about 6.5 W m-2.
let's say we want to replace a typical 1000-MW power plant, which
actually consumes about 2500 MW of thermal (fuel) power, converting it at
only 40% efficiency. This is 2.5
billion watts. We will need about
0.4 billion square meters. This is
400 square kilometers, or over 150 square miles. Of course, you don't have to make one
big plant, but the total area of many smaller plants has to be this
are much better ways of using land, even cheap land. Solar cells, or photovoltaics, easily
hit 11% efficiency, and new ones, not yet commercial, are exceeding
15%. Let's say that 13% is a decent
figure for plants that will be built.
This is 13% from sun to electricity – no other conversion
inefficiencies. This gives us 0.13
* 180 W m-2 = 23.4 W m-2. To get 1000 MW of power, we still need a
large area, almost 43 million square meters. This is 43 square kilometers or about 16
square miles…slightly more than 10% of what the algal pond would
take. Solar thermal power is about
as efficient. Both technologies are
proven to a high level. I attended
the American Geophysical Union meetings in 2007 and 2008 and the recent
Energy Summit in the Sandias. The
reality is that these technologies have only a short way to go to
large-scale commercialization. They
are far ahead of algal biofuels.
They don't readily make liquid fuels for transportation, but they
have a clear role in the energy economy.
They could even be pushed, with some conversion losses, to make
liquid fuels, as by making hydrogen gas from electricity to combine with CO2
in the air, generating alcohols and then hydrocarbons.
II. Possibly large water use
field crops use a great deal of water.
This is a physiological necessity that absolutely cannot be
altered. Some gains in what we term
water-use efficiency are possible, but they are marginal. It takes about 500 masses (pounds,
kilos, whatever) of water to make one mass of plant matter. I have done theory and experiments on
can be used in closed systems, with only minimal water loss. Some can also grow well in brackish
water. These plusses are balanced
against some minuses.
closing the system means that the containment vessel has to be
built. This is expensive in both
dollars and materials. The
materials cost a significant amount of energy to make and deploy. (The same is true of, say, photovoltaic
cells, but their energy payback is only 1.5 to 2 years, in a 20 to 30
year lifetime…a bargain).
the standing volume of water is large.
A reasonable depth for growth is at least 0.5 meter or about 1.5
feet. Let's go back to that algal
pond that replaces a 1000-MW power plant (and that needs such a
traditional plant nearby, to get high efficiency, by growing at high CO2). The area is 400 million square meters,
so the volume is 200 million cubic meters. This is about 7.2 billion cubic feet,
or 54 billion gallons, or about 1.65 million acre-feet. We don't have this to spare in fresh
water, so we'd go to brackish water.
We do have a lot of this.
We'd have to be careful not to spill much of it and salinize the
land. We'd also have to reuse it
very thoroughly. This is where my
knowledge is nearing its limit.
The water does accumulate metabolic byproducts of the algae, which
have to be removed. I'm not sure
how readily this is done by purification vs. partial disposal.
III. Potential for rapid loss of
All crops, conventional field crops or unconventional crops
like algae, are subject to losses. These
can come from the abiological environment, in the form of high or low
temperatures. Controlling high or low T
in an algal farm is likely to be quite expensive (fuel or electricity for
heating; water for evaporative cooling).
The threats can also come from biological sources. In the ocean, most algae and other plankton
die in a fraction of a day to several days, primarily from viral infections and
the like. In a contained culture, this
threat might be reduced. However, a
realized threat would spread with considerable speed, and decontamination is
difficult and costly. With ordinary
crops, soil microorganisms help control pathogens, if not completely. In algal farms, there is no such help. The risk is probably not insuperable, but it
cannot be costed out currently for large operations.
IV. Algal biofuels may require
large inputs of energy and funds for construction
This has been brought up in the other topics above. Containment vessels are costly, in both
dollars and energy. Let's say that the
vessel is polycarbonate (it has to be strong and tough, resistant to impact),
and that it's about ¼" or 6 mm thick, and on top and bottom, for a total
of about ½" or 12 mm. I haven't done detailed calculations on the energy
it takes to make this plastic, nor on
dollar costs for purchases in volume.
I'll make a preliminary estimate here.
The embodied energy (energy needed to manufacture an item, including the
energy value left in the product as a potential combustible fuel) in plastic is
likely to be at least 3 times the energy in the same amount of hydrocarbons,
which is about 40 kJ per gram. It is 1.2
times as dense as water, so that it weighs about 1200 kg per cubic meter. This huge pond container has 400 million
square meters x 0.012 m depth, or 4.8 million cubic meters of polycarbonate,
weighing about 5.8 million tons (5.8 trillion grams). The embodied energy, at
120 kJ per gram, is about 7 x 1017 Joules (J, or watt-seconds). A MW-year is 3.1x1013 J. Thus, it takes about 22,000 MW-years of energy. The 1,000-MW plant pays back its energy cost
in 22 years! No viable commercial plant
can bear this. The payback time has to
be far less than half the useful lifetime.
V. Major operating cost of
Vince Gutschick, GCCC director
The most costly nutrient to provide, in dollars and in
energy to produce fertilizer forms, is nitrogen. Ammonia manufacture for fertilizer consumes
3% of world energy currently. For
high-value food crops, the cost is sustainable by farmers, even if only in more
developed nations or subsidized regions.
For fuel, which is worth much less per mass, the cost of this input is very
high. There are some cyanobacteria that
fix nitrogen from the air and that might be co-cultured with true algae. This can be tricky. There is also the possibility of recovering a
substantial amount of the nitrogen in the algal biomass, if the whole organisms
are not dried and burned as fuel. Of
course, if the whole organism is not used – say, only 40% that is lipid (oil) –
a very generous figure, then this reduces the efficiency of algal growth for
fuel even more and increases the land use and water use.