Biofuel vs. Photovoltaics

In an earlier post “Power the World with Photovoltaics,” we demonstrate that the entire energy requirements of the human race could be fulfilled by a photovoltaic array 143,872 square miles in size. Insofar as this is only about one-quarter of one percent of the earth’s surface, or 668 square feet per person, there is no shortage of available space for photovoltaics.

With biofuel, however, there is a question as to whether or not there is enough land available to grow biofuel and also preserve farms and wilderness. For example, some of the best biofuel crops – biodiesel from jatropha and bioethanol from sugar cane – are able to produce about 6,000 barrels of fuel per square mile per year. This equates to about 55 million Btu’s of energy per square mile per year.

This means that using the best biofuel crops we’ve got today, to produce enough fuel to fulfill entire energy requirements of the human race (400 quadrillion Btu’s per year) we would need to devote 10.8 million square miles to growing biofuel. Considering there is only about 5.5 million square miles of arable farmland on the entire planet, this is not possible.

Biofuel is an important source of fuel, and in some parts of the world growing biofuel makes compelling economic sense, but today at least, biofuel doesn’t show nearly the potential of photovoltaics to efficiently turn sunshine into energy to power human civilization.

There is an interesting analysis “Widescale Biodiesel Production from Algae,” authored by Michael Briggs at the University of New Hampshire. He cites studies that indicate biofuel may soon be economically derived from algae. But he makes a huge assumption – stating that algae farms could yield “5,000 gallons per acre-year.” This equates to a yield over 10 times that of the best biofuel crops we’ve got.

Comparing various forms of solar energy boils down to how efficiently they convert sunlight into usable power. Since raw sunlight provides 100 watts per square foot, a photovoltaic array that produces 10 watts per square foot has an efficency of 10%. Some photovoltaic arrays can do much better than that, with efficiencies reported as high as 20% on high-quality production panels.

You can make the same calculaton with today’s best biofuel crops – diesel fuel extracted from jatropha and ethanol distilled from sugar cane both produce about 55 million Btu’s per square mile per year. Since raw sunshine provides about 41 trillion Btu’s per square mile per year, their efficiency is a paltry .13%.

If the promise of biodiesel extracted from algae is realized, you will see a ten-fold improvement in biofuel efficiency, to 1.3% (based on 5,000 gallons per acre-year). At that level of efficiency – less than one-tenth that of today’s photovoltaics, but cheaper to implement – it might be feasible for biofuel to become a realistic alternative to petroleum.

Categorized | Energy, Energy & Fuels, Solar
8 Responses to “Biofuel vs. Photovoltaics”
  1. e says:

    Great point. I believe that biodiesel is a good supplement today but not a long term solution. Implementation is very easy compared to solar cells as well. I guess if we converted solar energy to a more portable form (e.g. fuel cells) then cars could make better use. As far as I remember batteries still lack the capacity to go 1000′s of miles on a charge, until stations were common, or posses the ability to recharge in under 5 minutes (maybe zinc-air). Maybe by time we figure this part out, we will have figured out new algae hybrids, and crop production techniques to increase biodiesel efficiency another 20 times. Until then, solar could be a real good channel of fuel.

  2. William says:

    Good news. Charging times under 5 minutes have been demonstrated already. It’s just a question of economy of scale.

  3. Dana Shields says:

    Why is it that in articles such as these, aquatic species for biofuels are utterly ignored. It doesn’t take much to figure out that square footage calculations for land-based crops transform into cubic feet in water.

    To my knowledge, there’s nothing that could compete with algae or plankton if we learn the simple task of harvesting it. (and for heaven’s sake, you’d assume that a 200 years after the cotton gin was invented, someone could solve a problem this simple.)

    But this aspect of the equation is always blushed over as if it weren’t even a possibility, and we blithely move on without even asking the simplest questions.

    Shame on us.

  4. Dana Shields says:

    oops. There it is. At the bottom…sometimes the answer isn’t on the surface!

  5. Duane Navarre says:

    Algae Solution:

    They just need a way to seal the track ponds to stop
    massive evaporation, and then use a solar powered
    crawler to process the algae, and return it in place.

    Scaling this across any areas in the country that are
    largely unused and have high sun profile.

    12% of the sonora desert could in theory replace all
    foreign and domestic fossil oil needs.

    It would overnight make the middle east worthless.

    If the oil companies would get onboard with this now
    they could run the operation and still make their billions
    AND not have to buy it from the middle east at all.

    Also VW has a 99 mpg diesel Lupo right now, imagine it
    as a plug in hybrid for in city slow rush hour traffic.

  6. Tom Catino says:

    They have already figured out how to convert massive amounts of CO2 into massive amounts of algae/acre & algae into massive amounts of biofuel…all inside a CO2 Bioreactor

  7. Check out the Living Algae Machine by engineer Alphonz Veszolay which we are setting up at Ecoversity in Santa Fe- a promising path for small scale production of oil, biodiesel, and protein cake. (

  8. Steve Silos says:

    The question is whether or not we choose to eradicate our life on this planet or not before the sun implodes some billion years from today.

    If we stick to the combustion engine as is we will certainly not.

    Solar energy is clearly the most rational way to go.

    We already have the technology to do so. Economics in its full contextual consideration (i.e., including the value of our environment) is no obstacle. At least we could start by installing solar energy for all households thus relaxing on the use of combustion engines when generating electric energy.

    It is consumer demand that drives all improvements. Consumer demand is influenced by knowledge. Knowledge is disseminated by society. Society delegates this function and many other collective responsibilities to its elected government who receives all the means (apparatus) to arrange for such.

    Policies are thus set by government. The question is; does the education policy set by the elected government disseminate the information, “the knowledge” about the alternative energy route to walk?

    What does government inform you about solar energy and fuel cell? Does government use all means available to create sufficient incentives to encourage society to walk the alternative energy route?

    At the end of the day it is the development of and the adherence to quality legislation (international treaties, as well as domestic laws) that determines the level of sophistication of government’s education policy.

    We have to assure ourselves whether the ones we hire after they have solicited publically for the job of taking care of collective responsibility matters truly fulfill their duties.

    By reminding everyone about the necessity to continuously fulfill the constant expanding need (demand) for relevant information c.q. knowledge, you contribute to the improvement of the dissemination of knowledge.

    What does your government inform you about solar energy and fuel cell?


Leave a Reply

You must be logged in to post a comment.