Biomass Photovoltaics More Efficient and Economical than Ethanol

Published on January 18th, 2013 | by Joshua S Hill


Are Photovoltaics Or Biofuels Better At Energy Conversion?

January 18th, 2013 by  

Editor’s Update: I’ve added an extensive reader comment to bottom of this post.

“The energy source for biofuels is the sun, through photosynthesis. The energy source for solar power is also the sun. Which is better?”

This is the question posed by University of California – Santa Barbara Bren School of Environmental Science & Management Professor and life cycle assessments (LCA) expert Roland Geyer.

The premise is simple: in 2005 the US saw corn ethanol as the new wave of powering vehicles while doing the environment and the local economy a wealth of good. Subsequently, 4 billion gallons of renewable fuel were added to the gasoline supply in 2006, which rose to 4.7 billion gallons in 2007 and 7.5 billion in 2012.

Photovoltaics More Efficient and Economical than EthanolProblem is, ethanol isn’t all that great!

Life cycle assessments have shown that corn ethanol has little to no effect on reducing carbon dioxide emissions and may in fact increase them. On top of that, the farmland needed to grow all that corn is encroaching on natural habitats. Considering that in 2010 fuel ethanol consumed 40% of the US corn stocks, and the US is also responsible for 40% of the world’s corn supplies, corn prices have skyrocketed.

Since 2005, we’ve seen the battery electric vehicle (BEV) increase in popularity and efficiency, but charging an electric vehicle from fossil fuels doesn’t make a lot of sense (even though doing so is still much better for the environment than using petrol/gasoline). It would be ideal if we could charge our electric cars using renewable sources, like solar.

Here is where Geyer — and former BrenSchool researcher David Stoms and James Kallaos, of the Norwegian University of Science and Technology — re-enter the picture. They wanted to find out what would be better; corn grown from the sun turned into fuel or electric vehicles charged by the sun.

Even the laxest of CleanTechnica readers would be able to make an educated guess at the result.

According to the research, published in the journal Environmental Science & Technology, photovoltaics is a much more efficient option than biomass.

“PV is orders of magnitude more efficient than biofuels pathways in terms of land use – 30, 50, even 200 times more efficient – depending on the specific crop and local conditions,” says Geyer. “You get the same amount of energy using much less land, and PV doesn’t require farm land.”

And when you include recent WWF research that shows that land used for solar panels is being significantly underused, the biomass option seems absurdly outdated.

Geyer and his colleagues set about examining three ways in which sunlight is able to power cars:

  • convert corn or other plants to ethanol
  • convert energy crops into electricity for BEVs rather than producing ethanol
  • using photovoltaics to convert sunlight directly into electricity for BEVs

They then examined five prominent “sun-to-wheels” energy conversion pathways for every county in the contiguous US. These included:

  • ethanol from corn 
  • ethanol from switchgrass
  • electricity from corn
  • electricity from switchgrass
  • photovoltaic electricity 

By focusing the life cycle assessment on three key impacts of electricity generation — direct land use, life cycle greenhouse gas emissions, and fossil fuel requirements — they found that photovoltaic electricity for battery electric vehicles was easily the best option.

“Even the most efficient biomass-based pathway… requires 29 times more land than the PV-based alternative in the same locations,” the authors write. “PV BEV systems also have the lowest life-cycle GHG emissions throughout the U.S. and the lowest fossil fuel inputs, except in locations that have very high hypothetical switchgrass yields of 16 or more tons per hectare.”

What does this mean for the future? “What it says to me is that by continuing to throw money into biofuels, we’re barking up the wrong tree,” Geyer explains.

“That’s because of a fundamental constraint, which is the relative inefficiency of photosynthesis. And we can’t say that right now, biofuels aren’t so great but they’ll be better in five years. That fundamental problem for biofuels will not go away, while solar EVs will just continue to get more efficient and cheaper. If they’re already looking better than biofuels, in five years the gap will be even greater. A search for a silver bullet is under way through ‘synthetic photosynthesis,’ but using genetic engineering to improve the efficiency of photosynthesis is a pipe dream. If there is a silver bullet in energy, I think it’s solar power.”

Taking into account the previously mentioned WWF report — which detailed the fact that if 100% of the planet’s electricity was generated by solar farms the total land use would only amount to less than 1% — Geyer’s faith in photovoltaics is well held.

Putting aside for a moment the tremendous cost currently invested in developing and growing ethanol fuel crops, the other uses to which those funds (and crops) could be put to use, and the unsure science of “clean ethanol,” the reality is that photovoltaic power is turning out to be a more financially and economically efficient option.

Featured Reader Comment:

Hello Zach:  I’ve been a faithful reader of your great newsletter for several years.  I must admit you have provided me with a great education in the science and technology of renewable energy.  Now, I have to challenge your article published in today’s newsletter.  There are some basic inaccuracies in that article which are in need of clarification. 
1.  40% of the U.S corn crop may be used to produce corn ethanol but that does not CONSUME the corn.  Fermentation of the corn and production of ethanol yields distillers dried grains [DDG’s] as a byproduct of the process.  DDGs are used to feed livestock and produce food for the American public. This foodstuff for livestock (DDGs) replaces the equivalent amount of raw corn which would have been used for the same purpose.  So, the production of corn ethanol does NOT consume the corn–only the starch in the corn kernel–and the remaining protein is harvested and utilized as a high protein animal feed.  This is not to say that production of corn by current farming practices does not have adverse environmental impacts (i.e.: Runoff of Nitrate contaminated water from corn fields, and contamination of groundwater from over fertilization of cornfields).  That’s another issue for another forum of discussion.

2. Harvesting of algae for the production of biofuels may very well tip the scales in favor of biological efficiency.  Currently billions of gallons of treated wastewater are discharged into U.S. waterways laden with excessive Nitrogen and Phosphorus 
These nutrients could be utilized to grow algal biofuels instead of polluting our streams and lakes and causing noxious algae blooms and resultant fish kills.  Production of algal biofuels is a technology in it’s infancy.  Give it a few years and see how it competes with P-V production of electricity to chage our electric vehicle batteries.

So in summary I’m saying lets compare apples to apples.  Or better yet, let’s compare Jonathan apples to Jonathan apples (and not Red Delicious apples).

Your loyal reader 

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

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About the Author

I'm a Christian, a nerd, a geek, and I believe that we're pretty quickly directing planet-Earth into hell in a handbasket! I also write for Fantasy Book Review (, and can be found writing articles for a variety of other sites. Check me out at for more.

  • Bob_Wallace

    “PV is orders of magnitude more efficient than biofuels pathways in terms of land use – 30, 50, even 200 times more efficient – depending on the specific crop and local conditions,” says Geyer. “You get the same amount of energy using much less land, and PV doesn’t require farm land.”

    That’s only “one” of the “one-two punch” that knocks biofuel out of a major role in future ground transportation.

    Burn biofuel in an internal combustion engine and roughly 80% of the energy is lost, never gets used to turn the wheels.

    Use PV electricity in an EV and only 10% of the energy is lost.

    • Wow, that is another huge one that doesn’t get much attention.

  • visualeyes

    The one point no one EVER brings up with biofuels is that they give nothing back to the land. Corn eats topsoil at outrageous rates. At least PV panels give shade which will reduce moisture loss in the land they cover. I am concerned with the source of metals in PV, however, I still don’t see PV contributing to famine as biofuels are poised to do.

    • Bob_Wallace

      Most of the metal in solar panels is aluminum for the frame. Very abundant.
      Other metals are used in very small amounts and all the metals can be recovered during recycling.

      You’re right about some of the biofuel feedstocks. Stripping fields of crop “waste” will reduce the organic matter in soil making it necessary to use more fertilizer and increasing topsoil loss.

      The exceptions are some perennial plants such as switchgrass. Switchgrass, in particular, has an extensive root system and over years improves the soil by increasing the organic content of the soil It also sequesters carbon.

      Another biofuel feedstock which might actually help the soil is rapeseed/canola or other mustard plants which can be grown in between crops of wheat when the soil would normally be left bare. A inter-crop cover can protect the soil. If the seed are harvested and the stems disked back in there should be an improvement in the soil.

      • Thanks for that note on rapeseed. Tons of that stuff in Poland (beautiful yellow fields in the summer). Have always wondered about how ‘green’ it is, but haven’t gotten around to looking into it.

  • anderlan

    You look at the raw physics of this, PV conversion versus photosynthesis, and it’s a no-brainer. You don’t have to go into the details, unless you just want to be super duper duper sure and expository about it.
    It’s kind of like the raw physics of CO2 concentration increase. We don’t really need ice cores and hockey sticks. Politicians asked for them so they would be super duper duper sure they didn’t have to decimate their donor industry. There’s no debate.

  • Bob_Wallace

    This is from a piece that NPR did on biofuels a couple of days ago…

    “If you were to take every gram of crops produced anywhere in the world for all purposes — and that includes every grape, every ton of wheat, every ton of soybeans and corn — and you were to use that for biofuels and essentially stop eating, those crops would produce about 14 percent of world energy,” says Timothy Searchinger, an associate research scholar at Princeton University.

    G. Philip Robertson and colleagues at Michigan State University’s Kellogg Biological Station have been looking at plants that don’t require farm fields.

    “First, we discovered that the grasses and flowers that take over fields once you stop farming produce a fair amount of biomass, especially if you provide them a little bit of fertilizer,” Robertson says.

    Robertson and his colleagues surveyed the Midwest acre by acre and identified 27 million acres of marginal farmland where these plants could grow, and where the acreage falls into a compact enough area that someone might want to build a refinery to produce biofuels.

    They figured that it would become too expensive to transport this heavy and bulky plant material more than 50 miles, from field to refinery.

    “At the end of the day, we discovered we could produce enough biomass to supply 30 or so of these potential biorefineries,” Robertson says.

    The 27 million acres identified in the latest study would provide less than 0.5 percent of (US) national energy demand,

  • Bob_Wallace

    “if 100% of the planet’s electricity was generated by solar farms the total land use would only amount to less than 1%”

    Obviously few, if any, parts of the world would go 100% solar. A mix of inputs lowers the cost of storage. Solar might end up contributing 25% to 40% of the total supply.

    We could put that amount of solar on rooftops, over parking lots and landfills and shade parts of highways where drivers encounter stop and go traffic. We probably need to use zero farmland for solar.

    • anderlan

      Right on.
      0.2%: Land area that can power humanity (2008 levels) with current solar technology.
      0.4%: Land area covered by impervious structures.

    • Alan

      I see farms as a big part of the energy solution. We can grow biomass for fuel, grow food, and put up solar panels or wind turbines to produce energy. Basically a one stop place for every type of energy (grid, transportation/fuel, and food energy)

    • Bannor99

      That’s pretty much what I’ve been saying for years.
      When I look at the number of parking lots and malls or big box stores that have been built in the 30 yrs since I became interested in sustainable living, it’s obvious that we have lots of places to install solar that are already connected to the grid.

      • Bob_Wallace

        I think we’re going to see a huge increase in rooftop/parking lot solar happening over the next couple of years. The price has become very sweet and installation companies are starting to mature.

  • wattleberry

    I hope they didn’t spend too much on confirming the bleedin’ obvious which is that, at the beginning of a new technology, there is always, in the face of perceived risk from it, a ‘flight to safety’ in clinging on to the old for as long as possible to minimise that risk. Just a manifestation of our instinctive resistance to change which often serves us well and, in this instance, at least allows an orderly transition by addressing emissions with a minimum of delay.

  • Alan

    This article does make a valid point. But we should also look at how resource intensive making a car full of batteries is, as well as making PVs to power it. I know battery technology and PV technology are advancing, but I don’t buy into the single solution energy approach. We need to utilize all kinds of renewable energy: wind, solar, solar thermal, etc.

    A lot of work needs to be done on advancing not only battery technology and reducing their weight, but also in making them recyclable. PVs need to be made more efficient as well, and like batteries, should be made with more abundant resources. Advanced biofuels are a big part of the green transportation solution in my opinion. I’m not a fan of using food for fuel though. Thankfully there are plenty of other options popping up.

    • anderlan

      I agree batteries should be examined. However, I’m going to ballpark guess that PV is still an order of magnitude better, even including the effects of its storage medium.

      I will say that woody waste streams, including responsibly harvesting good old kindling, could be better exploited.

    • Bob_Wallace

      Not car batteries, but grid storage batteries.

      Aquion is now shipping. They make a sodium-ion battery that is made of inexpensive materials and 100% recyclable.

      I believe their target price is $300/kWh and they’ve been proven out at >5,000 100% DoD cycles by independent lab testing.

      At $300/kWh and 10k cycles they will be selling $0.03/kWh storage.

      Nighttime wind at 5 cents or less stored for 3 cents and with some loss and overhead yields stored electricity at less than 10 cents/kWh.

      Feed the grid a mixture of solar (10 cents) and wind (5 cents) and fill in with stored wind (10 cents) and we’ve hit affordable renewable. By the time you add in distribution and profits the price might be a few cents higher than the current US 12 cent average. That extra can be largely offset with efficiency.

      Initially wind/solar/storage will largely offset expensive peaking power. That will bring the cost of electricity down as it is doing now in Germany. If we improve efficiency during this phase then we may never feel pain.

      Prices will fall. Solar is on its way to 5 cents. Wind on its way to 3.

      Aquion thinks they can increase cycle life to 20,000 and drop price below $200/kWh. That would make storage less than 1 cent.

      • Alan

        I was talking more about transportation specifically. Biofuel doesn’t seem like much of a contributor to grid energy, but a solution to getting us off fossil fuels without being so resource intensive. Having said that, I agree with everything you say. We need a smarter grid with great storage capacity (batteries) and a variety of renewable sources.

        • Bob_Wallace

          Yeah, I knew that. I just couldn’t help myself…. ;o)

          Biofuel is going to be only a niche player. We might need it for airplane fuel, and hopefully we can get what we need from algae. Other sources of biofuel just don’t seem to be adequate to supply very much.

          I’m fairly certain we’ll get some good EV batteries in the next few years and biofuels for ground transportation will just not be needed. Electrovaya has started shipping batteries that have about 2x the capacity of the LEAF batteries. That would get us fairly close to the magic 200 mile range.

      • Bannor99

        I took a look at Aquion’s downloadable presentation and it seems the energy density of this battery is very low – barely 30 Wh / liter so perhaps 30% that of lead-acid.

        So it’ll have to win on cheaper and more reliable.

        • Bob_Wallace

          That’s where it wins. Energy density is less important for grid storage. Batteries can be packaged in “shipping containers” and stacked high. Cheap to house.

          If they can hit their targets, <$200/kWh and 20,000 cycles, then they would be providing $0.01/kWh storage. At this point in time anything less than $0.05/kWh would be a winner. It would make a ~100% wind/solar/geothermal/hydro/tidal grid affordable.

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