For many years, greentech leaders have been saying renewables are never going to make a major contribution to our energy needs until we have a better method for storing off-peak clean energy. For even longer, environmentalists and national security analysts have been seeking an alternative to fossil oil for our transportation needs. WindFuels, a small company in South Carolina, believes both of these needs can be met simultaneously with a new concept to store excess intermittent clean energy in standard hydrocarbon fuels (gasoline, jet fuel, and diesel) for transportation.

Doty Windfuels has been working on a system called RFTS, or Renewable Fischer Tropsch Synthesis. The process looks to use off-peak excess wind energy to recycle CO2 into standard fuels that work seamlessly in the one billion cars and trucks on the road around the world.  The chemistry is fundamentally simple and well understood.  First, variable off-peak energy is used to electrolyze water into hydrogen and oxygen; some of the hydrogen is used to reduce CO2 into CO and H2O in a catalyzed reaction called Reverse Water Gas Shift (RWGS); the balance of the hydrogen is combined with the CO in a Fischer Tropsch reactor to form a synthetic oil -- a mixture of mostly gasoline, jet fuel, and diesel -- just like the stuff from petroleum, but with no contaminants. The co-produced oxygen from the electrolysis is a byproduct. 

Fischer Tropsch chemistry has been well understood for seven decades.  During World War II, Germany synthesized some of its fuel by combining CO and H2 (derived from coal) in an FT reactor. Today, this process is commonly referred to as coal-to-liquids, or CTL. South Africa has the longest history of FTS generation of fuels.  Unfortunately, traditional coal-to-liquids production is even more environmentally destructive than tar sands or oil-shale-based petroleum because of its enormous on-site release of CO2.  However, if the H2 is obtained from water and excess carbon-neutral energy, and the CO is derived from CO2, the fuels are carbon neutral.

There is no question that it should be possible to synthesize standard liquid fuels from CO2 and water using off-peak clean energy.  The only step that has not been commercialized is the RWGS process – reducing CO2 to CO.  The question has not been whether such a system would work, but whether it would compete with traditional petroleum derived fuels.

Our analysis concludes that if the correct paths and system design are chosen, overall system efficiency (from input electrical energy to output energy in the liquid fuels) will exceed 58 percent.  If done at a reasonable scale, the synthetic fuels could be competitive when oil is as low as $50/bbl -- and always when oil is above $95/bbl.  After the R&D phase, the equipment capital costs are expected to be low enough to be recovered in two to three years. The goal is to develop a process that will allow the world to replace the use of petroleum and tar sands with clean, competitive, carbon-neutral fuels synthesized efficiently from CO2 and off-peak clean energy.

One of the team’s recent technical papers shows that the related direct-solar-fuels processes face daunting practical barriers because of fundamental laws of thermodynamics governing equilibria in one or more of the required steps. The RFTS process, on the other hand, eliminates such bottlenecks by starting with electrical energy rather than thermal energy or photons to get the needed hydrogen.  The technology for electrolysis is mature and efficient. After the electrolysis, there are no highly endothermic reactions, so there are no reactions that are difficult to get to work.

The “windfuels” name is apt because about 99 percent of the inexpensive, clean, off-peak energy that has come on-line in the past several years in the U.S. has been wind, although nuclear energy may be the best option in some places.  A few facts here put the scalability, climate benefit, and expected competitiveness of windfuels into perspective.

Approximately 25 TWh (yes, 25 terawatt-hours) of wind energy was curtailed (idled) in the U.S. last year to keep the off-peak grid energy price from frequently going negative.  That is about equal to the energy in 700 million gallons of gasoline just being thrown away. Curtailed wind energy in the U.S. appears likely to exceed 40 TWh in 2011.

Economically recoverable wind energy potential in the U.S. exceeds 70 PWh/yr -- enough  energy to synthesize twice the current U.S. transportation fuel needs just during the off-peak hours at the efficiency expected.

Point-source CO2 emissions in the U.S. total about 4 Gt/yr -- enough to synthesize twice the current domestic transportation fuel usage -- about 0.7 Gt/yr. Windfuels are expected to be 85 percent carbon-neutral (fully burdened), while most domestic biofuels are only 5 percent to 15 percent carbon neutral when land-use change is fully considered.
Windfuels provide the potential for the U.S. to transition from the world's largest importer of oil to the world’s largest exporter of carbon-neutral transportation fuels.   

The company is working on scaling windfuels plant designs down as small as practical with acceptable efficiency and capital cost, since changes in the financial markets argue that the more likely scale-up path would be thousands of 10-megawatt plants throughout the wind corridor rather than a much smaller number of gigawatt-scale plants near large nuclear reactors.  Recent simulations are showing 45 percent efficiency at the 2-megawatt plant size, 53 percent at 20 megawatts, and 58 percent at 250 megawatts.

The strong upwards trend in the price of oil in the last two years is bringing gasoline prices back into the media spotlight.  Doty expects to be showing laboratory results by the time the public is again insisting on solutions that show real promise for competing with OPEC.

David Doty, CEO of Doty Scientific, received his PhD in physics from the University of South Carolina in 1983 and immediately founded Doty Scientific, Inc.  He has been awarded more than 30 patents for his work in nuclear magnetic resonance (NMR) technology, radio frequency technology, turbomachinery, heat transfer, and alternative fuels and has more than 70 publications, presentations, and invited talks in these and other areas.  His primary focus for the past three years has been on the development of highly optimized processes for the synthesis of standard fuels from off-peak wind energy and CO2.  

Tags: co, doty, electrolysis, energy storage, fischer–tropsch, fischer-tropsch, liquid fuels, windfuels