Biofuels' Dubious Efficiency
Frequent commenter from the U.K. Gary Tulie writes on my piece this morning concerning creating biofuels from sugar beets:
… the efficiency of photosynthesis to energy stored in biomass is at the very best in the 3 to 5% range – and that with all the dominoes stacking perfectly….Having in a very good case converted perhaps 2 to 3% of the sun’s energy into plant material, the material then has to be processed, dried, pressed, fermented, pyrolysed or whatever has to be done to turn it into fuel.
Taking into account inputs such as energy, water, fertilizer, labor, buildings and farm tracks as well as everything else needed to produce the biofuel including the embodied emissions of all these processes, and I would be surprised if anyone has used biological systems to convert more than around 1% net of the sun’s energy falling on a field into useable biofuel.
Even then, if you use the fuel in an internal combustion engine, you may well average only around 15 to 20% energy at the wheel compared to chemical energy in the fuel.
On this basis, it would appear to make more sense in terms of net emissions to install solar panels or wind turbines almost anywhere that it is possible to displace fossil fuel use in a power plant than to grow any kind of crop purely as a biofuel.
Yes, Gary, this is my point exactly. If biofuels can get a percent or so efficiency on a good day — then we pay for the planting, irrigation, fertilization, harvesting, processing, transportation and distribution — then we lose 80% in our internal combustion engines — we’re one heck of a lot better off with wind or solar. Of course, the issue is portability; energy-dense liquid fuels will remain convenient until electric transportation (batteries in particular) replaces this whole mess.
There may be rare exceptions.
Pacific island countries with a low population density and plenty of coconut trees may find it more economical to use coconut oil than to use Diesel fuel in their Diesel engines. But as a significant source of energy for large countries, I don’t see how biofuels could have a place.
Regarding vehicles, it is too soon to know what the eventual rôle of electric cars will be. It may turn out to be more practical to use an economical energy source to manufacture liquid fuels, or both approaches might coexist. In either case, more non-fossil fuel power will be required so our electricity generating capacity will have to be greatly increased even with improvements in efficiency.
The US Department of Energy (DOE), at http://www.fueleconomy.gov states the following: Electric vehicles convert about 59–62% of the electrical energy from the grid to power at the wheels—conventional gasoline vehicles only convert about 17–21% of the energy stored in gasoline to power at the wheels.
Again using DOE numbers, a typical nuke plant or a typical fossil power plant is about 30% efficient converting the thermal energy into electricity, with subsequent transmission loss of about 6.5% to distribute. An oil refinery typically refines about 50% of crude oil into gasoline at total energy cost of between 12% and 18% of refined energy used in the process (not considering transporting the crude or distributing refined products, or the energy of protection and extraction of the original resource).
This indicates not only that electric cars are an improvement over internal combustion of liquid fuels in terms of energy efficiency – even with fossil fuel electricity generation – but also that electric cars also convert the source energy from largely foreign to largely domestic, and they open sourcing to renewable energy.
Incidentally, our average use of gasoline was about 367 million gallons a day in 2011. The US imported over 4.1 billion barrels of crude oil and petroleum products in 2011 alone (DOE numbers again). That number of barrels at the Brent average 2011 price per barrel for Crude Oil, $111.26, equals total of $461 billion spent by our nation on foreign oil in 2011 alone. That’s over $52 million lost from the country every hour.
Want a comparison for that kind of money? Even with the increases in tuition year on year, each hour’s foreign oil spending would have paid entirely for 364 four-year degrees at private colleges, or 782 four-year degrees at public colleges, for the freshmen of 2010. That’s the cost of 31.8 million private degrees, or 68.5 million public degrees in one year! The drain of foreign oil on our domestic economy is quite significant.
Add to this the huge expense, in lives and dollars, of defending our nation’s access to foreign oil, and the national security implications of our dependence.
If we did nothing else but shift our transportation to electric, the benefits to our nation would be appreciable.
Actually, our present nuclear plants have lower thermal efficiency than coal burning plants and therefore require more cooling. The reason is that our present nuclear plants operate at a lower temperature and, therefore, because of the laws of thermodynamics, have reduced efficiency.
The liquid fluoride thorium reactor (LFTR) can operate at much higher temperatures, use the Brayton cycle instead of the Rankine (steam) cycle, resulting in much higher thermal efficiency. As a result, it can use air cooling instead of water cooling.
Biofuels may work as fuel for aviation if it derived from the organic portion of municipal solid waste or sewage sludge. Aviation seems to be on a relentless drive to incorporate some portion of its fuel needs with biofuel to meet EU emission requirements.
I think a better use for biomass is to make chemicals that would otherwise be derived from crude oil.
I don’t think that biofuels are a good idea for the military. The Department of Defense is the largest fuel user on the planet so scalability would be an issue. A better idea,IMO, is to build a Coal-to-Liquids (CTL) plant to be used by the military in time of national emergency.
The comparison between biofuels and solar electricity to power vehicles is not as favorable as you make it out to be.
On a well-to wheels efficiency basis, solar panels only catch 15% of the sunlight striking them, but once you account for the incomplete coverage of the field, the extra space to avoid shading, you’re probably down to 5% at best. Then there are losses in conversion to AC, transmission, and distribution, and you’re down to 3-4%. Then there are additional losses when charging ad discharging the battery, so we’re only getting 2-3% of the sunlight to our vehicle’s wheels. Sure that’s still 10x better than biofuels, but the capital costs of all those solar panels are probably much more than costs of planting, harvesting, and converting the plants into biofuel.
Which is why a lot more cars are powered by biofuel than electricity.
I think biofuel will always have a place in our transportation system, but electricity has the potential to take a lot more marketshare from fossil fuels- if only because there is so much more room to remove costs than for biofuels.
As I have posted elsewhere, solar panels to heat water can operate at greater than 50% efficiency whereas PV panels, using current technology, operate at less than 20% efficiency. Therefore, in many situations, it would make more sense to use solar power for providing domestic hot water or for space heating.
Based on a paper from Warwick University (UK) I calculated that it would require about 0.7ha (7,000sq-m or about 1.8 acres) of sugar beet to produce enough ethanol for a typical year’s motoring in the UK in a typical car.
Using CPV (33% efficient & rising) in a sunny desert it would need 2 to 3 sq-m of panels (10-12sq-m of land) to power a Tesla Roadster for the same distance, a several HUNDRED times improvement and no arable land required.
I wish I could afford a Roadster.
I rest my case.
I think your allowance for space for CPV is not generous enough. Trackers need a lot of space between them to avoid shading.
And yes, the difference comes down to what you can afford. Most people could probably afford to buy an acre of land and a car to drive on the biofuels. The cost of the fraction of an acre of land in the CPV equation is not very significant, but the batteries and the CPV trackers are another story altogether.