Originally Posted by Mariss Freimanis  Why then isn't "easier" chosen if "laziness" is the reason? Sillier yet is comfortable "old ways" and learning "new stuff". Do brief review of the last 100 years.
Why not ask the question again but give it some thought before offering a reason. Maybe you'll find a problem with the question, perhaps the assumption it's "safer, cheaper and easier".
Non-renewable energy is fossil fuel and nuclear. Renewable energy is solar-cells, solar concentrators, biomass, ethanol, hydroelectric, windmills, wood-burning stoves, etc. All renewable energy is solar energy and that is a major problem. In fact it's a show-stopper for a technological civilization.
Solar energy is feeble. It is at best (noon, clear day, on the equator) 1kW per square meter. 10% of that is recoverable as usable energy so make it 100W per square meter.
Let's use it in a car. A car needs 75kW minimum at 100 kM/hr. To get that, 750 square meters of collector area is required. The collector diameter is 31 meters (about 100 feet) sitting atop your vehicle. OK, not practical.
Let's grow corn, convert it to ethanol and put it in the car. You drive 15,000 km a year, your car gets 10 km/l so you need 1,500 liters of ethanol a year. A square meter of land produces 0.3 liters of ethanol from corn a year. You need 5,000 square meters of farmland for your personal transportation needs.
That's 10,000 miles a year, 25 MPG, 400 gallons annually, 300 gallons ethanol per acre or 1.3 acres of corn. That's a lot of corn.
Solar energy conversion efficiency for ethanol is a not so hot 0.1%. A square meter receives 8 X 10^9 Joules of solar energy a year. A square meter produces 0.3 liters of ethanol a year whose energy content is 7 X 10^6 Joules.
The bigger picture. US per capita energy consumption is 4.5 X 10^11 Joules per year. Solar energy is 8 X 10^9 J / m^2 / yr. Assuming a very optimistic 5% conversion efficiency, every man, woman and child would need over 1000 square meters of solar "collector area". That's over a 1/4 acre per person of very expensive technology. Get it all from low-tech corn? Now you need 50 times more land; 50,000 m^2 or 12.5 acres per person.
Conclusion: There are no "alternative energy sources". It's oil or it's nuclear or we go back to a primitive agrarian existence.
I did the math myself. I hope I didn't slip a decimal point somewhere.
Mariss |
Hi Mariss,
The 400 gallons per year you mention. At 15 mpg that yields 6,000 miles. At 25 mpg that gives you 10,000 miles. Quite a saving, don't you think? It starts to make sense that greater efficiencies make solar more attractive. I agree it would take a lot of corn to do that. Not really practical as Geof pointed out. Biodiesel is a better and more efficient choice.
I quote: Does biodiesel take more energy to make than it gives back?
No. Biodiesel actually has the highest “energy balance” of any transportation fuel. The DOE/USDA lifecycle analysis shows for every unit of fossil energy it takes to make biodiesel, 3.2 units of energy are gained. This takes into account the planting, harvesting, fuel production and fuel transportation to the end user.
http://www.biodiesel.org/pdf_files/f...monlyAsked.PDF
I'm not sure how that corolates with your square meter analysis, I'm not sure how many acres per person would be required to produce fuel for that person. It does point out that increased efficiencies start producing results that make sense. I think that over the eons plants have developed amazing efficiencies in turning sunlight into fuel by photosynthesis. Ethanol is about a break even energy wise (takes about as much energy to produce as it provides). Biodiesel produces about 3 times as much energy as is required to make it and is much lower on pollution. When you are dealing with such small yields as we are talking about here ("a square meter of land produces 0.3 liters of ethanol from corn a year") slight increases in efficiency start producing profound results. If my logic is right then this is a three fold increase over your ethanol analysis. Again, I'm not sure just how many acres would be required to produce an amount of biodiesel that was equivalent to your ethanol.
Donna