sugar power?
Just a dumb thought - take a product that you can either "eat" or "fuel your car", what will you do? If there's plenty of food, you have surplus to use as fuel. BUT how much surplus can you really get AND how much will it cost?
Now consider a person say need 2500 Kcal/day to live. Now contrast to a car. Say a person "needs" to drive 40 miles/day (15000/year) and gets 20 mpg. They need 2 gallons of fuel per day. How much energy does a gallon of gasoline have?
http://www.lifeaftertheoilcrash.net/Research.html Says 38,000 kcal/gallon.
So my car "needs" to eat 76,000 kcal/day, and I need to eat 2500 kcal/day. So one car = 30 people!
Of course it takes energy to convert sugar to ethanol. Let's say you can get a 3:1 energy ratio on creating ethanol; that means you get 2/3 as much ethanol energy as the original sugar. (I've heard Brazil sugar cane can offer 3:1 ratios of input to output energy, although corn ethanol is much lower.)
So enough ethanol to hold 76,000 kcal will be made from sugar containing 114,000 kcal of energy.
So my car now up to about 46 people worth of food. Of course it is "only sugar" and people can't eat just sugar.
Now how much is sugar worth? $0.11/lb! http://www.sugaronline.com/ Wow!
How much energy does a lb of sugar have? I remember - 4 kcal/g --> 1800 kcal/lb.
So at these prices I can eat 1.4lb of sugar a day and my car can eat 63lb/day or about $7.00/day for my car. Well looking back to my assumpion - 40 miles/day that's about 1.5lb of sugar per mile. Oh, and back to an equivalent of 2 gallons of gas, that's about $3.50/gallon gas equivalent.
Overall I accept these numbers are nonsense, especially about sugar to ethanol conversion efficiency. The main thing maybe is to see the idea "Driving a car one mile uses as much food energy as one person per day."
It's not so profound - cars use more energy than people - surprised? We've been able to do this because we have fossil fuels which are concentrated energy from past biological (plant) growth and partial decay. Trying to do the same thing with "live solar energy" means we want to speed things up greatly, and even if we can do it, it can't scale up to what we want to replace.
As long as fossil fuels are "feeding people", the competition between people and machines for energy is hidden, but the more we try to replace fossil fuels with biomass the more we're going to risk conflicts and perhaps risk poor countries exporting crops for fuel while their local populations have problems getting enough food. Curious questions, and I don't know the answers except to assume we'll have less freedom to travel in the future without fossil fuels.
Now consider a person say need 2500 Kcal/day to live. Now contrast to a car. Say a person "needs" to drive 40 miles/day (15000/year) and gets 20 mpg. They need 2 gallons of fuel per day. How much energy does a gallon of gasoline have?
http://www.lifeaftertheoilcrash.net/Research.html Says 38,000 kcal/gallon.
So my car "needs" to eat 76,000 kcal/day, and I need to eat 2500 kcal/day. So one car = 30 people!
Of course it takes energy to convert sugar to ethanol. Let's say you can get a 3:1 energy ratio on creating ethanol; that means you get 2/3 as much ethanol energy as the original sugar. (I've heard Brazil sugar cane can offer 3:1 ratios of input to output energy, although corn ethanol is much lower.)
So enough ethanol to hold 76,000 kcal will be made from sugar containing 114,000 kcal of energy.
So my car now up to about 46 people worth of food. Of course it is "only sugar" and people can't eat just sugar.
Now how much is sugar worth? $0.11/lb! http://www.sugaronline.com/ Wow!
How much energy does a lb of sugar have? I remember - 4 kcal/g --> 1800 kcal/lb.
So at these prices I can eat 1.4lb of sugar a day and my car can eat 63lb/day or about $7.00/day for my car. Well looking back to my assumpion - 40 miles/day that's about 1.5lb of sugar per mile. Oh, and back to an equivalent of 2 gallons of gas, that's about $3.50/gallon gas equivalent.
Overall I accept these numbers are nonsense, especially about sugar to ethanol conversion efficiency. The main thing maybe is to see the idea "Driving a car one mile uses as much food energy as one person per day."
It's not so profound - cars use more energy than people - surprised? We've been able to do this because we have fossil fuels which are concentrated energy from past biological (plant) growth and partial decay. Trying to do the same thing with "live solar energy" means we want to speed things up greatly, and even if we can do it, it can't scale up to what we want to replace.
As long as fossil fuels are "feeding people", the competition between people and machines for energy is hidden, but the more we try to replace fossil fuels with biomass the more we're going to risk conflicts and perhaps risk poor countries exporting crops for fuel while their local populations have problems getting enough food. Curious questions, and I don't know the answers except to assume we'll have less freedom to travel in the future without fossil fuels.
posted by Ares Olympus at 3:27 PM
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