Energy Densities (Amount of energy released when the given substance completely combusts with oxygen at standard atmospheric conditions)
Coal : 10-24 MJ/kg
Wood : 14 MJ/kg
Gasoline*: 44.2 MJ/kg (31.7 MJ/litre)
Natural gas: 53.9 MJ/kg (0.038 MJ/litre)
LNG : 53.9 MJ/kg (22 MJ/litre)
Propane : 50 MJ/kg (25 MJ/litre)
Biogas : 28 MJ/kg (7 MJ/litre)
Hydrogen : 119 MJ/kg (8.1 MJ/litre)
Lead-acid batteries : 0.125 MJ/kg
Li-Ion batteries : 0.432 MJ/kg
Alkaline batteries : 0.594 MJ/kg
* Diesel and Kerosene are within 3% of this number
Let's switch to convenient energy units i.e., 1 unit = 1 kilo watt - hour = 3.6 MJ
So a kg of coal contains roughly 6 units of energy and a litre of Gasoline contains about 8.75 units of energy.
Note that the energy density of the best possible battery is about 100 times less than that of an equivalent mass of gasoline. Of course, electrical energy conversion is much more efficient than thermal energy conversion, but this fact is only going to buy us a factor of 2. In addition to being heavy, battery electrodes are quite expensive as well. Even though things are improving, you should get a sense of what electric cars are up against.
If you assume that gasoline costs $3.50 / gallon, the price you are paying per unit of energy content comes to 11 cents. This is quite interesting because we pay around 10 cents / unit of residential electricity.
Cost / unit of energy content (at wholesale prices) :
Coal : 0.4 cents / unit
Natural gas : 1.5 cents / unit
Crude oil : 5 cents / unit
Note that so far, we've been just talking about energy content in fuels and haven't considered conversion losses. If we take everything into account and go by the wikipedia definition:
Levelized Energy Cost (LEC) is an economic assessment of the cost of the energy-generating system including all the costs over its lifetime: initial investment, operations and maintenance, cost of fuel and cost of capital, this is what we get
The chart shows cost / Mega watt - hr, so divide the last column (which is in dollars) by 1000 to get cost / unit of electricity. So according to this chart, conventional sources cost less than 10 cents / unit and land-based wind energy is competitive. Solar energy continues to be off the charts expensive even with all the recent advances.
Coal and natural gas based energy is dirt cheap and the big 3 energy consumers (USA, China and India) have enough reserves to last out this century at least as far as electricity use is concerned. Transportation fuel may be a bit more complicated with the approach of peak oil (and such), but I think gas to liquid technologies will come to the fore. Note that if more stringent emission restrictions are brought in on fossil fuels, wind energy has a good chance to be very viable and Solar can become borderline competitive.
Overall, the cost of energy continues to be amazingly low considering the fact that the best cyclist in the planet can only give you 0.3 units of energy over an hour and animal labor isn't that much different. Yes! I compared the present situation with the stone age to make you feel better!
Coal : 10-24 MJ/kg
Wood : 14 MJ/kg
Gasoline*: 44.2 MJ/kg (31.7 MJ/litre)
Natural gas: 53.9 MJ/kg (0.038 MJ/litre)
LNG : 53.9 MJ/kg (22 MJ/litre)
Propane : 50 MJ/kg (25 MJ/litre)
Biogas : 28 MJ/kg (7 MJ/litre)
Hydrogen : 119 MJ/kg (8.1 MJ/litre)
Lead-acid batteries : 0.125 MJ/kg
Li-Ion batteries : 0.432 MJ/kg
Alkaline batteries : 0.594 MJ/kg
* Diesel and Kerosene are within 3% of this number
Let's switch to convenient energy units i.e., 1 unit = 1 kilo watt - hour = 3.6 MJ
So a kg of coal contains roughly 6 units of energy and a litre of Gasoline contains about 8.75 units of energy.
Note that the energy density of the best possible battery is about 100 times less than that of an equivalent mass of gasoline. Of course, electrical energy conversion is much more efficient than thermal energy conversion, but this fact is only going to buy us a factor of 2. In addition to being heavy, battery electrodes are quite expensive as well. Even though things are improving, you should get a sense of what electric cars are up against.
If you assume that gasoline costs $3.50 / gallon, the price you are paying per unit of energy content comes to 11 cents. This is quite interesting because we pay around 10 cents / unit of residential electricity.
Cost / unit of energy content (at wholesale prices) :
Coal : 0.4 cents / unit
Natural gas : 1.5 cents / unit
Crude oil : 5 cents / unit
Note that so far, we've been just talking about energy content in fuels and haven't considered conversion losses. If we take everything into account and go by the wikipedia definition:
Levelized Energy Cost (LEC) is an economic assessment of the cost of the energy-generating system including all the costs over its lifetime: initial investment, operations and maintenance, cost of fuel and cost of capital, this is what we get
Coal and natural gas based energy is dirt cheap and the big 3 energy consumers (USA, China and India) have enough reserves to last out this century at least as far as electricity use is concerned. Transportation fuel may be a bit more complicated with the approach of peak oil (and such), but I think gas to liquid technologies will come to the fore. Note that if more stringent emission restrictions are brought in on fossil fuels, wind energy has a good chance to be very viable and Solar can become borderline competitive.
Overall, the cost of energy continues to be amazingly low considering the fact that the best cyclist in the planet can only give you 0.3 units of energy over an hour and animal labor isn't that much different. Yes! I compared the present situation with the stone age to make you feel better!
