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Energy density

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[edit] Energy Density

[edit] Fuel Volumetric and Gravimetric Energy Density compared

[edit] Or neglected Real-world physics

Please post or send in (to inform@xtronics.com ) any other densities you are familiar with to add to this page.

[edit] Energy Density sorted by Wh/l

Material Volumetric Gravimetric Deep cycle life

Number of cycles
Until battery has 66% capacity

80% Cycle life

Number of 80% cycles
Until battery has 66% capacity

Approx cost Per

total kWh delivered
over the deep
cycle life of battery
or cost of fuel

Fission of U-235 4.7x1012 Wh/l 2.5x1010 Wh/kg
Boron 38,278 Wh/l 16361 Wh/kg
JP10 (dicyclopentadiene) 10,975 Wh/l 11,694
Diesel 10,942 Wh/l 13,762 Wh/kg
Gasoline 9,700 Wh/l 12,200 Wh/kg $0.0814/kwh 11-2007
Black Coal solid =>CO2 9444 Wh/l 6667 Wh/kg
LNG 7,216 Wh/l 12,100 Wh/kg
Propane (liquid) 7,050 +/-450 Wh/l 13,900 Wh/kg
Methane 6,400 Wh/l 15,400 Wh/kg
Black Coal Bulk =>CO2 6278 Wh/l 6667 Wh/kg
Ethanol 6,100 Wh/l 7,850 Wh/kg
hydrazine (Mono-propellant) 5,426 Wh/l 5,373 Wh/kg
Thermite Fe2O3(s) + 2Al(s) -> Al2O3(s) + 2Fe(s)
(mono fuel)
5,114 Wh/l 1,111 Wh/kg
Methanol 4,600 Wh/l 6,400 Wh/kg
Ammonia 4,325 Wh/l 4,318 Wh/kg
Sodium Borohydride

Theoretical Hydrogen battery
real is about 40% efficient

7,314 Wh/l theoretical

2,925 Wh/l real

7,100 Wh/kg theoretical

2,840 Wh/kg real

Liquid H2 2,600 Wh/l 39,000† Wh/kg
Hydrogen Peroxide 100%

(mono-propellant rocket fuel)
Often used at 30% or 90% and
correspondingly less dense.
when used, not all decomposes
consider this a maximum

1,187 Wh/l 813 Wh/kg
LiFePO4 970 Wh/l 439 Wh/kg 1000 ? method not specified..
Wood

Varies with
type of wood and
moisture content

700 +/-200 Wh/l 3154 +/-1554 Wh/kg
Silver Oxide 500 Wh/l 130 Wh/kg
150 Bar H2 405 Wh/l 39,000 † Wh/kg
Secondary Lithium - ion Polymer 300 Wh/l ?? 130 - 1200 Wh/kg
Secondary Lithium-Ion 300 Wh/l 110 Wh/kg
Primary Zinc-Air 240 Wh/l
1000Wh/l ??Best?
300 Wh/kg
440Wh/kg>
Dry ice sublimation 248 Wh/l 159 Wh/kg
Primary Lithium Sulfur Dioxide 190 Wh/l 170 Wh/kg
Nickel Metal Hydride

(not discounted for
high discharge rates)

100 Wh/l 60 Wh/kg
Wood pellets

(pelletizing energy subtracted?)

100 †† Wh/l
4,700 Wh/kg
Flywheel 210 Wh/l 120 Wh/kg
Ice to water 92.6 Wh/l 92.6 Wh/kg
Liquid N2 68 Wh/l 55 Wh/kg
Lead Acid Battery 40 Wh/l 25 Wh/kg 300 $1.58/kWh
Propane (Gas - 1 bar) 28.1 Wh/l 13,900 Wh/kg
Compressed Air 17 Wh/l 34 Wh/kg
STP H2 2.7 Wh/l 39,000 † Wh/kg
Boost cap 1.72 Wh/l 2.98 Wh/kg

† = without container Some numbers from Don Lancaster

†† - seems low?

††† Types of coal vary widely - coal => CO2 4816 - 8722 Wh/kg

Let's see.. Maybe gasoline is the fuel of choice ... because of it's volumetric energy density? And liquid hydrogen makes good rocket fuel because of its gravimetric energy density?

Reality: a gallon of Gasoline has more hydrogen than a gallon of liquid hydrogen - in other words gasoline is a great way to store hydrogen fuel. The only economic source of hydrogen at this time is oil anyway. You could write your congressman to change the laws of physics. Often, reality doesn't fit our emotional wants and desires, but reality can be a stubborn thing to deal with - it doesn't go away when you quit believing in it.

The numbers compiled here varied a bit - the definitions of gasoline and diesel are not precise; Gasoline and diesel fuel are a mixture of about 100 different molecules who's ratios vary from batch to batch. Diesel fuel should be very similar to gasoline. Diesel is preferred for trucks due to torque/rpm curves. A turbine should have about the best hydrocarbon economy - BUT it must be run in a very narrow range to achieve that and has a very slow ramp up making it uneconomical for cars and trucks.

[edit] Battery calculation that gets ignored

(We call this arm waving of 'venture vultures'1 -- note that venture vultures can't really fly no mater how hard they flap their arms)

On rechargeable batteries there is a cycle life time - often 100 - 400 (some claims of 1000 - but with hugely derated use). If you take the capacity of the battery times the number of cycles you get a total energy out over the life time of the battery. This then can be used to calculate a Wh/cost so it can be compared to primary fuels - such as gasoline. Even ignoring the cost of the energy required to recharge these batteries, the costs are not in the ball park for vehicular use.

Besides The best of lithium batteries are 36 TIMES larger than gasoline. Standard lead acid batteries are 200 times larger AND heavier.

[edit] Some Fuels that don't work

[edit] Bio Fuel

Very limited supply of used cooking oil - Moving from food crops to fuel will cause starvation and produce a lot of pollution. Recently(2007), the University of Wisconsin in Madison has come up with a way to convert sugar to a fuel (2,5-dimethylfuran (DMF)) with 40% more energy density than ethanol which would put it on par with gasoline. possible solution?.

[edit] Solar Cells

As of today (2007), it takes about 20 years of constant use to get the energy used in manufacturing back out of a solar generating SYSTEM [1] [2] - if the life span of solar cells last that long. Perhaps lower energy manufacturing methods will one day be figured out - they would have to be a magnitude or two improved to make these practical.

See discussion on talk page

As progress has been made that is supposed to be approaching $1/Watt (tell me where I can actually buy them at that price) I have decided to add a bit here to the topic. Such a panel has a peak output of 1 Watt - at high noon with panel pointed just so - such a panel in the real world will supply 4-5Wh/day -- that's right - not 12 - not 8 only 4 or so and note the unit is Wh not the kWh that you can buy for a dime or so and even less if in the form of natural gas for heat.

Now of course this fails to add the cost of the inverter, superstructure etc - AND the energy required to produce the support equipment. Power off the poll national average for a kWH for is $0.092 - so a years worth of operation (IF time of demand matched generation time) would generate some what less than 2kWh - or $.184 worth of power. dividing that dollar by $0.16 tells me it is about 5.4 years to break even while bending the numbers to the PV side and ignoring the fact that power generated when not needed is useless (don't start up about batteries - all that will say is you haven't done any of your homework). Now if you can buy a PV for $0.10/Watt perhaps it will be time to run the numbers again...

Taking money from the little people to subsidize PV so people can feel good about being green is totally immoral.

2013 - well the dollar has lost about 1/2 it's value so the new price to break even is about $0.20/watt - (Lancaster had said $0.25/Watt so lets say that in 2013 dollars someplace between $0.20 and $0.50 per watt ). This is starting to get interesting as one can actually buy panels at $1/watt on ebay. I would assume that $1/watt panels cost about $2/watt installed - but one can see that if the trends continue that solar cells might start to make sense for home power - say 2015? The only question is if the current price is a result of the technology or Chinese subsidies? Will the price go back up?

[edit] Hydrogen

Embrittles its container (explodes pores in metals - forms brittle hydrates) is one of the most dangerous gases to handle - explosive from 4 - 75% concentration. You would have to store vehicles outside - no tunnel use etc. Besides the most economical way to produce hydrogen is from oil - Best way to store hydrogen is as gasoline - as there is more hydrogen in a gallon of Gasoline than in a gallon of liquid hydrogen. In any article you read about hydrogen, it is a good idea to replace the words "hydrogen economy" with "boondoggle" to get a clearer meaning. We have moved some comments to the discussion area as it appears that some people think we will find a new 'brand' of hydrogen that is safer. NASA Hydrogen handling doc

There is a good and safe way to store hydrogen - start out with a chain of carbon and attach the hydrogen to this chain - as a liquid this will be hold more hydrogen than liquid hydrogen. This liquid could be distributed to underground tanks and pumped directly into a vehicles fuel tank. This liquid is called gasoline.

[edit] Batteries

No one talks about battery wear out - energy density goes down as the batteries wear out. Manufacturing exotic batteries causes more pollution than they could possibly prevent. Energy density is still 2 magnitudes from practical compared to Gasoline used in an ICE(Internal combustion Engine).

There is also the issue of battery efficiency. Energy efficiency is calculated on the amount of power used from the battery while discharging divided by the amount of power delivered to the batter while charging, multiplied by 100 to yield percent. Pout x 100 /Pin . A lead-acid battery has an efficiency of only 75-85%. The energy lost appears as heat and warms the battery. Keeping the charge and discharge rate of a battery low, helps keep a battery cool and improves the battery life.

The above losses don't include losses in the charging circuit which may have an efficiency of anywhere from 60% to 80% - thus the overall- total efficiency is the product of these efficiencies and ends up being 45 to 68%. (To further this example and to show why physics and not some corporate conspiracy is the reason we don't have electric cars - suppose the controls and motors on a car were 85% - the over all efficiency is now only 38 - 58%. You can see that an electric car would use about twice the energy than a conventional car - not to mention the great cost of the regular replacement of batteries. This is why batteries are best used where only intermittent, or very low power use is required.)

To further explain - If the electricity is generated from a gasoline engine - and that energy is converted to electricity, and then sent through power line transformers and power lines, and then converted to DC, and then converted to chemical energy, and then converted back to electrical energy, and then converted to rotary mechanical energy - it is clear that many losses have occurred. If the same gasoline motor was providing the rotary energy directly to the drive train, it is much more efficient.

Typical battery efficiencies: the percentage of power-out of power-in.
lead-acid 80%
lithium-ion 95%
Zinc air 60%

We can also take the cycle life of a battery times its capacity to get the total power delivered over the life of the battery. We can then look at that power as a cost per kWh and compare it with other forms of power - even this ignores the cost of the power used to charge them in the first place and it is clear that at this time batteries are not cost effective for cars.

[edit] Energy carriers vs fuels

An energy carrier is not a fuel. A fuel is found as it is used and burned to release energy. An example would be petroleum or coal. Hydrogen is an energy carrier - it only occurs naturally as a burned ash - called water. If we use electrolysis to produce hydrogen and then burn it later to release the energy we are using hydrogen as an energy carrier. (Of course that would be crazy, as it is much cheaper to produce hydrogen from petroleum! Boron would be a better candidate.)

Transferring energy to an energy carrier involves losses. Thus using storage batteries, hydrogen, or boron as energy carriers for cars tends to increase the total amount of energy required - there is no energy savings by using 'electric cars'.

[edit] Deaths/KWH

One way to look at the practicality of producing energy is to look at the deaths/KWH caused by the production and transfer of the energy. Nuclear fuel is by far the safest form of energy. Windmills and Solar(PVs) are dismal failures once one adds up the death from falls off the collection structures. Deaths in mining coal are numerous.



1 Venture vultures are those folks that make a living off of of the venture capital investment of folks that didn't study math or physics.

Uranium as a fuel. approximately 4,700,000,000,000 Wh/l and 25,000,000,000 Wh/kg


Carbon => CO2 9111Wh/kg

Carbon => CO 6306Wh/kg

coal 1.346 g/cc

Anhydrous ammonia has a hydrogen density of 0.12 gm/cm^3

Need to figure the pressure of compressed air above.

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