I was wondering what the energy density and energy/volume were of the batteries used in a Tesla compared to that of gasoline and diesel.
No one has addressed this yet so I’ll take a stab at it.
The P85D has an 85kWh lithium ion battery that weighs 1200 lbs. It has 7104 cells. The P90s introduced this summer are “range upgrades” with 90kWh batteries.
Here is a chart comparing energy densities of various battery chemistries.
I assume that “compared to that of gas and diesel” refers to the batteries in vehicles powered by those fuels.
This is one of those questions that has a simple, straightforward answer–that’s useless on its own.
As jimbuff314 points out, the 85 kWh pack has 7104 cells, so each stores 11.96 Wh. 18650 cells are about 50 g, so we get about 0.24 kWh/kg in energy density.
In comparison, gasoline is about 12.7 kWh/kg. So it’s about 53 times better. Diesel is slightly lower.
Of course, this is a misleading figure, since it ignores all the other stuff that go into building a vehicle. Right off the top you can divide that figure by roughly 3 to account for the thermodynamic inefficiencies inherent in internal combustion engines.
There is also the high efficiency of electric motors at high speed/low torque operation, potential for recovery of energy using regenerative braking, and from an operating cost standpoint, the recognition that electricity is fungible; that is, it can be generate from any supply of power from natural gas or nuclear fission to wind and solar power, which means you can (in theory) select the cheapest or most sustainable source versus a gasoline or diesel engine having to burn that fuel. (This isn’t strictly true; gasoline engines can also burn blends of ethonal and methanol with minor modifications, and diesels can burn kerosene and other liquid fuels as well as dimethyl ether, but all of those sources require intermediate refining or synthesis steps as well as physical distribution that put a lower limit on how inexpensive they could be.) As a solution for short distance commuter application or fixed-route long distance (e.g. trains) electric drive in the form of rechargable battery, hybrid-electric, or grid connected makes a lot of sense both fiscally and to accommodate future changes in energy production methods. However, for mid to long range commuter applications and variable route hauling, liquid combuation fuels of some kind will remain necessary barring some miraculous revolution in energy storage technology. The Tesla battery is about 40% of the cost of the base vehicle and has a limited life, although getting over 2000 hours of continuous service out of lithium polymer batteries–once considered impossible–is now an achieveable threshold with good designa nd power management.
However, despite Musk’s claim of cost reduction from building a battery “megafactory”, the economy of scale of litium battery manufacture is already close to being achieved and I don’t expect production costs to drop more than 15% to 20% at most. Lithium sulphur may offer slightly greater energy mass density (probably by a factor of 2) and lower constituant cost, but it still isn’t going to be light enough to be user replaceable or cheap enough to be considered a basic maintenance part like tires or starter batteries. Practical electric cars at a price range accessible to the typical commuter are likely to have a range somewhat less than 100 miles for the foreseeable future.
Stranger
Hmm. I assumed wrong. The OP did mean the energy density of those fuels. Don’t know why I didn’t see that when he plainly stated it. For some reason, I was thinking “apples/oranges”.
Thank you, Dr. Strangelove, for not skewering me when you had ample opportunity.
I don’t think that’s too out of line with what Tesla is claiming. The numbers I’ve seen claim a 30% reduction, but that’s fully integrated pack costs, and includes savings from changes in form factor, pack integration, etc. The cell-level cost reductions are probably <20%.
I reserve my skewering for factual inaccuracies :). Your information wasn’t wrong, just incomplete.
Well originally I was just trying to get a good idea of how far battery technology has progressed. I figured the batteries in the tesla P85D are some of the most advanced batteries that are in widespread use and thought it would be interesting to compare the amount of energy in a gallon of gasoline vs diesel vs (the equivalent of) tesla batteries. Both in size (volume) and weight.
I hadn’t thought of the efficiencies of ICE’s and electric motors when I made this thread, but it is interesting nonetheless. As mentioned their are literally millions of variables that can be brought up that make the comparison between an EV and traditional gasoline powered vehicle even more complicated, esp when you factor in cost as someone already did.
But keep the discussion going! It brings in new ideas and keeps things interesting.
Would appreciate the analysis of how this makes sense. Whats the return on investment for a commuter application comparison between a gasoline / battery / NG vehicle ?
(Bolding mine above). CNG performs well in this application - not sure why liquid fuels are necessary.
The cost comparison between gasoline, electric battery, and natural gas is going to depend on a number of factors, including the projected cost of fuels over the lifetime of the vehicle, but electric battery has two factors that way heavily in its favor; the aforementioned fungibility of the actual energy source to produce the electricity which charges the battery, and the reduced maintenance of all eliminating moving components of an internal combustion engine and liquid cooling/radiator system. A battery powered car will still have a suspension, may have a transmission (depending on layout), and of course all of the other maintenance items such as tires and non-powertrain fluids but its main motive systems are all electrical, which can be built to a high standard of reliability with almost negligible maintenance, the Lucas Automotive notwithstanding. Electric torque motors should last the life of the car and provide recovered cost in recycling the copper and magnets, so the major maintenance cost is the battery pack itself, which, while a big ticket item can be amortized over the entire operating life of somewhere between 5 and 8 years even with daily use.
CNG is a good fuel in fleet applications due to its low cost and easy fueling but for general commuter use and long range driving the energy mass density is just too low, and the need to carry it in large cylindrical tanks becomes a significant limitation for a form constrained vehicle such as a personal automobile to make equivalent range to a gasoline or diesel engine. Synthesized hydrocarbon fuels such as dimethyl ether, or liquid alcohol fuels such as methanol and ethanol, while offering somewhat lower mass energy density may, in optimized engine systems, give fuel economy similar to gasoline engines due to high cetane and octane ratings allowing for higher compression and better thermodynamic efficiency.
Stranger
Lithium-sulfur batteries, in theory, could have about a 10-fold increase in density. But no one lives in theory, so in practice it’ll probably be about what you say. But it makes a lot of room for incremental improvements.
Sulfur is one of the best materials to make a battery cathode from, but it has the unfortunate property that it degrades fairly quickly in use. Polysulfides, which naturally occur during use, dissolve in the electrolyte. Someone recently found a way to fix the problem by using thin sheets of manganese dioxide. It’ll probably take a while for this discovery to make it into actual batteries, though.
There are other technologies that may make superior batteries, but they’re further out and may never make it into actual production.