Battery pack
From Apterawiki
Since the manufacturer of Aptera's battery pack is still unannounced, details are speculative at best. The Typ-1e will have a 10 kWh (36 MJ) battery pack, most likely a Lithium Iron Phosphate battery augmented with supercapacitors.
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[edit] Quotes
"Since the Typ-1e (electric) and the Typ-1h (series plug in hybrid) have different battery needs, this may result in different battery manufacturers for the two models. The Typ-1e is designed to use a 10 kWh pack, while the Typ-1h uses a smaller pack. The cycles and DOD are different for both applications. We will announce further information regarding the battery lifespan and warranty policy well before we begin manufacturing the Typ-1 next October." – Aptera website
"Aptera is negotiating pricing and terms of supply agreements with multiple American battery manufacturers for the so-called "safe lithium" batteries that are currently the rage. "I think we could show that we could have a 10-year lifetime of a battery without any difficulty," Fambro says." – Edmunds.com, November 2007
"The two models are expected to carry different battery packs to cater for their needs (a 10 kWh pack for the electric model and a smaller pack for the hybrid). Both will use a "safe" Lithium system though details on the exact type of batteries to feature in the production models are yet to be released." – Gizmag, November 23rd, 2007
"The company also hopes to use off-the-shelf lithium phosphate batteries that are proven and safe, Fambro says." – USA Today, January 10th, 2008
"The 1500-pound Typ-1 e is an all-electric, rear-drive vehicle that uses a 10 kWh li-ion battery pack to juice the electric motor. … In addition to testing battery packs from known companies in the U.S. and one in China, Aptera has an electric motor supplier with over 14 million development miles on similar powertrains under the belt." –Popular Mechanics, May 1st, 2008
[edit] Chemistry
There are several varieties of "safe" lithium ion batteries which have relatively similar properties. They retain most of the advantages of traditional lithium-ion -- extremely efficient charge/discharge, no memory effect, low environmental impact, etc. They generally lose some energy density, dropping from ~160Wh/kg to ~100Wh/kg. In exchange, they gain power density, very long lifespans, the ability to charge very quickly, and fire resistance.
Since lithium phosphate was mentioned specifically, it is worth extra examination. First used in power tools, lithium phosphate batteries have since spread to numerous applications -- RC aircraft, robots, even the Killacycle electric motorcycle with its 0-60 time of less than one second. Lithium phosphate is one of the two competing chemistries for the Chevrolet Volt, and numerous other upcoming EVs are considering using it; it is perhaps the most well known "safe" lithium ion variant. A123 has tested their cells for over 7000 charge cycles[1] -- the equivalent of 840,000 miles in an Aptera. On RCGroups.com, an amateur, without a charger specifically designed for A123s, ran them through a thousand abusive cycles -- 3-4C charging, 6-8C discharging (he even did a set going down to 0V). To put that another way, that's charging in 15-20 minutes and discharging in a mere 8-10 minutes. After a thousand cycles, they had only lost 25% of their original capacity.[2] For a vehicle with a 120 mile range like the Aptera, that'd mean abusing your vehicle nonstop that badly for 120,000 miles.
[edit] Depth of Discharge and Available Energy
One important question about the battery pack is the amount of energy which it will actually supply. Because batteries like the ones supplied by A123 have a much longer life if not fully charged and discharged, the battery pack may not provide the number of kWh used in the nominal rating of the pack. For example, in order to ensure that the battery pack will last 10 years or 150,000 miles, GM plans to use only 8 kWh of the Chevy Volt's 16 kWh. The pack will only be charged to 80% of capacity and will cease providing power (presumably excepting emergencies) when the battery pack is discharged to 30% of its capacity.
Aptera has not provided any details about the depth of discharge (DOD) of its battery pack, but using a few known factors suggest a DOD of 50% - 60%. The known factors are that the range of the Aptera at 80 mph is approximately 70 miles, that the range is approximately 120 miles at 55 mph, and that the CdA of the Aptera is approximately .093 m².
Starting with the drag equation, which provides that the force of aerodynamic drag is equal to 1/2 (Air Density) * CdA * V², and assuming the density of air is 1.225 kg/m³, we find that at 80 mph the drag force of air on the Aptera will be 76.6 newtons and at 55 mph it will be 36.2 newtons.
The other drag force is attributable to the rolling resistance of the tires which is quantified as the Coefficient of Rolling Resistance (CRR). Assuming the Aptera will be using low rolling resistance tires, reasonable coefficients would be .01 at 80 mph and .008 at 55 mph. Plugging these into the Rolling Resistance Equation, which is Mass * RRC * Gravity, and assuming the Aptera had a mass of 800 kg when tested, the force needed to overcome tire friction would be 78.4 newtons at 80 mph and 62.72 newtons at 55 mph. (800 kg * 9.8 m/s² * .01 or .008).
The power needed to overcome the forces of aerodynamic and tire resistance drag is Force * Velocity. This means that the power required is 5683 watts at 80 mph and 2493 watts at 55 mph (155 N * 36.67 m/s and 98.92 N * 25.21 m/s). Since the energy used over an hour would be 5683 kWh or 2493 kWh, and since the distance travelled would be 132 km or 90.75 km, the energy used per kilometer would be 43.05 Wh/km at 80 mph and 27.48 Wh/km at 55 mph (5683 Wh/132 km or 2493 kWh/90.75).
The distance travelled before the battery pack reaches it's desired state of discharge is the number of kWh expended divided by the kWh used per km (kWh Expended/kWh used per mile = Distance, kWh/(kWh/km) = km). Since we know the actual distances travelled, we can calculate the number of kWh discharged by the pack by multiplying the derived kWh/km times that distance. In the 80 mph case this would be 4973 kWh (115.5 km * 43.05 kWh/km) and in the 55 mph case it would be 5441 kWh (198 km * 27.48 Wh/km).
These numbers are reasonably close but far less than the 10,000 kWh nominally available from the Aptera battery pack. While they do not take into account the drive train losses, which should run in the 10% range, they represent only about 50% to 60% of the nominal energy of the pack, suggesting that, like the Volt's, the DOD of the Aptera battery pack will be in the 50% to 60% range.
[edit] Manufacturers
A123Systems is known to have talked to Aptera.[3]
