Frequently Asked Questions
Today, there are three common battery cell formats in use as “traction” energy storage in Electric Vehicles (EVs).
1. Cylindrical Cells are slightly larger and longer than standard AA flashlight batteries. Almost 9000 of these Panasonic brand 18650 cells are used in the large battery option, Tesla Model S.
2. Pouch or Laminate Cells benefit from automated manufacturing processes and excellent heat dissipation ability, and they encase electrolyte in a durable, foil-like material. These cells are arranged into battery packs with typical examples being the Chevy Volt Plug-In Hybrid (18.4 kWh, LG Chem brand) and the All-Electric Nissan Leaf (24-30kWh, AESC brand).
3. Prismatic Cells are sizeable rectangular format cells usually having a hard case made of high-strength plastic or aluminum. These are typically used in large vehicles (trucks, buses) and for stationary grid-connected, energy storage. Each cell type has specific benefits and thus, best applications.
ADOMANI primarily utilizes Lithium Iron Phosphate (LiFePO4) cells also sometimes referred to as Lithium Ion cells. LiFePO4 cells are ordinary base chemistry for battery cells used for “traction” (inside vehicles) and stationary, emergency backup/energy storage applications. Individual battery cell manufacturers have proprietary and differentiating anode and cathode chemical variations to this base LiFePO4 chemistry. As a manufacturer of electric and hybrid drivetrain systems, ADOMANI is careful to maintain relationships with multiple battery cells manufactures both domestically and internationally.
BMS stands for “Battery Management System.” The BMS is a vital element of any battery pack intended for long life and full utilization. The ADOMANI BMS actively and passively manages the power levels and behavior of the individual cells within the battery packs. This system is active at all times when the vehicle is charging or in motion, and also measures temperatures within the battery pack.
ADOMANI® battery pack are carefully integrated with an advanced Battery Management System (BMS), and by default, the typical Depth of Discharge (DoD) is limited to around 80%. These precautions, along with thoughtful active and passive thermoregulation of the battery packs, the LiFePO4 chemistry is expected to deliver at least 2000 charge/discharge cycles (cycle life) before significant energy density degradation is observed.
Original Equipment Manufacturers (OEM) in the EV industry are finding a variety of creative “second life” applications for vehicles batteries including Grid-connected, stationary energy storage used for emergency backup power and Grid frequency regulation.
There are three standard EV charging hardware delineations:
- Level 1 Charger ($300+/home use) utilizes standard household 120VAC (15A) current and is best suited to EV’s with small battery packs, plug-in hybrids or occasional use, EV drivers. It can take 17+ hours to fully charge a Nissan Leaf’s 24kWh battery pack (1.4kW onboard charger).
- Level 2 Chargers ($600+/home use, $3000+/commercial use) utilize 208-240VAC (30-70A) circuits. The range of power that can be transferred to an EV from a public access Level 2 charger is often limited to 6.6 kW (from a 19.2kW maximum), and at this rate, the Leaf would take 3.5 hours (6.6 kW onboard charger) to charge from an “empty” state fully. Level 1 and 2 charging equipment has a standard connector and receptacle based on the SAE J1772 standard developed by SAE International.
- DC Fast Chargers, sometimes also called Level 3 chargers ($6,500-$50,000 commercial use) utilize 208-600 VAC for charging rates of up to 100kW. With the appropriate onboard charger and receptacle (such as CHAdeMO), the Leaf could charge in under 30 minutes. The Tesla Supercharger Network is another, proprietary example of this high-level charging system.
It’s important to realize that charging times for particular vehicles are dependent on several factors. The amount of power the stationary (home or commercial) charging equipment, often called the Electric Vehicle Supply Equipment (EVSE) can transfer from the building’s electrical system (and ultimately from the Utility Grid) to the vehicle, is the first limiting factor. The onboard charging system of the vehicle has its own upper limits and the vehicle’s current State of Charge (SoC) directly relates to total charge time.
For example, often you are only charging your electric vehicle from a partially depleted level not from “empty.” The battery pack’s chemistry and specifically it’s C-Rating (essentially a measure of how quickly energy can be charged/discharged to/from a cell) is another primary consideration. Large, LiFePO4 batteries often have a rating of 0.5C to 1.5C.
Yes, along with a significantly higher price (2-3 times that of LiFePO4) there are alternative chemistries such as Lithium Titanate Oxide (LTO) cells that have a much higher C-rating and therefore, much faster charging times. For example, a large transit style bus with LTO battery packs could fully charge in 20 minutes.
Ultra (or Super) Capacitors are another energy storage device similar to batteries, but they currently have a lower energy density, (energy stored per unit of area) making the energy storage packs needed to move a large vehicle a significant distance too large.
ADOMANI zero-emission electric and hybrid drivetrains/vehicles are typically built to utilize standard Level 1 and Level 2 charging systems. As an option, a higher level of charging is available to fleet customers.
Onsite renewable energy generation (photovoltaic panels, wind turbines, and hydroelectric) and stationary battery packs to store both renewable energy, and Grid energy (at times of lowest cost) that is then used to charge an EV fleet, have real advantages. The stationary energy storage could allow for modest electric energy cost arbitrage and the avoidance of Utility Provider “demand fees” that can hit EV fleet operators when numerous vehicles are charged simultaneously, and at peak power demand hours.
ADOMANI realizes EV’s are merely the portable component of a larger grid-integrated system that may eventually bring the possibility of financial returns to EV fleet operators over and above the reduction of traditional fuel (diesel, gas, CNG) and maintenance costs.
Studies such as, “A cost-benefit analysis of a V2G-capable electric school bus compared to a traditional diesel school bus” by Lance Noel and Regina McCormack of the University of Delaware, point out there are ancillary utility markets the owners of EV fleet vehicles may be able to tap and monetize. These Vehicle-To-Grid (V2G) related markets are a growing area of keen interest in the EV industry. Participation could be through Utility Provider power services auctions and could include: forward reserve, frequency regulation, voltage support, and black-start services.
One should also realize that there are studies that come to the opposite conclusion and argue that grid-connected vehicle projects are not financially feasible beyond the already attractive non-grid connected cost benefits they already provide.
ADOMANI® believes that at an initial level, larger fleet vehicles (buses/trucks) can provide a meaningfully large source of mobile stored electrical power that could be relocated and utilized in emergency situations, like natural disasters.
School bus fleets represent an excellent platform that local, State and Federal agencies could utilize in a variety of emergency scenarios especially those weather-related, that occur regularly often with some notice.