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FAQs

• What is the difference between a BEV, HEV and PHEV?
• What are the important metrics and units of measure for an EV? What is the difference between a kilowatt and a kilowatt-hour?
• What are the components in a Battery Electric Vehicle?
• How much do batteries cost? How long will they last?
• How long does it take to charge a BEV?  What infrastructure do you need?  Are all chargers and charging stations the same?
• Why electric trucks? Aren’t trucks too big to be electric?
• Fuel consumption/maintenance cost comparisons between BEVs and traditional diesel vehicles

 

 

 

1. What is the difference between a BEV, HEV and PHEV?

 

BEV - or battery electric vehicle, is a type of electric vehicle (EV) that uses chemical energy stored in rechargeable battery packs. BEVs use electric motors and motor controllers instead of internal combustion engines (ICEs) for propulsion.

A battery-only electric vehicle or all-electric vehicle derives all its power from its battery packs and thus has no internal combustion engine, fuel cell, or fuel tank.

By the end of December 2011, Nissan had shipped about 10,000 all-electric Leafs. First shipments were in early 2011. By the end of December 2011, Nissan had shipped over 27,000 Leafs worldwide.

HEV - or hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle, or better performance.

More than 4.5 million hybrid electric vehicles have been sold worldwide by the end of December 2011, led by Toyota Motor Company with more than 3.5 million Lexus and Toyota hybrids, followed by Honda Motor Co., Ltd. with cumulative sales of more than 800 thousand hybrids, and Ford Motor Corporation with more than 185 thousand hybrids sold in the United States by December 2011.

PHEV – or plug-in hybrid electric vehicle (PHEV), plug-in hybrid vehicle (PHV), or plug-in hybrid is a hybrid vehicle which utilizes rechargeable batteries, that can be restored to full charge by connecting a plug to an external electric power source (usually a normal electric wall socket). A PHEV shares the characteristics of both a conventional hybrid electric vehicle, having an electric motor and an internal combustion engine (ICE); and of an all-electric vehicle, having a plug to connect to the electrical grid. Most PHEVs on the road today are passenger cars, but there are also PHEV versions of commercial vehicles and vans, utility trucks, buses, trains, motorcycles, scooters, and military vehicles.

The most popular PHEV to date is the Chevy Volt which has shipped 6,400 cars till end 2011.  BYD has shipped about 1000 F3DMs in China since 2008. (source Wikipedia)

 

2. What are the important metrics and units of measure for an EV? What is the difference between a kilowatt and a kilowatt-hour?

 

Three quantities are measured for vehicles – power, energy, and efficiency.

 

Power.  In conventional vehicles, we are used to seeing engine horsepower.  Usually, BEV’s measure power in kilowatts (kW) instead of horsepower (HP).  One kW is equal to 1.34 HP.

 

Energy.  In conventional vehicles, we rarely discuss energy, except in a brief mention of how much fuel the fuel tank holds.  However, for BEVs, energy may be the most important metric to consider.  A kilowatt-hour is a unit of energy.  One kWh is an amount of energy equal to supplying one kW of power for one hour, continuously.  So, a battery that has 10 kWh could supply 1 kW of power for 10 hours, or it could supply 5 kW of power for 2 hours.

Note that the cost of a conventional vehicle is driven by power; you pay for the bigger engine, and can drive as far as you want.  The cost of a BEV is driven by energy – you pay for more range, and the motor power is less consequential to your driving experience.  As such, this makes energy a much more important metric for BEVs than people may be used to with conventional vehicles.

Efficiency.  In conventional vehicles, efficiency may be measured in miles per gallon (MPG).  There is an implicit assumption here that one gallon of fuel holds a certain amount of energy, and the efficiency is measured by how many miles the vehicles can go using the energy in one gallon of fuel.  In a BEV, efficiency may be measured as kWh per mile.  This measurement is the inverse – it is a measure of how much energy it takes to drive the vehicle one mile, with energy measured in kWh.  While both of these measure efficiency, note there is an inversion.  For conventional cars, higher MPG is better.  For BEVs, lower kWh/mile is better.

 

3. What are the components in a Battery Electric Vehicle?

 

In a BEV, most of the vehicle is the same as a traditional vehicle. Typically, the same chassis and body can be used. The powertrain is what is different. The powertrain is that portion of the vehicle responsible for making it move – everything from the gas and brake pedals through the wheels. The powertrain of a traditional vehicle includes the engine, transmission, fuel and exhaust systems, driveline, and axles. The powertrain for a BEV includes the traction motor and associated power electronics, battery, battery controls, charging system, and axles. Note that the BEV powertrain has very few moving parts compared to a traditional powertrain. Also note the complexity shift between the two powertrains – in a conventional vehicle, the complexity is all mechanical. In a BEV, the complexity is in the unseen software.

 

4. How much do batteries cost? How long will they last?

 

Batteries are the most expensive components in BEVs. Their cost and lifetime are a complex topic that is the focus of many consumers and fleets looking at going electric.

The US Department of Energy expects battery costs to be $300/kWh in 2014. However, this single point estimate can be misleading.  The price of batteries varies widely, and just like other products, you get what you pay for.

The battery can be divided into three cost drivers: cells, packaging, and battery management system (BMS). For a reliable, long-lasting battery, all three of these important design elements must be carefully designed and tested. In today’s battery designs, typically 50% of the battery cost goes into packaging and the BMS. Excellent battery cells that are not safely packaged or do not have a BMS calibrated and tested for use with those cells will not last a long time.

Today, batteries cost $600/kWh to $1000/kWh. Battery cells can be found for ½ of that price, but they lack proper packaging and BMS. The lifetime of batteries, when used according to manufacturer’s recommendations (primarily controlling the internal temperature of the cell) is 5 to 10 years – plenty of time to pay back their high initial costs through fuel savings.

 

5. How long does it take to charge a BEV? What infrastructure do you need? Are all chargers and charging stations the same?

 

Most BEVs today are smaller vehicles and charge using a standard developed by the Society of Automotive Engineers (SAE) known as SAE J1772, Level 2. Level 1 also exists, but is too slow for most cars because it uses standard wall outlet voltage, 120 VAC. SAE J1772 Level 2 is a charging standard that uses split-phase 240 VAC. Split-phase 240 VAC is a voltage found in most homes. It is used for electric stoves and for electric dryers. The higher the voltage, the faster the BEV can charge.

For larger BEVs, such as electric trucks, there is not yet an appropriate charging standard. Most of these larger BEVs can charge from SAE J1772 Level 2, but charge times may be long.

Emerging standards for high-power charging are at higher voltages. Motiv is committed to being compatible with these emerging standards and has representation on the relevant SAE committees. The typical voltages available in the U.S. above split-phase 240 VAC is 208 VAC three-phase, 440 VAC three-phase, and 600 VAC three-phase. Three-phase power is preferable for high-power chargers. The other emerging idea for high-power chargers is using DC power. DC power has advantages, but there is no installed DC power infrastructure, so DC power would need to be rectified from three-phase AC power at the charger, essentially providing the same service as a three-phase charger provides. The charger in the Motiv ePCS is compatible with SAE J1772 but may also be connected to 208, 440, or 600 VAC three-phase for faster charging.

 

6. Why electric trucks? Aren’t trucks too big to be electric?

 

Local delivery trucks run by companies like UPS, Fedex, Staples, Coca Cola, etc, airport and hotel shuttle buses, garbage trucks and municipality/commercial work trucks generally drive in local areas with pre-defined or known routes. These vehicles also park in a local depot at night with plenty of time for charging. These truck applications are the perfect candidates for electric trucks. On this type of routes, electric trucks may pay back their up-front cost in as little as three years. A large number of urban routes are shorter than 50 miles (these would require half the batteries for a more cost effective vehicle). The goal for electric truck applications are to find routes that drive 30,000 or more miles per year, yet never exceed 80 to 100 miles per day. If the yearly mileage is low, the electric truck does not offset enough diesel fuel, but with too many miles on any day between nighttime charges, the battery pack must be sized larger, increasing up-front cost. It is possible to find other situations (such as a mid-day charge) that make electric trucks work for various applications, but the above drive profiles are widely used and truck electrification in these pays back quickly.

 

7. Fuel consumption/maintenance cost comparisons between BEVs and traditional diesel vehicles

 

Fuel cost for an EV is about 1/6th the cost of operation for an equivalently powered diesel truck. A medium-duty truck that gets 6 to 8 MPG uses approximately 1 kWh to go 1 mile. To drive each mile, a conventional truck uses 1/6th of a gallon, which is $0.67 with diesel at $4/gallon. A comparable electric truck would use 1 kWh of electricity to go the same mile, which costs $0.10 to $0.12. As the cost of diesel continues to increase, the economics behind BEVs is even better. Additionally, the maintenance cost for an EV is about ½ the maintenance cost of a comparable conventional diesel truck since EVs have far fewer moving parts.