Category Archives: electric cars

Cars and Cold Weather

Anyone who pays even passing attention to their fuel economy know that regardless of the vehicle driven, colder weather means poorer performance for a myriad of reasons. Important to all vehicles is inefficiency due to rolling resistance and wind resistance. Electric cars have additional inefficiencies due to battery issues.

In cold weather lubricants, which keep parts which move with respect to each other moving, are more viscous and therefore more resistant to movement causing drag. Another source of resistance to motion comes from the lower tire pressure in cold weather. Students in introductory chemistry classes learn Guy-Lussac’s Law: Pressure is directly proportional to temperature. Lower temperatures mean lower tire pressures.

Both friction due to viscous lubricants and lower tire pressure are overcome because both cause friction and friction generates heat. Depending on how cold it is, and how long the vehicle is driven, parts warm up lowering lubricant viscosity and tires gain pressure as they heat up.

Even the air itself conspires in cold weather. Vehicle designers pay careful attention to “slipperiness,” as wind resistance is a big factor especially for a fast moving car or truck. Wind resistance is a function of the density of air and air density is inversely proportional to temperature. Colder air is denser air and provides more resistance.

Internal combustion engines (ICEs) have to be tuned to run rich to get started in cold weather. This means that more fuel is used to get the engine started and up to operating temperature. Additionally, in the winter people tend to start up their engines to warm up the interior of the car before it even hits the road.

Hybrids, plug-in hybrids, and pure electric vehicles suffer an additional problem, because they all are powered to some degree by a battery and batteries in cold weather are a problem. A hybrid electric vehicle like a Toyota Prius has a traditional ICE connected to the drive wheels, with an electric motor which supplements the ICE. Plug-in hybrids are a little different. They have an electric drive train with an ICE used exclusively as a generator to charge the battery when it is discharged. Of course all electric vehicles have only the electric motor and a comparatively large battery to extend the range on a charge.

Two factors contribute to cold weather reduced range in battery powered cars. The colder a battery is the less charge in will accept, thus lowering the vehicles range until the next charge. A factor called internal resistance increases as the temperature decreases. This means you don’t have as much energy stored from the outset. Further reducing range is the process which converts chemical to electrical energy. The distance you can travel on a unit of energy is lowered in colder weather.

Electric cars have reduced range on a given charge in cold weather, but overall are still cheaper to operate than an ICE vehicle. Basically the cost of electricity for a given amount of travel is much less than the cost of gasoline for an ICE vehicle, even at today’s greatly reduced cost for gas.

Fuel Cell Vehicles

Auto manufacturers, both here and abroad are scrambling to produce electric vehicles. The most successful out of the gun has been the high end Tesla model S. Others include the Nissan Leaf and BMW i3. Chevrolet will be introducing the Bolt in the near future. All these cars are whisper quite and perform well. They all however suffer the drawback of limited range on a charge and a rather long recharge time at least compared to the time to fill a tank of gasoline.

Notably missing from the cars listed above is the world’s largest car manufacturer – Toyota. They set the standard for hybrid cars with the introduction of the Prius in 2001. It is powered by a internal combustion engine (ICE) which is supported by a electric motor and battery that results in quite high mileage compared to other ICE powered cars.

Although Toyota has yet to produce an all-electric car, they seem to be hedging their bet on the development of an alternative to electric cars with batteries. In development is an electric car that runs off of a fuel cell that is powered by Hydrogen. The chemistry of the fuel cell is just the opposite of the high school CHEM class experiment called electrolysis. If you pass an electric current through water it cause the production of Hydrogen and Oxygen from the water. This process consumes electrical energy.

In a fuel cell powered vehicle, hydrogen gas is stored at high pressure in a tank. When electrical energy is needed, the gas is passed into the fuel cell where it combines with oxygen from the air to produce electrical energy. The principle is simple but in practice fuel cells are complex devices that require unique and often expensive catalysts to make the chemical reaction proceed at a sufficient rate to power a vehicle. The real advantage to this technology is the range of the vehicle between refills. It should be possible to store enough Hydrogen in a vehicle to get a lot more range than can be achieved with charging batteries.

A problem with the use of Hydrogen is one of thermodynamics. It takes more energy to produce Hydrogen than you can get back when used. Basically any time you do work, energy will be wasted. Thermodynamically work is the use of energy to drive a process, be it chemical , electrical or mechanical. In the case of Hydrogen energy losses occur when it is created from water by electrolysis, when it is compressed for transportation, when it is decompressed for use, and when it is used in a fuel cell. Each of these processes constitute an inefficiency where energy is lost.

Another problem is that Hydrogen is a gas and somewhat difficult to handle. Hydrogen stored in metal containers, or piped in metal pipes causes embrittlement. The metals become more fragile and likely to fail under pressure on exposure to Hydrogen. It is also problematic in that it has a low energy density by volume. It takes a lot of space to store a given weight of Hydrogen.

Toyota is betting that these difficulties with the production, storage and utilization of Hydrogen can be overcome.

Why Electric Cars?

At the dawn of the automotive age electric cars were, in proportion, more numerous than today. With cheap gasoline and the much greater range the internal combustion engine (ICE) came to dominate the market and continues to do so to this day.

The tide is beginning to turn, slowly, but it is turning. First fuel is not so cheap anymore. In 1970 the price of a barrel of oil was about 3 dollars. This was the last time the US was a net exporter of oil and therefore had some control of the price. Adjusted for inflation that would be about 18 dollars currently. Even at the recently depressed price of around 50 dollars a barrel, it is several times more expensive than in 1970. A car getting 25 miles per gallon will cost the driver of an ICE powered car about 2.50 $ to cover 25 miles.

How does that compare with an electric powered vehicle? Modern vehicles running on electricity, whether they are hybrids, plug-in hybrids, or pure electric get around 4 miles per kiloWatt-hour (kWh). Locally electricity costs are around 9 cents a kWh. To cover that same 25 miles in this comparison means that the fuel cost for an electric car is 75 cents, less than a third the cost for gasoline.

An important feature of electric cars is their ability to recapture some of the energy consumed after accelerating up to speed – when you take your foot off the accelerator in an electric car the motor acts like a generator sending power back to the battery. It’s immensely important in stop and go traffic. This is a principle reason why hybrid cars such as the Prius get such good mileage, even thought they have only a small supplemental electric motor/battery for an otherwise gas powered car.

Gasoline engines have hundreds of moving parts. The parts need lubrication, and cooling and exhausting, and on and on. It is interesting to note that Forbes magazine has described the maintenance shop at new car dealerships as the principle profit center. You may negotiate a lower price for a new car but I doubt any negotiating room to lower the cost for labor and parts in the shop.

For an electric engine there is essentially one moving part, the rotor. No significant lubricants are needed, no coolants to maintain, no exhaust system, you don’t even need a transmission except to go forwards or backwards. Hence maintenance of an an electric car is significantly cheaper than ICE powered cars.

There are a couple of current drawbacks. Modern electric cars are produced as yet in small numbers and therefore don’t benefit from economies of scale. As they become more popular costs will fall. The biggest limiter right now is range and charging time. The high end Tesla with a 120 kWh battery has a range of over 250 miles. The charging time with one of their “superchargers” is about an hour.

The Chevrolet Volt, at half the price of the Tesla model S, has a 40 mile range on electric but the range is extended by an on board ICE that serves only to charge the battery on the fly.