The Battery Powered Car

Diagram of Series Hybrid
Elec. motor to existing drive train
generator on side of truck bed
batteries on undercarriage
(elec=R, batt=G, diesel=O)

Hybrid cars, which combine the power of an electric motor with a gasoline engine, are often presented as a transitional technology that will eventually be supplanted by fuel cell cars. This argument rests on an assumption which may or may not be valid – that on-board hydrogen, used to create electricity using fuel cells – is a better electricity storage medium than batteries. Examining this assumption reveals some strong challenges to the idea that batteries are going to go away, or that hydrogen fuel cells are the ultimate vehicle technology.

The first thing to understand is that hydrogen – at least green and renewable hydrogen – generally requires electricity to exist. While hydrogen can be extracted from some crops, it is impossible to grow enough crops to supply the world with clean hydrogen energy. To extract hydrogen from fossil fuel may result in cleaner energy production than simply burning the fossil fuel, but fossil fuel isn’t renewable. The only way hydrogen, theoretically, can be supplied in the quantities necessary for it to become the primary fuel used in the world is to manufacture hydrogen via electrolysis. This is the process whereby electricity and water are combined to separate the hydrogen from the water.

In all its forms, therefore, hydrogen is a fuel that’s manufactured from other fuels, either biomass, fossil fuel, or electricity. In this sense hydrogen is similar to electricity, since electricity also requires some other fuel to create it.

When one considers hydrogen-powered cars, one must ask where all the electricity is going to come from to produce all the hydrogen. One must also ask whether or not hydrogen is a better carrier to store electricity than the common battery. The problem with batteries isn’t their expense – fuel cells cost orders of magnitude more than batteries do. Moreover, the problem with batteries isn’t their efficiency storing electricity – a battery will discharge to an electric motor 90% of the electricity used to charge it. If that same electricity were used to electrolyse hydrogen, at least 30% of the energy would be lost, and if that hydrogen were then ran through an on-board fuel cell to power an electric motor, another 40% of the energy would be lost. That is, if you put 100 kilowatt-hours into a battery, you’ll get 90 kilowatt-hours back to power your motor. If on the other hand, you put 100 kilowatt-hours into electrolysing hydrogen, then in-turn convert that hydrogen back into electricity to power your motor, you will only have 42 kilowatt-hours available from your original 100. For storing electricity, a battery is more than twice as efficient as a fuel cell.

Diagram of Series Hybrid
Four powerful in-wheel motors
independent 360 degree steering
(elec=R, batt=G, diesel=O)

So why don’t we use all this technology to manufacture cars powered exclusively by batteries? The answer is batteries weigh too much, but this is changing. Typical lead-acid batteries get about 60 watt-hours to the kilogram. The newer nickel metal hydride batteries used to power hybrid cars get up to 120 watt-hours to the kilogram. Still further advanced lithium-ion batteries are approaching 200 watt-hours to the kilogram. This means that whatever range an electric car may have had using lead-acid batteries can now be doubled, or even tripled.

Advances in battery technology spurred by hybrid vehicle development may lead to the hybrid car not giving way to a fuel cell car, but, at least for many applications, to a 100% electric car. It isn’t like this hasn’t been tried before. General Motor’s EV-1 is a legendary example of an electric car that was ahead of its time. This vehicle had a range of 100 miles on a charge, and it had a top speed on 180 MPH! The car was equipped with a governor to keep the drivers from going that fast. When GM made the heartbreaking decision to discontinue the EV-1, it looked like electric cars would go the way of the steam locomotive. But with advances in battery technology, electric cars are making a comeback.

Today there are hybrid car owners who are making their hybrid cars capable of being plugged in. Other tinkerers are adding additional batteries to their hybrid cars. But why not go 100% electric? Just think – no twin drive train for the gas engine and the electric motor, no transmission, and a far less complex power-management system. Why wouldn’t someone want to just come home and plug their car in? No more gas stations. No more expensive gas.

Table of Cost to Drive 100% Electric Car
At $.06 US per KWh, a battery-powered car costs $.02 per mile on grid electricity

As the table shows, not only are batteries very efficient ways to store electricity, but electric motors are very efficient ways to convert electricity to traction. Unlike internal combustion engines, which at best might convert 35% of the energy in gasoline into horsepower, an electric motor will convert 90% of the electrical input into horsepower. Since a kilowatt of output is equivalent to 1.341 horsepower of output, it is possible to calculate how a given amount of grid electricity – expressed in kilowatt-hours – will be available in the form of “horsepower-hours” to power a vehicle.

In the example above, the average car requires 20 horsepower to drive at a speed of 50 miles-per-hour on a level surface. On this basis, the average car requires 370 watt-hours of power to go one mile. At $10 per kilowatt-hour, it only costs you 3.7 cents to travel one mile. Compare this to an economy sedan that gets 30 miles per gallon. At $3.00 per gallon gasoline, it will cost nearly three times as much, $.10 per mile, to drive this car using gasoline. And at night when electric cars are being charged, electricity rates are often much lower than $.10 per kilowatt-hour. It is possible to drive an electric car for as little as $.02 per mile! This arbitrage between the cost per mile of gasoline power vs. the cost per mile of electrical power is an awesome opportunity, but only one that can be exploited by battery-powered cars, which can convert 90% of grid electricity into power going into the motor, compared to the electrolyser / fuel cell combination, which only can deliver 42% of grid electricity into power going into the motor.

Table for Car Battery Weight
At only 100 watt-hours per KG, 1,000 lbs. of batteries gets 123 miles

Advances in battery technology are inevitable, as hybrid cars enter the mainstream of automotive technology. Toyota is planning on manufacturing, per year, over one million hybrid cars by 2010. Other manufacturers are following suit. At the least, vehicle batteries are going to get cheaper, more temperature tolerant, longer lasting, and cleaner to recycle and reprocess. At best, vehicle batteries, such as the lithium ion batteries, will enter mass production, allowing 200+ watt-hour per kilogram batteries to power electric cars. Weight as a core problem for electric cars will begin to disappear entirely if lithium ion batteries ever enter mass production.

In the meantime, it’s safe to say nickel metal hydride batteries are here to stay, and they are becoming increasingly available, durable, and cheap. The EV-1 had a battery pack that weighed 1,600 pounds. This is quite a payload. Using nickel metal hydride batteries, the battery payload can be reduced to 1,000 pounds, concentrated along the center spine of the car. Assuming 100 watt-hours per kilogram, which is easily attainable using today’s nickel metal hydride batteries, such a car fully charged would have 45 kilowatt-hours available to power the motor. Assuming 2.7 miles per kilowatt-hour, a car with a 1,000 pound battery payload at 100 watt-hours per kilogram of batteries will have a range of 123 miles. Is this great? No. Is this enough to get to work and back? At two cents per mile, you bet it is, and all you do is plug the car in at night. No more gas stations.

Diagram of Electric Car
photovoltaic skin
optimally aerodynamic
(elec=R, batt=G, diesel=O)

The biggest problem with electric cars, unlike gasoline powered cars – or hydrogen-powered cars, for that matter – is the time it takes to recharge the batteries. This is why gasoline-electric hybrids are getting an early foothold in the battle for the car of the future. When a gas/electric hybrid’s batteries run out of juice, the car can still limp along, powered solely by the gasoline engine. This is also why hybrid mileage is somewhat misleading. The more battery power is used, the better the mileage. For stop and go, low speed driving, the gasoline engine can divert energy to recharging the batteries faster than they’re being depleted. On extended runs at high speeds, or up hills, however, the gasoline engine must use all its energy to power the car, assisted by the battery-powered electric motor. This drains the batteries and turns the hybrid, basically, into an underpowered gas-powered car that has to carry a lot of dead weight. In these scenarios, mileage plummets. In a nutshell, the hybrid car has a lot of the same weaknesses as a battery-powered car, except it won’t leave you stranded when the batteries run low, just hobbled.

The idea that a 100% battery-powered car isn’t a viable vehicle solution because of its limited range, however, is to ignore the duty cycle that the vast majority of vehicle trips entails – a short range errand or commute. Most American families have two cars. Why wouldn’t it make sense – particularly at two-cents per mile – for one of those two cars be a 100% electric car?

If an electric car is defined as a vehicle that derives 100% of its horsepower from an electric motor, there are many ways to supplement the cars range. For example, a hybrid car typically depends on two engines to power the vehicle, an electric motor combined with a gasoline engine usually between 40-60 horsepower. But what if a gasoline engine, perhaps a highly efficient biodiesel engine, were used to power an onboard generator and was completely disconnected from the drive train?

Table for Car with Diesel Generator
An on-board 20 horsepower generator doubles the range of batteries

This is the case for the serial hybrid. An ultra-efficient, steady-RPM clean diesel motor – turning an electric generator – running whenever the car was operating, could recharge on-board batteries at a rate at or near the amount they’re depleted. If only a ten horsepower generator were used, assuming a generator efficiency of 90%, then for every hour on the road, 18 miles of range would be added. Using the example above, a car with a 1,000 lb. battery pack has a range of 123 miles per charge; at 60 mph the car has extended its range another 47 miles (or so), which means that now the car can go 170 miles on a charge – with a few gallons of biodiesel. Remember, this engine is less than one fourth the size of the already tiny gas engines in hybrid cars.

If in your serial-hybrid car – where a diesel powered generator powers a battery-pack that powers an electric motor – you use a 20 horsepower diesel powered on-board generator, the range becomes very practical. Running a 20 horsepower generator, still a very small engine, will allow you to add 36 miles of range for every hour your battery-powered car is driven. Now you can drive your car 250 miles on a charge. Such a trip would require four gallons of gas and 45 kilowatt-hours of grid electricity. At $3.00 per gallon & .10 per kilowatt-hour, your combined-fuel cost per mile would be about five cents.

The advanced electric car can be built using advanced technology and materials – a lightweight ultra-strong frame, aerodynamic exoskeleton, in-wheel motors with independent 360 degree wheel rotation in all four wheels, driver control by wire, autopilot, lithium ion batteries, photovoltaic sides and windows, the works.

Series Hybrid Truck Diagram
Generic photovoltaic flat-panels
placed on cover to truck bed.
(elec=R, batt=G, diesel=O)

But a practical electric car can also be built by converting a small gasoline pickup truck, removing the gas engine and replacing it with an electric one. The transmission could be replaced by a single-speed reduction box that would last forever. In the bed of the pickup a 10-20 horsepower diesel generator could be bolted on, to power a battery-pack which would fill much of the rest of the bed of the pickup. Additional batteries could be installed on racks riding on the car’s undercarriage starting where the gas tank is removed. The top of the bed of the pickup would have a flat hood covered completely with photovoltaic panels, enough to add scores of miles per day of range to the battery pack. You would have a commuting truck you could refuel with either a plug into the wall, a pump at the gas station, or parking in the sun.

Entrepreneurs, investors, electrical engineers, auto-mechanics: All you need are used gasoline cars, electric motors and batteries. Who will make the electric car that refuels in the sun?


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