Plug-in electrics are starting to be more seriously discussed lately. I’m trying to do a few calculations on cost and don’t know one essential piece of information. How many hp are really required for a passenger car to be useful from a practical standpoint? How many to maintain constant highway speeds? How many to accelerate from 0-60 in about 15 sec? How many to maintain 40 mph city driving?
I figure that if a car can do all this with an average of 50kW, it would be cost competitive with current gasoline prices (giving gasoline cars a generous 30 mpg). This sounds low to me since 50 kW is only 67 hp.
Anything else I’m missing (besides the battery issues, of course)?
Actual used HP will be exactly the same as for an identical gasoline car of the identical weight. If there are weight differences, you should be able to extrapolate them.
I always thought that electric cars have an advantage in performance over regular cars with the same horsepower. They have torque over most of the band which leads to very good acceleration.
It seems to me a more fundamental consideration needs to be addressed. For those of us who live in areas where electricity in produced by butning coal, plugs-ins just move the pollution from the tail pipe to the smoke stack. Shouldn’t we looking for cars that are less polluting and contribute less to climate change? emproche
The environmental advantage of plug-in is the ability to use non-greenhouse-gas-emitting power generation (Nuke, solar, solar thermal, hydro, geothermal, etc.), or put co2 capture technology at the power plant. Admittedly, it’s not perfect, but it’s a step in the right direction.
Even if the electricity used is produced in a coal burning power plant, power plants are considered more efficient than automotive engines.
From [wikipedia](Ther - Wikipedia
modynamic_efficiency)
67 HP is more than enough to power a car, especially if it’s a lightweight car. I have a 1987 Chevy Sprint ER with a Suzuki 3 Cylinder 1.0 liter engine that only produces 50 HP. The car weighs right around 1000 pounds and it’ll do 0 to 60 in about 15 seconds.
I think the rating you need to look for is torque more than horsepower. I’ve read that these electric motors generate a lot more torque than a gasoline engine.
This probably requires a good understanding of the definition of torque and I’m not the person to give that…hopefully someone else can elaborate.
1000 is way too light for the Chevy Sprint.
A quick Google turned up around 1600.
Cite: Suzuki Cultus - Wikipedia
The questions of the OP are in fact questions best answered by looking at a vehicle’s horsepower. I’m not inclined to explain in depth, but suffice it to say that gas engines can effectively compensate for their uneven torque output (relative to an electric motor) by means of using a large number of gears and/or a torque converter.
Why? I did say identical car, so there’d be no difference in aerodynamics. It takes th same amount of power to move the same weight the same distance in the same amount of time, everything else being equal. Source of power is not relevant. Of course different power plants have different weights, so like I said, you’d have to account for the difference. Take a look at this web site and you can learn to see how much horsepower is required to move your car at a certain rate, taking into account things like rolling resistance, wind resistance, etc. Notice that mass, speed, and delta speed are all you need to know. Power plant isn’t important.
Thanks for the terrific posts. It seems to me that most typical gasoling cars will incur about 10-20 cents per mile in fuel costs while most plug-in electrics will run about 5-15 cents per mile. Some improvement could be made with regenerative braking, as well.
I think it’s easier to control pollution (and CO2) at a power plant than on individual cars, so this is viable in a number of respects.
I’m thinking we may see practical plug-in electric cars next year (and affordable ones by 2010).
One other thought: heat and A/C - is this going to be a substantial impediment?
I have looked up how plug-in electrics will generate heat. We have serious winter days here and a regular car generates heat as a waste product. Electrics generate no heat. Cars will probably become a lot better insulated, but generating heat from electricity is very inefficient. There will probably have to be a small gas fueled heater.
Umm…electrics generate plenty of heat. 1000W is roughly equivalent to 3400 BTUs of heat. Ever wonder why you have fans in your computer? Why your TV vents are warm? Electronics generate heat, and at a very predictable rate. Sure, generating heat from electricity isn’t as efficient as from fuel like natural gas, but there are plenty of electric space heaters, duct heaters, water heaters, furnaces, etc.
Now, you do you have a good point: weather they can channel the heat of the motor into the cabin as a heater without resorting to very high consumption electric heat is debatable.
Here’s a factor I haven’t seen anyone mention. Gasoline powered vehicles pay around $0.02 per mile on fuel and road use taxes. The early adopters will benefit from the fact that these taxes don’t apply to their plug in electricity, but if enough people start driving plug in sooner or later the government is going to look around and say “Whoa, where the hell did our revenues go?”. Then you’ll see some pretty serious efforts to recover the taxes. I predict a per mile tax for plug ins.
Electricity is much, much more efficient at generating heat than combustion is, not counting the electric plant. No waste. Don’t confuse the fact that it’s more expensive as meaning that it’s less efficient.
As for insulation, there’s not a whole lot of room in a car to add insulation.
The bottleneck issue for many parts of the country is that the electric grid is already running at near capacity. Building new plants of any type will take years.
Siting the plants is even more of an issue. Nobody, especially in the already built up northeast, wants a plant near them, nor do they want giant transmission lines running through their backyards. There is almost literally no place to build the new plant capacity that would be forecast just by predicted growth in electricity usage, let alone the big upsurge (literally) that would come along with a high percentage of electric plug-in cars replacing the current fleet.
Something would have to give if the cars become standard, and it’s hard to predict which components will create the most problems.
The one loophole in this is that proponents hope that vehicles will be changed overnight, off-peak, so that the load is regularized throughout the day, but I don’t know just how high a percentage shift this can accommodate.
You have valid points and I should have said not much usuable heat, unless you want to add a complete heat recovery system, which is expensive in complexity and weight.
I was very much counting the power plant that produces it in the first place as opposed to burning gas directly, and the cost of the extra batteries required to carry extra electricity just to produce heat.
My ex- worked for a state public utilities commission. She used to eat numbers for breakfast, looking at propositions in the short- as well as long-term. This wasn’t just dollars and cents, either.
For instance, she used to say that people thought of solar panels as a “green” measure but in fact, the manufacturing process created more pollution than the solar panels would “eliminate” over their useful lifetime. At that time (say, 1992), I thought it was ironic that people would pay a premium to do something for the earth but ultimately do more damage to the environment.
The total environmental impact of a plan has to be considered, I think. That may include mining or manufacturing or emissions or other issues. Find the perfect solution and the average guy may not be able to afford it.