How many miles per kilowatt?

1 Kilometer = 0.6123 mile

i.e 1 mile = 1.601 kilometer

Simple question with a complicated answer. Range will vary depending on a variety of factors...terrain,speed,load,traffic conditions,even temperature. Do some on line searching and find web site for "EV discussion list" the archives will provide a wealth of information, also you can subscribe to "electrifying times" 63600 Deschutes Market Rd. Bend, Oregon 97701 for the latest EV (electric vehicle) info. Vince

I'm getting at where you are going, but I think maybe what you may be looking for is [miles per kWH], or [miles per MegaJoule] or [km per MegaJoule], rather than the [miles per kW]? This would be closer to the traditional [miles per gallon]

The rate at which the energy is consumed then will of course be the power in [kW]

Neil

You'll have more luck with Miles/Kilowatt/Hour old chum.

In the way you formulate your question there is a basic error:

kilowatt is a power unit so that you can for instance speak of miles or km/h

If you want to have a number of km (or miles) then you should use the energy unit which is the kilowatt-hour. The capacity of an accumulator is in Ah since the voltage is constant. You could also ask for an estimation of km/miles per Ah.

As an other participant very correctly wrote it is possible to give an order of magnitude only if the travel conditions are defined: for instance at Xmiles/h on a straight horizontal road. It should also be specified which kind of road cover.

As a couple of posters have pointed out watts or kilowatts are actually a measure of power or the rate you are consuming or producing energy and you actually need to t measure energy itself.

With the SI system the unit for energy is the Joule and a watt is defined as being one joule per second. That means a kilowatt hour is 1,000 watts for one hour or

1Kwh = 1,000 watts x 1 hour = 1,000 watts x 3,600 seconds = 3.6 Mj

To compare to miles per gallon you need to find out how much energy is stored in a gallon of petrol. A liter of petrol contains about 34.831 Mj which when converted to US gallons is 131.86 Mj per gallon.

If you divide 131.86 Mj by the miles per gallon performance of a petrol vehicle it will give you how much energy in megaloules is consumed per mile for the petrol vehicles. You can then compare this figure with the electric vehicle and see which one is more energy efficient. It will also give you a way of comparing the cost of the petrol to the cost of the electricity so you will have an idea of the comparative running costs.

When you do the comparison you will find that electric cars are considerably more efficient that petrol driven vehicles and there are a couple of reasons for this. Firstly an internal combustion engine is roughly 20-30% efficient at converting the energy in the fuel to mechanical energy while electric motors are around 80-90% efficient at converting electrical energy to mechanical energy. Secondly with an electric vehicle the often uses a system called regenerative breaking where the energy that is normally lost bringing a vehicle to a stop is recovered and used to charge the batteries. Put all this together and you end up with a system that at the vehicle is more efficient.

However, the story is not that simple and if you look at how electricity is generated it is a completely different story. Slightly over 50% of the worlds electricity is generated by burning coal and this coupled with the power distribution system is about 30% efficient overall. If you now couple this with the efficiency of the vehicle you end up with an overall efficiency of around 25% which is no better than the average internal combustion engine. Considering over half the worlds electricity is generated by burning coal, a fuel that is far moor polluting than petrol, you may end up producing more pollution with an electric vehicle than a petrol fired internal combustion engine driven vehicle.

Don't get me wrong, I think electric vehicles have a lot to offer but you need to look at the problem as a whole and where the energy you are using to charge the electric vehicle is coming from. If the electricity is coming from a renewable or not polluting source like wind, hydro, geothermal then yes they are a good idea and can reduce our impact on the environment. You can also use the surplus generating capacity and off peek tariffs to charge the vehicle in which case you are using energy that would normally be wasted so again you can minimize the impact and pollution. Off peak tariffs can also be heavily discounted and can make an electric vehicle far more economic.

I hope this has helped and you can now compare apples with apples but if you have any further questions please don't hesitate to ask.

There is no answer of any value to this question. The nature of the drive train of a hybrid vehicle to is to interchange the electric drive with the combustion engine as driving conditions warrant. I googled the concept of a Prius out of gas

http://ask.metafilter.com/29512/Miracle-car-drives-after-it-runs-out-of-gasor-does-it

and the consensus seems to be that you get a few miles or maybe enough to get to a gas station if you can see it, but it may be damaging to the batteries if overly discharged. One report is the car won't start if out of gas. They say that overseas there is an EV switch for battery only as much as possible but the car can override.

From Toyota: http://www.toyota.com/vehicles/2007/prius/faq.html

Though Prius can operate in electric-only mode when gasoline is in the tank, it is not designed to run without gasoline. Doing so could cause severe damage to the hybrid system, so drivers should be sure to keep gas in the tank at all times.

Therefore the car requires gasoline so knowing how much electricity it will consume per mile is meaningless becaue there will always be some gas consumption.

I would have to agree with sail4ever, there is not an accurate answer to the queries in the post. It would be like asking " How many square inches of grass does a horse have to eat so you could ride him 1 mile"? Too many unknowns.

But to quote a disclaimer that has become an expression: "Your mileage may vary".

Hello: The best way to determine how many KWHR, are being used per mile, is to attach a meter to the electric motor, and do the same determination one does for calculating MPG. KWHR used divided by the miles driven.

Another way would be to measure the kWh taken from the mains power supply, though you'd need to do it over a number of cycles to get a realistic figure. Could use domestic meter if you switch off everything else during charging, otherwise dedicated meter.

Miles per mains kWh is presumably what bmorrow492 is looking for i.e. taking account of charge/discharge losses and a figure to work out costs from.

"what you may be looking for is [miles per kWH]"

Yes, of course, that's what I meant to type. Thanks for the correction.

The question still stands, though. It should be no more difficult to measure miles per kilowatt-hour than it is to measure miles per gallon of gas. How come nobody publishes that figure?

Bill Morrow

Quote: "How come nobody publishes that figure?"

Probably because it would be a figure that would not have much meaning by itself.

KWH can be converted to a measure of horsepower used in an hour of time. KWH X 1.34 = HPH. Now you have to figure backwards how much gasoline is required to make enough horsepower to power the vehicle in question for one hour. To have a comparable figure, you would have to find and use the formula that uses RPM, speed, accelaration and load to arrive at the same figure that the manufacturers (actually I believe it's the EPA that makes that happen) do.

Once you have found that figure (mpg) there is a spread between city and highway.

Using the same criteria on your hybrid, run the tests and see how much power it uses. Then you will have some useful data. Unfortunately you didn't ask the question of the efficiency range (mph/kph) of the hybrids vs the efficiency of a petrol burner. Is horsepower linear with rpm in hybrid engines and under load? Where is the highest efficiency of power?

Then you could compare apples to apples, because then you would have an apple, which is what you are after, not just any fruit!

Otherwise most would care about cost and availability of the particular "fuel" (probably why the MPKW isn't advertised). If your hybrid achieved 20 mpg (converted from MPKW) at a cost of .05 EU per mile and your gas powered Opel got 40 mpg at .20 EU per mile would you be disappointed and get rid of the hybrid?

But it's your question.

KWH can be converted to a measure of horsepower used in an hour of time. KWH X 1.34 = HPH. Now you have to figure backwards how much gasoline is required to make enough horsepower to power the vehicle in question for one hour. To have a comparable figure, you would have to find and use the formula that uses RPM, speed, accelaration and load to arrive at the same figure that the manufacturers (actually I believe it's the EPA that makes that happen) do.

It is important to compare apples with apples but I would always recommend sticking with established units like Joules for energy rather than inventing a new one called a HpH. If you use the figures that I supplied in post #6 you can easily convert everything to Joules.

As for actually getting a figure for how much energy you will be putting into the car from the mains electricity there should be some sort of information on how much electricity it will consume to charge the batteries fully. If they give you some sort of expected range you can then easily calculate the energy consumption in Joules per kilometer and bingo you are comparing apples with apples.

I agree with you Bill.

Vehicle manufacturers would need to include a voltage and current sensor, which would be multiplied with each other to yield the power, and then integrated with respect to time to yield the energy consumed over a period. These calculations are all easily done with a microprocessor. All four parameters (battery voltage, current, power and energy) would be useful to some drivers like the more numerate of us engineers, and the smarter maintenance people.

Vehicle manufacturers would normally be measuring these parameters for their power train management systems anyway; but do think they will make these parameters available through the driver display consol? I don't think so, because they want to tie the purchaser up with maintenance plans etc, because often this is where they make their money!

Neil

Manufcaturers indicate already "l/km" for gas or diesel engines why should they not do it in case of electrical drives?

Hi Guest,

I agree that vehicle manufacturers will eventually give the equivalent of [litre per km] in electrical terms; but I would bet that they will not give the INDIVIDUAL parameters such as [volts], [amps], or [kW]. The reason why I say this is that I drive a car that has one of those fancy driver display clusters that show everything except the real basics such as battery voltage and current. However, there must be current & voltage sensors within the car that enables the car computer to come to the conclusion "accumulator disfunctional, see the workshop"!!! So, you then need to go to those workshops that have purchased that vehicle's ATE (Automated Test Equipment) to get it checked out, by using the original manufacturers kit. Crafty auto-manufacturers! It would be more helpful if car manufacturers would rather build into the car some BITE (Built In Test Equipment).

Neil

Somewhere there is a correlation across all modes of transport giving kilowatt-hours consumed per ton-mile travelled. Can any subscriber locate the link, please? From memory, the bicycle is at the top of the list, and the electric train not far behind it.

If You had im mind miles per kilowatthour, then You could expect some 3..6miles/kWh extra from plug in energy used, depending on driving, speed, city/highway...

Hi guys, I have drawn up the following table that you can use to compare miles per gallon to every sort of performance figure I could think of including miles per KwH.

Unfortunately, as you can see, trying to post large spreadsheets to CR4 threads produces a less than desirable results. However, if you would kike a copy of the original excel spreadsheet then follow this link to the CR4 personal mail system and send me a message with your email address and I will mail it to you directly. Please don't publicize you email address here, it's a public forum and you can never be sure about who is reading it.

PS if you can think of a performance figure I havn't included use the link above to drop me a line and I will do my best to add it to the spreadsheet.

Hi Bill:

There is certainly a lot of equivocating in this thread. I think only one poster actually gave you a number: 3-6 miles per kWh. I think that is pretty close for a car like a Prius. Hymotion makes an enlarged battery pack for the Prius, to convert it into a plug-in hybrid. Their add-on is 5kWh. The stock battery is 1.5kWh. The combination gives 50 km range on battery alone, per Hymotion lit. (This is an exaggeration, I'm sure.) So let's say 25 miles on 6.5 kWh. About 4 miles per kWh. That figure is widely quoted for electric cars in general, as a rule of thumb.

Interestingly, the Hymotion pack is about $10,000, or was last I checked. It weighs 160 lbs. 5kWh of lead acid batteries are about 260lb (figure six 45 lb batteries). $600 would buy 6 pretty good lead acid batteries. Quite a premium to lose 100lb. At $10,000, it would be very hard to justify the cost.

Here, elec is $.10 per kWh. A Prius could therefore go 50 miles on either $1.25 worth of elec, or $3.00 worth of gas. In 100 miles, you'd save $3.50. in 1000, $35.00. In 100,000, $3500. In 300,000 you'd save the cost of the batteries, but only if you drive your Prius a short commute (25 miles round trip) to and from work, so the gas engine never runs. 250 work days x 25 miles = 6250 miles per year. 300,000 miles would be a lot of years. But it gets worse: You won't get much more than 1000 full charge/discharge cycles out of the batteries, so 4 years is about it for battery life. That's 25,000 miles at $35.00 per thousand, or $875 saved before battery replacement time. Spending $10,000 to save $875 doesn't seem to make sense. Granted, if you charge up only overnight, then you can get a discount on the elec, but still the economics are disastrous.

Speaking of meaningless MPG numbers, Hymotion says this: Hymotion PHEV system can average more than 100 miles per gallon. And if used only for short trips, 500 miles per gallon is possible. They might just as well say that for short enough trips, 10,000 MPG is possible. As you say, the MPG figures are meaningless if the batteries are charged from an external source. On the highway, the hymotion system would get poorer mileage than a standard Prius, because rolling resistance would be about 5% higher, due to the extra weight. That should reduce MPG by about 2 percent.

I suspect Toyota will have the plug-in economics worked out a little better. Lithium titanate batteries show tremendous promise with far longer life. Dunno if that's what they are planning to use.

In any case, with a Prius or the hybrid Camry, you could hardly go wrong.

Excellent information, Ken. Thanks

Bill

All this conjecture about electric vehicle range and miles per kilowatt are just that, conjecture, unless you live on a perfectly flat terrain. Any slope will make a good dent in range, add a 12% grade and range will disappear at an alarming rate and miles per kilowatt will plummet. Regeneration will not recover all that is lost on up slopes or hills. If you live in an area with appreciable hills think twice about how far an electric vehicle will go. Regeneration will do no good if you live at the top of a hill and descend with a full battery. The battery you topped off over night would not accept additional charge and no gain in range. That's an extreme example, but keep in mind the range you will get depends on your local terrain.

All very good comments. Unfortunately the public has no idea how NON-Green electric vehicles are... For example, I have been told that a Prius has 1000 galloons of gasoline equivalent more energy in it than a hummer.. due to the nickel and lithium in the batteries. Since about 50% of electricity come from coal (for the foreseeable future), one has to account for the energy used to mine, transport and burn the coal and convert it to electricity and transport it to the car. The combination of high energy content in the Prius (or similar) to begin with and the net energy to get power to the car, they may sound good and green but really the electric cars as LESS green than standard. A natural gas car is much more green. The best green plan is to use wind and solar to generate hydrogen locally at filling stations and fuel cars with hydrogen. We can CONVERT EXISTING cars and trucks to run on hydrogen. Even if EVERY new car was pure electric, we would not decrease demand and need for gasoline for a couple of decades. The only way to reduce gasoline demand is to convert existing cars and trucks to hydrogen. But also consider we would have to build a very large number of power plants to build enough solar and wind generators to make any difference in any reasonable period of time. The leftist greenies that think wind and solar are the solution are smoking way too much medical weed.